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Kirsten A. Dalrymple, Walter F. Bischof, David Cameron, Jason J. S. Barton, Alan Kingstone; Inefficient eye movements correlate with difficulties in perceiving global stimuli in Balint's syndrome. Journal of Vision 2007;7(9):23. doi: 10.1167/7.9.23.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with Balint's syndrome often report Local portions of visual scenes, but not the Global percept. Other researchers have reported that the eye movements of Balint's patients while they identified Local and Global levels of hierarchical letters do not differ between successful and unsuccessful trials. We replicated and extended this experiment by recording eye movements of a Balint's patient (SL) and of controls while they identified, on separate trials, letters at Global or Local levels of hierarchical stimuli. Controls were highly accurate for Global and Local trials and made only a few fixations, most of which landed at centre-screen. SL took longer and made more fixations per second than controls, with fewer fixations to centre-screen. She had normal accuracy for identifying Local elements, but poor accuracy during Global trials. SL's performance differed between Global and Local tasks, with Global trials showing longer reaction times, fewer fixations per second, and a lower proportion of fixations overlapping with the letter stimulus. When comparing SL's successful to unsuccessful Global trials, while there were no significant differences in the distribution of fixations in different regions of the screen, SL did have shorter reaction times and a higher proportion of fixations overlapping with the letter stimulus per second during successful trials than during unsuccessful trials. We conclude that SL demonstrates a need to explore Global and Local letters more than controls, reflecting her difficulty with information accrual during fixations, consistent with her attentional difficulties. The more difficult Global task is associated with a reduced fixation rate and less fixation-stimulus overlap. Fixation-stimulus overlap is further decreased in Global trials on which she made errors. These features suggest that any preserved Global perception in SL may be dependent on local fixations of the stimulus, consistent with a spatial constriction of attention.
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