"Real-time" obstacle avoidance in the absence of primary visual cortex.
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.
Striemer
Christopher L
CL
Canadian Institutes of Health Research Group on Action and Perception, Centre for Brain and Mind, Department of Psychology, The University of Western Ontario, London, Ontario, Canada N6A 5C2.
Chapman
Craig S
CS
Goodale
Melvyn A
MA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D006423:Hemianopsia / Q000209:etiology / Q000503:physiopathology* / Q000523:psychology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology; D013037:Spatial Behavior / Q000502:physiology; D020521:Stroke / Q000150:complications / Q000473:pathology / Q000503:physiopathology / Q000523:psychology; D013647:Task Performance and Analysis; D014793:Visual Cortex / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology; D014794:Visual Fields; D014795:Visual Pathways / Q000293:injuries / Q000473:pathology / Q000503:physiopathology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult