Expectancy in educable subnormal children and their normal mental age controls

The long reaction times of mentally subnormal children have commonly been attributed to an inability to build up an adequate preparatory set. The experiment reported attempted to test this suggestion by comparing the ability of normal and subnormal children to anticipate a regularly occurring event. The performance of educable subnormal (ESN) children was found to be inferior to that of normal children matched on mental age (NMA) both in terms of the accuracy and the variability of their anticipations. However, this inferiority disappeared when visual input was restricted to the relevant events. It is concluded that ESN children suffer both in the accuracy and in the variability with which they estimate time intervals. It is suggested that these deficits may be mediated either by a relatively high level of distractability or by a relatively low level of arousal.