ABSTRACT
The finding that it often takes less time to determine that two stimuli are the same than to determine that two stimuli are different is discussed. Several hypotheses that have been put forth to account for the finding are considered. It is concluded that none of these hypotheses adequately accounts for the finding, except in an ad hoc fashion, but several of them identify factors that probably play some role in determining the relationship between SAME and DIFFERENT RT. The question is raised as to how the difference between SAME and DIFFERENT RT relates to several other judgmental asymmetries that have been reported, and as to whether these assymmetries may have a common explanation.
