The Journal of the Acoustical Society of America, 2014
Changing the shape of the outer ear using small in-ear molds degrades sound localization performa... more Changing the shape of the outer ear using small in-ear molds degrades sound localization performance consistent with the distortion of monaural spectral cues to location. It has been shown recently that adult listeners re-calibrate to these new spectral cues for locations both inside and outside the visual field. This raises the question as to the teacher signal for this remarkable functional plasticity. Furthermore, large individual differences in the extent and rate of accommodation suggests a number of factors may be driving this process. A training paradigm exploiting multi-modal and sensory-motor feedback during accommodation was examined to determine whether it might accelerate this process. So as to standardize the modification of the spectral cues, molds filling 40% of the volume of each outer ear were custom made for each subject. Daily training sessions for about an hour, involving repetitive auditory stimuli and exploratory behavior by the subject, significantly improved the extent of accommodation measured by both front-back confusions and polar angle localization errors, with some improvement in the rate of accommodation demonstrated by front-back confusion errors. This work has implications for both the process by which a coherent representation of auditory space is maintained and for accommodative training for hearing aid wearers.
Recent studies have shown a decrease in the amplitude and an increase in the threshold of the cat... more Recent studies have shown a decrease in the amplitude and an increase in the threshold of the cat's auditory brainstem evoked response (ABER) during severe hypoxia (PaO2 of 20 to 30 Torr). In this study we have examined the effects of euoxia (end tidal PO2 100 Torr) and mild hypoxia (end tidal PO2 of 45 to 50 Torr) on the latency of the ABER in 6 human subjects. Hypoxia resulted in a blood O2 saturation of between 75 to 85% and caused a significant prolongation of the latency of wave V of the ABER by 0.185 +/- 0.045 ms (Mean +/- S.D; p < 0.01). The prolongation of the ABER during severe hypoxia has previously been attributed to a change in peripheral sensitivity. Using the stimulus level/response latency relationship obtained for each subject under normal breathing conditions, the change in latency produced by mild hypoxia can be interpreted as a mean shift in auditory sensitivity of 5.1 +/- 3.4 dB. These results suggest that the auditory system is sensitive to much smaller changes in blood O2 saturation than previously thought.
Virtual auditory space (VAS) refers to the synthesis and simulation of spatial hearing using earp... more Virtual auditory space (VAS) refers to the synthesis and simulation of spatial hearing using earphones or a speaker system. High-fidelity VAS requires the use of individualized head-related transfer functions (HRTFs) which describe the acoutic filtering properties of the listener's external auditory periphery. Because HRTFs are unique for each individual ("the auditory thumbprint"), a primary hurdle in establishing high-fidelity VAS for
The information age, combining rapidly developing information technology and massive growth in bi... more The information age, combining rapidly developing information technology and massive growth in biomedical and clinical data, is placing special demands on healthcare workers. Further, radical changes in access to information in our society are affecting the doctor-patient relationship. These changes necessitate a new approach to primary and continuing medical education. A number of imperatives for medical education are identified and some practical changes to a medical curriculum are described.
The Journal of the Acoustical Society of America, 2014
This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a m... more This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a mannequin for 393 spatial locations and for five different hearing aid styles: Invisible-in-the-canal (IIC), completely-in-the-canal (CIC), in-the-canal (ITC), in-the-ear (ITE), and behind-the-ear (BTE). The spectral distortions of each style compared to the bare ear were described qualitatively in terms of the gain and frequency characteristics of the prominent spectral notch and two peaks in the HRTFs. Two quantitative measures of the differences between the HRTF sets and a measure of the dissimilarity of the HRTFs within each set were also computed. In general, the IIC style was most similar and the BTE most dissimilar to the bare ear recordings. The relative similarities among the CIC, ITC, and ITE styles depended on the metric employed. The within-style spectral dissimilarities were comparable for the bare ear, IIC, CIC, and ITC with increasing ambiguity for the ITE and BTE styles. When the analysis bandwidth was limited to 8 kHz, the HRTFs within each set became much more similar.
