ABSTRACT
An auditory localisation task involving 360 degrees azimuth was performed by three subjects in a large anechoic chamber. A single sound source of a rotating form was employed. Responses were measured to the nearest 10 degrees of azimuth. Under a control condition of 'no helmet' localisation was within measurement errors for all degrees of azimuth. Under conditions of a DH-178 helmet in passive mode, the response field narrowed considerably, and with DH-178 active a further narrowing of the response field occurred. A DH-140 helmet in active mode showed the most degradation of response field. With the helmets in the active mode all sounds were heard as emanating from inside the head.
ABSTRACT
A rotating boom positioned a loudspeaker at ear height at a distance of 4 ft from the center of the head of S, who was seated in a darkened large anechoic chamber (684 ft); 750-msec bursts of pink noise, separated by 3.25 sec, at 54 db SPL, were presented. During the interstimulus interval the speaker was moved cw or ccw in the presence of a masking noise at 73 db SPL. Practiced young adults (2F, 1 M) judged azimuth "same" or "different"; minimum discriminable angle (MDA) was taken as P(c) = .70, corrected for false alarms (judgments "s" or "d" with no movement). Standard azimuths relative to S were at the 8 cardinal points. MDAs were best at 0 degree (c. 4.5 degrees) but were still relatively good (c. 8.5 degrees) at 180 degrees. In general, MDAs were poorer in the rear quadrants. One S excelled at MDA and exhibited the lowest false alarm rate. The effect of the masker, and random selection of standard and azimuth and of comparison stimuli at every trial, help explain the rather large MDAs compared with the minimum audible angles in the literature. The rather large determination at 90 degrees azimuth as determined by Mills (1958) was not found in these data.
Subject(s)
Auditory Perception , Discrimination, Psychological , Sound Localization , Adult , Differential Threshold , Female , Humans , Male , Perceptual Masking , Psychology/methodsABSTRACT
Experienced Ss identified (2IFC) the signal complex that contained a gap. When the complexes were of the same frequency, gap detection remained constant over the durations employed (up to 300 msec). When duration of the signal was 10 msec no changes in gap threshold occurred over the range of frequency disparities between signals (up to 120 Hz at F0 = 1 kHz). However, as signal duration increased (beyond 10 msec) there was an increase in gap threshold with increased frequency disparity. The degradation in gap threshold was greater for longer-duration events. Gap threshold was shown to decrease as a function of increase in intensity of the signals.
