David W. Chandler
Audiol. Sect., Madigan Army Med. Ctr., Tacoma, WA 98431
D. Wesley Grantham
Vanderbilt Univ., Nashville, TN 37212
Marjorie R. Leek
Walter Reed Army Med. Ctr., Washington, DC 20307
The horizontal-plane minimum audible angle (MAA) was measured for single components of a five-tone sequence, where each component was a 1000-Hz burst 100 ms in duration. The five components were presented in a pseudorandom order from the following five azimuths: -54(degrees), -19(degrees), 0(degrees), +23(degrees), and +56(degrees). The target component whose azimuth change was to be detected was at either -54(degrees) or 0(degrees), and could occur in temporal position 2 or 5 in the sequence. Stimulus uncertainty was varied from a minimal level to a high level by randomly varying target temporal position, target azimuth, or both from trial to trial. When the target position and azimuth within the sequence was unchanged from trial to trial (minimum stimulus uncertainty), MAAs for targets presented in the last temporal position at both target azimuths were as small as for tones presented in isolation. However, for targets presented earlier in the sequence, MAAs were elevated at both azimuths. The MAAs at 0(degrees) at both temporal positions were unaffected as uncertainty increased, but there were large effects of uncertainty at -54(degrees) azimuth. Results suggest that in a task requiring spatial resolution in the horizontal plane, when the time of arrival and location of an auditory signal are unknown, listeners focus their attention near midline, where resolution is typically most precise. [Work supported by U.S. Army and NIH DC00185.]