Factors affecting saccadic latency in persons with mental retardation

The goals of the present study were to determine the factors affecting saccadic latency in persons with mental retardation from the viewpoints of intellectual function and ability of behavioral regulation, and to clarify the relationship among the factors. Participants were 44 persons with mental retardation aged between 13 and 57 years whose IQ was between 14 and 70. The ability of behavioral regulation was evaluated by the test of sustained simple motor action. A predictive visually-guided saccade paradigm was used. The mean value and coefficient of variance (CV) of saccadic latency were calculated. Multiple regression analysis was conducted to clarify the factors affecting the mean value and CV of saccadic latency. The independent variables used were age, IQ and presence/absence of disability of behavioral regulation. The mean value was significantly related to the IQ, and the CV had significant relevance to the ability of behavioral regulation. Accordingly, participants were divided into three groups. The participants whose IQ was 55 and more without disability of behavioral regulation consisted of group A. Group B was made up of the participants whose IQ was 55 and below without disability of behavioral regulation. Group C was composed by participants whose IQ was 55 and below with disability of behavioral regulation. Analysis of variance was conducted to examine the intergroup differences in the mean value and CV. The results were as follows. (1) There was no statistically significant difference in both mean value and CV between group A and B. (2) Saccadic latency in group C was significantly longer than group A. (3) The difference in CV between group B and C were significant. These results suggest that the intactness of the ability of behavioral regulation may attenuate the effect of lower IQ on saccadic latency.