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

Abstract

PURPOSE. Classically understood as a deficit in spatial vision, amblyopia is increasingly recognized to also impair audiovisual multisensory processing. Studies to date, however, have not determined whether the audiovisual abnormalities reflect a failure of multisensory integration, or an optimal strategy in the face of unisensory impairment. We use the ventriloquism effect and the maximum-likelihood estimation (MLE) model of optimal integration to investigate integration of audiovisual spatial information in amblyopia.METHODS. Participants with unilateral amblyopia (n ¼ 14; mean age 28.8 years; 7 anisometropic, 3 strabismic, 4 mixed mechanism) and visually normal controls (n ¼ 16, mean age 29.2 years) localized brief unimodal auditory, unimodal visual, and bimodal (audiovisual) stimuli during binocular viewing using a location discrimination task. A subset of bimodal trials involved the ventriloquism effect, an illusion in which auditory and visual stimuli originating from different locations are perceived as originating from a single location. Localization precision and bias were determined by psychometric curve fitting, and the observed parameters were compared with predictions from the MLE model. RESULTS.Spatial localization precision was significantly reduced in the amblyopia group compared with the control group for unimodal visual, unimodal auditory, and bimodal stimuli. Analyses of localization precision and bias for bimodal stimuli showed no significant deviations from the MLE model in either the amblyopia group or the control group.CONCLUSIONS. Despite pervasive deficits in localization precision for visual, auditory, and audiovisual stimuli, audiovisual integration remains intact and optimal in unilateral amblyopia.

Intramodal cortical plastic changes after moderate visual impairment in human amblyopia

“…In a study by Rauschecker and Harris (1983), the superior colliculus elicited a more rigorous response in eyelid-sutured than in normal cats. Despite the previous evidence on increased neuronal responses to auditory information after different types of visual sensory deprivation, the causal or Recent studies on auditory localization performance in humans diagnosed with amblyopia argue against compensatory performance in the auditory modality (Richards et al, 2018(Richards et al, , 2019a. These reported reduced auditory localization skills in individuals with amblyopia compared to sighted controls.…”

“…Recent studies on auditory localization performance in humans diagnosed with amblyopia argue against compensatory performance in the auditory modality ( Richards et al., 2018 , 2019a ). These reported reduced auditory localization skills in individuals with amblyopia compared to sighted controls.…”

“…On the other hand, it has been shown that the temporal integration of auditory and visual events might be intact in human amblyopia, which was observed via the temporal ventriloquist effect (see Richards et al., 2018 ). In this task, participants have to detect the order of onsets of two light flashes.…”

“…Taken together, it might be suggested that instead of a “primary multisensory deficit” to integrate audio-visual information, the abnormalities of multisensory processing in amblyopia might be related to “reduced temporal resolution in unisensory perception or in the mechanism for cross-modal matching (i.e., nonintegrative comparison of unisensory features)” (p.129, Richards et al., 2018 for further discussion).…”

Impaired Spatial Hearing in Amblyopia: Evidence for Calibration of Auditory Maps by Retinocollicular Input in Humans

“…[21][22][23][24] Surprisingly, a recent investigation by our laboratory suggested that people with amblyopia may also have greater difficulty localizing sounds, even in complete darkness. 25 As with spatial acuity in the human visual system, spatial acuity in the auditory system follows a developmental trajectory through childhood. Binaural localization is immature at birth, but improves dramatically during the first several years of life.…”