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Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings
Published on: August 1, 2018
Retinotopic encoding of the direction aftereffect
1Department of Psychology, Macquarie University, Sydney, NSW 2109, Australia. peterw@vision.psy.mq.edu.au
Vision Research
|July 16, 2008
Summary
Visual adaptation in the MT (V5) area is spatially specific for gratings but less so for dots. This psychophysical study challenges claims of strong spatiotopicity in human MT, suggesting retinotopic processing is more dominant.
Area of Science:
- Neuroscience
- Visual Perception
- Computational Neuroscience
Background:
- Previous research by Kohn and Movshon indicated spatially specific neuronal adaptation to visual motion in the MT (V5) area of macaque monkeys.
- This spatial specificity led to the hypothesis that adaptation originates in V1 and is inherited by MT, due to V1's smaller receptive fields and retinotopic organization.
- Contradictory findings exist regarding whether human MT (hMT) exhibits spatiotopic or retinotopic selectivity, prompting further investigation using psychophysical methods.
Purpose of the Study:
- To investigate the spatial specificity of visual motion adaptation in human MT (hMT) using psychophysical measures.
- To compare the spatial specificity of adaptation for grating stimuli versus dot stimuli.
- To provide evidence regarding the spatiotopic versus retinotopic organization of hMT.
Main Methods:
- Three experiments were conducted using the direction aftereffect (DAE) paradigm.
- DAEs were induced and tested with drifting gratings and drifting dots under varying spatial and retinotopic location changes between adaptation and test phases.
- Stimulus locations were manipulated to be changed retinotopically, spatiotopically, or both.
Main Results:
- Spatial specificity of the direction aftereffect was significantly greater for drifting gratings than for drifting dots.
- The results support the prediction that dot stimuli, potentially adapting MT cells more directly, exhibit less spatial specificity.
- Very small spatiotopic effects were observed, questioning recent claims of high spatiotopicity in hMT.
Conclusions:
- Visual motion adaptation in hMT shows greater spatial specificity for extended stimuli like gratings compared to discrete stimuli like dots.
- The findings suggest that adaptation mechanisms in hMT are not exclusively spatiotopic and that retinotopic processing plays a significant role.
- This study provides psychophysical evidence that challenges the notion of a predominantly spatiotopic map in human MT.
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