Sound Source Distance Research Articles

Electrophysiological studies of auditory spatial attention

Recordings of event-related potentials (ERPs) from the scalp can track the processing of auditory signals through the afferent pathways from brainstem to cortex. ERP components elicited in auditory cortex during the time range 50–200 ms are highly sensitive to selective attention, with attended sounds eliciting greater amplitudes than unattended sounds. Using combined ERP and behavioral measures, the allocation of auditory attention was studied in a free-field array of seven or eight speakers. Brief noise bursts were presented in a random, fast-paced sequence from all the speakers, and subjects were required to attend to the sounds at one location while ignoring the others. Both behavioral detection responses and ERP amplitudes were highest for stimuli at the attended location, with a progressive falloff for responses to increasingly distant sound sources. These data revealed the shape of spatial tuning curves for auditory attention in free-field and support gradient models of attentional allocation. An analysis of ERP waveforms indicated that spatial selectivity is established by consecutive stages of progressive fine-tuning over the time range 50–350 ms poststimulus. [Work supported by Grants from NIMH and ONR.]

Perceiving Distances of Nearby Sound Sources: An Investigation of Marler's Canonical Features of Locatable Sounds

Perceiving Distances of Nearby Sound Sources: An Investigation of Marler's Canonical Features of Locatable Sounds

Scaling perceived distance of virtual sound sources

Magnitude estimation and paired-comparison scaling methods were applied to the problem of measuring perceived auditory distance. Stimuli consisted of binaural recordings made in a reverberant hallway at distances of 1, 2, 4, 8, 16, 32, and 64 ft. A loudspeaker produced broadband noise burst, 100 ms in duration, served as the distal stimulus. Insert-style microphones were placed in the ears of a single individual, with measurements made from two directions, extending in distance either from the individual’s front or left side. Construction of virtual sound source stimuli in this fashion insured that the stimulation reaching the listener was naturalistic and therefore possessed the acoustic cues thought to be important in the real-world perception of auditory distance. Five listeners were presented these stimuli in several variants of both the magnitude estimation and paired-comparison paradigms. Though relatively large individual variability exists, the resulting scales are all compressed when compared to the corresponding scale of physical distance. The amount of compression is shown to be approximately constant across scaling method, thereby providing validation for each method’s measurement of a similar underlying psychological process. [Work supported by NASA.]

能動的に音源を定位し識別する自律移動ロボット

We present a mobile robot that can actively localize a sound source behind an object, approach it by avoiding obstacles on its path, and discriminate whether the source is a human or not. The robot has a unit of three microphones for ears and a CCD camera for an eye. The direction is estimated based on time differences among signal onsets received by the microphones, located at each vertex of an equilateral triangle. In a complex scene where a source is not visible from the robot, it estimates tentative goal direction based on diffracted sound at the edge of an object occluding a sound source. Repeating source localization at different positions, the robot find the source and discriminate it by block matching an image captured by the camera mounted on the robot with template image memorized in advance. We have implemented these methods and obtained satisfactory results demonstrating the effectiveness of the methods. We also describe a method for estimating sound source distance based on observations at different positions.

Auditory Reachability: An Affordance Approach to the Perception of Sound Source Distance

The literature on perception of sound source distance reveals a wide range of listener accuracy. Most experiments have listeners perform unintuitive tasks, using unnatural sounds presented in impoverished acoustic environments. The present experiments implement an affordance paradigm for which listeners judge the reachability of a natural, live sound source in a familiar acoustic environment. Results reveal that listeners are quite accurate in judging whether the source is reachable and are sensitive to the advantage afforded by two vs. one degree of freedom reaches. Further analyses reveal that when scaled to an intrinsic bodily dimension, judgment differences between listeners disappear, implicating intrinsically scaled specificational informa. tion. A follow-up experiment explores the potential informational support for these judgments testing the usefulness of head movements and binaural hearing. Results reveal that whereas head movements had no bearing on either judgment accuracy or consistency, bina...

Effects of reverberation cues on distance identification in virtual audio displays

Although reverberation is known to play an important role in the perception of distance, it is not possible to isolate the effects of early and late reflections in a real environment. A virtual audio display, however, can be used to examine the effects of early and late reflections on distance identification. In this experiment, a virtual audio display simulates distant sound sources under 4 conditions: Without reflections, with an early reflection (floor reflection) only, with late reflections (reverberation) only, and with both early and late reflections. In each trial, the subjects identify the distance of the simulated sound source from one of 5 possible distances: 2, 4, 8, 16, and 32 ft. Numbered targets are placed at the locations of the simulated sound sources, allowing the subjects to visualize the distances involved. White noise and speech are used as stimuli in the experiment, and their amplitudes are randomized over 24 dB to prevent identification based on intensity alone. The results will be analyzed to measure the percentage of correct responses at each distance and the information transfer in each of the 4 conditions.

