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T Z Strybel

Publications and source records attributed to T Z Strybel.

11 recordsLinked to original sources
PubMed1992

Minimum audible movement angle as a function of the azimuth and elevation of the source.

In the future auditory directional cues may enhance situational awareness in cockpits with head-coupled displays. This benefit would depend, however, on the pilot's ability to detect the direction of moving sounds at different locations in space. The present investigation examined this ability. Auditory motion acuity was measured by the minimum audible movement angle (MAMA): the minimum angle of travel required for detection of the direction of sound movement. Five experienced listeners were instructed to indicate the direction of travel of a sound source (broadband noise at 50 dBA) that moved at a velocity of 20 deg/s. Nine azimuth positions were tested at 0 deg elevation. Five elevations were then tested at 0 deg azimuth. Finally two azimuth positions were tested at an elevation of 80 deg. The position of the source did not significantly affect the MAMA for azimuth locations between +40 and -40 deg and elevations below 80 deg. Within this area the MAMA ranged between 1 and 2 deg. Outside this area the MAMA increased to 3 to 10 deg.

Aircraft↗
PubMed1992

Auditory apparent motion in the free field: the effects of stimulus duration and separation.

The effects of stimulus duration and spatial separation on the illusion of apparent motion in the auditory modality were examined. Two narrow-band noise sources (40 dB, A-weighted) were presented through speakers separated in space by 2.5 degrees, 5 degrees, or 10 degrees, centered about the subject's midline. The duration of each stimulus was 5, 10, or 50 msec. On each trial, the sound pair was temporally separated by 1 of 10 interstimulus onset intervals (ISOIs): 0, 2, 4, 6, 8, 10, 15, 20, 50, or 70 msec. Five subjects were tested in nine trial block; each block represented a particular spatial-separation-duration combination. Within a trial block, each ISOI was presented 30 times each, in random order. Subjects were instructed to listen to the stimulus sequence and classify their perception of the sound into one of five categories: single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds. Each subject was also required to identify the location of the first-occurring stimulus (left or right). The percentage of continuous-motion responses was significantly affected by the ISOI [F(9,36) = 5.67, p less than .001], the duration x ISOI interaction [F(18,72) = 3.54, p less than .0001], and the separation x duration x ISOI interaction [F(36,144) = 1.51, p less than .05]. The results indicate that a minimum duration is required for the perception of auditory apparent motion. Little or no motion was reported at durations of 10 msec or less. At a duration of 50 msec, motion was reported most often for ISOIs of 20-50 msec.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Aurally aided visual search in the central visual field: effects of visual load and visual enhancement of the target.

Visual search performance was examined in a two-alternative, forced-choice paradigm. The task involved locating and identifying which of two visual targets was present on a trial. The location of the targets varied relative to the subject's initial fixation point from 0 to 14.8 deg. The visual targets were either presented concurrently with a sound located at the same position as the visual target or were presented in silence. Both the number of distractor visual figures (0-63) present in the field during the search (Experiments 1 and 2) and the distinctness of the visual target relative to the distractors (Experiment 2) were considered. Under all conditions, visual search latencies were reduced when spatially correlated sounds were present. Aurally guided search was particularly enhanced when the visual target was located in the peripheral regions of the central visual field and when a larger number of distractor images (63) were present. Similar results were obtained under conditions in which the target was visually enhanced. These results indicate that spatially correlated sounds may have considerable utility in high-information environments (e.g., piloting an aircraft).

Adult↗
PubMed1990

A comparison of the effects of spatial separation on apparent motion in the auditory and visual modalities.

In the present investigation, the effects of spatial separation on the interstimulus onset intervals (ISOIs) that produce auditory and visual apparent motion were compared. In Experiment 1, subjects were tested on auditory apparent motion. They listened to 50-msec broadband noise pulses that were presented through two speakers separated by one of six different values between 0 degrees and 160 degrees. On each trial, the sounds were temporally separated by 1 of 12 ISOIs from 0 to 500 msec. The subjects were instructed to categorize their perception of the sounds as "single," "simultaneous," "continuous motion," "broken motion," or "succession." They also indicated the proper temporal sequence of each sound pair. In Experiments 2 and 3, subjects were tested on visual apparent motion. Experiment 2 included a range of spatial separations from 6 degrees to 80 degrees; Experiment 3 included separations from .5 degrees to 10 degrees. The same ISOIs were used as in Experiment 1. When the separations were equal, the ISOIs at which auditory apparent motion was perceived were smaller than the values that produced the same experience in vision. Spatial separation affected only visual apparent motion. For separations less than 2 degrees, the ISOIs that produced visual continuous motion were nearly equal to those which produced auditory continuous motion. For larger separations, the ISOIs that produced visual apparent motion increased.

