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Yusuke Nakashima, So Kanazawa, Masami K Yamaguchi; Development of human infants’ receptive field mechanisms in motion processing. Journal of Vision 2019;19(10):118c. doi: https://doi.org/10.1167/19.10.118c.
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Discrimination of motion direction is more difficult when the size of high-contrast motion stimuli is increased (Tadin et al., 2003). This is considered to be a perceptual phenomenon that reflects surround suppression in MT neurons. Using this effect, we examined the development of receptive field mechanisms of motion processing in human infants. To clarify when surround suppression in motion processing is acquired, we measured motion direction discrimination with small and large drifting gratings in 3- to 8-month-old infants using familiarization/novelty-preference procedure. During the familiarization phase, a grating moving leftward or rightward was presented repeatedly. In the test phase, gratings moving leftward and rightward were presented simultaneously. Small and large motion stimuli were used in separate sessions. If infants have surround suppression, higher novelty preference would be observed for the small stimulus than for the large stimulus. Our results showed that infants at 6–8 months exhibited higher novelty preference for the small stimulus. In contrast, infants at 3–5 months showed higher novelty preference for the large stimulus. These results suggest that surround suppression in motion processing emerges at around 6 months of age. To investigate developmental change in the size of the receptive field’s center region, we estimated the receptive field size in infants at 3–4 months and 7–8 months using a similar method. The results showed that the size of the receptive field center was larger in 3–4 month-old infants than in 7–8 month-old infants, suggesting that the excitatory center region of receptive fields shrinks with age. The present results are consistent with theories on the development of receptive fields in human infants derived from developmental changes of the contrast sensitivity function.
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