Reassessment of the role of head movements in human sound localization

This project sought to quantify both the nature and consequences of a listener’s head movements during a sound localization task. The task required listeners to report the apparent direction and distance of virtual sound sources. The virtual source stimuli were synthesized from measurements of each listener’s own head-related transfer functions and were presented over headphones so that the acoustical consequences of head movements could be controlled. In one condition head movements were discouraged, and the stimuli delivered to the headphones were not influenced by movements of the listener’s head. In another condition the listener was encouraged to use small head movements to aid localization. The position of the listener’s head was tracked and the synthesis of each virtual source was modified in real time, in accordance with the head movements, to simulate a stationary external source. For those listeners who demonstrated a high rate of front–back confusions in the first condition, head movements apparently provided the information needed to resolve those confusions, since the confusion rate was near zero in the second condition. There was also some improvement in elevation perception with head movement information provided. Analyses of the head movement trajectories support the hypothesis that the major role of head movements is resolution of the confusions that result from reliance on interaural time and intensity cues. [Work supported by NIH, NASA, and the ONR.]

Passive synthetic acoustic arrays for ocean acoustics applications.

This paper gives a brief review, based on the concept of the inverse radiation problem, on the formulation of a synthetic virtual receiving array formed by scanning a single sensor following a designed locus in a stationary acoustic field. Both the beamforming method and the signal decomposition analysis are used to examine the parameters needed for determining the radiation sources’ locations. Studies show that considerable angular resolution can be achieved for observing distant sound sources through adaptive signal processing techniques. Applications in ocean acoustics for directional acoustic field measurement are discussed for two special types of synthetic arrays, linear and circular. Problems involved with the directionality ambiguity due to Doppler frequency shift, angular resolution degradation originated from array deformation, effects caused by instability of ocean conditions, and deployment feasibility are also addressed. The concluding results may be used to establish the guidelines for engineering design and deployment of passive synthetic arrays for ocean acoustics applications.

Perception of the relative distances of nearby sound sources

The pressure of a sound varies systematically with a listener's distance from a sound source, providing a useful cue for perceiving changes in the distance between a listener and a sound-producing object. The pressure-discrimination hypothesis predicts that thresholds for discriminating changes in distance are constrained by the underlying ability to discriminate the resulting changes in sound pressure--specifically, that the smallest discriminable change in distance should be about 5% of the reference distance. Previous studies reported thresholds of about 5% for reference distances greater than a few meters but surprisingly worse thresholds for closer reference distances. In the present study, thresholds at two close distances, 1 and 2 m, were within the 5% range predicted from the pressure-discrimination hypothesis. Moreover, thresholds were significantly worse in a control condition in which the pressure cue was removed. Results of previous studies were adjusted to take into account the possibility of conservative response tendencies by the subjects. These adjusted findings agree well with the results of the present study and the pressure-discrimination hypothesis. It is concluded that variations in sound pressure are very useful for perceiving changes in listener-source distances, even at close distances.

Effects of auditory cortical lesions on pure-tone sound localization by the albino rat.

Two-choice and three-choice tests were used to evaluate the effects of bilateral auditory cortical lesions on pure-tone sound localization by the albino rat. Both tests required that animals approach a distant sound source to obtain water reinforcement. Stimuli were single noise and tone bursts, 65 ms in duration including 20-ms rise and fall times. Tone frequencies were 2, 4, 8, 16, and 32 kHz adjusted to 40 dB (SPL) above the rat's absolute threshold. Five animals were tested in the two-choice situation following bilateral ablation of auditory cortex. Some reduction in performance was observed relative to normals, but impairments were not severe. Similar results were obtained for 2 brain-damaged animals tested in the three-choice situation. Thus, the ability to localize sounds in space remained intact after complete destruction of auditory cortex, and there was no indication of a frequency-dependent deficit.

Determination of the site of production of respiratory sounds by subtraction phonopneumography.

