Instructions and decision times of size-constancy responses

The current study investigated the effect of instructions and stimulus discriminability on size-constancy responses and decision times in a task allowing separate evaluation of the effects of instructions and of dimensional choices by the subjects in the size-constancy task. Objective, perspective, or distance matches were influenced both by the instructions given the subject and by the relative discriminability of the stimuli in each dimension, so that subjects did not always successfully follow their instructions. Decision times were found to be fastest with perspective rather than objective or apparent instructions, but times taken to produce objective and perspective matches did not differ. Apparently, both objective and perspective judgments are available to the perceiver before a response is made, but instructions affect postperceptual response times.