Effects of Altering Spectral Cues in Infancy on Horizontal and Vertical Sound Localization by Adult Ferrets

We investigated the behavioral consequences of removing the pinna and concha of the external ear bilaterally in infancy on the sound localization ability of adult ferrets. Altering spectral cues in this manner has previously been shown to disrupt the development of the neural representation of auditory space in the superior colliculus. Using broadband noise stimuli, we tested pinnae-removed ferrets and normal ferrets in three sound localization tasks. In each case, we found that both groups of animals performed significantly better when longer duration noise bursts were used. In a relative localization task, we measured the acuity with which the ferrets could discriminate between two speakers in the horizontal plane. The speakers were placed symmetrically either around the anterior midline or around a position 45° lateral to the midline. In this task, the pinnae-removed ferrets achieved very similar scores to the normal ferrets. By contrast, in another relative localization task that measured localization ability in the midsagittal plane, pinnae-removed ferrets performed less well than normals. In an absolute localization task, 12 speakers were spaced at 30° intervals in the horizontal plane at the level of the ferrets' ears. Overall, the pinnae-removed ferrets also performed poorly in this task compared with normal ferrets: they made significantly fewer correct responses, larger localization errors and more front-back errors. Both normal and pinnae-removed animals showed an improvement in performance with practice, although the pattern of improvement differed for each group. The largest improvements in localization accuracy were achieved by the pinnae-removed ferrets, particularly at the frontal positions, and their performance eventually approached that of the normal animals. Nevertheless, some intergroup differences were still present. In particular, the pinnae-removed ferrets continued to make significantly more front-back errors than the normals. These deficits can be attributed to differences in the spectral localization cues available to the animals. Acoustical measurements showed that, compared with normal animals, the head-related transfer functions in the horizontal plane were largely ambiguous around the interaural axis and also contained fewer location-dependent features in the midsagittal plane.

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A Comparison of the Contrast Effects in Sound Localization in the Horizontal and Vertical Planes

Experimental Psychology (formerly Zeitschrift für Experimentelle Psychologie) ◽

10.1026//1618-3169.50.2.131 ◽

2003 ◽

Vol 50 (2) ◽

pp. 131-141 ◽

Cited By ~ 5

Author(s):

Stephan Getzmann

Keyword(s):

Sound Localization ◽

Contrast Effect ◽

Pulse Train ◽

Horizontal Plane ◽

Vertical Plane ◽

Broadband Noise ◽

Contrast Effects ◽

Noise Stimulus ◽

Spectral Localization ◽

Localization Information

Abstract. The effect of a background sound on the auditory localization of a single sound source was examined. Nine loudspeakers were arranged crosswise in the horizontal and the median vertical plane. They ranged from -20° to +20°, with the center loudspeaker at 0° azimuth and elevation. Using vertical and horizontal centimeter scales, listeners verbally estimated the position of a 500-ms broadband noise stimulus being presented at the same time as a 2 s background sound, emitted by one of the four outer loudspeakers. When the background sound consisted of continuous broadband noise, listeners consistently shifted the apparent target positions away from the background sound locations. This auditory contrast effect, which is consistent with earlier findings, equally occurred in both planes. But when the background sound was changed to a pulse train of noise bursts, the contrast effect decreased in the horizontal plane and increased in the vertical plane. This discrepancy might be due to general differences in the processing of interaural and spectral localization information.

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Gravitoinertial Force Magnitude and Direction Influence Head-Centric Auditory Localization

Journal of Neurophysiology ◽

10.1152/jn.2001.85.6.2455 ◽

2001 ◽

Vol 85 (6) ◽

pp. 2455-2460 ◽

Cited By ~ 19

Author(s):

Paul DiZio ◽

Richard Held ◽

James R. Lackner ◽

Barbara Shinn-Cunningham ◽

Nathaniel Durlach

Keyword(s):

