A Computational Neuroscience Account of Visual Neglect
Dietmar Heinke, Gustavo Deco, Josef Zihl, Glyn W. Humphreys
Abstract Draft version
On the basis of a computational and neurodynamical model, we investigate a cognitive impairment in stroke patients termed visual neglect. The model is based on the "biased competition hypothesis" and is structured in several network modules which are related to the dorsal and ventral pathway in the visual cortex. By damaging the model, visual neglect can be simulated and explained as an unbalanced neurodynamical competition. We predict that acquiring knowledge of objects can increase the frequency of saccades to previously ignored object parts. This prediction is confirmed in a single case study by monitoring eye movements of a neglect patient.
Neurocomputing, in press.
Last updated: Fri Mar 22 13:18:56 GMT 2002
Unconscious, transient binding by time: Neuropsychological evidence from anti-extinction
Glyn W. Humphreys, M. Jane Riddoch, Gudrun Nys, Dietmar Heinke
Anti-extinction occurs when there is poor report of a single stimulus presented on the contralesional side of space, but better report of the same item when it occurs concurrently with a stimulus on the ipsilesional side (Goodrich & Ward, 1997). We report a series of experiments that examine the factors that lead to anti-extinction in a patient GK, who has bilateral parietal lesions but more impaired identification of left-side stimuli. We show a pattern of anti-extinction when stimuli are briefly presented, which is followed by an extinction effect when stimuli are left for longer in the visual field. In Experiments 1 and 2 we present evidence that the anti-extinction effects are defined by offsets. In Experiments 3 and 4 we report that performance is not strongly affected by whether the same of different tasks are performed on the ipsi- and contralesional stimuli, and the anti-extinction effect also survives trials where eye movements are made to right-side stimuli. Experiment 5 provides evidence that anti-extinction is due to temporal grouping between stimuli, rather than cueing attention to the contralesional side. Experiment 6 demonstrates that anti-extinction dissociates from GK's conscious perception of when contra- and ipsilesional stimuli occur together. We interpret the data as indacting that there is unconscious and transient temporal binding in vision.
Cognitive Neuropsychology, 19(4):361-380, 2002.