doi:10.1016/j.brainres.2005.01.101 
Copyright © 2005 Elsevier B.V. All rights reserved.
Research report
Auditory compensation in myopic humans: involvement of binaural, monaural, or echo cues?
O. Després
, 
, V. Candas and A. Dufour
Centre d’Etudes de Physiologie Appliquée 21, rue Becquerel, 67087 Strasbourg Cedex, France
Accepted 31 January 2005.
Available online 23 March 2005.
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Abstract
The purpose of this paper is to investigate the involvement of various auditory localization mechanisms in the improvement of auditory spatial sensitivity in the case of partial visual deprivation. We compared sensitivity to binaural, monaural, and echo cues between normal-sighted and myopic subjects. In an auditory task, which depended solely upon binaural processing, myopic and normal-sighted subjects showed an almost equal localization performance. We also found that myopic subjects were no more disturbed than normal-sighted subjects when spectral shape cues were removed. On the other hand, near-sighted subjects exhibited better echolocation skills and a higher sensitivity to echo cues than normal-sighted subjects. We can therefore conclude that an improved auditory spatial sensitivity in myopic subjects may result from the increased use of echo information.
Keywords: Visual deficit; Auditory compensation; Binaural cues; Monaural cues; Echo cues
Neuroscience classification codes: Sensory system, Auditory systems: central physiology
Fig. 1. Schematic of experiment 1 in the frontal condition. Eight loudspeakers were located at 5°, 10°, 15°, and 20° on either side of the subjects' mid-sagittal plane (dashed line) along the outer circumference of the shelf. At each trial, an auditory target was delivered through a randomly selected loudspeaker. Subjects had to point towards the auditory target with the right index finger on which was attached a laser pointer.
Fig. 2. Procedure of experiment 4. Subject sat on a chair with his head fixed in a straight-ahead position. A device was composed of a mobile wooden board. A loudspeaker (L), placed on the table, was directed toward the device. At each trial, the board was randomly set at one of 3 positions: two positions (1 and 2) were eccentric and enabled reverberation of the auditory stimuli (see the box), one position (3) was aligned with of the mid-sagittal plane of the subject and did not enable sound reverberation. The loudspeaker emitted a train of white broadband sound and subject had to assess the position (right or left with respect to the mid-sagittal plane) of the board by processing echo cues.
Fig. 3. Schematic of experiment 5. Eight loudspeakers were located at 5°, 10°, 15°, and 20° on either side of the subjects' mid-sagittal plane along a circumference of the shelf (2 m from the subject). At each trial, an auditory target was delivered through a randomly selected loudspeaker. Subjects had to point towards the auditory target with the right finger on which was attached a laser pointer. Subjects performed pointing task in two experimental conditions: (a) subjects and the loudspeaker displays were placed at an equal distance from the lateral walls (solid line) and (b) they were placed at a proximal distance (1 m) from one of the lateral walls (dashed line).
Fig. 4. MAE scores and standard errors (degrees) of the finger-pointing task for normal-sighted and myopic subjects and for each spatial session (frontal/posterior).
Fig. 5. Mean MAE scores and standard errors (degrees) of the finger-pointing task in the vertical dimension (left box) and in the horizontal dimension (right box) for both groups in both hearing conditions.
Fig. 6. Percentages of correct right/left position discrimination and reaction times of correct responses for normal-sighted and myopic subjects. Error bars are standard errors.
Fig. 7. Auditory localization bias and standard errors (degrees) of the finger-pointing task for each group in both positions.
Table 1.
Characterization of the fifteen myopic subjects
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