13735592
Evaluating the Sources and Functions of Gradiency in Phoneme Categorization: An Individual Differences Approach
During spoken language comprehension listeners transform continuous acoustic cues into categories (e.g., /b/ and /p/). While long-standing research suggests that phonetic categories are activated in a gradient way, there are also clear individual differences in that more gradient categorization has been linked to various communication impairments such as dyslexia and specific language impairments (Joanisse, Manis, Keating, & Seidenberg, 2000; López-Zamora, Luque, Álvarez, & Cobos, 2012; Serniclaes, Van Heghe, Mousty, Carré, & Sprenger-Charolles, 2004; Werker & Tees, 1987). Crucially, most studies have used 2-alternative forced choice (2AFC) tasks to measure the sharpness of between-category boundaries. Here we propose an alternative paradigm that allows us to measure categorization gradiency in a more direct way. Furthermore, we follow an individual differences approach to (a) link this measure of gradiency to multiple cue integration, (b) explore its relationship to a set of other cognitive processes, and (c) evaluate its role in individuals’ ability to perceive speech in noise. Our results provide validation for this new method of assessing phoneme categorization gradiency and offer preliminary insights into how different aspects of speech perception may be linked to each other and to more general cognitive processes.
18880030
Speech perception is hearing sounds, not tongues.
Three types of evidence are reviewed which cast doubt on claims that recovery of the speaker's articulations is an inherent part of speech perception: (a) Phonological data (e.g., universal tendencies of languages' segment inventories, phonotactic patterns, sound changes, etc.) show unmistakably that the acoustic-auditory properties of speech sounds, not their articulations, are the primary determinant of their behavior. (b) Infants and various nonhuman species can differentiate certain sound contrasts in human speech even though it is highly unlikely that they can deduce the vocal tract movements generating the sounds. (c) Humans can differentiate many nonspeech sounds almost as complex as speech, e.g., music, machine noises, as well as bird and monkey vocalizations, where there is little or no possibility of recovering the mechanisms producing the sounds.
10117886
The discrimination of speech sounds within and across phoneme boundaries.
In listening to speech, one typically reduces the number and variety of the many sounds with which he is bombarded by casting them into one or another of the phoneme categories that his language allows. Thus, a listener will identify as b, for example, quite a large number of acoustically different sounds. Although these differences are likely to be many and various, some of them will occur along an acoustic continuum that contains cues for a different phoneme, such as d. This is important for the present study because it provides a basis for the question to be examined here: whether or not, with similar acoustic differences, a listener can better discriminate between sounds that lie on opposite sides of a phoneme boundary than he can between sounds that fall within the same phoneme category. There are grounds for expecting an affirmative answer to this question. The most obvious, perhaps, are to be found in the common experience that in learning a new language one often
2979748
Gradient effects of within-category phonetic variation on lexical access
In order to determine whether small within-category differences in voice onset time (VOT) affect lexical access, eye movements were monitored as participants indicated which of four pictures was named by spoken stimuli that varied along a 0-40 ms VOT continuum. Within-category differences in VOT resulted in gradient increases in fixations to cross-boundary lexical competitors as VOT approached the category boundary. Thus, fine-grained acoustic/phonetic differences are preserved in patterns of lexical activation for competing lexical candidates and could be used to maximize the efficiency of on-line word recognition.
13554466
Continuous Perception and Graded Categorization
Speech sounds are highly variable, yet listeners readily extract information from them and transform continuous acoustic signals into meaningful categories during language comprehension. A central question is whether perceptual encoding captures acoustic detail in a one-to-one fashion or whether it is affected by phonological categories. We addressed this question in an event-related potential (ERP) experiment in which listeners categorized spoken words that varied along a continuous acoustic dimension (voice-onset time, or VOT) in an auditory oddball task. We found that VOT effects were present through a late stage of perceptual processing (N1 component, ~100 ms poststimulus) and were independent of categorization. In addition, effects of within-category differences in VOT were present at a postperceptual categorization stage (P3 component, ~450 ms poststimulus). Thus, at perceptual levels, acoustic information is encoded continuously, independently of phonological information. Further, at phonological levels, fine-grained acoustic differences are preserved along with category information.
16895507
Perception of speech reflects optimal use of probabilistic speech cues
Listeners are exquisitely sensitive to fine-grained acoustic detail within phonetic categories for sounds and words. Here we show that this sensitivity is optimal given the probabilistic nature of speech cues. We manipulated the probability distribution of one probabilistic cue, voice onset time (VOT), which differentiates word initial labial stops in English (e.g., "beach" and "peach"). Participants categorized words from distributions of VOT with wide or narrow variances. Uncertainty about word identity was measured by four-alternative forced-choice judgments and by the probability of looks to pictures. Both measures closely reflected the posterior probability of the word given the likelihood distributions of VOT, suggesting that listeners are sensitive to these distributions.
39641327
Robust speech perception: recognize the familiar, generalize to the similar, and adapt to the novel.
Successful speech perception requires that listeners map the acoustic signal to linguistic categories. These mappings are not only probabilistic, but change depending on the situation. For example, one talker's /p/ might be physically indistinguishable from another talker's /b/ (cf. lack of invariance). We characterize the computational problem posed by such a subjectively nonstationary world and propose that the speech perception system overcomes this challenge by (a) recognizing previously encountered situations, (b) generalizing to other situations based on previous similar experience, and (c) adapting to novel situations. We formalize this proposal in the ideal adapter framework: (a) to (c) can be understood as inference under uncertainty about the appropriate generative model for the current talker, thereby facilitating robust speech perception despite the lack of invariance. We focus on 2 critical aspects of the ideal adapter. First, in situations that clearly deviate from previous experience, listeners need to adapt. We develop a distributional (belief-updating) learning model of incremental adaptation. The model provides a good fit against known and novel phonetic adaptation data, including perceptual recalibration and selective adaptation. Second, robust speech recognition requires that listeners learn to represent the structured component of cross-situation variability in the speech signal. We discuss how these 2 aspects of the ideal adapter provide a unifying explanation for adaptation, talker-specificity, and generalization across talkers and groups of talkers (e.g., accents and dialects). The ideal adapter provides a guiding framework for future investigations into speech perception and adaptation, and more broadly language comprehension.
12224868
Integration of featural information in speech perception.
A model for the identification of speech sounds is proposed that assumes that (a) the acoustic cues are perceived independently, (b) feature evaluation provides information about the degree to which each quality is present in the speech sound, (c) each speech sound is denned by a propositional prototype in longterm memory that determines how the featural information is integrated, and (d) the speech sound is identified on the basis of the relative degree to which it matches the various alternative prototypes. The model was supported by the results of an experiment in which subjects identified stop-consonant-vowel syllables that were factorially generated by independently varying acoustic cues for voicing and for place of articulation. This experiment also replicated previous findings of changes in the identification boundary of one acoustic dimension as a function of the level of another dimension. These results have previously been interpreted as evidence for the interaction of the perceptions of the acoustic features themselves. In contrast, the present model provides a good description of the data, including these boundary changes, while still maintaining complete noninteraction at the feature evaluation stage of processing.
2583106
Within-category VOT affects recovery from "lexical" garden paths: Evidence against phoneme-level inhibition.
Spoken word recognition shows gradient sensitivity to within-category voice onset time (VOT), as predicted by several current models of spoken word recognition, including TRACE (McClelland & Elman, Cognitive Psychology, 1986). It remains unclear, however, whether this sensitivity is short-lived or whether it persists over multiple syllables. VOT continua were synthesized for pairs of words like barricade and parakeet, which differ in the voicing of their initial phoneme, but otherwise overlap for at least four phonemes, creating an opportunity for "lexical garden-paths" when listeners encounter the phonemic information consistent with only one member of the pair. Simulations established that phoneme-level inhibition in TRACE eliminates sensitivity to VOT too rapidly to influence recovery. However, in two Visual World experiments, look-contingent and response-contingent analyses demonstrated effects of word initial VOT on lexical garden-path recovery. These results are inconsistent with inhibition at the phoneme level and support models of spoken word recognition in which sub-phonetic detail is preserved throughout the processing system.
10104073
Acoustic characteristics of American English vowels.
The purpose of this study was to replicate and extend the classic study of vowel acoustics by Peterson and Barney (PB) [J. Acoust. Soc. Am. 24, 175-184 (1952)]. Recordings were made of 45 men, 48 women, and 46 children producing the vowels /i,I,e, epsilon,ae,a, [symbol: see text],O,U,u, lambda,3 iota/ in h-V-d syllables. Formant contours for F1-F4 were measured from LPC spectra using a custom interactive editing tool. For comparison with the PB data, formant patterns were sampled at a time that was judged by visual inspection to be maximally steady. Analysis of the formant data shows numerous differences between the present data and those of PB, both in terms of average frequencies of F1 and F2, and the degree of overlap among adjacent vowels. As with the original study, listening tests showed that the signals were nearly always identified as the vowel intended by the talker. Discriminant analysis showed that the vowels were more poorly separated than the PB data based on a static sample of the formant pattern. However, the vowels can be separated with a high degree of accuracy if duration and spectral change information is included.
10751216
Effects of consonant environment on vowel formant patterns.
A significant body of evidence has accumulated indicating that vowel identification is influenced by spectral change patterns. For example, a large-scale study of vowel formant patterns showed substantial improvements in category separability when a pattern classifier was trained on multiple samples of the formant pattern rather than a single sample at steady state [J. Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099-3111 (1995)]. However, in the earlier study all utterances were recorded in a constant /hVd/ environment. The main purpose of the present study was to determine whether a close relationship between vowel identity and spectral change patterns is maintained when the consonant environment is allowed to vary. Recordings were made of six men and six women producing eight vowels (see text) in isolation and in CVC syllables. The CVC utterances consisted of all combinations of seven initial consonants (/h,b,d,g,p,t,k/) and six final consonants (/b,d,g,p,t,k/). Formant frequencies for F1-F3 were measured every 5 ms during the vowel using an interactive editing tool. Results showed highly significant effects of phonetic environment. As with an earlier study of this type, particularly large shifts in formant patterns were seen for rounded vowels in alveolar environments [K. Stevens and A. House, J. Speech Hear. Res. 6, 111-128 (1963)]. Despite these context effects, substantial improvements in category separability were observed when a pattern classifier incorporated spectral change information. Modeling work showed that many aspects of listener behavior could be accounted for by a fairly simple pattern classifier incorporating F0, duration, and two discrete samples of the formant pattern.
144157716
Speaking Rate and Segments: A Look at the Relation between Speech Production and Speech Perception for the Voicing Contrast
Abstract When listeners process segmentally relevant properties of the speech signal they do so in a rate-dependent manner. This is seen as a shift in the perceptual category boundary; as rate declines and overall syllable duration increases, the category boundary moves toward a longer value of the acoustic property in question. Focusing on the /b/-/p/ distinction specified by voice onset time (VOT), we investigated whether the acoustic modifications that occur with an alteration in speaking rate accord with this pattern of perceptual boundary shift. Two main findings emerged. First, as speaking rate became slower and overall syllable duration became longer, the VOT value of the consonant, especially that of the voiceless /p/, also became longer. Second, and most important, the VOT value that optimally separated the /b/ and /p/ VOT distributions also changed with rate, increasing with increasing syllable duration. However, the magnitude of the boundary shift obtained for these production data was greater than that typically found in perceptual experiments. This suggests the existence of constraints on the extent to which the perceptual system can accommodate for alterations due to rate of speech.
34797718
Reaction times to comparisons within and across phonetic categories
Same-different reaction times (RTs) were obtained to pairs of synthetic speech sounds ranging perceptually from /ba/ through /pa/. Listeners responded “same” if both stimuli in a pair were the same phonetic segments (i.e., /ba/-/ba/ or /pa/-/pa/) or “different” if both stimuli were different phonetic segments (i.e., /ba/-/pa/ or /pa/-/ba/). RT for “same” responses was faster to pairs of acoustically identical stimuli (A-A) than to pairs of acoustically different stimuli (A-a) belonging to the same phonetic category. RT for “different” responses was faster for large acoustic differences across a phonetic boundary than for smaller acoustic differences across a phonetic boundary. The results suggest that acoustic information for stop consonants is available to listeners, although the retrieval of this information in discrimination will depend on the level of processing accessed by the particular information processing task.
44457414
Modeling phoneme perception. I: Categorical perception.
On the basis of a number of vowel and stop-consonant discrimination experiments (AX and 2IFC fixed and roving) with natural stimuli, it is concluded that stop-consonant perception is highly categorical: there were few significant differences between the discrimination results and the phoneme identification results. Moreover, the discrimination and identification response maxima differed significantly from the other data points. Vowel perception was much less categorical: the maxima in the functions were much less significant, and there were significant differences between the various paradigms. Consonant discrimination was much less (if at all) subject to range effects than vowel discrimination. All these results point to different memory types for stop consonants and vowels, and, consequently, to a combination of two different theories of speech sound discrimination: dual-process theory (DPT) for consonants, and trace-context theory (TCT) for vowels.
8686819
Auditory Cortex Accesses Phonological Categories: An MEG Mismatch Study
The studies presented here use an adapted oddball paradigm to show evidence that representations of discrete phonological categories are available to the human auditory cortex. Brain activity was recorded using a 37-channel biomagnetometer while eight subjects listened passively to synthetic speech sounds. In the phonological condition, which contrasted stimuli from an acoustic /d/-/t/ continuum, a magnetic mismatch field (MMF) was elicited in a sequence of stimuli in which phonological categories occurred in a many-to-one ratio, but no acoustic many-to-one ratio was present. In order to isolate the contribution of phonological categories to the MMF responses, the acoustic parameter of voice onset time, which distinguished standard and deviant stimuli, was also varied within the standard and deviant categories. No MMF was elicited in the acoustic condition, in which the acoustic distribution of stimuli was identical to the first experiment, but the many-to-one distribution of phonological categories was removed. The design of these studies makes it possible to demonstrate the all-or-nothing property of phonological category membership. This approach contrasts with a number of previous studies of phonetic perception using the mismatch paradigm, which have demonstrated the graded property of enhanced acoustic discrimination at or near phonetic category boundaries.
22795389
Event-Related Potentials to Infrequent Changes in Synthesized Phonetic Stimuli
Event-related potentials (ERPs) to synthetic consonantvowel syllables were recorded. Infrequent changes in such a syllable elicited a "mismatch negativity" as well as an enhanced N100 component of the ERP even when subjects did not pay attention to the stimuli. Both components are probably generated in the supratemporal auditory cortex suggesting that in these areas there are neural networks that are automatically activated by speech-specific auditory stimulus features such as formant transitions.
12252728
On the relation of speech to language
There are two widely divergent theories about the relation of speech to language. The more conventional view holds that the elements of speech are sounds that rely for their production and perception on two wholly separate processes, neither of which is distinctly linguistic. Accordingly, the primary motor and perceptual representations are inappropriate for linguistic purposes until a cognitive process of some sort has connected them to language and to each other. The less conventional theory takes the speech elements to be articulatory gestures that are the primary objects of both production and perception. Those gestures form a natural class that serves a linguistic function and no other. Therefore, their representations are immediately linguistic, requiring no cognitive intervention to make them appropriate for use by the other components of the language system. The unconventional view provides the more plausible answers to three important questions: (1) How was the necessary parity between speaker and listener established in evolution, and how maintained? (2) How does speech meet the special requirements that underlie its ability, unique among natural communication systems, to encode an indefinitely large number of meanings? (3) What biological properties of speech make it easier than the reading and writing of its alphabetic transcription?
