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PubMed1997

Across-frequency nonlinear inhibition by GABA in processing of interaural time difference.

The barn owl uses the interaural time difference (ITD) to determine the azimuth of a sound source. Narrowband ITD-sensitive neurons cannot distinguish a given ITD from those that produce the same interaural phase difference (phase ambiguity). Neurons in the external nucleus of the inferior colliculus (ICx) resolve the ambiguity by gathering ITD information across many frequencies, thereby suppressing false responses (side peaks, SP) relative to the true ITD (the main peak, MP) in a response versus ITD curve. This process was quantitatively studied by comparing the ITD curve for a pair of tones presented simultaneously (two-tone curve) to the simple sum (predicted curve) of the individual ITD curves for the same tones presented separately. Sixteen of the 39 neurons tested did not show a significant difference in MP and SP responses between these curves (category I); 14 neurons showed significant SP suppression (category II). During iontophoretic application of bicuculline methiodide, a GABA(A) antagonist, most (n = 7/8) category II neurons lost nonlinear SP suppression and became linear, whereas category I neurons retained linear summation (n = 3/3). Thus, the nonlinear cross-frequency interaction of ITD responses in ICx neurons was mediated mostly by GABAergic inhibition, which enhanced SP suppression, and helped resolve phase ambiguity.

Acoustic Stimulation↗
PubMed1997

Positional, directional and speed selectivities in the primary auditory cortex of the cat.

Responses of high-frequency primary auditory cortex (A1) neurons of the cat to noise stimulation were obtained in a quasianechoic chamber using a static and an apparently moving stimulus presented at similar azimuths. Simulated motion toward right or left as well as different simulated velocities were used. Under static stimulation, most units were contralateral-preferring followed by ipsilateral- and midline-preferring. Some were omnidirectional and a few were unclassifiable. Width of tuning was similar for contralateral-, ipsilateral- and midline-preferring units. Overall, about 25% were finely tuned (< 20 degrees) and the remaining were broadly tuned (> or =20 degrees). All cells sampled with static stimulation responded to apparent motion. About one quarter of the units were sensitive to the direction of the simulated moving noise in that they responded at least twice as much to one direction as to the other. Almost all directional contralateral-preferring units responded more when the apparent motion was directed toward ipsilateral azimuths, whereas all directional ipsilateral-preferring units responded preferentially to contralaterally oriented motion. In some units, up to five apparent speeds were tested. About half the units were not speed-selective (46%). The other cells were tuned to a preferential speed (40%), decreased their response as the apparent speed increased (10%) or displayed direction-dependent speed selectivity (4%). These results indicate that moving-sound sources are processed by some A1 single units.

Acoustic Stimulation↗
PubMed1997

Changes in lateralization and loudness judgements during one week of unilateral ear plugging.

The aim of this study was to determine whether lateralization judgements show adaptation during a period of unilateral ear plugging. Six normally hearing young adults were tested repeatedly using pure tone stimuli of 500 and 4000 Hz to determine (i) the threshold in each ear, (ii) the interaural sensation level difference (ISLD) at which sounds presented alternately to the two ears were of equal loudness, and (iii) the ISLD at which sounds presented simultaneously to the two ears produced a centered internal sound image. Subjects were tested 9-14 times over one week before an ear plug, producing a nominal attenuation of 21 dB (at both frequencies), was placed in one ear. Subjects wore the plug continuously for a further week, and were tested daily during this period, with the plug in place. After unplugging, subjects were tested less frequently for one final week. Net changes in binaural hearing were measured by subtracting the equal loudness ISLD from the centering ISLD. Four subjects showed no net change, either during or after plugging, but a small (< 3 dB) adaptation occurred during plugging in two subjects.

Adaptation, Physiological↗
PubMed1998

Perceptual consequences of the interactions between spontaneous otoacoustic emissions and external tones. I. Monaural diplacusis and aftertones.

Research into monaural diplacusis has led to the concept of idiotones (tone-like stimuli of cochlea origin). Spontaneous otoacoustic emissions (SOAEs) are tone-like stimuli generated by the cochlea and detected in the ear canal. In diplacusis, the existence of idiotones is inferred from disturbances of the perception of single tones. Spontaneous otoacoustic emissions are measured by placing a small microphone at the entrance to the ear canal. Many of the puzzling properties of the hypothesized idiotones are consistent with measurements of the interaction of SOAEs with external tones. The interactions of the SOAEs with external tones were analyzed acoustically. The perceptual properties evoked by 250 ms pulses (presented twice a second) of the acoustic stimuli used in the OAE experiments were systematically investigated. At some stimulus levels, all subjects reported the perception of a second tone alternating with the external tone. The relative pitch of this percept was consistent with the frequency of the SOAE. The frequency dependence of the signal levels needed for the percept had many aspects in common with the suppression tuning curves of the SOAEs. At lower levels of the external tone the subjects sometimes reported a perception of two simultaneous tones. This would be consistent with the subject detecting SOAEs when they are frequency shifted, but not suppressed. The consumption of aspirin by one subject reduced the SOAE into the noise floor and eliminated the monaural diplacusis.

