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Spatial and temporal processing in a subject with cortical blindness following occipital surgery
Ceri T Trevethan1, Arash Sahraie
1Vision Research Laboratories, Department of Psychology, King's College, University of Aberdeen, AB24 2UB, Aberdeen, UK.
Neuropsychologia
|May 22, 2003
Summary
Blindsight mechanisms in subject VN show temporal band-pass characteristics, similar to other cases. These findings suggest residual vision may not require spared visual cortex areas.
Area of Science:
- Neuroscience
- Visual Perception
- Psychophysics
Background:
- Blindsight, the ability to respond to visual stimuli without conscious awareness, is typically better for rapid events.
- Detailed temporal characteristics of blindsight mechanisms have been studied in only one subject (GY).
- Investigating these characteristics in other blindsight cases is crucial for understanding the phenomenon.
Observation:
- A systematic study of spatio-temporal properties of blindsight mechanisms was conducted on subject VN.
- VN has a lower right quadranopia post-surgery with no remaining visual cortex in the affected area.
- Pupillary responses were used to predict residual vision and showed spatial characteristics similar to psychophysical findings.
Findings:
- Blindsight mechanisms in VN exhibit narrowly tuned band-pass temporal characteristics, peaking at 20Hz.
- Performance was above chance at temporal frequencies between 10Hz and 33Hz.
- The spatial channel demonstrated low-pass characteristics with an upper cut-off below 3.5c/degrees, extensive spatial summation, and no temporal summation.
Implications:
- The spatio-temporal characteristics in VN are similar to those in subjects with ischemic lesions.
- This suggests that blindsight capacities may not solely depend on spared areas of the visual cortex.
- These findings challenge existing models of visual processing in the absence of conscious awareness.