46077125
Noncategorical perception of stop consonants differing in VOT.
The discriminability of bilabial stop consonants differing in VOT (the Abramson-Lisker bilabial series) was measured in a same-different task, an oddity task, and a dual response, discrimination--identification task. Subjects showed excellent within-category discrimination in all three tasks after a moderate amount of training in a same-different task with a fixed standard and with feedback. In addition, discrimination performance continuously improved with increasing stimulus difference for both intra- and intercategory comparisons. Also, subjects were able to alter their identification responses so that well-defined category boundaries fell at arbitrary values determined by the experiments. These results are not compatible with a strict interpretation of the categorical perception of stop consonants.
19596648
Categorical perception depends on the discrimination task
Speech sounds are said to be perceivedcategorically. This notion is usually operationalized as the extent to which discrimination of stimuli is predictable from phoneme classification of the same stimuli. In this article, vowel continua were presented to listeners in a four-interval discrimination task (2IFC with flankers, or 4I2AFC) and a classification task. The results showed that there was no indication of categorical perception at all, since observed discrimination was found not to be predictable from the classification data. Variation in design, such as different step sizes or longer interstimulus intervals, did not affect this outcome, but a 2IFC experiment (without flankers, or 2I2AFC) involving the same stimuli elicited the traditional categorical results. These results indicate that the four-interval task made it difficult for listeners to use phonetic information and, hence, that categorical perception may be a function of the type of task used for discrimination.
42203879
Categorical and noncategorical modes of speech perception along the voicing continuum.
Native speakers of English identified and then discriminated between stimuli which varied in voice onset time (VOT). One group of listeners identified a randomized sequence of stimuli; another group identified an ordered sequence of stimuli, in which stimuli from the VOT continuum were presented in a consecutive order. Half of the Ss in each group then received one of two discrimination formats: the ABX discrimination test in which X was identified with A or with B, or 4IAX test of paired similarity in which two pairs of stimuli—one pair always the same and one pair always different—were presented on each trial. Noncategorical perception of the voicing distinction, reflected by an improvement in discrimination within phonetic categories, was obtained for the group of listeners who experienced both the sequential identification procedure and the 4IAX discrimination test. The results are interpreted as providing evidence for separate auditory and phonetic levels of discrimination in speech perception.
123609
Linear Coding of Voice Onset Time
Voice onset time (VOT) provides an important auditory cue for recognizing spoken consonant-vowel syllables. Although changes in the neuromagnetic response to consonant-vowel syllables with different VOT have been examined, such experiments have only manipulated VOT with respect to voicing. We utilized the characteristics of a previously developed asymmetric VOT continuum [Liederman, J., Frye, R. E., McGraw Fisher, J., Greenwood, K., & Alexander, R. A temporally dynamic contextual effect that disrupts voice onset time discrimination of rapidly successive stimuli. Psychonomic Bulletin and Review, 12, 380386, 2005] to determine if changes in the prominent M100 neuromagnetic response were linearly modulated by VOT. Eight right-handed, English-speaking, normally developing participants performed a VOT discrimination task during a whole-head neuromagnetic recording. The M100 was identified in the gradiometers overlying the right and left temporal cortices and single dipoles were fit to each M100 waveform. A repeated measures analysis of variance with post hoc contrast test for linear trend was used to determine whether characteristics of the M100 were linearly modulated by VOT. The morphology of the M100 gradiometer waveform and the peak latency of the dipole waveform were linearly modulated by VOT. This modulation was much greater in the left, as compared to the right, hemisphere. The M100 dipole moved in a linear fashion as VOT increased in both hemispheres, but along different axes in each hemisphere. This study suggests that VOT may linearly modulate characteristics of the M100, predominately in the left hemisphere, and suggests that the VOT of consonant-vowel syllables, instead of, or in addition to, voicing, should be examined in future experiments.
17787165
The effect of subphonetic differences on lexical access
This study investigated whether lexical access is affected by inherent acoustic variations that contribute to the identity of a phonetic feature and ultimately a phonetic segment. Two experiments were conducted to determine whether the magnitude of semantic (associative) priming in a lexical decision task is influenced when the acoustic manifestation of the initial voiceless stop consonant (specifically, voice onset time) of a prime word semantically related to a lexical decision target was systematically manipulated (e.g., prime: "king"; target: "queen"). Results showed no effect of the acoustic manipulations at the longer interstimulus interval (250 ms); however, at the shorter interstimulus interval (50 ms), the magnitude of semantic facilitation decreased as a function of the voice onset time manipulations. In addition, there was a tendency toward slower lexical decision latencies when the prime word had a real word voiced counterpart than when it did not. These results suggest that activation levels of words in the lexicon are graded, depending on the subphonetic shape of the input word. Results also suggest that words which are phonologically similar to the intended word candidate are activated to some extent, whether the input provides a relatively poor phonetic representation of the intended word or a good one.
25509842
Effects of subphonetic and syllable structure variation on word recognition
This study explored whether natural acoustic variations as exemplified by either subphonetic changes or syllable structure changes affect word recognition processes. Subphonetic variations were realized by differences in the voice-onset time (VOT) value of initial voiceless stop consonants, and syllable structure variations were realized by vowel deletion in initial unstressed syllables in multisyllable words. An auditory identity priming paradigm was used to determine whether the amount of facilitation obtained to a target stimulus in a lexical decision task was affected by the presence of these acoustic variations in a prime stimulus. Results revealed different patterns for the two types of variability as a function of lexical status. In the case of subphonetic variations, shortening of VOT resulted in reduced facilitation for words but not for nonwords, whereas in the case of syllable structure variation, vowel deletion in an unstressed syllable resulted in reduced facilitation for nonwords and increased facilitation for words. These findings indicate that subphonetic variability interferes with word recognition, whereas syllable structure variability does not, and that this effect is independent of the magnitude of the acoustic difference between a citation form and its variant. Furthermore, the results suggest that the lexical status of the target item plays a crucial role in the processing of both types of variability. Results are considered in relation to current models of word recognition.
17359901
Echoes of echoes? An episodic theory of lexical access.
In this article the author proposes an episodic theory of spoken word representation, perception, and production. By most theories, idiosyncratic aspects of speech (voice details, ambient noise, etc.) are considered noise and are filtered in perception. However, episodic theories suggest that perceptual details are stored in memory and are integral to later perception. In this research the author tested an episodic model (MINERVA 2; D. L. Hintzman, 1986) against speech production data from a word-shadowing task. The model predicted the shadowing-response-time patterns, and it correctly predicted a tendency for shadowers to spontaneously imitate the acoustic patterns of words and nonwords. It also correctly predicted imitation strength as a function of "abstract" stimulus properties, such as word frequency. Taken together, the data and theory suggest that detailed episodes constitute the basic substrate of the mental lexicon.
16796807
A unified account of categorical effects in phonetic perception
Categorical effects are found across speech sound categories, with the degree of these effects ranging from extremely strong categorical perception in consonants to nearly continuous perception in vowels. We show that both strong and weak categorical effects can be captured by a unified model. We treat speech perception as a statistical inference problem, assuming that listeners use their knowledge of categories as well as the acoustics of the signal to infer the intended productions of the speaker. Simulations show that the model provides close fits to empirical data, unifying past findings of categorical effects in consonants and vowels and capturing differences in the degree of categorical effects through a single parameter.
