Rotation Angle and Task Demands Influence Encoding of Ordinal Stimuli in the Ordinal Stimuli’s Location Activated Context

Although previous studies have investigated how ordinal stimuli are encoded in contexts that vary in locational congruency, conclusions regarding the encoding mechanism are inconsistent. The present study utilized Chinese Heavenly Stem characters, which are an ordinal sequence used to record astronomical phenomena in ancient China and are still frequently used to date, as stimuli to investigate the influence of rotation angle and task demands on the encoding of ordinal stimuli in contexts that varied in locational congruency. We randomly presented six of these characters at varying rotation angles (0 degrees or 180 degrees) on the left or right side of the screen. Participants were then instructed to classify the stimulus order (Experiment 1), location (Experiment 2) and color (Experiment 3) in a bimanual classification task. The results were as follows: (a) When participants classified stimuli according to order, both the ordinal position effect and the Simon effect were detected for unrotated stimuli. However, only the ordinal position effect was detected for rotated stimuli. (b) When participants classified stimuli according to spatial location, we observed only the spatial stimulus-response compatibility effect. (c) When participants classified stimuli according to color, we observed the Simon effect in all trials. However, the ordinal position effect was detected only in location-congruent trials. These results suggest that encoding of ordinal stimuli in contexts that varied in locational congruency was moderated by the processing difficulty of the stimuli and the task demands.