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As with some patients with primary visual cortex (V1) damage, transcranial magnetic stimulation (TMS) over V1 reliably induces blindsight, whereby observers can correctly discriminate the attributes of visual stimuli despite being unable to detect them. This TMS-induced blindsight has been demonstrated to reflect a form of unconscious vision that relies upon different neural pathways than with conscious vision. However, the timing of the neural processes mediating TMS-induced blindsight has been unclear, especially when considering suggestions that TMS interferes with feedback processes to V1 that mediate conscious visual perception. To better elucidate the neural mechanisms that give rise to blindsight, we tested TMS-induced blindsight for the orientation of visual stimuli across a range of stimulus onset asynchronies (SOAs) to assess how different latencies of visual cortex disruption, relative to a visual stimulus, affect detection rates and forced-choice discrimination accuracy. At all TMS latencies, including at SOAs with substantial visual suppression from TMS, discrimination performance was significantly above-chance, demonstrating the consistency of TMS-induced blindsight. Crucially, we observed two windows of maximum visual suppression from TMS at SOAs between 65 and 105 ms, but consistent above-chance discrimination performance accuracy across these windows. However, at longer SOAs, detection and discrimination covaried, suggesting a dependency of discrimination performance on detection only when detection rates exceed threshold levels of normal vision. Taken together, these results indicate that unconscious discrimination occurs independently of detection, including at TMS intervals that optimally interfere with conscious visual perception. They further suggest that forced-choice discrimination is less dependent on feedback processes to V1 than visual awareness and that TMS-induced blindsight is not the same as near-threshold vision., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Early visual cortex activity is influenced by both bottom-up and top-down factors. To investigate the influences of bottom-up (saliency) and top-down (task) factors on different stages of visual processing, we used transcranial magnetic stimulation (TMS) of areas V1/V2 to induce visual suppression at varying temporal intervals. Subjects were asked to detect and discriminate the color or the orientation of briefly-presented small lines that varied on color saliency based on color contrast with the surround. Regardless of task, color saliency modulated the magnitude of TMS-induced visual suppression, especially at earlier temporal processing intervals that reflect the feedforward stage of visual processing in V1/V2. In a second experiment we found that our color saliency effects were also influenced by an inherent advantage of the color red relative to other hues and that color discrimination difficulty did not affect visual suppression. These results support the notion that early visual processing is stimulus driven and that feedforward and feedback processing encode different types of information about visual scenes. They further suggest that certain hues can be prioritized over others within our visual systems by being more robustly represented during early temporal processing intervals., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The dorsal visual processing stream has been suggested to be involved with the unconscious processing of visual information for visually guided actions. In this study, transcranial magnetic stimulation (TMS) was used to gate input into the dorsal visual processing stream by disrupting primary visual cortex (V1) function. Despite restricting geniculostriate processing contributions in the dorsal stream, consistent effects on reaching performance from unconscious visual events were nonetheless measured. These results suggest a functionally intact, albeit unconscious, projection to the dorsal pathway that bypasses V1 and implicates a functional input into the dorsal stream from the superior colliculus.

Previous work has found a left visual field (LVF) advantage for various judgements on faces, including identity and emotional expression. This has been related to possible right-hemisphere specialisation for face processing, and it has been proposed that this might reflect configural processing. We sought to determine whether a similar LVF advantage may also exist for gaze perception. In two experiments, normal adult subjects made judgements for seen gaze direction (left, right or straight). To assess how visual field may influence perception of gaze direction, eye stimuli were briefly presented unilaterally or bilaterally. In the latter case, the gaze direction of the two seen eyes could be congruent or incongruent (i.e. the two eyes could gaze in the same or different directions). For unilateral displays, performance was more accurate for LVF stimuli than RVF. With bilateral incongruent gaze, the LVF eye influenced judgements more strongly than the RVF eye. No such LVF advantage was found in a control experiment, in which subjects judged pupil size for similar eye stimuli. Taken together, these results reveal a LVF advantage for perception of gaze direction. Since only the eye region was visible, our results cannot be due to a LVF bias in processing the entire face context. Instead they suggest lateralisation specifically in processing the direction of seen gaze.

We localized the neuroanatomical correlates for control of saccadic eye movements and for finger movements using a combined transcranial magnetic stimulation (TMS) and magnetic resonance imaging (MRI) approach. Two participants underwent TMS while performing an endogenous saccade task. The motor hand area was localized by TMS and the region anterior to it was mapped to identify the borders of a region where TMS produced delays in generating contralateral saccades. MRI scans were then obtained with fiducial markers placed over the motor hand area and 2 cm anterior to it, the common cortical region that produced saccadic delays in these two subjects. It was also shown that the structural anatomy of the hand area, physiologically defined by visible contractions of the contralateral hand following TMS, corresponded to the knob-like structure recently reported [18, 19]. These results demonstrate that TMS can be a precise, non-invasive tool for neuroanatomical mapping of cortical structures when combined with structural images of the brain.

The role of lateral prefrontal cortex in transducing perception into action was studied in 10 patients with chronic, unilateral lesions. They identified colors in the center of a visual display, while a flanking, distractor color was presented simultaneously in either the ipsilesional or contralesional field. The flanker could be either the same color as the target, or incompatible with the correct response. The effects of compatible and incompatible flankers on reaction time (RT) served as a measure of response channel activation by the flanker. Flankers in the contralesional field influenced RT less than did those in the ipsilesional field. These results suggest that the lateral prefrontal cortex is involved in maintaining stimulus-response channels.

A patient with left hemispatial neglect, while completely unaware of features on the left side of figures, nevertheless perceived geometric illusions dependent on these features. Bisection errors were amplified not only by increasing line length, but also by perceived line length induced by these illusions. Bisection of Judd illusion figures was as much influenced by neglected features on the left as by perceived features on the right. These observations demonstrate that geometric illusions are generated through preattentive processes. They also suggest that in visual neglect there may be preattentive processing of location as well as shape information.