Attention problems have long been recognized as a central characteristic of schizophrenia. Furthermore, similar attention deficits have been found in children at risk for schizophrenia. Results showing significant deviance in the attentional performance of a subgroup of these children at risk suggest that attentional deficits may be a biological marker of vulnerability to schizophrenia. Thus, a genetic predisposition to attentional deficits may be linked to a genetic predisposition to schizophrenia. If so, determining the degree of heritability underlying the various components of attentional functioning in normal children could help to pinpoint which components of attention are genetically disruptible in populations at risk for schizophrenia. We propose to use a new attention task which can delve below the surface of the attention deficits identified by tasks like the Continuous Performance Test (CPT) and Span of Apprehension Test (SOA). This new attention task presents multiple word stimuli for a prespecified duration and requires subjects to identify any word followed by a question mark. By varying the types of words (predictable versus nonpredictable), the exposure duration, and the subject's instructions (divide attention, focus attention, detect targets), we can measure attention under a variety of perceptual processing situations and pinpoint whether attentional deficits reflect a processing speed problem, an inefficient resource allocation strategy, or an inability to sustain attention over time. The new attention task together with the CPT and the SOA will be administered to children and young adults ranging from 10 to 21 years of age. In this way, the normal developmental progression in attentional functioning can be traced from age 10 onwards in order to identify those components of attentional processing that show the greatest change with age versus those that remain relatively stable. At each age level, half the subjects will be MZ twins and half will be DZ twins. The extent to which the attentional performance profile of MZ twins pairs is more similar than that of DZ twins pairs will provide an indication of the heritability of each component of attention. We would thus be able to identify those components of attention which are most genetically disruptible. The long-range goal is to identify the specific components that are most likely to be disrupted in children at risk for schizophrenia and to show at what age such disruptions are likely to appear.