144484551
Assimilation and Anticipation in Continuous Spoken Word Recognition
Abstract English coronal place assimilation is one of many productive phonological processes that change the phonological form of words. It may, for example, cause speakers to pronounce green as something approximating [grin] or [grim] in different contexts. The present work examines how listeners recognize words that have undergone this modification. Current accounts are broadly differentiated by two issues: (1) whether listeners generally recognize words that have undergone word-final, single-feature modification, and (2) how context effects in the perception of assimilated speech are interpreted. Experiment 1 employs form priming to demonstrate that listeners tolerate single-feature mismatch resulting from both phonologically plausible and phonologically implausible word form modification when recognizing words heard in context. Experiments 2 and 3 employ phoneme monitoring and negative rhyme priming paradigms, respectively, to demonstrate that listeners use assimilation to anticipate upcoming context. Evidence for anticipation is contrasted with claims that listeners use context to regressively infer the underlying form of place-assimilated segments.
17184138
Anticipatory coarticulation facilitates word recognition in toddlers
Children learn from their environments and their caregivers. To capitalize on learning opportunities, young children have to recognize familiar words efficiently by integrating contextual cues across word boundaries. Previous research has shown that adults can use phonetic cues from anticipatory coarticulation during word recognition. We asked whether 18-24 month-olds (n=29) used coarticulatory cues on the word "the" when recognizing the following noun. We performed a looking-while-listening eyetracking experiment to examine word recognition in neutral vs. facilitating coarticulatory conditions. Participants looked to the target image significantly sooner when the determiner contained facilitating coarticulatory cues. These results provide the first evidence that novice word-learners can take advantage of anticipatory sub-phonemic cues during word recognition.
15868867
Immediate effects of anticipatory coarticulation in spoken-word recognition.
Two visual-world experiments examined listeners' use of pre word-onset anticipatory coarticulation in spoken-word recognition. Experiment 1 established the shortest lag with which information in the speech signal influences eye-movement control, using stimuli such as "The … ladder is the target". With a neutral token of the definite article preceding the target word, saccades to the referent were not more likely than saccades to an unrelated distractor until 200-240 ms after the onset of the target word. In Experiment 2, utterances contained definite articles which contained natural anticipatory coarticulation pertaining to the onset of the target word (" The ladder … is the target"). A simple Gaussian classifier was able to predict the initial sound of the upcoming target word from formant information from the first few pitch periods of the article's vowel. With these stimuli, effects of speech on eye-movement control began about 70 ms earlier than in Experiment 1, suggesting rapid use of anticipatory coarticulation. The results are interpreted as support for "data explanation" approaches to spoken-word recognition. Methodological implications for visual-world studies are also discussed.
23065567
Recognition of vowels from information in fricatives: perceptual evidence of fricative-vowel coarticulation.
Four studies investigated the perceptual effects of spectral variations in fricatives produced in different vowel contexts. The alveolar and palatal fricatives, [s, z, integral of, 3], were produced by two talkers in the context of the vowels [a, i, u], generating 12 fricative-vowel combinations. A computer-controlled editing procedure was used to excise fricative segments of 150-ms duration, as measured back from vowel onset. These excised segments were used as test stimuli in the four experiments. In the first experiment, fricative identification was highly accurate, especially for segments produced in the [a] context. The results of the subsequent three vowel identification experiments, revealed that the high vowels [i] and [u] were identified 60%--80% of the time in all fricative contexts, with the exception of [i] produced in the context of [integral of]. In contrast, identification scores for [a] were close to chance in all fricative contexts. Acoustic analyses of the stimuli revealed that the fricative segments with high vowel identification scores exhibited clear evidence of spectral changes associated with the vowels, while those segments with the highest fricative identification scores exhibited spectra most similar to fricatives produced in isolation. These results, in combination with more extensive acoustic analyses [S. D. Soli, J. Acoust. Soc. Am. 70, 976--984 (1981)] are discussed in terms of variations in the articulatory compatibility of tongue movements required to produce fricative-vowel sequences.
45031483
On the dissociation of spectral and temporal cues to the voicing distinction in initial stop consonants.
It has been claimed that a rising first‐formant (F1) transition is an important cue to the voiced–voiceless distinction for syllable‐initial, prestressed stop consonants in English. Lisker [J. Acoust. Soc. Am. 57, 1547–1551 (L) (1975)] has pointed out that the acoustic manipulations suggesting a role for F1 have involved covariation of the onset frequency of F1 with the duration, and hence the frequency extent, of the F1 transition; he has argued that effects hitherto ascribed to the transition are more properly attributed to its onset. Two experiments are reported in which F1 onset frequency and F1 transition duration/extent were manipulated independently. The results confirm Lisker’s suggestion that the major effect of F1 in initial voicing contrasts is determined by its perceived frequency at the onset of voicing and show that a periodically excited F1 transition is not, per se, a positive cue to voicing. In further experiments, the relative levels and the frequencies at the onset of voicing of both F1...
30695509
Roles of voice onset time and F0 in stop consonant voicing perception: effects of masking noise and low-pass filtering.
PURPOSE
The contributions of voice onset time (VOT) and fundamental frequency (F0) were evaluated for the perception of voicing in syllable-initial stop consonants in words that were low-pass filtered and/or masked by speech-shaped noise. It was expected that listeners would rely less on VOT and more on F0 in these degraded conditions.


METHOD
Twenty young listeners with normal hearing identified modified natural speech tokens that varied by VOT and F0 in several conditions of low-pass filtering and masking noise. Stimuli included /b/-/p/ and /d/-/t/ continua that were presented in separate blocks. Identification results were modeled using mixed-effects logistic regression.


RESULTS
When speech was filtered and/or masked by noise, listeners' voicing perceptions were driven less by VOT and more by F0. Speech-shaped masking noise exerted greater effects on the /b/-/p/ contrast, while low-pass filtering exerted greater effects on the /d/-/t/ contrast, consistent with the acoustics of these contrasts.


CONCLUSION
Listeners can adjust their use of acoustic-phonetic cues in a dynamic way that is appropriate for challenging listening conditions; cues that are less influential in ideal conditions can gain priority in challenging conditions.
10489100
Gradient sensitivity to within-category variation in words and syllables.
Five experiments monitored eye movements in phoneme and lexical identification tasks to examine the effect of within-category subphonetic variation on the perception of stop consonants. Experiment 1 demonstrated gradient effects along voice-onset time (VOT) continua made from natural speech, replicating results with synthetic speech (B. McMurray, M. K. Tanenhaus, & R. N. Aslin, 2002). Experiments 2-5 used synthetic VOT continua to examine effects of response alternatives (2 vs. 4), task (lexical vs. phoneme decision), and type of token (word vs. consonant-vowel). A gradient effect of VOT in at least one half of the continuum was observed in all conditions. These results suggest that during online spoken word recognition, lexical competitors are activated in proportion to their continuous distance from a category boundary. This gradient processing may allow listeners to anticipate upcoming acoustic-phonetic information in the speech signal and dynamically compensate for acoustic variability.
16006408
The Perception of Voice Onset Time: An fMRI Investigation of Phonetic Category Structure
This study explored the neural systems underlying the perception of phonetic category structure by investigating the perception of a voice onset time (VOT) continuum in a phonetic categorization task. Stimuli consisted of five synthetic speech stimuli which ranged in VOT from 0 msec ([da]) to 40 msec ([ta]). Results from 12 subjects showed that the neural system is sensitive to VOT differences of 10 msec and that details of phonetic category structure are retained throughout the phonetic processing stream. Both the left inferior frontal gyrus (IFG) and cingulate showed graded activation as a function of category membership with increasing activation as stimuli approached the phonetic category boundary. These results are consistent with the view that the left IFG is involved in phonetic decision processes, with the extent of activation influenced by increased resources devoted to resolving phonetic category membership and/or selecting between competing phonetic categories. Activation patterns in the cingulate suggest that it is sensitive to stimulus difficulty and resolving response conflict. In contrast, activation in the posterior left middle temporal gyrus and the left angular gyrus showed modulation of activation only to the best fit of the phonetic category, suggesting that these areas are involved in mapping sound structure to its phonetic representation. The superior temporal gyrus (STG) bilaterally showed weaker sensitivity to the differences in phonetic category structure, providing further evidence that the STG is involved in the early analysis of the sensory properties of speech.
