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William Curran, Catherine Lynn; Monkey and humans exhibit similar motion-processing mechanisms. Journal of Vision 2010;10(7):815. doi: https://doi.org/10.1167/10.7.815.
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Single cell recording studies have provided detailed understanding of motion-sensitive neurons in nonhuman primates. Previous research has revealed linear and non-linear increases in spike discharge rate in response to increasing motion coherence and density, respectively, and a division-like inhibition between neurons tuned to opposite directions. It is not known to what extent these response properties mirror those of motion-sensitive neurons in the human brain. We used an adaptation phenomenon, the direction aftereffect (DAE), to investigate whether motion-sensitive neurons in the human brain respond to varying motion density and coherence in a similar manner to macaque. Motion adapters that evoke a stronger response in neurons usually result in greater changes in the neurons' direction tuning functions, which are thought to impact on DAE magnitude. If motion-sensitive neurons in the human brain respond in a similar manner to macaque, increasing motion density and coherence will result in changes in neural spike discharge similar to those reported for macaque. Given the relationship between neural spiking and aftereffect magnitude, changes in the levels of neural activity will be revealed through DAE measurements; with increasing neural activity leading to increasing DAE magnitude. We measured DAE magnitude as a function of 1) varying adapter dot density; 2) repeating the experiment while adding dots moving in the opposite direction; and 3) varying motion coherence of the adapter. The resultant DAE tuning functions show that changes in activity of human motion-sensitive neurons to changes in motion density and coherence bear a strong resemblance to macaque data. We also show a division-like inhibition between neural populations tuned to opposite directions, which also mirrors neural inhibitory behaviour in macaque. These findings strongly suggest that motion-sensitive neurons in human and nonhuman primates share common response and inhibitory characteristics.
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