| The function of the visual cortex of early blind participants was investigated through the recording of high-density event-related potentials (HD-ERPs) and the application of equivalent current dipole (ECD) source analysis. Two opposing views of the function of the visual cortex of blind individuals are either that the visual cortices of the blind remain undifferentiated, with co-activation occurring when they perform tasks that are attentionally demanding, or alternatively that their visual cortical areas have plastically reorganized to be involved in early, discriminatory processing of input from non-visual modalities, such as audition. The current study draws from both views to articulate a theory of visual-cortical spatial function, such that the visual-cortices of the blind function to process complex spatial information of non-visual modalities. A preliminary study on sighted participants established the efficacy of an auditory oddball task utilizing complex spatial sequences of tones to elicit early auditory processing ERP components such as the N2, MMN, N2b, and P300. For the final study, twelve early blind participants and twelve sighted participants performed three oddball experiments. Findings indicate that blind participants do not utilize their visual cortices for early auditory discriminatory function or spatial processing, but that these areas do appear to activate when attentional compensation is necessary during task performance. Sighted participants appear to utilize their visual cortical areas for early auditory processing during the performance of tasks which require complex spatial discrimination. Source analysis findings show that cingulate and superior frontal gyrus activity explained a significant amount of variance for both groups. It is posited that for the performance of spatial tasks, people use a non modality-specific attentional system to modulate modality-specific processing of information. |
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