Sound Localization ◽

Acoustic Stimulus ◽

Median Plane ◽

Broadband Noise ◽

Auditory Localization ◽

Slow Rotation ◽

Angular Deviation ◽

Midsagittal Plane ◽

Gravitoinertial Force ◽

Straight Ahead

We measured the influence of gravitoinertial force (GIF) magnitude and direction on head-centric auditory localization to determine whether a true audiogravic illusion exists. In experiment 1, supine subjects adjusted computer-generated dichotic stimuli until they heard a fused sound straight ahead in the midsagittal plane of the head under a variety of GIF conditions generated in a slow-rotation room. The dichotic stimuli were constructed by convolving broadband noise with head-related transfer function pairs that model the acoustic filtering at the listener's ears. These stimuli give rise to the perception of externally localized sounds. When the GIF was increased from 1 to 2 g and rotated 60° rightward relative to the head and body, subjects on average set an acoustic stimulus 7.3° right of their head's median plane to hear it as straight ahead. When the GIF was doubled and rotated 60° leftward, subjects set the sound 6.8° leftward of baseline values to hear it as centered. In experiment 2, increasing the GIF in the median plane of the supine body to 2 g did not influence auditory localization. In experiment 3, tilts up to 75° of the supine body relative to the normal 1 g GIF led to small shifts, 1–2°, of auditory setting toward the up ear to maintain a head-centered sound localization. These results show that head-centric auditory localization is affected by azimuthal rotation and increase in magnitude of the GIF and demonstrate that an audiogravic illusion exists. Sound localization is shifted in the direction opposite GIF rotation by an amount related to the magnitude of the GIF and its angular deviation relative to the median plane.

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Role of Auditory Cortex in Sound Localization in the Midsagittal Plane

Journal of Neurophysiology ◽

10.1152/jn.00444.2007 ◽

2007 ◽

Vol 98 (3) ◽

pp. 1763-1774 ◽

Cited By ~ 18

Author(s):

Jennifer K. Bizley ◽

Fernando R. Nodal ◽

Carl H. Parsons ◽

Andrew J. King

Keyword(s):

Auditory Cortex ◽

Sound Localization ◽

Primary Auditory Cortex ◽

Midsagittal Plane ◽

Spectral Localization ◽

Approximate Location ◽

Before And After ◽

Significant Deficit ◽

Vertical Localization

Although the auditory cortex is known to be essential for normal sound localization in the horizontal plane, its contribution to vertical localization has not so far been examined. In this study, we measured the acuity with which ferrets could discriminate between two speakers in the midsagittal plane before and after silencing activity bilaterally in the primary auditory cortex (A1). This was achieved either by subdural placement of Elvax implants containing the GABAA receptor agonist muscimol or by making aspiration lesions after determining the approximate location of A1 electrophysiologically. Psychometric functions and minimum audible angles were measured in the upper hemifield for 500-, 200-, and 40-ms noise bursts. Muscimol-Elvax inactivation of A1 produced a small but significant deficit in the animals’ ability to localize brief (40-ms) sounds, which was reversed after removal of the Elvax implants. A similar deficit in vertical localization was observed after bilateral aspiration lesions of A1, whereas performance at longer sound durations was unaffected. Another group of ferrets received larger lesions, encompassing both primary and nonprimary auditory cortical areas, and showed a greater deficit with performance being impaired for long- and short-duration (500- and 40-ms, respectively) stimuli. These data suggest that the integrity of the auditory cortex is required to successfully utilize spectral localization cues, which are thought to provide the basis for vertical localization, and that multiple cortical fields, including A1, contribute to this task.

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S222 – Sound Localization in Subjects with Tinnitus

Otolaryngology ◽

10.1016/j.otohns.2008.05.397 ◽

2008 ◽

Vol 139 (2_suppl) ◽

pp. P149-P150

Author(s):

Il Ho Shin

Keyword(s):

Sound Localization ◽

Horizontal Plane ◽

Normal Hearing ◽

Intensity Difference ◽

Control Group ◽

Interaural Intensity Difference ◽

Interaural Difference ◽

The Subject ◽

Localization Ability ◽

Localization Score

Objectives Sound localization in subjects with normal hearing is done by recognition of interaural difference of time, intensity, and phase of sound source. The defect of sound localizing ability may increase the chance of accident, decrease public conversation. Individuals with tinnitus, deprived of the binaural cues, are expected to have difficulty in localizing sound. The purpose of the research is to investigate the sound localizing ability in subjects with tinnitus to localize sound in horizontal plane by comparing with normal control group. Methods 3 groups of subjects participated in this study. The first group consisted of 30 subjects with unilateral tinnitus without hearing disturbance, the second group consisted of 30 subjects with unilateral tinntus, hearing disturbance. Control group was 20 normal hearing adults. Sound localization ability was assessed by means of an array of 8 loudspeakers positioned at the azimuth of 45°each in the horizontal plane at a distance of 100 cm from the subject. Results The localization score increased significantly as tinnitus with hearing disturbance as compared with control group(p<0.05). In the tinnitus without hearing disturbance group as compared with the control group, the localization score increased but there is no stastical significance. Conclusions In the tinnitus without hearing disturbance group, the sound localization ability was decreased but there is no stastical significance. This means that tinnitus has relatively small effect of interaural intensity difference in usual living. It needs further study with similar tinnitus intensity, pitch.

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