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Silvia Cirstea, Andrew Kolarik, Shahina Pardhan; Differences In Perceiving Auditory Distance Between Visually Impaired And Severely Visually Impaired. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4357.
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The study investigated how sight impaired subjects use level and reverberation cues to discriminate distances to sound sources in comparison with age-matched normal vision subjects.
Pairs of 90 ms broadband noise sounds were presented over headphones. Stimuli were filtered to sound as if originating from distances between 1 and 8 m in front of the listener, in a reverberant virtual room of 9 x 5.4 x 2.5 m, simulated using an image-source model. In each pair, one of the sounds was at a reference distance (2 m or 5 m) and the other sound was at a comparison distance. Percentage correct judgement of which sound was closer was measured. Listeners performed the task in three conditions: level only, reverberation only, and both cues available. They were screened for both hearing and vision prior to the study; the hearing was within normal range for their age. The sight impaired were categorised into a ‘Visually Impaired’ group (logMAR 0.17-1.24, n = 6, mean age 75.3 years) and a ‘Severely Visually Impaired’ group (light perception or worse, n = 5, mean age 42.5 years). Age-matched normal vision control groups were considered.
Non-parametric statistical tests indicate that level provided more accurate distance information than reverberation for all impaired and control subjects. The Visually Impaired group performed in all conditions very similarly to the age-matched control group. At the same time, when comparing the performance of the Severely Visually Impaired group with its age-matched control group, it has been found that the Severely Visually Impaired show significantly better performance using both level and reverberation cues separately, both in the near (around 2 m) and further field (around 5 m). Reverberation is shown to become a useful cue for the control groups and the Visually Impaired group only for sounds in the far field (over 5 m), while the Severely Visually Impaired display better performance in the use of the reverberation cue in both near and further field.
This study shows that Severely Visually Impaired subjects have superior ability to process environmental auditory cues in the near as well as further field, while Visually Impaired subjects with residual vision perform at a comparable level with normal vision subjects.
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