The Journal of the Acoustical Society of America, 2014
"Representational Momentum&a... more "Representational Momentum" (RM) is a mislocalization of the endpoint of a moving target in the direction of motion. In vision, RM has been shown to increase with target velocity. In audition, however, the effect of target velocity is unclear. Using a perceptual paradigm with moving broadband noise targets in Virtual Auditory Space resulted in a linear increase in RM from 0.9° to 2.3° for an increase in target velocity from 25°/s to 100°/s. Accounting for the effect of eye position also reduced variance. These results suggest that RM may be the result of similar underlying mechanisms in both modalities.
The role of the superior colliculus in attending and orienting to sensory stimuli is facilitated ... more The role of the superior colliculus in attending and orienting to sensory stimuli is facilitated by the presence within this midbrain nucleus of superimposed maps of different sensory modalities. We have studied the steps involved in the development of topographically-aligned maps of visual and auditory space in the ferret superior colliculus. Injections of fluorescent beads into the superficial layers showed that the projection from the contralateral retina displays topographic order on the day of birth (PO). Recordings made from these layers at the time of eye opening, approximately 1 month later, revealed the presence of an adult-like map of visual space. In contrast, the auditory space map in the deeper layers emerged gradually over a much longer period of postnatal life. In adult ferrets in which one eye had been deviated laterally just before eye opening, the auditory spatial tuning of single units recorded in the contralateral superior colliculus was shifted by a correspondin...
Spectral localization cues provided by the outer ear are utilized in the construction of the audi... more Spectral localization cues provided by the outer ear are utilized in the construction of the auditory space map in the superior colliculus (SC). The role of the outer ear in the development of this map was examined by recording from the SC of anesthetized, adult ferrets in which the pinna and concha had been removed in infancy. The acoustical consequences of this procedure were assessed by recording outer ear impulse responses via a probe-tube microphone implanted in the wall of the ear canal. Both monaural and binaural spectral cues normally show a number of asymmetric features within the horizontal plane, which allow azimuthal locations on either side of the interaural axis to be discriminated. These features were eliminated or altered by chronic pinnectomy. The responses of auditory units in the SC to noise bursts presented in the free field were examined at sound levels of approximately 10 and 25 dB above unit threshold. After bilateral pinnectomy, the representation of auditory...
ABSTRACT Despite the importance of spatial hearing in everyday listening, little is known about t... more ABSTRACT Despite the importance of spatial hearing in everyday listening, little is known about the accuracy of sound localization in a complex mixture of sounds. Here we measured, for the frontal audio-visual horizon, how accurately listeners could localize a female-voice target amidst four spatially distributed male-voice interferers in a moderately reverberant room. To examine whether listeners can make use of a priori knowledge about the configuration of the scene, we compared performance when the interferer locations were fixed (in one of five known patterns) to when the locations varied from trial to trial. The presence of interferers disrupted target localization, even after accounting for reduced target detectability. Randomizing the interferer locations had a moderate influence, degrading performance in some configurations but improving it in others. All effects were magnified when the target-to-interferer intensity ratio was reduced. The results confirm that spatial perception is disrupted by interfering sounds, and that this disruption is modified to some extent by listeners' expectations about the spatial arrangement of the scene. [Work supported by HFSP, NIH, VEGA, ARC and a Univ. of Sydney Postdoctoral Fellowship.].
ABSTRACT The current study investigated the temporal dynamics of audio-visual moving targets, exa... more ABSTRACT The current study investigated the temporal dynamics of audio-visual moving targets, examining the effects of velocity and acoustical environmental cues on the sensitivity of audio-visual cohesion. The acoustical stimuli were generated using Virtual Auditory Space, and two types of moving sounds were presented: (1) an immersive stimulus using Binaural Room Impulse Responses (BRIRs), that were recorded for each subject in situ in the testing room; thereby containing the combined spectral and temporal acoustic transformation due to both head-related filtering and the room’s characteristic response; (2) an environmentally impoverished stimulus using individualised Head-Related Impulse Responses (HRIRs) recorded in an anechoic chamber that lacked any reverberant cues. Apparent visual motion was generated by the sequential activation of LED’s along the same radial path as the auditory motion, 1 m away from the subjects. Moving stimuli were presented with a random temporal offset between each stimuli ranging from [−400 ms, 400 ms] (auditory or visual leading). Using a 2AFC paradigm, subjects reported which modality they perceived as leading for velocities of 25, 50 and 100°/s. At 25°/s the stimuli were perceived to be coincident when the visual stimulus was actually leading but, counter intuitively, the offset decreased as a function of increased velocity. The offset at PSE was greater for HRIRs than for BRIRs but the psychometric functions were significantly steeper for the HRIRs suggesting greater spatio-temporal resolution. This may reflect the degradation of the auditory cues produced by reverberation.
