Alterations in audiovisual simultaneity perception in amblyopia

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.

Temporal Ventriloquism Reveals Intact Audiovisual Temporal Integration in Amblyopia

“…23,28,29,32 Previous work has shown that unilateral amblyopia is associated with symmetric widening of the temporal window of audiovisual simultaneity perception 21,22 and reduced susceptibility to the McGurk effect under both monocular and binocular viewing conditions. [18][19][20] In addition, a study of the sound-induced flash illusion in amblyopia suggested that the temporal binding window for the illusion is extended under binocular conditions when the clicks lead the flash.…”

“…24 Like the soundinduced flash illusion, the temporal ventriloquism effect is also dependent on perceptual binding of asynchronous auditory and visual signals in the temporal dimension. Therefore, reduced sensitivity to audiovisual asynchrony, as evidenced by a widened simultaneity window, 21,22 would likely not diminish susceptibility to the temporal ventriloquism effect, but enable integration over a wider range of SOAs. Indeed, a widened audiovisual temporal binding window in amblyopia is suggested by the significant relation between susceptibility to the temporal ventriloquism effect and the extent of the stereo acuity and visual acuity deficits (Figs.…”

“…For example, in audiovisual simultaneity judgment tasks, the temporal window of perceived simultaneity is broadened on both the visual-lead and auditory-lead sides for people with unilateral amblyopia. 21,22 In the sound-induced flash illusion, 23 a broader temporal window of auditory dominance over vision when the sound precedes the flash also is evident. 24 These multisensory perceptual abnormalities are observed under binocular viewing conditions, and so cannot be fully explained by visual anomalies in the amblyopic eye alone.…”

“…Alternatively, a wider audiovisual simultaneity window may represent entirely nonintegrative factors, such as a criterion shift toward simultaneity, 30 or temporal uncertainty in the unisensory streams that feed into the neural machinery of multisensory integration. 22 Indeed, some empirical data suggest that the width of the audiovisual simultaneity window may not be a function of multisensory integration, but rather of nonintegrative cross-modal matching of temporal features encoded within the unisensory streams. 31 Finally, because testing paradigms for the McGurk effect, sound-induced flash illusion, and audiovisual simultaneity window typically involve a single interval with a ''target present'' versus ''target not present'' response, they are more susceptible to interindividual response bias than traditional 2-alternative forced choice (2AFC) paradigms that have a predictable noise floor.…”

Optimal Audiovisual Integration in the Ventriloquism Effect But Pervasive Deficits in Unisensory Spatial Localization in Amblyopia

“…For example, the ability to detect asynchrony between auditory and visual stimuli is diminished in amblyopia. 29,30 While insensitivity to audiovisual asynchrony may indicate abnormal audiovisual integration, 31 it may also be caused by noisy encoding of visual temporal information that feeds into a normal upstream multisensory processing network. 32 Considering these possibilities, it becomes clear that the origin of these multisensory abnormalities in amblyopia remains an unresolved question.…”