6199399
The cortical organization of speech processing
Despite decades of research, the functional neuroanatomy of speech processing has been difficult to characterize. A major impediment to progress may have been the failure to consider task effects when mapping speech-related processing systems. We outline a dual-stream model of speech processing that remedies this situation. In this model, a ventral stream processes speech signals for comprehension, and a dorsal stream maps acoustic speech signals to frontal lobe articulatory networks. The model assumes that the ventral stream is largely bilaterally organized — although there are important computational differences between the left- and right-hemisphere systems — and that the dorsal stream is strongly left-hemisphere dominant.
23667359
Noise differentially impacts phoneme representations in the auditory and speech motor systems
Significance Contentious debate remains regarding the role of the redundant motor activation during speech perception. In this functional MRI study, multivariate pattern analysis revealed stronger multivoxel phoneme discrimination in speech motor regions than auditory cortices when the speech phonemes were moderately degraded by noise. Our findings provide neuroimaging evidence for the sensorimotor integration account. Preserved phoneme discrimination in speech motor areas may compensate for loss of specificity in noise-impoverished speech representations, which aids speech perception under adverse listening conditions. Although it is well accepted that the speech motor system (SMS) is activated during speech perception, the functional role of this activation remains unclear. Here we test the hypothesis that the redundant motor activation contributes to categorical speech perception under adverse listening conditions. In this functional magnetic resonance imaging study, participants identified one of four phoneme tokens (/ba/, /ma/, /da/, or /ta/) under one of six signal-to-noise ratio (SNR) levels (–12, –9, –6, –2, 8 dB, and no noise). Univariate and multivariate pattern analyses were used to determine the role of the SMS during perception of noise-impoverished phonemes. Results revealed a negative correlation between neural activity and perceptual accuracy in the left ventral premotor cortex and Broca’s area. More importantly, multivoxel patterns of activity in the left ventral premotor cortex and Broca’s area exhibited effective phoneme categorization when SNR ≥ –6 dB. This is in sharp contrast with phoneme discriminability in bilateral auditory cortices and sensorimotor interface areas (e.g., left posterior superior temporal gyrus), which was reliable only when the noise was extremely weak (SNR > 8 dB). Our findings provide strong neuroimaging evidence for a greater robustness of the SMS than auditory regions for categorical speech perception in noise. Under adverse listening conditions, better discriminative activity in the SMS may compensate for loss of specificity in the auditory system via sensorimotor integration.
13472127
Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients.
The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.
7559550
Children with specific language impairments perceive speech most categorically when tokens are natural and meaningful.
PURPOSE
To examine perceptual deficits as a potential underlying cause of specific language impairments (SLI).


METHOD
Twenty-one children with SLI (8;7-11;11 [years;months]) and 21 age-matched controls participated in categorical perception tasks using four series of syllables for which perceived syllable-initial voicing varied. Series were either words or abstract nonword syllables and either synthesized or high-quality edited natural utterances. Children identified and discriminated (a) digitally edited tokens of naturally spoken "bowl"-"pole", (b) synthesized renditions of "bowl"-"pole", (c) natural "ba"-"pa", and (d) synthetic "ba"-"pa".


RESULTS
Identification crossover locations were the same for both groups of children, but there was modestly less accuracy on unambiguous endpoints for children with SLI. Planned comparisons revealed these effects to be limited to synthesized speech. Children with SLI showed overall reduced discrimination, but these effects were limited to abstract nonword syllables.


CONCLUSION
Overall, children with SLI perceived naturally spoken real words comparably to age-matched peers but showed impaired identification and discrimination of synthetic speech and of abstract syllables. Poor performance on speech perception tasks may result from task demands and stimulus properties, not perceptual deficits.
6222060
Categorical speech perception deficits distinguish language and reading impairments in children.
We examined categorical speech perception in school-age children with developmental dyslexia or Specific Language Impairment (SLI), compared to age-matched and younger controls. Stimuli consisted of synthetic speech tokens in which place of articulation varied from 'b' to 'd'. Children were tested on categorization, categorization in noise, and discrimination. Phonological awareness skills were also assessed to examine whether these correlated with speech perception measures. We observed similarly good baseline categorization rates across all groups; however, when noise was added, the SLI group showed impaired categorization relative to controls, whereas dyslexic children showed an intact profile. The SLI group showed poorer than expected between-category discrimination rates, whereas this pattern was only marginal in the dyslexic group. Impaired phonological awareness profiles were observed in both the SLI and dyslexic groups; however, correlations between phonological awareness and speech perception scores were not significant. The results of the study suggest that in children with language and reading impairments, there is a significant relationship between receptive language and speech perception, there is at best a weak relationship between reading and speech perception, and indeed the relationship between phonological and speech perception deficits is highly complex.
23973629
Perception of formant transition cues to place of articulation in children with language impairments.
Discrimination and phonetic identification abilities of 5- to 6-year-old children with language impairments were compared to those of 4-year-olds with normally developing language and to previous findings from 5- to 6-year-olds and adults for synthetic stimuli ranging from [ba] to [da]. Results showed similar discrimination sensitivity to the second- and third-formant transition cues of stimuli by all children, with poorest sensitivity by the youngest. Phonetic categorization by children with language impairments was most different from the groups with normal language abilities, evidenced by a difference in the percent of tokens labeled as "BA" and by greater variability in labeling and in placement of phonetic category boundaries. Results support hypotheses by Gathercole and Baddeley (1990) suggesting that the phonological component of working memory may be disordered in children with language impairments. Results are also suggestive of specific difficulties with left-hemisphere processing associated with language learning rather than with problems related to sensitivity to formant transitions of the speech tokens.
7971028
Speech perception in severely disabled and average reading children.
ll has been hypothesized thai children with specific disabilities in reading may have subtle auditory and/or speech perception deficits. To address this question, recent investigations have focussed on whether reading disabled children show categorical speech perception. These efforts have yielded equivocal results. The present study was designed to attempt to help resolve this controversy by comparing the performance of severely disabled readers with normal readers in four speech perception tasks. Results indicated that perception was significantly less categorical among the severely disabled readers in ihrcc of the lour speech perception tasks. The possible implications of this small, but significant, difference arc discussed. KESUME II a ete suggcre que des cnlants ayant des diflicultcs a lire pouvaicnt avoir des deficits subtils d'audition ct/ou de perception du langagc. Les eludes qui se sont aftaquccs a ce problcmc ont produit des rcsultats pour le moins equivoques. L'ctudc presentee ici a tenUS dc rcsoudre cette controverse en comparant la performance d'enfants en difficultc dc lecture avee des enfants normaux dans quatre taches dc perception du langagc. Les resultats ont montrc que la perception etait significativement moins categoriquc the/, les enfants handicapes dans trois des quatre taches. Les implications de cettc difference, petite mais significative, sont discuses. The relation between speech perception and the process of reading has been outlined previously (Godfrey, Syrdal-Lasky, Millay, & Knox, 1981). Basically, in reading, the printed word has to be mapped on to the underlying phonologic representation (Liberman, 1983; Read, 1971). This process includes converting individual graphemes to phonemes and strings of graphemes to the overlapping and highly encoded (Liberman, Cooper, Shankweiler, & Studdert-Kennedy, 1967) larger linguistic units such as syllables and words. In order to make this conversion, the reader must have a stable, context-independent phonological representation available on which to map the linguistic units. Research in speech perception has shown that adults, children, and even prelinguistic infants tend to perceive speech sounds in a categorical fashion. That is, when presented with several varying naturally produced speech syllables or *We wish to thank the students, staff, and board members of the Kenneth Gordon School in New Westminster, B C and the students, staff, and school board ol'licc of the Vancouver Public Schools for their participation and cooperation in this project. Special thanks are extended to Margaret Follis, principal of the Kenneth Gordon School. Our appreciation is also extended to Dr. Alvin M. Liberman, Director, Haskins Laboratory, for making us welcome at Haskins, to Dr. Ignatious Mattingly for help synthesizing the stimuli, and to Dr. Patrice Dunn for serving as a consultant to the grant. Special thanks to Kathy Searcy for all the hours she spent collecting the data and to Margaret Arab for performing the data analyses. This research was supported by a grant from the British Columbia I lealth Care Research Foundation ( # 103(81 2)) to the authors. Address reprint requests to Janet V. Werker, Department of Psychology, The University of British Columbia, Vancouver, BC, Canada V6T IY7
21267898
Individual differences in language ability are related to variation in word recognition, not speech perception: evidence from eye movements.