Journal of Speech Language and Hearing Research, 2014
The aim of this study was to examine attention, memory, and auditory processing in children with ... more The aim of this study was to examine attention, memory, and auditory processing in children with reported listening difficulty in noise (LDN) despite having clinically normal hearing. Twenty-one children with LDN and 15 children with no listening concerns (controls) participated. The clinically normed auditory processing tests included the Frequency/Pitch Pattern Test (FPT; Musiek, 2002), the Dichotic Digits Test (Musiek, 1983), the Listening in Spatialized Noise-Sentences (LiSN-S) test (Dillon, Cameron, Glyde, Wilson, & Tomlin, 2012), gap detection in noise (Baker, Jayewardene, Sayle, & Saeed, 2008), and masking level difference (MLD; Wilson, Moncrieff, Townsend, & Pillion, 2003). Also included were research-based psychoacoustic tasks, such as auditory stream segregation, localization, sinusoidal amplitude modulation (SAM), and fine structure perception. All were also evaluated on attention and memory test batteries. The LDN group was significantly slower switching their auditory attention and had poorer inhibitory control. Additionally, the group mean results showed significantly poorer performance on FPT, MLD, 4-Hz SAM, and memory tests. Close inspection of the individual data revealed that only 5 participants (out of 21) in the LDN group showed significantly poor performance on FPT compared with clinical norms. Further testing revealed the frequency discrimination of these 5 children to be significantly impaired. Thus, the LDN group showed deficits in attention switching and inhibitory control, whereas only a subset of these participants demonstrated an additional frequency resolution deficit.
The Journal of the Acoustical Society of America, 2014
Changing the shape of the outer ear using small in-ear molds degrades sound localization performa... more Changing the shape of the outer ear using small in-ear molds degrades sound localization performance consistent with the distortion of monaural spectral cues to location. It has been shown recently that adult listeners re-calibrate to these new spectral cues for locations both inside and outside the visual field. This raises the question as to the teacher signal for this remarkable functional plasticity. Furthermore, large individual differences in the extent and rate of accommodation suggests a number of factors may be driving this process. A training paradigm exploiting multi-modal and sensory-motor feedback during accommodation was examined to determine whether it might accelerate this process. So as to standardize the modification of the spectral cues, molds filling 40% of the volume of each outer ear were custom made for each subject. Daily training sessions for about an hour, involving repetitive auditory stimuli and exploratory behavior by the subject, significantly improved the extent of accommodation measured by both front-back confusions and polar angle localization errors, with some improvement in the rate of accommodation demonstrated by front-back confusion errors. This work has implications for both the process by which a coherent representation of auditory space is maintained and for accommodative training for hearing aid wearers.
Recent studies have shown a decrease in the amplitude and an increase in the threshold of the cat... more Recent studies have shown a decrease in the amplitude and an increase in the threshold of the cat's auditory brainstem evoked response (ABER) during severe hypoxia (PaO2 of 20 to 30 Torr). In this study we have examined the effects of euoxia (end tidal PO2 100 Torr) and mild hypoxia (end tidal PO2 of 45 to 50 Torr) on the latency of the ABER in 6 human subjects. Hypoxia resulted in a blood O2 saturation of between 75 to 85% and caused a significant prolongation of the latency of wave V of the ABER by 0.185 +/- 0.045 ms (Mean +/- S.D; p < 0.01). The prolongation of the ABER during severe hypoxia has previously been attributed to a change in peripheral sensitivity. Using the stimulus level/response latency relationship obtained for each subject under normal breathing conditions, the change in latency produced by mild hypoxia can be interpreted as a mean shift in auditory sensitivity of 5.1 +/- 3.4 dB. These results suggest that the auditory system is sensitive to much smaller changes in blood O2 saturation than previously thought.
