SPATIAL COMPATIBILITY OF SIGNAL-RESPONSE POSITION IN POINTING

Two experiments are reported in which, by means of a pointing task, we studied the stimulus-position effect, i.e. the inverted U-shape form of the reaction-time function in relation to stimulus position in task s in which stimuli and/or responses are arranged in a horizontal array . The response consisted of aiming the index finger from a central sta rting point at a target area on a screen. Reaction time was the main d ependent variable. The spatial relation between the position of the im perative signal and the position of the response was manipulated by va rying the spatial S-R compatibility and physical distance that separat ed the positions of stimulus and response. The stimulus-position effec t was shown to depend on the compatibility of the S-R relation (Exp. 1 ). In Exp. 2 it was found that the modulation of the stimulus-position effect by spatial compatibility disappeared completely when the dista nce between the positions of stimulus and response was reduced. None o f the experiments revealed that the stimulus position effect depended on signal discriminability, which renders an interpretation of this ef fect in terms of perceptual processes unlikely. We argue that the atte ntional model of spatial coding provides the most reasonable explanati on of the obtained reaction-time patterns.