Figure 5.

Effects of chronic monaural occlusion on auditory spatial acuity. (A) Schematic view of chamber used to measure minimum audible angles (MAA) in ferrets. The animals were trained to initiate a trial by standing on the start platform and licking the center spout. This action triggered a noise burst (800 Hz to 24 kHz, 100-ms duration) from one of the two speakers placed symmetrically about the anterior midline. Ferrets were rewarded for licking the water spout in the same hemifield as the active speaker. The separation of the speakers was reduced between testing sessions according to the method detailed in ref. 44. Psychometric functions were measured by reducing the angular separation of the speakers from 90° to 6° or until performance did not differ from chance (56.5%, binomial distribution). (B) Mean (± SD) psychometric functions for normal ferrets (Normals, n = 6), ferrets plugged in infancy (Infant-plug, n = 4), and ferrets plugged as adults (Adult-plug, n = 3). These data were obtained with the earplug in place. deg, degree. (C) MAAs (defined as the speaker separation corresponding to 75% correct performance) were calculated from the psychometric function data. Note that adult-plugged ferrets failed to reach 75% correct, even at the maximum speaker separation of 90°; their MAAs are therefore indicated by >90°.