Virtual auditory space (VAS) refers to the synthesis and simulation of spatial hearing using earp... more Virtual auditory space (VAS) refers to the synthesis and simulation of spatial hearing using earphones or a speaker system. High-fidelity VAS requires the use of individualized head-related transfer functions (HRTFs) which describe the acoutic filtering properties of the listener's external auditory periphery. Because HRTFs are unique for each individual ("the auditory thumbprint"), a primary hurdle in establishing high-fidelity VAS for
The information age, combining rapidly developing information technology and massive growth in bi... more The information age, combining rapidly developing information technology and massive growth in biomedical and clinical data, is placing special demands on healthcare workers. Further, radical changes in access to information in our society are affecting the doctor-patient relationship. These changes necessitate a new approach to primary and continuing medical education. A number of imperatives for medical education are identified and some practical changes to a medical curriculum are described.
The Journal of the Acoustical Society of America, 2014
This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a m... more This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a mannequin for 393 spatial locations and for five different hearing aid styles: Invisible-in-the-canal (IIC), completely-in-the-canal (CIC), in-the-canal (ITC), in-the-ear (ITE), and behind-the-ear (BTE). The spectral distortions of each style compared to the bare ear were described qualitatively in terms of the gain and frequency characteristics of the prominent spectral notch and two peaks in the HRTFs. Two quantitative measures of the differences between the HRTF sets and a measure of the dissimilarity of the HRTFs within each set were also computed. In general, the IIC style was most similar and the BTE most dissimilar to the bare ear recordings. The relative similarities among the CIC, ITC, and ITE styles depended on the metric employed. The within-style spectral dissimilarities were comparable for the bare ear, IIC, CIC, and ITC with increasing ambiguity for the ITE and BTE styles. When the analysis bandwidth was limited to 8 kHz, the HRTFs within each set became much more similar.
The Journal of the Acoustical Society of America, 2014
"Representational Momentum&a... more "Representational Momentum" (RM) is a mislocalization of the endpoint of a moving target in the direction of motion. In vision, RM has been shown to increase with target velocity. In audition, however, the effect of target velocity is unclear. Using a perceptual paradigm with moving broadband noise targets in Virtual Auditory Space resulted in a linear increase in RM from 0.9° to 2.3° for an increase in target velocity from 25°/s to 100°/s. Accounting for the effect of eye position also reduced variance. These results suggest that RM may be the result of similar underlying mechanisms in both modalities.
The role of the superior colliculus in attending and orienting to sensory stimuli is facilitated ... more The role of the superior colliculus in attending and orienting to sensory stimuli is facilitated by the presence within this midbrain nucleus of superimposed maps of different sensory modalities. We have studied the steps involved in the development of topographically-aligned maps of visual and auditory space in the ferret superior colliculus. Injections of fluorescent beads into the superficial layers showed that the projection from the contralateral retina displays topographic order on the day of birth (PO). Recordings made from these layers at the time of eye opening, approximately 1 month later, revealed the presence of an adult-like map of visual space. In contrast, the auditory space map in the deeper layers emerged gradually over a much longer period of postnatal life. In adult ferrets in which one eye had been deviated laterally just before eye opening, the auditory spatial tuning of single units recorded in the contralateral superior colliculus was shifted by a correspondin...
Spectral localization cues provided by the outer ear are utilized in the construction of the audi... more Spectral localization cues provided by the outer ear are utilized in the construction of the auditory space map in the superior colliculus (SC). The role of the outer ear in the development of this map was examined by recording from the SC of anesthetized, adult ferrets in which the pinna and concha had been removed in infancy. The acoustical consequences of this procedure were assessed by recording outer ear impulse responses via a probe-tube microphone implanted in the wall of the ear canal. Both monaural and binaural spectral cues normally show a number of asymmetric features within the horizontal plane, which allow azimuthal locations on either side of the interaural axis to be discriminated. These features were eliminated or altered by chronic pinnectomy. The responses of auditory units in the SC to noise bursts presented in the free field were examined at sound levels of approximately 10 and 25 dB above unit threshold. After bilateral pinnectomy, the representation of auditory...
