| dc.description | Visual hemineglect provided within-patient comparison of information processing in the intact and neglected fields. Experiment One, addressed whether N400 amplitudes for centralized picture-targets that were preceded by lateralized picture-primes would reflect the implicit semantic priming reported for stimuli in the neglected visual field (e.g. McGlinchey-Berroth et al., 1993, 1996). In Experiment Two, an oddball paradigm was used to determine whether P300 amplitudes are sensitive to manipulations of stimulus target-value and relative stimulus probability for target and non-target letters in the neglected field when concurrent behavioral responses indicate subjective unavailability of the eliciting stimuli. Both paradigms had behavioral components to evaluate the extent to which the contralesional stimuli remained subjectively unavailable. The implicit behavioral priming results of Experiment One are compatible with accumulating evidence that considerable processing occurs for information in the neglected field even when it remains subjectively unavailable. Moreover, the N400 provides a robust correlate of the semantic associations formed automatically between the targets and primes. In Experiment Two, P300 amplitudes were sensitive to the targetness of lateralized stimuli bilaterally for the controls but only in the intact field of the patients. For patients, P200 amplitudes were sensitive to the targetness of the lateralized stimuli whether in the intact or neglected field, even when concurrently obtained behavioral responses indicated no subjective awareness of the contralesional stimuli. Thus, for these patients with hemineglect, as for other brain-damaged groups, disruption of cortical top-down processing can be associated with the release of earlier and more automatic neural responses with which P200 amplitudes correlate. Finally, for half of the patients (n = 5), reliable P300 amplitude differentiation was elicited for stimuli in the neglected field, including two patients who showed no awareness of the stimuli. This stimulus differentiation, for stimuli of which the patients were unaware, highlights ambiguities related to for P300 interpretation. | en_US |
