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Partial cortical blindness is a visual deficit caused by unilateral damage to the primary visual cortex, a condition previously considered beyond hopes of rehabilitation. However, recent data demonstrate that patients may recover both simple and global motion discrimination following intensive training in their blind field. The present experiments characterized motion-induced neural activity of cortically blind (CB) subjects prior to the onset of visual rehabilitation. This was done to provide information about visual processing capabilities available to mediate training-induced visual improvements. Visual Evoked Potentials (VEPs) were recorded from two experimental groups consisting of 9 CB subjects and 9 age-matched, visually-intact controls. VEPs were collected following lateralized stimulus presentation to each of the 4 visual field quadrants. VEP waveforms were examined for both stimulus-onset (SO) and motion-onset (MO) related components in postero-lateral electrodes. While stimulus presentation to intact regions of the visual field elicited normal SO-P1, SO-N1, SO-P2 and MO-N2 amplitudes and latencies in contralateral brain regions of CB subjects, these components were not observed contralateral to stimulus presentation in blind quadrants of the visual field. In damaged brain hemispheres, SO-VEPs were only recorded following stimulus presentation to intact visual field quadrants, via inter-hemispheric transfer. MO-VEPs were only recorded from damaged left brain hemispheres, possibly reflecting a native left/right asymmetry in inter-hemispheric connections. The present findings suggest that damaged brain hemispheres contain areas capable of responding to visual stimulation. However, in the absence of training or rehabilitation, these areas only generate detectable VEPs in response to stimulation of the intact hemifield of vision., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The attentional blink (AB), characterized as a failure to detect a second target following correct identification of a previous target in a rapid serial visual presentation (RSVP), has become a useful measure for investigation of the temporal dynamics of attention. In our previous work, we proposed a two-stage concurrent inhibition model that attributes AB not only to capacity limitations at the central, working memory but also to the lack of proper inhibitory processes, which depend in part on the integrity of white matter. To test the hypothesis that attentional blink can be influenced by the integrity of the white matter, we investigated AB in patients with multiple sclerosis (MS), where the dominant neuropathology is demyelination-related cortical white matter impairments. We tested 22 MS patients and 22 age-matched controls with RSVP task. MS patients were further examined with standard tests of motor functioning (9 Hole Peg Test-9HPT and 8m walking test) and 2 tests of working memory (Paced Auditory Serial Addition Test-PASAT and Digit Ordering test-DOT). On average, MS patients did not show working memory impairments, but greater and longer AB. Our results thus support the hypothesis that one potential mechanism of attentional impairments in MS could be unreliable inhibitory processes. We propose that in MS inhibitory processes depend on white matter integrity, i.e., functional connectivity between the perceptual and working memory modules. Future research should focus on concurrent measurements of neuroanatomical and attentional features of MS patients to further support our findings., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The relationship between cognitive processing stages and event-related potential components has been extensively researched for single components, but even the simplest task comprises multiple electrophysiological and cognitive components. Here we examined the relationship between behavioral measures and several visual evoked potentials (VEPs) related to global motion onset during a visual motion discrimination task. In addition to reaction time and accuracy, the EZ diffusion model was used to characterize elements of the decision process. Results showed that latencies, but not amplitudes, from three VEP components reliably predicted about 40% of the variance in reaction times for motion discrimination. These included the latency from stimulus motion onset to N2 onset, the latency from N2 onset to N2 peak, and the latency from the N2 peak to the peak of a late positive potential. These latencies were also able to predict the rate of information accumulation during the decision process and the duration of non-decision processes, but not the observer's threshold (boundary) for making a response. This pattern of results is consistent with an interpretation of these three latencies as reflecting a non-specific visual perceptual process, a motion-specific process, and a decision process, respectively. The relationship between the earliest interval and drift rate estimated with the EZ model also supports the notion that early perceptual processing might be a constituent part of the decision process itself., (Copyright © 2010 Elsevier Ltd. All rights reserved.)