Four subjects were tested in a two-alternative, forced-choice, three down-one up adaptive paradigm in which two 200-ms signals were presented sequentially with a 200-ms interstimulus interval. The subject's task was to indicate whether the second stimulus was to the right or left of the first. Tests were conducted with 57 dB (A-weighted), 1.0-kHz high-pass noise, the minimum audible angle (MAA) task, and with lights emitting 620 nm at a luminance level of 200 mL, the minimum visible angle (MVA) task. Localization performance in the MAA task was equal to or better than that obtained in the MVA task for all regions of the frontal field with only one exception, presentations at 0 degrees azimuth. The implications of these results are discussed.
Grantham [Grantham, J. Acoust. Soc. Am. 79, 1939-1949 (1986)] has proposed that subjects are able to resolve the velocity of a moving sound source simply by determining the distance traveled and the time required to complete the movement. In the current experiment, subjects were able to discriminate between accelerated and decelerated movements which were identical on both parameters; that is, the accelerated and decelerated movements began and ended at the same locus and required the same amount of time to be completed. The minimum duration required to discriminate between these two movement patterns was 310 and 90 ms, respectively, for displacements of 9 degrees and 18 degrees. These results suggest that, under some conditions, the perception of velocity in the auditory modality may be based upon something more than a simple comparison of the total distance traveled and the time required to complete the movement.
The relation between minimum audible and minimum visible angle was measured in a sequential localization task and compared. The frontal spatial fields of the visual and auditory systems are superior to their peripheral regions [Wertheim (1894); Mills (1958)]. Localization tasks were related to Vernier’s acuity, except the timing was in a sequential pattern for both the visual and auditory systems. The spatial acuity of the auditory system defined space better at approximately 20-deg azimuth and beyond then the visual system. Four subjects participated, two male and two female, ranging in ages from 23–49. Significant differences were found in the main effects of angles [F(4,3)=30.59, p<0.01] and the interaction between conditions and angle [F(4,3)=3,89, p<0.05]. The implications of these results will be discussed.
Since Ebata et al. [ 537–541 (1968)], little experimental or theoretical work has been done on the perception of multiple echoes. In the current experiment, listeners seated in an anechoic chamber were presented with 4-ms noise bursts in a lead-lag-lag configuration. The lead burst was presented from a loudspeaker at 45° left of midline and one lag burst (lag A) was presented at midline. Listeners discriminated the location of a second lag burst (lag B) presented from a loudspeaker at either 35° or 55° right of midline. Keeping the delay between lead and lag B constant, a range of delays between lead and lag A was presented to determine whether changing the delay of lag A had an effect upon the perception of lag B. Presentation of lag A interfered with the perception of lag B over a wide range of lag A delays, such that subjects’ discrimination of the location of lag B was poorer when compared to the discrimination of lag B when lag A was absent. The data suggest that the introduction of an earlier echo serves to suppress directional information from a subsequent echo. [Work supported by NIH grant DC01625.]
Auditory resolution of a moving sound source was determined in a real motion paradigm. Minimum audible movement angle (MAMA) and minimum visible movement angle (MVMA) thresholds were obtained for five subjects in a two-alternative, forced-choice, three-up/one-down, adaptive procedure as a function of velocity. Velocities from 0.15°/s to 40°/s were utilized to give a wide range of motion thresholds. The low-ended velocities are of particular interest because in a previous study Saberi and Perrott showed an increase of approximately 4–5 deg for velocities below 1°/second indicating a U-shaped function in the detection of MAMA thresholds [Saberi and Perrott, J. Acoust. Soc. Am. 88, 2639–2644 (1990)]. The results of the current study suggest that MAMA thresholds flatten or decrease for velocities below 1°/s. However, it should be noted that in the current study, real motion was employed in contrast to that of simulated motion which utilized a 1.8-ms click train with 5.7-cm speakers in the Saberi and Perrott study. In addition, when MAMA and MVMA thresholds are compared at the lowest velocities, MAMA thresholds are at or below MVMA thresholds. Implications of results will be discussed. [Work supported by NSF (BNS-9025118).]
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