Spatial coding and central patterns: Is there something special about the eyes?

In this study we investigated in a Simon-like taskwhether task-irrelevant spatial information, delivered bycentrally presented patterns, interfered with response selectionin the same way as laterally presented stimuli. Second,we asked whether such interference was equal for differentkinds of stimuli. Participants were required to respond tothe colour of two framed squares, two arrows, or twoschematic eyes by pressing one of two lateralized responsekeys. The results consistently show that the Simon effectoccurs independently of the nature of the stimulus, as classicallyreported for lateralized stimuli. Response times wereinfluenced by the direction and frame-relative position ofthe stimuli, being faster for responses corresponding to thedirection indicated by the stimuli than for noncorrespondingresponses regardless of stimulus types. Contrary to findingswith lateralized nondirectional stimuli, such an effectincreased with increasing RTs indicating that for centrallypresented patterns the extraction of spatial information istime consuming.