Abstract
BackgroundVisual neglect is an attentional deficit typically resulting from parietal cortex lesion and sometimes frontal lesion. Patients fail to attend to objects and events in the visual hemifield contralateral to their lesion during visual search.Methodology/Principal FindingThe aim of this work was to examine the effects of parietal and frontal lesion in an existing computational model of visual attention and search and simulate visual search behaviour under lesion conditions. We find that unilateral parietal lesion in this model leads to symptoms of visual neglect in simulated search scan paths, including an inhibition of return (IOR) deficit, while frontal lesion leads to milder neglect and to more severe deficits in IOR and perseveration in the scan path. During simulations of search under unilateral parietal lesion, the model's extrastriate ventral stream area exhibits lower activity for stimuli in the neglected hemifield compared to that for stimuli in the normally perceived hemifield. This could represent a computational correlate of differences observed in neuroimaging for unconscious versus conscious perception following parietal lesion.Conclusions/SignificanceOur results lead to the prediction, supported by effective connectivity evidence, that connections between the dorsal and ventral visual streams may be an important factor in the explanation of perceptual deficits in parietal lesion patients and of conscious perception in general.
Highlights
Visual neglect can result from a lesion typically to the posterior parietal cortex [1]
Our aim was to apply a unilateral lesion to the parietal module in order to simulate a right hemisphere parietal lesion, which has been associated with severe symptoms of visual neglect in search scan paths [32,33]
Re-visiting Locations in the Scan Path In addition to frontal lesion resulting in difficulties re-orienting attention and perseverance, we found that unilateral parietal lesion resulted in increased rates of re-visiting the same locations during the scan path
Summary
Visual neglect ( referred to as ‘‘unilateral neglect’’, ‘‘hemispatial neglect’’ or ‘‘hemineglect’’) can result from a lesion typically to the posterior parietal cortex [1] It is sometimes associated with frontal lobe lesions [2,3] or lesion of the thalamus [4]. Neglect patients are able to make saccades in the contralesional direction during visual search, their fixations tend to be concentrated in the ipsilesional hemifield [1,5] Examples of such a scan path and patient target detection performance are shown in figure 1. Orbitofrontal lesion has been linked to increased re-fixation in search scan paths [7] Unlike those associated with parietal injury, re-fixation errors following frontal lesion do not appear to increase with time since first fixating a location [1]. Patients fail to attend to objects and events in the visual hemifield contralateral to their lesion during visual search
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