Experimental disentangling of spatial-compatibility and interhemispheric-relay effects in simple reaction time (Poffenberger paradigm).

Spatial-compatibility effects can be obtained in simple reaction time (SRT) provided that spatially distinct responses are frequently required. Since this effect is limited to trials with relatively long reaction times (RTs), Hommel (1996b) proposed that if the response does not occur shortly after stimulus detection, then the spatial code of the stimulus can interfere with that of the response. A series of experiments is reported showing that (a) spatial compatibility in SRT to lateralized stimuli is not an alternative, but rather a complementary, explanation to interhemispheric transfer time (contrary to what Hommel surmised), and (b) the spatial compatibility component is essentially limited to the first trial after shifting response preparation from one-half of the visual fields to the other, suggesting a mechanism akin to an orienting response.