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Monika Harvey, Stephen Butler, Keith Muir, Ian Reeves; Dissociation between eye-movements and right perceptual biases in chimeric face processing in right hemisphere lesioned patients. Journal of Vision 2007;7(9):654. doi: 10.1167/7.9.654.
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Using blended chimeric facial stimuli, where the left and the right sides of the face are different, we have previously shown that both young and older observers tend to bias their responses significantly toward the information on the left, supposedly reflecting a right-hemisphere advantage in this task (Butler, Gilchrist, Burt, Perrett, Jones & Harvey, 2005, Neuropsychologia, 43, 52–59; Harvey & Butler, 2004, Perception, 33, 106). Analyses of the eye movement patterns further indicated a tendency for both groups to initially scan to the left side of the chimeric image, presumably reflecting the tendency to first inspect the side of the face better suited to face analysis (left side of face/right hemisphere). As expected, patients with right hemisphere lesions based their gender decisions mainly on the right side of the chimeric face and this was not only the case for patients who suffered from spatial neglect (Mattingley, Bradshaw, Phillips, Bradshaw, 1993, Brain and Cognition, 23, 145–165). More interestingly though, there was no clear relationship between perceptual and eye-movements biases to chimeric stimuli. Although most patients showed more right-sided saccades and longer rightward fixations this was not necessarily reflected in the rightward perceptual bias. One patient in particular showed rightward saccades only, yet based his gender decision on the left hemi-face half the time when he should have shown 100% rightward hemi-face judgements. We would argue that although in healthy subjects face biases and eye-movement biases are tightly coupled, this relationship breaks down with brain damage and that for such patients eye-movement patterns are not a good indicator of perceptual processing (see also Ferber, Danckert, Joanisse, Goltz, Goodale, 2003, Neurology, 60 1826–1829 and Harvey, Olk, Muir, K, 2003, Neuropsychologia, 41, 1114–1121 for supporting evidence).
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