Optimal audiovisual integration in people with one eye.

People with one eye show altered sensory processing. Such changes might reflect a central reweighting of sensory information that might impact on how multisensory cues are integrated. We assessed whether people who lost an eye early in life differ from controls with respect to audiovisual integration. In order to quantify the relative weightings assigned to each sensory system, participants were asked to spatially localize audiovisual events that have been previously shown to be optimally combined and perceptually fused from the point of view of location in a normal population, where the auditory and visual components were spatially disparate. There was no difference in the variability of localizing unimodal visual and auditory targets by people with one eye compared to controls. People with one eye did however, demonstrate slower reaction times to localize visual stimuli compared to auditory stimuli and were slower than binocular and eye-patched control groups. When localizing bimodal targets, the weightings assigned to each sensory modality in both people with one eye and controls were predictable from their unimodal performance, in accordance with Maximum Likelihood Estimation and the time it took all three groups to localize the bimodal targets was faster than for vision alone. Regardless of demonstrating a longer response time to visual stimuli, people with one eye appear to integrate the auditory and visual components of multisensory events optimally when determining spatial location.

No Colavita effect: equal auditory and visual processing in people with one eye.

Previous research has shown that people with one eye have enhanced spatial vision implying intra-modal compensation for their loss of binocularity. The current experiments investigate whether monocular blindness from unilateral eye enucleation may lead to cross-modal sensory compensation for the loss of one eye. We measured speeded detection and discrimination of audiovisual targets presented as a stream of paired objects and familiar sounds in a group of individuals with monocular enucleation compared to controls viewing binocularly or monocularly. In Experiment 1, participants detected the presence of auditory, visual or audiovisual targets. All participant groups were equally able to detect the targets. In Experiment 2, participants discriminated between the visual, auditory or bimodal (audiovisual) targets. Both control groups showed the Colavita effect, that is, preferential processing of visual over auditory information for the bimodal stimuli. The monocular enucleation group, however, showed no Colavita effect, and further, they demonstrated equal processing of visual and auditory stimuli. This finding suggests a lack of visual dominance and equivalent auditory and visual processing in people with one eye. This may be an adaptive form of sensory compensation for the loss of one eye and could result from recruitment of deafferented visual cortical areas by inputs from other senses.

Superior voice recognition in a patient with acquired prosopagnosia and object agnosia.

Anecdotally, it has been reported that individuals with acquired prosopagnosia compensate for their inability to recognize faces by using other person identity cues such as hair, gait or the voice. Are they therefore superior at the use of non-face cues, specifically voices, to person identity? Here, we empirically measure person and object identity recognition in a patient with acquired prosopagnosia and object agnosia. We quantify person identity (face and voice) and object identity (car and horn) recognition for visual, auditory, and bimodal (visual and auditory) stimuli. The patient is unable to recognize faces or cars, consistent with his prosopagnosia and object agnosia, respectively. He is perfectly able to recognize people's voices and car horns and bimodal stimuli. These data show a reverse shift in the typical weighting of visual over auditory information for audiovisual stimuli in a compromised visual recognition system. Moreover, the patient shows selectively superior voice recognition compared to the controls revealing that two different stimulus domains, persons and objects, may not be equally affected by sensory adaptation effects. This also implies that person and object identity recognition are processed in separate pathways. These data demonstrate that an individual with acquired prosopagnosia and object agnosia can compensate for the visual impairment and become quite skilled at using spared aspects of sensory processing. In the case of acquired prosopagnosia it is advantageous to develop a superior use of voices for person identity recognition in everyday life.