PURPOSE
The authors examined speech perception deficits associated with individual differences in language ability, contrasting auditory, phonological, or lexical accounts by asking whether lexical competition is differentially sensitive to fine-grained acoustic variation.


METHOD
Adolescents with a range of language abilities (N = 74, including 35 impaired) participated in an experiment based on McMurray, Tanenhaus, and Aslin (2002). Participants heard tokens from six 9-step voice onset time (VOT) continua spanning 2 words (beach/peach, beak/peak, etc.) while viewing a screen containing pictures of those words and 2 unrelated objects. Participants selected the referent while eye movements to each picture were monitored as a measure of lexical activation. Fixations were examined as a function of both VOT and language ability.


RESULTS
Eye movements were sensitive to within-category VOT differences: As VOT approached the boundary, listeners made more fixations to the competing word. This did not interact with language ability, suggesting that language impairment is not associated with differential auditory sensitivity or phonetic categorization. Listeners with poorer language skills showed heightened competitors fixations overall, suggesting a deficit in lexical processes.


CONCLUSION
Language impairment may be better characterized by a deficit in lexical competition (inability to suppress competing words), rather than differences in phonological categorization or auditory abilities.
775364
The fragile nature of the speech-perception deficit in dyslexia: Natural vs. synthetic speech
A number of studies reported that developmental dyslexics are impaired in speech perception, especially for speech signals consisting of rapid auditory transitions. These studies mostly made use of a categorical-perception task with synthetic-speech samples. In this study, we show that deficits in the perception of synthetic speech do not generalise to the perception of more naturally sounding speech, even if the same experimental paradigm is used. This contrasts with the assumption that dyslexics are impaired in the perception of rapid auditory transitions.
32387184
Categorical perception of speech by children with specific language impairments.
Previous research has suggested that children with specific language impairments (SLI) have deficits in basic speech perception abilities, and this may be an underlying source of their linguistic deficits. These findings have come from studies in which perception of synthetic versions of meaningless syllables was typically examined in tasks with high memory demands. In this study, 20 children with SLI (mean age = 9 years, 3 months) and 20 age-matched peers participated in a categorical perception task. Children identified and discriminated digitally edited versions of naturally spoken real words in tasks designed to minimize memory requirements. Both groups exhibited all hallmarks of categorical perception: a sharp labeling function, discontinuous discrimination performance, and discrimination predicted from identification. There were no group differences for identification data, but children with SLI showed lower peak discrimination values. Children with SLI still discriminated phonemically contrastive pairs at levels significantly better than chance, with discrimination of same-label pairs at chance. These data suggest that children with SLI perceive natural speech tokens comparably to age-matched controls when listening to words under conditions that minimize memory load. Further, poor performance on speech perception tasks may not be due to a speech perception deficit, but rather to a consequence of task demands.
12364477
Performance of dyslexic children on speech perception tests.
Abstract Several researchers who have compared the performance of dyslexic and normal-reading children on a variety of different tasks have suggested that dyslexic children may have subtle deficits in the phonemic analysis of spoken as well as written language. Thus it is of interest to know how children who have extraordinary difficulty learning to read can perform explicity auditory-phonetic tasks. Seventeen dyslexic children (10 years of age) and a group of 17 controls were administered tests of identification and discrimination of synthesized voiced stop consonants differing in place of articulation. These were tests of the type used to study categorical perception in adults, adapted for use with young children. Significant differences between dyslexics and controls were found in both kinds of tasks; the pattern of identification and discrimination differences suggests an inconsistency in the dyslexics' phonetic classification of auditory cues. A significant relationship was found between reading level and speech discrimination.
345880
Perceptual discrimination of speech sounds in developmental dyslexia.
Experiments previously reported in the literature suggest that people with dyslexia have a deficit in categorical perception. However, it is still unclear whether the deficit is specific to the perception of speech sounds or whether it more generally affects auditory function. In order to investigate the relationship between categorical perception and dyslexia, as well as the nature of this categorization deficit, speech specific or not, the discrimination responses of children who have dyslexia and those of average readers to sinewave analogues of speech sounds were compared. These analogues were presented in two different conditions, either as nonspeech whistles or as speech sounds. Results showed that children with dyslexia are less categorical than average readers in the speech condition, mainly because they are better at discriminating acoustic differences between stimuli belonging to the same category. In the nonspeech condition, discrimination was also better for children with dyslexia, but differences in categorical perception were less clear-cut. Further, the location of the categorical boundary on the stimulus continuum differed between speech and nonspeech conditions. As a whole, this study shows that categorical deficit in children with dyslexia results primarily from an increased perceptibility of within-category differences and that it has a speech-specific component. These findings may have profound implications for learning and re-education.
8629386
Language deficits in dyslexic children: speech perception, phonology, and morphology.
We investigated the relationship between dyslexia and three aspects of language: speech perception, phonology, and morphology. Reading and language tasks were administered to dyslexics aged 8-9 years and to two normal reader groups (age-matched and reading-level matched). Three dyslexic groups were identified: phonological dyslexics (PD), developmentally language impaired (LI), and globally delayed (delay-type dyslexics). The LI and PD groups exhibited similar patterns of reading impairment, attributed to low phonological skills. However, only the LI group showed clear speech perception deficits, suggesting that such deficits affect only a subset of dyslexics. Results also indicated phonological impairments in children whose speech perception was normal. Both the LI and the PD groups showed inflectional morphology difficulties, with the impairment being more severe in the LI group. The delay group's reading and language skills closely matched those of younger normal readers, suggesting these children had a general delay in reading and language skills, rather than a specific phonological impairment. The results are discussed in terms of models of word recognition and dyslexia.
143071366
Individual Differences in Categorical Perception Are Related to Sublexical/Phonological Processing in Reading
This article examines the relationship between individual differences in speech perception and sublexical/phonological processing in reading. We used an auditory phoneme identification task in which a /ba/-/pa/ syllable continuum measured sensitivity to classify participants into three performance groups: poor, medium, and good categorizers. A lexical decision task manipulated syllable and word frequency. We found that the two tasks were associated. Poor categorizers did not present the typical syllable frequency effect; however, the other groups were sensitive to phonological information to differing degrees and showed the inhibitory syllable frequency effect only for low-frequency words. These results suggest that auditory phoneme identification efficiency may be related to the sublexical processes involved in reading words.
