SPATIAL S-R COMPATIBILITY EFFECTS WITH UNIMANUAL 2-FINGER CHOICE REACTIONS FOR PRONE AND SUPINE HAND POSITIONS

The influence of spatial stimulus-response (S-R) compatibility on unimanual two-finger choice reactions was investigated. Subjects had to react as fast as possible to a flash of light that was presented in the right or left visual field. They used the index or middle fingers of their left or right hands to press the spatially same (compatible) key or the spatially different (incompatible) key. In Condition 1 the subjects'' palms faced down (pronation); in Condition 2 their palms faced up (supination) so that the spatial order of the fingers was reversed. A strong compatibility effect between right and left field of stimulation and spatially right and left finger was found under both conditions. Compatible reaction times were shorter than incompatible reaction times by 52 msec in the palm-down condition and by 61 msec in the palm-up condition. The results are interpreted as supporting the coding hypothesis of spatial compatibility.