CATEGORICAL VERSUS COORDINATE SPATIAL PROCESSING - EFFECTS OF BLURRING AND HEMISPHERIC-ASYMMETRY

The present experiment examined the effects of dioptric blurring on th e performance of two different spatial processing tasks using the same visual stimuli. One task (the above/below, categorical task) required subjects to indicate whether a dot was above or below a horizontal li ne. The other task (the coordinate, near/far task) required subjects t o indicate whether the dot was within 3 mm of the line. For both tasks , the stimuli on each trial were presented to either the right visual field and left hemisphere (RVF/LH) or the left visual field and right hemisphere (LVF/RH). For the above/below task, dioptric blurring consi stently increased reaction time (RT) and did so equally on LVF/RH and RVF/LH trials. Furthermore, there was no significant difference betwee n the two visual fields for either clear or blurred stimuli. For the n ear/far task, dioptric blurring had no consistent effect on either RT or error rate for either visual field. On an initial block of trials, however, there were significantly fewer errors an LVF/RH than on RVF/L H trials, with the LVF/RH advantage being independent of whether the s timuli were clear or blurred. This initial LVF/RH advantage disappeare d quickly with practice, regardless of whether the stimuli were clear or blurred. This pattern of results suggests that for both cerebral he mispheres, somewhat different aspects of visual information are releva nt for categorical versus coordinate spatial processing and that the r ight hemisphere is superior to the left for coordinate (but not catego rical) spatial processing.