Choice and stimulus-response compatibility affect duration of response selection

In general, for movements to visual targets, response times increase with t he number of possible response choices. However, this rule only seems to ho ld when an incompatibility exists between the stimulus and response, and is absent when stimulus and response are highly compatible (e.g., when reachi ng toward the location of the stimulus). Stimulus-response (S-R) compatibil ity can be manipulated either at the level of stimulus and response charact eristics, or at the level of the mapping between elements of the stimulus a nd response sets. The current study was undertaken to determine the extent of the interaction between choice and each of these two levels of S-R compa tibility. Subjects used a joystick to move a cursor in response to two, fou r or eight possible cues, with S-R compatibility manipulated along two dime nsions (type of stimulus, and mapping between stimulus and response sets) i n separate blocks of trials. Choice effects were absent when S-R relationsh ips were highly compatible, moderate when incompatible in either of the two dimensions, and greatest when incompatible in both dimensions. These resul ts indicate that choice affects response selection at each stage in the dec oding of S-R relationships. Similar but smaller effects were seen for trial s in which the stimulus was the same as that presented in the immediately p receding trial, suggesting that repeated stimulus-response transformations are faster and more efficient due to the priming effects of previous trials . (C) 1999 Elsevier Science B.V. All rights reserved.