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Shlomit Ben-Ami, Nikolaus F. Troje, Pawan Sinha; How the Brain Learns to See Biological Motion After Recovering from Visual Deprivation. Journal of Vision 2019;19(10):191a. doi: https://doi.org/10.1167/19.10.191a.
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The perception of biological motion is handled effortlessly by our visual system and found even in animals and human neonates. Prior studies testing patients years after recovering from congenital blindness have revealed that this skill is spared, with subjects showing preserved behavioral and electro-physiological responses to visual displays of human coordinated movement even after prolonged periods of congenital blindness. These evidences of an early developing and resilient sensitivity have led to questioning if visual experience is at all required for development of specialization for biological motion or if development of neural systems for processing of biological motion may be independent of visual input. We addressed this question by testing the longitudinal development of the ability to detect biological motion and to extract meaningful information from it in 18 individuals aged 7–21 years with profound congenital visual deprivation, immediately after treatment with sight-restoring surgery. Subjects were shown unmasked point light displays and asked to identify a person by choosing between displays of actions and their inverted, spatially-scrambled or phase-scrambled version in experiment 1, and to determine walking direction in experiment 2. We found that the ability to discriminate biological motion and to determine walking direction were both correlated with visual acuity. We did not find such a correlation in age-matched controls with comparable simulated acuity-reduction. Together, these results paint a picture attesting to the role of visual experience in the emergence of biological motion perception. We probed the use of local cues by sight-restored patients for assessing walking direction in an additional experiment, by manipulating each individual dot and inverting its trajectory’s directionality. We found reduced reliance of the patient group on local motion information, in contrast to healthy sighted adults and controls observing displays with comparable blur. This difference remained evident over the course of six months following surgery.
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