Adult↗
PubMed1990

Auditory psychomotor coordination and visual search performance.

In Experiments 1 and 2, the time to locate and identify a visual target (visual search performance in a two-alternative forced-choice paradigm) was measured as a function of the location of the target relative to the subject's initial line of gaze. In Experiment 1, tests were conducted within a 260 degree region on the horizontal plane at a fixed elevation (eye level). In Experiment 2, the position of the target was varied in both the horizontal (260 degrees) and the vertical (+/- 46 degrees from the initial line of gaze) planes. In both experiments, and for all locations tested, the time required to conduct a visual search was reduced substantially (175-1,200 msec) when a 10-Hz click train was presented from the same location as that occupied by the visual target. Significant differences in latencies were still evident when the visual target was located within 10 degrees of the initial line of gaze (central visual field). In Experiment 3, we examined head and eye movements that occur as subjects attempt to locate a sound source. Concurrent movements of the head and eyes are commonly encountered during auditorily directed search behavior. In over half of the trials, eyelid closures were apparent as the subjects attempted to orient themselves toward the sound source. The results from these experiments support the hypothesis that the auditory spatial channel has a significant role in regulating visual gaze.

Adult↗
PubMed1989

Minimum audible angle thresholds obtained under conditions in which the precedence effect is assumed to operate.

Two experiments were conducted to examine the ability of human listeners to localize the "lag" or "echo" source in a precedence effect paradigm. A 5-ms noise burst was presented from a source located between 554-279 cm from the subject. This "lead" source was always located at 0 degrees azimuth. At the same time, one of two sources located at a distance of 610 cm from the subject was also activated with the same 5-ms noise burst. The subject's task was to identify which lag source had been active. Across sessions, the angular distance between the lag sources was varied, so as to allow a determination of the minimum audible angle (MAA) that could be resolved. Tests were run in a room designed to minimize reflections and in a hallway that was acoustically quite complex. No systematic differences in MAA thresholds were observed as a function of the environment employed. MAA thresholds obtained without the signal from the lead speaker were less than 1 degree for four of the five subjects tested. The precedence effect, as measured by the change in the MAA threshold, appears to have only a modest influence on localization performance. Under conditions in which the lead source was concurrently active, the thresholds were generally elevated by only 2 degrees-4 degrees. A reduction of this magnitude in the ability to resolve the position of the lag source does not seem to be sufficient, in itself, to account for the excellent localization performance frequently observed in reflective environments.

Acoustic Stimulation↗
PubMed1989

Auditory apparent motion under binaural and monaural listening conditions.

This investigation examined the ability of listeners to perceive apparent motion under binaural and monaural listening conditions. Fifty-millisecond broadband noise sources were presented through two speakers separated in space by either 10 degrees, 40 degrees, or 160 degrees, centered about the subject's midline. On each trial, the sources were temporally separated by 1 of 12 interstimulus onset intervals (ISOIs). Six listeners were asked to place their experience of these sounds into one of five categories (single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds), and to indicate either the proper temporal sequence of presentation or the direction of motion, depending on whether or not motion was perceived. Each listener was tested at all spatial separations under binaural and monaural listening conditions. Motion was perceived in the binaural listening condition at all spatial separations tested for ISOIs between 20 and 130 msec. In the monaural listening condition, motion was reliably heard by all subjects at 10 degrees and 40 degrees for the same range of ISOIs. At 160 degrees, only 3 of the 6 subjects consistently reported motion. However, when motion was perceived in the monaural condition, the direction of motion could not be determined.

Attention↗
PubMed1987

Conditions under which the Haas precedence effect may or may not occur.

