“Real-time” obstacle avoidance in the absence of primary visual cortex

Abstract

When we reach toward objects, we easily avoid potential obstacles located in the workspace. Previous studies suggest that obstacle avoidance relies on mechanisms in the dorsal visual stream in the posterior parietal cortex. One fundamental question that remains unanswered is where the visual inputs to these dorsal-stream mechanisms are coming from. Here, we provide compelling evidence that these mechanisms can operate in ''real-time'' without direct input from primary visual cortex (V1). In our first experiment, we used a reaching task to demonstrate that an individual with a dense left visual field hemianopia after damage to V1 remained strikingly sensitive to the position of unseen static obstacles placed in his blind field. Importantly, in a second experiment, we showed that his sensitivity to the same obstacles in his blind field was abolished when a short 2-s delay (without vision) was introduced before reach onset. These findings have far-reaching implications, not only for our understanding of the time constraints under which different visual pathways operate, but also in relation to how these seemingly ''primitive'' subcortical visual pathways can control complex everyday behavior without recourse to conscious vision.blindsight ͉ dorsal stream ͉ visuomotor control ͉ visual pathways ͉ consciousness

Acting without seeing: eye movements reveal visual processing without awareness

“…Together with a parallel study in healthy observers [51], this suggests an involvement of the retino-collicular pathway in the processing of unperceived visual information for eye movements. This pathway is also implicated in blindsight studies assessing hand movements–reaching [77] and pointing [78]. …”

Rehabilitation of damage to the visual brain

“…As well as compensation to simply shift the field of view to the unaffected side, some work has suggested that saccadic eye movements (Barbur et al, 1988) and obstacle avoidance (Striemer et al, 2009) can be influenced by unseen stimulation within the blind hemifield.…”

Ventral and dorsal streams as modality-independent phenomena

“…Even stronger evidence for a sharp dissociation between visuomotor performance and awareness comes from a recent paper by Striemer, Chapman, and Goodale (2009) showing that a patient with a dense hemianopia following an occipital lesion could avoid obstacles placed in his blind field in a reaching task, even though he never reported seeing those obstacles. Given the demonstrated role of dorsal stream mechanisms in the control of obstacle avoidance Schindler et al, 2006), this new work further suggests that those mechanisms can make use of visual inputs that bypass the geniculo-striate pathway.…”

“…Comparable abilities may be found in the perceptual domain, without the corresponding inference that perceptual processing is always unconscious. Goodale and Milner responded by citing another example of action-blindsight (Striemer, Chapman, & Goodale, 2009). While undeniably impressive, this case does not affect our original argument.…”