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J. Kortvelyes, E. Banko, V. Gal, P. Domsa, J. Nemeth, Z. Vidnyanszky; Neural Correlates of Fovea-related Impairment of Visual Object Processing in Amblyopia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3820.
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Recent results suggest that object perception is impaired in amblyopia. We used event-related potentials (ERP) to investigate the neural correlates of object processing in amblyopia in the case of foveal and perifoveal presentation of visual objects.
Amblyops (N=16) and healthy controls (N=18) participated in the study. Face and hand grayscale images were used as stimuli (2 and 15 deg in diameter for foveal and perifoveal presentation, respectively). Images were presented without adding noise or at three different noise levels. Observers performed a 2AFC face vs hand discrimination task. Neuronal activity was measured using EEG (64 electrodes).
In the amblyops, object discrimination performance was significantly decreased when stimuli were presented to the amblyopic eye compared to the fellow eye only in the foveal, but not in the perifoveal presentation condition. Performance with the ambylopic eye was also worse than the performance of the control group. In the case of foveal presentation, the amplitudes of early ERP components (including the face-specific N170 component) were strongly reduced and their latencies were increased when stimuli were presented to the amblyopic eye as compared to the fellow eye. Furthermore, we found that increasing the noise level of the images results in increased amplitude of the P220 ERP component in controls and in the case of the fellow eye of the amblyops. However, in the case of the amblyopic eye, noise-dependent modulation of P220 component was strongly reduced in the foveal presentation condition.
Our results provide evidence for strong fovea-related deficits in processing of visual objects in amblyops. ERP correlates of visual object processing in amblyops suggest that foveal representation of visual objects is impaired at the higher, face-specific stages of visual processing. Furthermore, our results also revealed that the P220 component represents an ERP marker of inefficient neural processing of visual objects in the presence of noise in ambylops.
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