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Jennifer Luu, Dennis Levi; Feature integration and sensitivity to synchronicity for biological motion impaired by amblyopia. Journal of Vision 2009;9(8):623. doi: 10.1167/9.8.623.
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© ARVO (1962-2015); The Authors (2016-present)
Spatio-temporal processing may be impaired in strabismic amblyopes (Asper et al., 2000; Popple & Levi, 2008; Roelfsema et al., 1994). The goals of this experiment were two-fold. First, we examined whether the amblyopic visual system retains the higher-level processing capabilities to detect biological motion. Second, we established whether synchronicity sensitivity (detection of synchronized versus desynchronized interactions) is impaired in amblyopic observers relative to normal control observers. We showed point-light displays generated from the trajectories of the major joints of two human agents performing a dancing routine. We used the method of constant stimuli to present the biological motion stimulus at five different stimulus levels, varying the strength of biological motion by varying the number of dot trajectories. Synchronized and desynchronized trials were randomly presented. Each trial consisted of two intervals, ‘target’ and ‘non-target’. In the non-target interval, the dot trajectories of one agent were scrambled. Observers were asked to indicate the target interval that showed two agents dancing. Our results show that the ability to detect biological motion requires more samples (dot trajectories) in both eyes of strabismic amblyopes than in normal control observers. The increased sample threshold is not the result of low-level losses (dot trajectories were visible) but may reflect losses in feature integration due to undersampling in the amblyopic visual system (Levi et al., 1987; Levi et al., 1999; Levi & Klein, 1986). However, like normal observers, amblyopes are more sensitive to synchronized versus desynchronized interactions, indicating that higher-level processing of biological motion remains intact, as previously reported (Neri et al., 2007; Thompson et al., 2008). In contrast, synchronicity sensitivity is impaired in the amblyopic visual system, because disruption due to desynchronization is especially strong. The presence or absence of binocular function may determine whether or not an observer possesses normal sensitivity to synchronicity.
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