The site of origin of the vesicular lung sound has long been in question. A technique (subtraction phonopneumography) is described here for determining the relative distance of a sound source from the chest wall. This technique involves the simultaneous recording of lung sounds from two different sites on the chest wall, phase inversion of one of the signals, and then mixing the signals in a summing amplifier. The degree of cancellation that results is inversely proportional to the number of sources and the degree to which each source is detected by both microphones simultaneously. A study of six normal subjects revealed little or no cancellation of inspiratory vesicular sounds with microphones separated by 10 cm. During expiration, cancellation did occur at distances well beyond 10 cm and was detectable over several homologous segments of opposite lungs. This finding is consistent with an intrapulmonic and probably intralobar source for the inspiratory component and an upper airway source for at least some of the expiratory component.

Simulation of the Localization of Distant Sound Sources by Earphones

Subjects made forced choices to either side of a reference direction (0°, 30°, 60°, 75°) to locate the image of pure tones presented through earphones. Various combinations of interaural intensity differences (IIDs) and interaural time differences (ITDs) were used, including some combinations that do not occur in nature. Psychometric functions confirmed the expected apparent azimuth of IID/ITD combinations based on free-field diffraction theory and microphone measurements. The relative dominance of the intensive and temporal cues was examined at each frequency (500, 1000, 8000 Hz). The shape of the psychometric plane for the bidimensional matrix of IID/ITD combinations centered around 30° azimuth showed possible nonlinearities in the trading relation for 1 kHz. Data were also collected from the same subjects using the same signals presented by means of distant loudspeakers in an open field. When the free-field data were compared with the data from earphone simulated sounds, they showed similar angular acuities, being approximately the size of those reported in the literature. Equations are presented for computing the IID/ITD combinations necessary at any frequency for any apparent frontal azimuth. [This research was partially supported by the Office of Naval Research and Columbia University.]

Dual role of frequency spectrum in determination of auditory distance.

Manipulation of frequency content of click stimuli shows apparent distance of sound source from an observer is decreased by increasing high frequency content.

Electrophysiological studies of central auditory mechanisms in cetaceans

Electrophysiological studies of central auditory mechanisms in cetaceans

Horizontal Range Difference Method of Locating Hydrophones Forming a Near-Vertical Array

A method for determining the difference in horizontal position between two hydrophones, A and B, on a nominally vertical array, is discussed. The difference in horizontal range from a distant underwater sound source to A and to B, plotted in polar coordinates, as a function of bearing angle from the source to the array, describes two coincident circles, one diameter of which passes through the origin and the horizontal coordinates of B relative to A. Experimental results, using a surface ship and a taut-wire hydrophone array, were obtained. Successive runs using the same hydrophones, and an independent least-square determination of the coordinates, show consistent results. Results of an error analysis indicate that the method requires only approximate average speed of sound data, and approximate source and array depth information, although accurate values of the vertical separation of the hydrophones is required. The method is computationally suited to on-site determination of the relative horizontal location of hydrophones using a small low-speed computer.

Acoustic threshold in goldfish and its relation to the sound source distance

1. 1. Acoustic threshold levels have been obtained for goldfish in classical conditioning experiments, stimulating the fish with pure tones of different frequencies (50–5000 c/s). The threshold intensity for response has been established for different distances (0·1–2·0 m) between the fish and the underwater loudspeaker. 2. 2. Sound pressure thresholds (given in decibels re 1 μBar) for frequencies below 600–700 c/s are strongly dependent upon distance to the sound source, while no significant threshold differences were found for higher frequencies. Tests with an air loudspeaker gave thresholds similar to those obtained with the underwater loudspeaker at 2 m distance. 3. 3. Lowest threshold (−42 to −45 db) are in the 100–1500 c/s range, increasing to −10 db for 5000 c/s and to −6 db (at 2 m distance) or −38 db (at 0·1 m distance) for 50 c/s. 4. 4. The variation in threshold with distance is probably due to the physical characteristics of the sound stimulus. Close to the sound source, i.e. within a distance equal to the wavelength divided by 2π, the near-field water displacement amplitude is considerable. Calculated particle displacement at threshold is roughly the same for all distances for any given frequency and particle acceleration is the same for all distance and frequencies.

Performance of the Anechoic Room in the Parmly Laboratory

The anechoic room of the Parmly Laboratory is being used by the Armour Research Foundation in its acoustic research. Performance of the room has been evaluated by the following means: 1. inverse-square-law measurements from 60 to 17,000 cycles per second; 2. measurements of the effect of nearness of the walls on the response curves and the acoustic impedance of loudspeakers; 3. ability to obtain consistent data with different geometrical arrangements. Results of these experiments will be presented and some of the techniques of measurement will be discussed. A method of measuring the wall attenuation will be described. It is estimated that it would be necessary to have a distant sound source produce an average intensity of 10−7 watts per square centimeter at the walls to be heard within the room.