Abstract
Amblyopia is a developmental visual impairment that is increasingly recognized to affect higher-level perceptual and multisensory processes. To further investigate the audiovisual (AV) perceptual impairments associated with this condition, we characterized the temporal interval in which asynchronous auditory and visual stimuli are perceived as simultaneous 50% of the time (i.e., the AV simultaneity window). Adults with unilateral amblyopia (n = 17) and visually normal controls (n = 17) judged the simultaneity of a flash and a click presented with both eyes viewing. The signal onset asynchrony (SOA) varied from 0 ms to 450 ms for auditory-lead and visual-lead conditions. A subset of participants with amblyopia (n = 6) was tested monocularly. Compared to the control group, the auditory-lead side of the AV simultaneity window was widened by 48 ms (36%; p = 0.002), whereas that of the visual-lead side was widened by 86 ms (37%; p = 0.02). The overall mean window width was 500 ms, compared to 366 ms among controls (37% wider; p = 0.002). Among participants with amblyopia, the simultaneity window parameters were unchanged by viewing condition, but subgroup analysis revealed differential effects on the parameters by amblyopia severity, etiology, and foveal suppression status. Possible mechanisms to explain these findings include visual temporal uncertainty, interocular perceptual latency asymmetry, and disruption of normal developmental tuning of sensitivity to audiovisual asynchrony.
Highlights
Amblyopia is a developmental visual impairment caused by abnormal visual experience during a critical period in early childhood
The AV simultaneity window in adults with unilateral amblyopia was broadened by 134 ms, or 37%, compared to control participants (F(1,32) = 11.313, p = 0.002) when viewing binocularly (Fig 3 and Table 2)
The auditory-lead side of the AV simultaneity window was wider by 48 ms (36%; F(1,32) = 11.012, p = 0.002), and the visual-lead side was wider by 86 ms (37%; F(1,32) = 6.00, p = 0.02)
Summary
Amblyopia is a developmental visual impairment caused by abnormal visual experience during a critical period in early childhood. Adults with early pattern vision deprivation from bilateral congenital cataracts have an AV simultaneity window that is selectively broadened on the visual-lead side,[69] as well as diminished audiovisual interaction in speech perception,[30] and a shift in attentional balance toward audition.[70] In contrast, the AV simultaneity window of adults with unilateral congenital cataract is symmetrically broadened, similar to that seen in typically-developing children.[69] Audiovisual interactions have been studied in monocular adults with a history of early enucleation Like those with unilateral amblyopia, this population shows reduced susceptibility to the McGurk effect, but demonstrate normal responses to illusions involving temporal audiovisual integration such as the sound-induced flash illusion and AV simultaneity judgments.[71] This suggests that AV integration deficits may be specific to the nature of the visual sensory disturbance during the critical period. Based on this evidence from visually normal adults and our previous studies showing that adults with amblyopia are less susceptible to the McGurk effect,[23, 24] we hypothesized that unilateral amblyopia will show a symmetrically broadened AV simultaneity window under binocular and monocular viewing conditions, indicating a higher-level alteration in audiovisual integration that is generalized beyond speech
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