Vertical Visual-Field Differences in Schematic Persistence for Colour Information
The functional specialisation in the upper and lower visual fields is related to the distinction between far and near vision, and may parallel differences between the ventral and dorsal processing streams. Here, we studied possible differences in colour processing. According to postulates of Previc (1990 Behavioral and Brain Sciences13 519 – 575), we expected longer persistence and an advantage in colour classification for stimuli presented in the upper visual field. Performance was tested in a modified partial-report task to estimate duration of schematic persistence for colour and verbal information. The targets were letter strings—either red, yellow, blue, or green—presented in three combinations: (a) nonsense strings, (b) congruent colour-words, and (c) incongruent colour-words. Eight targets were simultaneously presented in a circular array for 60 ms. After a variable interstimulus interval (ISI, 0 – 900 ms), a coloured marker was briefly displayed pointing to one of the original target positions, and the participants had to report whether the colours of target and marker were identical or not. The responses were analysed separately for upper and lower visual-field presentations. The verbal content of the targets did not affect performance. There were no differences in performance between the two visual fields. However, analyses of both accuracy and reaction latencies showed significant interactions between visual field and ISI, ie performance decreased at a slower rate in the upper visual field. These results suggest longer schematic persistence for colour stimuli presented in the upper visual field.