This investigation explored the stimulus conditions of the existence region in the free field of the Haas "precedence" effect. Experienced normal-hearing adults (N:5) listened to 50-msec bursts (0.2 msec rise-fall) of broadband noise from 2 loudspeakers at 1 m distance at ear level, at +/- 20 degrees re midline. Bursts from the loudspeakers were separated by interstimulus onset intervals (ISO-Is) between 0 and 50 msec. In one condition, uncorrelated noise was produced by separate generators; in a second condition (correlated noise), the signal from one generator was split and led to each speaker. Ss classified their experience of each presentation into one of five defined categories:: (1) single non-moving sound image; (2) 2 stationary but spatially distinct sound images; (3) single sound moving from lead to lag source; (4) as (3) but motion interrupted or broken; and (5) 2 successive sound images, with no apparent motion. In addition, Ss indicated direction (L-R; R-L) of any apparent motion. At 0 msec ISOI, directional judgments with either correlated or uncorrelated bursts were at or near chance level, as expected, and with correlated noises a single image was usually (71%) experienced, presumably at an apparent location at or near the midline. But with uncorrelated noises, 2 simultaneous but distinct sound images were usually (68%) perceived. At 2 msec ISOI, a weak precedence effect was exhibited for correlated noise, where the "single" response was often (55%) made; but even here the effect of the second burst was not "suppressed" entirely since direction judgments were 83% accurate. At 4 msec ISOI, "single" responses had declined to 36% for correlated and to 6% for uncorrelated noises, while by 8+ msec, "single" responses were dominated more or less completely by perceptions of dual sources. We conclude that the precedence effect is often confined to extremely brief ISOIs, and that the parameters of stimulus duration and complexity, of rise-fall times, absolute placement and angular separation of sound sources, subject differences, and a variety of types of perceptual experiences need to be addressed experimentally before the existence region of the precedence effect is well defined or uncritically accepted; and that it is too soon to attempt to posit neurophysiological mechanisms in explaining the phenomenon.

Acoustic Stimulation↗
PubMed1979

Dynamic auditory localization: systematic replication of the auditory velocity function.

Two experiments explored the capability of normal-hearing adults to judge the apparent velocity of an unseen moving sound source. In exper. I, 9 naive and, 1 experienced S judged the velocity of a moving source emitting a .5-kc/s tone at 50 db SPL. S's head was in the center of a circle of 1.88-m radius swept by a small loudspeaker. In exper. II the sound was a low-pass-filtered (0.1-1 kc/s) noise at 50 db sound spectrum level. In both experiments perceived velocity was directly proportional to the actual velocity of the source. These results support out initial observations (Waugh et al, J. Aud. Res., 1979, 19, 103-1 10) that auditory velocity discrimination can be described as a power function with an exponent of 1.0. In exper. II the Ss also varied the sound source velocity by means of a variable resistor to produce a perceived velocity of 100 degrees/sec. Performance on the adaptive velocity production task was successfully predicted from the data of the absolute velocity judgment task. The Weber fraction was .052 for relatively fast-moving sound sources (100 degrees/sec). The ability to discriminate sound source velocity appears to be a well-defined feature of the dynamic binaural spatial system.

Audiometry↗
PubMed1979

Perception of moving sounds: velocity discrimination.

Two experiments investigated auditory velocity perception. Exper. I compared auditory to visual velocity estimates. Five adults judged, in miles/hr, the motion of a sound source (a small loudspeaker) moving on a 1.88-m boom around S's head at each of 7 velocities from 15 to 360 degrees/sec. The sound source was either visible or not visible. Velocity judgments were shown in both modalities to be a power function of source velocity, with a slope of approximately 0.90. No significant difference was found between the auditory and visual functions. A control Exper. II determined with 14 naive adults that the similarities between the functions in each modality could not be attributed to either previous visual experience or proprioceptive feedback. Ss estimated the velocity of the visible moving loudspeaker while tracking the source with their eyes (N: 7) or while fixating on a small stationary light (N: 7). Eye motion was recorded from electrodes on the canthi. No significant differences were found between these conditions. The estimates were again shown to be a power function of source velocity (though slightly higher slopes of 0.99 for visual pursuit and 1.0 for visual fixation were obtained than in Exper. I). These experiments suggest a surprising degree of similarity in the perception of velocity in auditory and visual spatial functions.

Adult↗