Effects of dual task demands on the accuracy of smooth pursuit eye movements

The effect of attention allocation on smooth pursuit eye movements (SPEM) was investigated. Eye movements were electrooculographically recorded in 27 healthy subjects who tracked a visual target that moved horizontally with constant or unpredictably varying velocity. In some trials, subjects performed additional auditory discrimination tasks varying in difficulty. Pursuit error decreased when attention was divided between both tasks. The pattern of results is incompatible with the assumption made in previous research that attention enhancement improves SPEM accuracy. Rather, ocular smooth pursuit appears to be executed in the automatic mode, although intentional and selective processes must contribute. Moreover, controlled attention directed to the tracking task interfered with smooth pursuit. A reinterpretation of earlier studies in which visual monitoring tasks were used to improve eye tracking is needed.