The purpose of the proposed research is to determine what proportion of variance in standard measures of intellectual performance can be predicted by parameters of cognitive functioning and to what entent mentally retarded persons differ from normal persons on these parameters. The first year of research will be devoted to developing ten reliable, computer-based tasks yielding about 35 parameters of cognitive functioning representing various portions of a composite information processing model. There is some indication that each of the parameters is sensitive to group differences between mentally retarded and normal subjects. During this phase of research, each parameter wil be determined to be equally reliable within groups of mentally retarded and normal subjects. During the second year of research, the parameters of cognitive functioning developed during the first year will be assessed for three groups of 50 subjects having IQ ranges of 41-70, 71-100, or 101-130. The parameters will be used to predict performance on a vocabulary test developed for research purposes, the Wechsler Adult Intelligence Scale, or subscales of this test. A method which has been developed to include subject and task sources of variation within the same prediction equation will be used in the analyses. The question of primary interest in this phase of research is how much of the dependent variable variance is predictable from cognitive task parameters. From pilot work there is good reason to expect multiple correlations between a measure of intellectual functioning and cognitive parameters of greater than .80. Further, pilot data indicate that at least some of these parameters will represent independent sources of variation (i.e, will not be correlated amongst themselves). The third year will be devoted to determining which of the parameters identified during the second year as predictive of intellectual functioning is most importantly implicated in mental retardation. This will be done by assessing the relative deficit among these parameters using a modification of the methodology proposed by Chapman and Chapman.