Intelligence, reaction time, and inspection time.

Forty-eight subjects with IQ scores ranging from 57 to 138 discriminated between two lines of markedly different length, exposed for varying periods of time. Estimates of inspection time, lambda, a measure assumed to reflect the rate at which sensory input is processed, were obtained from the pattern of errors made by each subject and, therefore, independently from the reaction time (RT) required to respond. lambda correlated negatively with IQ scores. RTs of nonretarded subjects increased as stimulus-exposure duration decreased, whereas for retarded subjects RTs remained constant. This is interpreted as indicating differences between the groups in response strategy under conditions of difficult discrimination. The rate of information processing was also estimated in a different choice RT situation, using as an index the reciprocal of the slope of the function relating RT to degree of stimulus choice. Retarded subjects had slower rates and longer RTs than nonretarded subjects. A second experiment controlling for response-selection factors confirmed that this slowness could not be attributed to gross-movement difficulties and that a slower rate of information transmission seemed to be involved.