Abstract
Purpose: We have previously shown that right parietal patients are impaired at performing attentive tasks of apparent motion in both visual fields, not just the left field where they show other attention-related deficits. We hypothesized a loss in how their transient attention processes object appearance and disappearance. Method: To test this possibility we devised an experiment where six squares (three in each visual field) were flickering at the same temporal frequency and the target to be detected was flickering out of phase. The stimuli were reversed sinusoidally at temporal frequencies varying from 2–9 Hz. We used the method of adjustment and varied the temporal frequency progressively until the subject reported the target correctly. Results: Neglect patients showed a severe loss in both hemifields, while left parietal patients performed like age-matched controls. In experiment 1 the onsets and offsets of the target stimulus were always 180? shifted out phase with the distractors. Therefore the appearance and disappearance of the target and the distractors were aligned in time. In a control experiment we shifted the phase of the flicker in the test relative to the distractors such that the onsets and offsets were not aligned (the phase of the target's flicker was shifted 90?). The performance of neglect patients improved dramatically. Conclusion: Since these same patients detect flicker normally, we conclude that the deficit affects a higher level of processing possibly where attentional mechanisms assign transient onsets and offsets to the appearances and disappearance of objects.