13719007
Word Recognition Variability With Cochlear Implants: “Perceptual Attention” Versus “Auditory Sensitivity”
Objectives: Cochlear implantation does not automatically result in robust spoken language understanding for postlingually deafened adults. Enormous outcome variability exists, related to the complexity of understanding spoken language through cochlear implants (CIs), which deliver degraded speech representations. This investigation examined variability in word recognition as explained by “perceptual attention” and “auditory sensitivity” to acoustic cues underlying speech perception. Design: Thirty postlingually deafened adults with CIs and 20 age-matched controls with normal hearing (NH) were tested. Participants underwent assessment of word recognition in quiet and perceptual attention (cue-weighting strategies) based on labeling tasks for two phonemic contrasts: (1) “cop”–“cob,” based on a duration cue (easily accessible through CIs) or a dynamic spectral cue (less accessible through CIs), and (2) “sa”–“sha,” based on static or dynamic spectral cues (both potentially poorly accessible through CIs). Participants were also assessed for auditory sensitivity to the speech cues underlying those labeling decisions. Results: Word recognition varied widely among CI users (20 to 96%), but it was generally poorer than for NH participants. Implant users and NH controls showed similar perceptual attention and auditory sensitivity to the duration cue, while CI users showed poorer attention and sensitivity to all spectral cues. Both attention and sensitivity to spectral cues predicted variability in word recognition. Conclusions: For CI users, both perceptual attention and auditory sensitivity are important in word recognition. Efforts should be made to better represent spectral cues through implants, while also facilitating attention to these cues through auditory training.
14290873
Using speech sounds to test functional spectral resolution in listeners with cochlear implants.
In this study, spectral properties of speech sounds were used to test functional spectral resolution in people who use cochlear implants (CIs). Specifically, perception of the /ba/-/da/ contrast was tested using two spectral cues: Formant transitions (a fine-resolution cue) and spectral tilt (a coarse-resolution cue). Higher weighting of the formant cues was used as an index of better spectral cue perception. Participants included 19 CI listeners and 10 listeners with normal hearing (NH), for whom spectral resolution was explicitly controlled using a noise vocoder with variable carrier filter widths to simulate electrical current spread. Perceptual weighting of the two cues was modeled with mixed-effects logistic regression, and was found to systematically vary with spectral resolution. The use of formant cues was greatest for NH listeners for unprocessed speech, and declined in the two vocoded conditions. Compared to NH listeners, CI listeners relied less on formant transitions, and more on spectral tilt. Cue-weighting results showed moderately good correspondence with word recognition scores. The current approach to testing functional spectral resolution uses auditory cues that are known to be important for speech categorization, and can thus potentially serve as the basis upon which CI processing strategies and innovations are tested.
8682131
Discrimination of speech sounds by children with dyslexia: comparisons with chronological age and reading level controls.
Previous studies have shown that children suffering from developmental dyslexia have a deficit in categorical perception of speech sounds. The aim of the current study was to better understand the nature of this categorical perception deficit. In this study, categorical perception skills of children with dyslexia were compared with those of chronological age and reading level controls. Children identified and discriminated /do-to/ syllables along a voice onset time (VOT) continuum. Results showed that children with dyslexia discriminated among phonemically contrastive pairs less accurately than did chronological age and reading level controls and also showed higher sensitivity in the discrimination of allophonic contrasts. These results suggest that children with dyslexia perceive speech with allophonic units rather than phonemic units. The origin of allophonic perception in the course of perceptual development and its implication for reading acquisition are discussed.
15995021
Allophonic mode of speech perception in dyslexia.
Perceptual discrimination between speech sounds belonging to different phoneme categories is better than that between sounds falling within the same category. This property, known as "categorical perception," is weaker in children affected by dyslexia. Categorical perception develops from the predispositions of newborns for discriminating all potential phoneme categories in the world's languages. Predispositions that are not relevant for phoneme perception in the ambient language are usually deactivated during early childhood. However, the current study shows that dyslexic children maintain a higher sensitivity to phonemic distinctions irrelevant in their linguistic environment. This suggests that dyslexic children use an allophonic mode of speech perception that, although without straightforward consequences for oral communication, has obvious implications for the acquisition of alphabetic writing. Allophonic perception specifically affects the mapping between graphemes and phonemes, contrary to other manifestations of dyslexia, and may be a core deficit.
1954327
Effects of syllable-initial voicing and speaking rate on the temporal characteristics of monosyllabic words.
Two speech production experiments tested the validity of the traditional method of creating voice-onset-time (VOT) continua for perceptual studies in which the systematic increase in VOT across the continuum is accompanied by a concomitant decrease in the duration of the following vowel. In experiment 1, segmental durations were measured for matched monosyllabic words beginning with either a voiced stop (e.g., big, duck, gap) or a voiceless stop (e.g., pig, tuck, cap). Results from four talkers showed that the change from voiced to voiceless stop produced not only an increase in VOT, but also a decrease in vowel duration. However, the decrease in vowel duration was consistently less than the increase in VOT. In experiment 2, results from four new talkers replicated these findings at two rates of speech, as well as highlighted the contrasting temporal effects on vowel duration of an increase in VOT due to a change in syllable-initial voicing versus a change in speaking rate. It was concluded that the traditional method of creating VOT continua for perceptual experiments, although not perfect, approximates natural speech by capturing the basic trade-off between VOT and vowel duration in syllable-initial voiced versus voiceless stop consonants.
7729871
Effect of speaking rate on the perceptual structure of a phonetic category
When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener’s adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.
11789260
Anticipatory Eye Movements Reveal Infants' Auditory and Visual Categories.
We introduce a new paradigm for the assessment of auditory and visual categories in 6-month-old infants using a 2-alternative anticipatory eye-movement response. Infants were trained by 2 different methods to anticipate the location of a visual reinforcer at 1 of 2 spatial locations (right or left) based on the identity of 2 cuing stimuli. After a training phase, infants were presented with a series of generalization trials in which novel (untrained) stimuli served as the cue to the anticipatory eye movement. Four experiments illustrated that infants can learn the 2-choice discriminative response during training. Infants also showed anticipatory eye movements to novel stimuli, indicating sensitivity to variations along a variety of stimulus dimensions (e.g., color, shape, orientation, spatial frequency, pitch, and duration). In addition, the paradigm can be used to assess categorization in individual infants, thereby revealing the stimulus dimensions to which infants naturally attend.
8139983
Individual differences in categorical perception of speech: Cue weighting and executive function
This study examined individual differences in categorical perception and the use of multiple acoustic cues in the perception of the stop voicing contrast. Goals were to investigate whether gradiency of speech perception was related to listeners' differential sensitivity to acoustic cues and to individual differences in executive function. The experiment included two speech perception tasks (visual analogue scaling [VAS] and anticipatory eye movement [AEM]) administered to 30 English-speaking adults in two separate experimental sessions. Stimuli were a /ta/ to /da/ continuum that systematically varied VOT and f0. Findings were that some listeners had a more gradient pattern of responses on the VAS task; the listeners who had a gradient response pattern on the VAS task also showed more sensitivity to f0 on the AEM task. The patterns were consistent across individuals tested on two separate occasions. These results suggest that variability in how categorically listeners perceive speech sounds is consistent and systematic within individuals.
