Available response choices affect localization of sound

Abstract

Successful replication of an experiment by Butler and Humanski (1992) showed that listeners are able to proficiently localize sources on a lateral vertical plane on the basis of interaural differences alone, When a lateral horizontal array was included in the test setup, that finding was replicated only for a broadband signal interacting with the pinna, not for ones (lowpass and pure tone) providing only interaural differences. Cross-plane errors conforming to "cones of confusion" were observed for those latter sounds. In a second experiment, response options were made more unconstrained, which clarified the nature of the cross-plane confusions. Lowpass signals from lateral vertical plane sources tend to be heard at or close to the horizon. Measurement of cue values needs to take account of the response options available to listeners, as well as signal properties.Classical theory of sound localization in space has stressed the role of the binaural system. Early research (Stevens & Newman, 1936) showed that the auditory system is sensitive to interaural time differences for lowfrequency sounds and interaural level differences for sounds of high frequency. The low-frequency cue is considered to be largely an effect of time and phase difference detection; the high-frequency cue is the result ofincreasingly sharp acoustic shadowing by the head. In classical theory, the head is assumed to be a perfect sphere, with the ears as holes located at the extremes of a diameter through the sphere (Mills, 1972). Using this model, interaural differences specify the horizontal angle of the sound source to' the left or right of the median vertical plane (MVP). Absence of difference specifies that the source is somewhere on the MVP. Such differences cannot unambiguously specify the vertical angle of the sound source relative to the horizontal plane nor, relatedly, whether it lies forward or rearward of, or above or below, the interaural axis. In normal listening conditions, and with a broadband noise signal, those aspects of spatial whereabouts seemingly not revealed by "classical" interaural differences can nonetheless be distinguished.In a recent report, Butler and Humanski (1992) presented results showing that listeners could accurately discriminate the whereabouts of sound sources displaced at 15 0 intervals in a quadrant above the interaural axisin the lateral vertical plane (LVP). Proficient performance was observed for bursts of 3-kHz highpass filtered noise. Such short wavelength signals interact withThe authors thank Bruce Stevenson for valuable advice about the design of Experiment 2.

Auditory Spatial Perception Dynamically Realigns with Changing Eye Position

“…First, the pointer provides an unlimited, continuous array of response choices with a range extending beyond that of the targets. Thus, localization is not biased by spatial quantization because of limited response choices, windowing, or expectation effects (Perrett and Noble, 1995). Second, the minute projected beam of the laser pointer provides superior spatial resolution in the pointing device, thereby ensuring that responses reflect the subject's localization performance, not the pointing technique itself.…”

“…The speaker/LED assembly was installed on a two-axis servo-controlled robotic arm hidden behind the cylindrical screen. The setup enabled rapid, accurate, and precise positioning of the speaker in cylindrical coordinates and provided an unlimited, continuous array of targets over the range of Ϯ65°azimuth and Ϯ25°elevation (Perrett and Noble, 1995).…”

Misperception of exocentric directions in auditory space

“…In this study, as in ours, broad-band stimuli were used, participants were allowed to move their head during stimulus presentation in one condition, and responses were unconstrained (i.e., not limited to a fixed set of possible responses; see Perrett & Noble, 1995). Unlike our study, head pointing was used to measure perceived location (following an extensive training period involving 10-20 sessions with error feedback), and the study was conducted in an anechoic environment.…”

“…A variety of studies have investigated directional localization of auditory targets; many of these involved responses that required moving the entire body or a hand-held instrument from a body-centered (presumably egocentric-referenced) starting location all the way to the perceived sound source location (e.g., Brungart, Durlach & Rabinowitz, 1999;Langendijk & Bronkhorst, 2002;Loomis, Klatzky, Philbeck & Golledge, 1998). Other studies have used verbal reports of the sound source location (Wightman & Kistler, 1989) or turning the head to face the sound source (Bronkhorst, 1995;Carlile, Leong & Hyams, 1997;Makous & Middlebrooks, 1990;Perrett & Noble, 1995). Gilkey, Good, Ericson, Brinkman and Stewart (1995) asked participants to use a stylus to indicate the perceived source location on a spherical model located just in front of them.…”

“…Other studies have used verbal reports of the sound source location (Wightman & Kistler, 1989) or turning the head to face the sound source (Bronkhorst, 1995;Carlile, Leong & Hyams, 1997;Makous & Middlebrooks, 1990;Perrett & Noble, 1995). Gilkey, Good, Ericson, Brinkman and Stewart (1995) asked participants to use a stylus to indicate the perceived source location on a spherical model located just in front of them.…”