The present experiment examined the effects of dioptric blurring on the 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 line. The other task (the coordinate, near/far task) required subjects to 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 consistently increased reaction time (RT) and did so equally on LVF/RH and RVF/LH trials. Furthermore, there was no significant difference between the two visual fields for either clear or blurred stimuli. For the near/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 on LVF/RH than on RVF/LH trials, with the LVF/RH advantage being independent of whether the stimuli were clear or blurred. This initial LVF/RH advantage disappeared quickly with practice, regardless of whether the stimuli were clear or blurred. This pattern of results suggests that for both cerebral hemispheres, somewhat different aspects of visual information are relevant for categorical versus coordinate spatial processing and that the right hemisphere is superior to the left for coordinate (but not categorical) spatial processing.

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