Location vs feature: reaction time reveals dissociation between two visual functions.

Reaction time in a detection or a location discrimination task was longer when a target appeared at the same location as in the previous trial (inhibition of return; IOR). However, it became shorter when the task was color or orientation discrimination (facilitation of return: FOR). This dichotomy was observed in the single target as well as in the popout displays. In additional experiments, vernier, size, and luminance discriminations all led to FOR, whereas eye-movement and arm-reaching tasks led to IOR. Moreover, identical stimuli could lead to the opposite patterns of result depending on the nature of the task: inhibition in global location tasks, and facilitation in feature analysis tasks. These may correspond to "where" vs "what" or "action" vs "recognition" pathways neurophysiologically.