Temporal Binding Window of the Sound-Induced Flash Illusion in Amblyopia.

Purpose: Amblyopia is a neurodevelopmental visual disorder caused by abnormal visual experience in childhood. In addition to known visual deficits, there is evidence for changes in audiovisual integration in amblyopia using explicit tasks. We examined audiovisual integration in amblyopia using an implicit task that is more relevant in a real-world context. Methods: A total of 11 participants with amblyopia and 16 controls were tested binocularly and monocularly on the sound-induced flash illusion, in which flashes and beeps are presented concurrently and the perceived number of flashes is influenced by the number of beeps. The task used 1 to 2 rapid peripheral flashes presented with 0 to 2 beeps, at 5 stimulus onset asynchronies, that is, beep (-200 milliseconds, -100 milliseconds) or flash leading (100 milliseconds, 200 milliseconds) or simultaneous (0 milliseconds). Participants reported the number of perceived flashes. Susceptibility was indicated by a "2 flashes" response to "fission" (1 flash, 2 beeps) or "1 flash" to "fusion" (2 flashes, 1 beep). Results: For fission with the beep leading during binocular viewing, controls showed an expected decrease in illusion strength as stimulus onset asynchronies increased, whereas the illusion strength remained constant in participants with amblyopia, indicating a wider temporal binding window in amblyopia (P = 0.007). For fusion, participants with amblyopia showed reduced illusion strength during amblyopic eye viewing (P = 0.044) with the flash leading. Conclusions: Amblyopia is associated with the widening of the temporal binding window, specifically for fission when viewing binocularly with the beep leading. This suggests a developmental adaptation to delayed amblyopic eye visual processing to optimize audiovisual integration.

Developmental Trajectory of McGurk Effect Susceptibility in Children and Adults With Amblyopia.

PURPOSE: The McGurk effect is an audiovisual illusion that involves the concurrent presentation of a phoneme (auditory syllable) and an incongruent viseme (visual syllable). Adults with amblyopia show less susceptibility to this illusion than visually normal controls, even when viewing binocularly. The present study investigated the developmental trajectory of McGurk effect susceptibility in adults, older children (10-17 years), and younger children (4-9 years) with amblyopia. METHODS: A total of 62 participants with amblyopia (22 adults, 12 older children, 28 younger children) and 66 visually normal controls (25 adults, 17 older children, 24 younger children) viewed videos that combined phonemes and visemes, and were asked to report what they heard. Videos with congruent (auditory and visual matching) and incongruent (auditory and visual not matching) stimuli were presented. Incorrect responses on incongruent trials correspond to high McGurk effect susceptibility, indicating that the viseme influenced the phoneme. RESULTS: Participants with amblyopia (28.0% ± 3.3%) demonstrated a less consistent McGurk effect than visually normal controls (15.2% ± 2.3%) across all age groups (P = 0.0024). Effect susceptibility increased with age (P = 0.0003) for amblyopic participants and controls. Both groups showed a similar response pattern to different speakers and syllables, but amblyopic participants invariably demonstrated a less consistent effect. CONCLUSIONS: Amblyopia is associated with reduced McGurk effect susceptibility in children and adults. Our findings indicate that the differences do not simply indicate delayed development in children with amblyopia; rather, they represent permanent alterations that persist into adulthood.

Audiovisual perception in adults with amblyopia: a study using the McGurk effect.

PURPOSE: The effects on multisensory integration have rarely been examined in amblyopia. The McGurk effect is a well-established audiovisual illusion that is manifested when an auditory phoneme is presented concurrently with an incongruent visual phoneme. Visually healthy viewers will hear a phoneme that does not match the actual auditory stimulus, having been perceptually influenced by the visual phoneme. This study examines audiovisual integration in adults with amblyopia. METHODS: Twenty-two subjects with amblyopia and 25 visually healthy controls participated. Participants viewed videos of combinations of visual and auditory phonemes, and were asked to report what they heard. Some videos had congruent video and audio (control), whereas others had incongruent video and audio (McGurk). The McGurk effect is strongest when the visual phoneme dominates over the audio phoneme, resulting in low auditory accuracy on the task. RESULTS: Adults with amblyopia demonstrated a weaker McGurk effect than visually healthy controls (P = 0.01). The difference was greatest when viewing monocularly with the amblyopic eye, and it was also evident when viewing binocularly or monocularly with the fellow eye. No correlations were found between the strength of the McGurk effect and either visual acuity or stereoacuity in subjects with amblyopia. Subjects with amblyopia and controls showed a similar response pattern to different speakers and syllables, and subjects with amblyopia consistently demonstrated a weaker effect than controls. CONCLUSIONS: Abnormal visual experience early in life can have negative consequences for audiovisual integration that persists into adulthood in people with amblyopia.