Object Recognition and Goal-Directed Eye or Hand Movements are Coupled by Visual Attention

A dual-task paradigm required the preparation of a goal-directed movement (hand or eye) concurrently with a letter discrimination task. In the first experiment a hand movement to a location on a virtual circle was required and indicated by a central cue. Simultaneously, the ability to discriminate between the symbols “E” and “3”, presented tachioscopically with various delays on a circular position within surrounding distractors, was taken as a measure of selective perceptual performance. The location of discrimination target remained constant within blocks and was known to the subjects. In the second experiment a saccadic eye movement was required instead of a pointing movement. The data in both experiments clearly demonstrate that discrimination performance is superior when the discrimination target location (DT) is identical to the location of the movement target (MT). When DT and MT refer to different objects, performance deteriorates drastically. We conclude that it is not possible to maintain attention on a stimulus for the purpose of discrimination while preparing a movement to a spatially separate object. This holds, in a quantitatively similar way, for both saccades and manual pointing.