Speed of Saccadic Responses and Intelligence: An Exponential-Gaussian Analysis

Individual differences in the speed of making rapid eye movements (saccades) may have potential for exploring the link between neural conduction and cognitive abilities. Participants (N = 56) performed tasks devised to measure the speed at which humans started to move an eye towards a stimulus which appeared in peripheral vision (saccade) or in the opposite direction (anti-saccade). Cognitive abilities were measured using the Wide Range Intelligence Test, and ex-Gaussian parameters from the eye-movement tasks were correlated with these abilities. The findings showed that scores on the pro- and anti-saccade tests correlated substantially and that the anti-saccade condition led to consistently longer, more variable and more skewed responses. None of the parameters correlated significantly with the cognitive abilities assessed. The findings do not support the theory that nerve conduction velocity explains the correlation between reaction times and cognitive abilities. However, the findings do provide evidence of the existence of individual differences in saccadic eye-movements that can be captured by ex-Gaussian analysis of reaction time and also show that saccadic movements do not follow Hick's Law when task difficulty is manipulated.