24825878
Development and Validation of the AzBio Sentence Lists
Objectives: The goal of this study was to create and validate a new set of sentence lists that could be used to evaluate the speech perception abilities of hearing-impaired listeners and cochlear implant (CI) users. Our intention was to generate a large number of sentence lists with an equivalent level of difficulty for the evaluation of performance over time and across conditions. Design: The AzBio sentence corpus includes 1000 sentences recorded from two female and two male talkers. The mean intelligibility of each sentence was estimated by processing each sentence through a five-channel CI simulation and calculating the mean percent correct score achieved by 15 normal-hearing listeners. Sentences from each talker were sorted by percent correct score, and 165 sentences were selected from each talker and were then sequentially assigned to 33 lists, each containing 20 sentences (5 sentences from each talker). List equivalency was validated by presenting all lists, in random order, to 15 CI users. Results: Using sentence scores from the CI simulation study produced 33 lists of sentences with a mean score of 85% correct. The results of the validation study with CI users revealed no significant differences in percent correct scores for 29 of the 33 sentence lists. However, individual listeners demonstrated considerable variability in performance on the 29 lists. The binomial distribution model was used to account for the inherent variability observed in the lists. This model was also used to generate 95% confidence intervals for one and two list comparisons. A retrospective analysis of 172 instances where research subjects had been tested on two lists within a single condition revealed that 94% of results were accurately contained within these confidence intervals. Conclusions: The use of a five-channel CI simulation to estimate the intelligibility of individual sentences allowed for the creation of a large number of sentence lists with an equivalent level of difficulty. The results of the validation procedure with CI users found that 29 of 33 lists allowed scores that were not statistically different. However, individual listeners demonstrated considerable variability in performance across lists. This variability was accurately described by the binomial distribution model and was used to estimate the magnitude of change required to achieve statistical significance when comparing scores from one and two lists per condition. Fifteen sentence lists have been included in the AzBio Sentence Test for use in the clinical evaluation of hearing-impaired listeners and CI users. An additional eight sentence lists have been included in the Minimum Speech Test Battery to be distributed by the CI manufacturers for the evaluation of CI candidates.
19085705
Individual differences in online spoken word recognition: Implications for SLI
Thirty years of research has uncovered the broad principles that characterize spoken word processing across listeners. However, there have been few systematic investigations of individual differences. Such an investigation could help refine models of word recognition by indicating which processing parameters are likely to vary, and could also have important implications for work on language impairment. The present study begins to fill this gap by relating individual differences in overall language ability to variation in online word recognition processes. Using the visual world paradigm, we evaluated online spoken word recognition in adolescents who varied in both basic language abilities and non-verbal cognitive abilities. Eye movements to target, cohort and rhyme objects were monitored during spoken word recognition, as an index of lexical activation. Adolescents with poor language skills showed fewer looks to the target and more fixations to the cohort and rhyme competitors. These results were compared to a number of variants of the TRACE model (McClelland & Elman, 1986) that were constructed to test a range of theoretical approaches to language impairment: impairments at sensory and phonological levels; vocabulary size, and generalized slowing. None of the existing approaches were strongly supported, and variation in lexical decay offered the best fit. Thus, basic word recognition processes like lexical decay may offer a new way to characterize processing differences in language impairment.
1262463
NIH Toolbox for Assessment of Neurological and Behavioral Function
At present, there are many studies that collect information on aspects of neurologic and behavioral function (cognition, sensation, movement, emotion), but with little uniformity among the measures used to capture these constructs. Further, available measures are generally expensive, normed on homogenous nondiverse populations, not easily administered, do not cover the lifespan (or have easily linked pediatric and adult counterparts for the purposes of longitudinal comparison), and not based on the current thinking in the neuroscience community. There is also a paucity of measurement tools to gauge normal children in the motor and sensation domain areas, and many of these measures rely heavily on proxy reporting. Investigators have expressed the need for brief assessment tools that could address these issues and be used as a form of “common currency” across diverse study designs and populations. This ability to assess functionality along a common metric and “crosswalk” across measures is essential to the process of being able to pool data, which is often necessary when a large and diverse sample is needed. When individual studies employ unique assessment batteries, comparisons between studies and combining data from multiple studies can be problematic. The contract for the NIH Toolbox for the Assessment of Neurological and Behavioral Function (www.nihtoolbox.org) was initiated by the NIH Blueprint for Neuroscience Research (www.neuroscienceblueprint.nih.gov) to develop a set of state-of-the-art measurement tools to enhance collection of data in large cohort studies and to advance the biomedical research enterprise.
12012872
Effects of noise letters upon the identification of a target letter in a nonsearch task
During a 1-sec tachistoscopic exposure, Ss responded with a right or left leverpress to a single target letter from the sets H and K or S and C. The target always appeared directly above the fixation cross. Experimentally varied were the types of noise letters (response compatible or incompatible) flanking the target and the spacing between the letters in the display. In all noise conditions, reaction time (RT) decreased as between-letter spacing increased. However, noise letters of the opposite response set were found to impair RT significantly more than same response set noise, while mixed noise letters belonging to neither set but having set-related features produced intermediate impairment. Differences between two target-alone control conditions, one presented intermixed with noise-condition trials and one presented separately in blocks, gave evidence of a preparatory set on the part of Ss to inhibit responses to the noise letters. It was concluded that S cannot prevent processing of noise letters occurring within about 1 deg of the target due to the nature of processing channel capacity and must inhibit his response until he is able to discriminate exactly which letter is in the target position. This discrimination is more difficult and time consuming at closer spacings, and inhibition is more difficult when noise letters indicate the opposite response from the targe
2520731
Psychometric Functions of Dual-Task Paradigms for Measuring Listening Effort
Objectives: The purpose of the study was to characterize the psychometric functions that describe task performance in dual-task listening effort measures as a function of signal to noise ratio (SNR). Design: Younger adults with normal hearing (YNH, n = 24; experiment 1) and older adults with hearing impairment (n = 24; experiment 2) were recruited. Dual-task paradigms wherein the participants performed a primary speech recognition task simultaneously with a secondary task were conducted at a wide range of SNRs. Two different secondary tasks were used: an easy task (i.e., a simple visual reaction-time task) and a hard task (i.e., the incongruent Stroop test). The reaction time (RT) quantified the performance of the secondary task. Results: For both participant groups and for both easy and hard secondary tasks, the curves that described the RT as a function of SNR were peak shaped. The RT increased as SNR changed from favorable to intermediate SNRs, and then decreased as SNRs moved from intermediate to unfavorable SNRs. The RT reached its peak (longest time) at the SNRs at which the participants could understand 30 to 50% of the speech. In experiments 1 and 2, the dual-task trials that had the same SNR were conducted in one block. To determine if the peak shape of the RT curves was specific to the blocked SNR presentation order used in these experiments, YNH participants were recruited (n = 25; experiment 3) and dual-task measures, wherein the SNR was varied from trial to trial (i.e., nonblocked), were conducted. The results indicated that, similar to the first two experiments, the RT curves had a peak shape. Conclusions: Secondary task performance was poorer at the intermediate SNRs than at the favorable and unfavorable SNRs. This pattern was observed for both YNH and older adults with hearing impairment participants and was not affected by either task type (easy or hard secondary task) or SNR presentation order (blocked or nonblocked). The shorter RT at the unfavorable SNRs (speech intelligibility < 30%) possibly reflects that the participants experienced cognitive overload and/or disengaged themselves from the listening task. The implication of using the dual-task paradigm as a listening effort measure is discussed.
206286122
Cognitive processing load across a wide range of listening conditions: insights from pupillometry.
The pupil response to speech masked by interfering speech was assessed across an intelligibility range from 0% to 99% correct. In total, 37 participants aged between 18 and 36 years and with normal hearing were included. Pupil dilation was largest at intermediate intelligibility levels, smaller at high intelligibility, and slightly smaller at very difficult levels. Participants who reported that they often gave up listening at low intelligibility levels had smaller pupil dilations in these conditions. Participants who were good at reading masked text had relatively large pupil dilation when intelligibility was low. We conclude that the pupil response is sensitive to processing load, and possibly reflects cognitive overload in difficult conditions. It seems affected by methodological aspects and individual abilities, but does not reflect subjective ratings.