Relative discriminability of visually-presented letter pairs using a same-different choice-reaction time task

Twenty-three pairs of capital letters representing the four combinations of high and low visual and auditory similarity, and 17 pairs of identical letters were used as stimuli in a same-different choice-reaction time task. Eight Ss (four of each sex) performed on 780 discrimination trials. Results indicated that same-different judgments were made essentially on the basis of visual characteristics, with letter pairs of high visual similarity having slower RTs than pairs of low visual similarity. Left-to-right order of letters in a pair had no effect, nor did auditory similarity. "Same" judgments had a more restricted range of RT and tended to be slower than "different" judgments.