Abstract
Despite their subjective invisibility, stimuli presented within regions of absolute cortical blindness can both guide forced-choice behavior when they are task-relevant and modulate responses to visible targets when they are task-irrelevant. We here tested three hemianopic patients to learn whether their performance in an attention-demanding rapid serial visual presentation task would be affected by task-irrelevant stimuli. Per trial, nine black letters and one white target letter appeared briefly at fixation; the white letter was to be named at the end of each trial. On 50% of trials, a task-irrelevant disk (−0.6 log contrast) was presented to the blind field; in separate blocks, the same or a very low negative contrast distractor was presented to the sighted field. Mean error rates were high and independent of distractor condition, although the high-contrast sighted-field disk impaired performance significantly in one participant. However, when trials with and without distractors were considered separately, performance was most impaired by the high-contrast disk in the blind field, whereas the same disk in the sighted field had no effect. As this disk was least visible in the blind and most visible in the sighted field, attentional suppression was inversely related to visibility. We suggest that visual awareness, or the processes that generate it and are compromised in the blind hemisphere, enhances or enables effective attentional suppression.
Highlights
Lesions that destroy or denervate the primary visual cortex (V1, striate cortex, Brodmann Area 17) cause homonymous fields of cortical blindness in the contralesional hemifield (Inouye, 1909; Holmes, 1918; Teuber et al, 1960)
We suggest that visual awareness, or the processes that generate it and are compromised in the blind hemisphere, enhances or enables effective attentional suppression
When the proportion of errors was calculated irrespective of whether or not a disk had been presented during a trial, and compared between distractor conditions, not a single difference met the statistical criterion in HK or WF
Summary
Lesions that destroy or denervate the primary visual cortex (V1, striate cortex, Brodmann Area 17) cause homonymous fields of cortical blindness in the contralesional hemifield (Inouye, 1909; Holmes, 1918; Teuber et al, 1960). They can give rise to a variety of non-reflexive visual functions that include detection, localization, and discrimination of blind-field stimuli that differ in flux, orientation, motion, wavelength, facial expression (De Gelder et al, 1999), and, possibly, motion direction (Pizzamiglio et al, 1984; Perenin, 1991; Barton and Sharpe, 1997; Benson et al, 1998; Azzopardi and Cowey, 2001; Morland et al, 2004) and shape (Weiskrantz et al, 1974; Weiskrantz, 1987; Perenin and Rosetti, 1996; Trevethan et al, 2007; for reviews see Weiskrantz, 1986, 1990; Stoerig and Cowey, 1997; Cowey, 2010) These functions rely on the retinofugal pathways that, despite the effects of the lesion and the degeneration it provokes, continue to transmit visual information to the retinorecipient nuclei which, in turn, project it directly or indirectly to the extrastriate cortical areas (Pasik and Pasik, 1982; Cowey and Stoerig, 1991; Payne et al, 1996; Ptito et al, 1999; Goebel et al, 2001). The blind-field stimuli are task-irrelevant in this indirect type of paradigm, they can affect the responses to, as well as the appearance and meaning of seen stimuli
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