Mental retardation, inspection time, and central attentional impairment

Performance of mentally retarded and nonretarded adults on simple visual discrimination tasks was compared. Experiment 1 involved a lines-discrimination task used in previous research to measure inspection time. A dichoptic stimulus presentation procedure was employed, with target and masking stimuli presented to different eyes so that only central masking could occur. Experiment 2 involved a discrimination between two lights in different positions, demonstrating that masking was characterized by constant stimulus-onset-asynchrony, because the relationship between target duration and the interval between target offset and mask onset was additive. Results from both experiments confirmed that for both retarded and nonretarded subjects, the backward masking procedures used interfered with visual processing at a central level. In Experiment 3 markedly deviant smooth pursuit eye movements in a pendulum tracking task occurred among retarded subjects but not among nonretarded subjects. This deviancy was additional to other indications of poor attention. In the retarded group the correlation between estimates of inspection time and deviant eye tracking was .64, but other instances of inattentiveness were not related to either of these two measures. This finding was interpreted in terms of an involuntary dysfunction within some central attentional system that involves at least three qualitatively different levels.