Mental rotation and visual familiarity

Mental rotation functions often evidence a curvilinear trend indicating relative indifference to small departures from the upright. In Experiment 1, this was true only for normal letters whereas reflected letters yielded a largely linear rotation function. This suggested that the internal representation of familiar visual patterns is characterized by broad orientation tuning that allows recognition despite small disorientations. Since familiar stimuli are often encountered slightly tilted from the upright, broad orientation tuning may reflect this ecological distribution. Experiment 2, however, indicated the possible involvement of two additional processes. Subjects were first trained on unfamiliar nonsense characters that appeared only in their "upright" positions. This was followed by a normal-reflected mental rotation task on these characters. Initially, rotation functions were more curvilinear for normal than for reflected characters. This suggested that practice with upright stimuli automatically contributes to broad tuning. Further practice resulted in a curvilinear trend for reflected characters as well, despite the fact that they appeared with equal probability in all orientations. This suggested that the very process of mentally rotating stimuli to the upright orientation increases insensitivity to slight departures from this orientation. Experiment 3 established that the different functions found for normal and reflected characters were due to stimulus rather than response factors.