A modal model of information-processing was used to select a battery of nine tasks of basic cognitive ability (learning, relearning, reaction time, probe recall, Sternberg search, self-paced probe, stimulus discrimination, tachistoscopic full report, tachistoscopic partial report). Parameters from these tasks operationalized the model. After extensive pilot testing of the tasks to establish reliability, we tested 40 subjects (20 with mental retardation and 20 college students) on all tasks and the WAIS-R. The parameters from the tasks were generally reliable (.7 through .9) and had low correlations with IQ (average about .37). Nearly all of the major cognitive parameters differentiated significantly between groups. A subset of the basic cognitive parameters predicted IQ with an estimated multiple correlation in the general population of .72. Prediction of IQ using basic cognitive parameters was better for subjects with mental retardation than for college students. A modified version of the modal model was supported. Results show that individual differences in higher mental processes are highly dependent on basic cognitive abilities and can be predicted from them. These findings have substantial implications for the development of models of information-processing.