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Michael D. Richards, Herbert C. Goltz, Agnes MF Wong; Novel sound localization deficit in unilateral amblyopia. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1954. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Evidence from animals and blind humans suggests that early visual experience influences the calibration of sound localization during development. Despite the link between early visual impairment and altered spatial hearing, sound localization has never been investigated in the most common early-onset visual disorder—amblyopia. Amblyopia affects 3% of the population, and typically presents as unilateral vision loss associated with a history of strabismus and/or anisometropia during a sensitive period of brain development. Hypothesizing that unilateral amblyopia may involve deficits in spatial hearing, we measured the precision and accuracy of sound localization in this clinical population.
All participants passed a standard hearing test. Experiment 1 measured the minimum audible angle (the smallest reliably perceptible change in sound source position) in 10 adults with amblyopia and 10 controls. Participants listened to a sequence of two clicks from different speakers in an 11-speaker array (subtending the central 30°) and judged whether the second click was located left or right relative to the first. Experiment 2 measured sound localization error in 14 adults with amblyopia and 16 controls. Participants listened to a click train from one of 9 virtual sound sources in the central 32° and aligned a visual cursor to the perceived click location using a mouse.
In Experiment 1, the minimum audible angle (mean ± SEM) was significantly greater in the amblyopia group (3.6 ± 0.4°) compared to controls (2.0 ± 0.1°), t(18) = -4.28, p = .001. In Experiment 2, the overall absolute sound localization error (mean ± SEM) was significantly greater in the amblyopia group (4.7 ± 0.4°) compared to controls (3.5 ± 0.4°), F(1,26) = 4.35, p = .047. The amblyopia group also showed abnormal asymmetry in absolute sound localization error, with greater error in the hemifield ipsilateral to the amblyopic eye (F(1,13) = 5.44, p = .036). Within the amblyopic hemifield, the absolute error correlated positively with deficits in visual acuity (p < .01) and stereo acuity (p < .01).
Sound localization precision and accuracy are impaired in unilateral amblyopia. The asymmetric pattern of sound localization errors suggest that amblyopic vision may interfere with the development of spatial hearing via the retinocollicular pathway.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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