ABSTRACT Despite the importance of spatial hearing in everyday listening, little is known about t... more ABSTRACT Despite the importance of spatial hearing in everyday listening, little is known about the accuracy of sound localization in a complex mixture of sounds. Here we measured, for the frontal audio-visual horizon, how accurately listeners could localize a female-voice target amidst four spatially distributed male-voice interferers in a moderately reverberant room. To examine whether listeners can make use of a priori knowledge about the configuration of the scene, we compared performance when the interferer locations were fixed (in one of five known patterns) to when the locations varied from trial to trial. The presence of interferers disrupted target localization, even after accounting for reduced target detectability. Randomizing the interferer locations had a moderate influence, degrading performance in some configurations but improving it in others. All effects were magnified when the target-to-interferer intensity ratio was reduced. The results confirm that spatial perception is disrupted by interfering sounds, and that this disruption is modified to some extent by listeners' expectations about the spatial arrangement of the scene. [Work supported by HFSP, NIH, VEGA, ARC and a Univ. of Sydney Postdoctoral Fellowship.].
ABSTRACT The current study investigated the temporal dynamics of audio-visual moving targets, exa... more ABSTRACT The current study investigated the temporal dynamics of audio-visual moving targets, examining the effects of velocity and acoustical environmental cues on the sensitivity of audio-visual cohesion. The acoustical stimuli were generated using Virtual Auditory Space, and two types of moving sounds were presented: (1) an immersive stimulus using Binaural Room Impulse Responses (BRIRs), that were recorded for each subject in situ in the testing room; thereby containing the combined spectral and temporal acoustic transformation due to both head-related filtering and the room’s characteristic response; (2) an environmentally impoverished stimulus using individualised Head-Related Impulse Responses (HRIRs) recorded in an anechoic chamber that lacked any reverberant cues. Apparent visual motion was generated by the sequential activation of LED’s along the same radial path as the auditory motion, 1 m away from the subjects. Moving stimuli were presented with a random temporal offset between each stimuli ranging from [−400 ms, 400 ms] (auditory or visual leading). Using a 2AFC paradigm, subjects reported which modality they perceived as leading for velocities of 25, 50 and 100°/s. At 25°/s the stimuli were perceived to be coincident when the visual stimulus was actually leading but, counter intuitively, the offset decreased as a function of increased velocity. The offset at PSE was greater for HRIRs than for BRIRs but the psychometric functions were significantly steeper for the HRIRs suggesting greater spatio-temporal resolution. This may reflect the degradation of the auditory cues produced by reverberation.
Journal of Speech Language and Hearing Research, 2014
The aim of this study was to examine attention, memory, and auditory processing in children with ... more The aim of this study was to examine attention, memory, and auditory processing in children with reported listening difficulty in noise (LDN) despite having clinically normal hearing. Twenty-one children with LDN and 15 children with no listening concerns (controls) participated. The clinically normed auditory processing tests included the Frequency/Pitch Pattern Test (FPT; Musiek, 2002), the Dichotic Digits Test (Musiek, 1983), the Listening in Spatialized Noise-Sentences (LiSN-S) test (Dillon, Cameron, Glyde, Wilson, & Tomlin, 2012), gap detection in noise (Baker, Jayewardene, Sayle, & Saeed, 2008), and masking level difference (MLD; Wilson, Moncrieff, Townsend, & Pillion, 2003). Also included were research-based psychoacoustic tasks, such as auditory stream segregation, localization, sinusoidal amplitude modulation (SAM), and fine structure perception. All were also evaluated on attention and memory test batteries. The LDN group was significantly slower switching their auditory attention and had poorer inhibitory control. Additionally, the group mean results showed significantly poorer performance on FPT, MLD, 4-Hz SAM, and memory tests. Close inspection of the individual data revealed that only 5 participants (out of 21) in the LDN group showed significantly poor performance on FPT compared with clinical norms. Further testing revealed the frequency discrimination of these 5 children to be significantly impaired. Thus, the LDN group showed deficits in attention switching and inhibitory control, whereas only a subset of these participants demonstrated an additional frequency resolution deficit.
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