Acoustic Stimulation↗
PubMed1999

The localisation of spectrally restricted sounds by human listeners.

The two principal binaural cues to sound location are interaural time differences (ITDs), which are thought to be dominant at low frequencies, and interaural level differences (ILDs), which are thought to dominate at mid to high frequencies. The outer ear also filters the sound in a location dependent manner and provides spectral cues to location. In these experiments we have examined the relative contribution of these cues to the auditory localisation performance by humans. Six subjects localised sounds by pointing their face toward the perceived location of stimuli presented in complete darkness in an anechoic chamber. Control stimuli were spectrally flat (400 Hz to 16 kHz), while the relative contribution of location cues in the low frequency channels was determined using noise high passed at 2 kHz and in the high frequency channels using stimuli low passed at 2 kHz. The removal of frequencies below 2 kHz had little effect on either the pattern of systematic errors or the distribution of localisation estimates with the exception of an increase in the size of the standard deviations associated with a few rear locations. This suggests considerable redundancy in the auditory localisation information contained within a broadband sound. In contrast, restricting the target spectrum to frequencies below 2 kHz resulted in a large increase in the cone-of-confusion errors as well as a subject dependent biasing of the front-to-back or back-to-front confusions. These biases and the reduction in localisation accuracy for high pass stimuli at some posterior locations are consistent with a contribution of spectral information at low frequencies.

Acoustic Stimulation↗
PubMed2000

Responses of cells to stationary and moving sound stimuli in the anterior ectosylvian cortex of cats.

The azimuthal, directional and angular speed sound selectivities of single units were examined in the posterior part of the anterior ectosylvian cortex. Broadband noise bursts and simulated moving sounds were delivered from 16 loudspeakers fixed on the horizontal plane in a quasi-anechoic sound-isolation chamber. The activity of 78 neurons was recorded and quantitatively analyzed. Most cells responded to at least the static sound. The relative strengths of their responses suggested that the cells could be classed as omnidirectional (37.2%), contralateral hemifield (29.5%), ipsilateral hemifield (2.5%) and azimuth (7.7%) selective. The remaining 23.1% could not be classified. All cells responded to a simulated moving sound displaced at five different speeds. A majority (88%) of them showed some directional preference in that they discharged at least twice as strongly for one direction as for the other for at least one speed. 14.7% displayed angular speed selectivity. Different patterns of neuronal discharges were evoked. For static sounds, most of the cells gave ON-type responses. A large proportion (60%) of the cells responded in a sustained manner to maintained stimulation. Among these, 68% also gave sustained discharges to moving sounds. The spatial tuning and the directional and angular speed selectivity of neurons in the posterior part of the AEC suggest that this area is involved in the processing of static and moving sounds.

Acoustic Stimulation↗
PubMed1991

A case of pure word deafness associated with Landau-Kleffner syndrome: a long-term study of auditory disturbance.

A long-term study of auditory disturbance of a female case who had suffered from pure word deafness associated with Landau-Kleffner syndrome was reported. The patient developed this syndrome at age 4, and we continued the follow-up until she reached 20. The following became clear after the investigation: (1) even by the age of 20 her auditory defect had not improved significantly; (2) from an early stage she could not identify either vowels or consonant-vowel syllables; (3) later she had no difficulty identifying vowels, but her consonant-discrimination score hardly improved; and (4) her problem in consonant identification was unique in that she could discriminate between the voiced and voiceless group but had great difficulty identifying the consonants within each group. These findings led to the conclusion that the patient is unable to recognize short time duration consonants due to an insensibility to loudness and a defect in temporal resolution.

Agnosia↗
PubMed1998

Robots, crickets and ants: models of neural control of chemotaxis and phonotaxis.

Neural control in animals can be investigated using robot models. Two simple behaviours are focused on: pheromone trail following in ants and sound source localization in crickets. Our models address the real sensorimotor constraints and physiological underpinnings of these behaviours. Using alcohol gas sensors on a robot it is shown that a simple neural architecture can reproduce a range of trail-following behaviours that qualitatively resemble the results reported for ants. Building a more detailed auditory sensor based on the cricket ear it is shown that preference for song frequency and pattern does not require a recognition mechanism, using real cricket song as stimuli. Finally the spiking neuron models that enable us to examine exactly how these robust forms of motor control can emerge from small networks of neurons are introduced.

Journal Article↗
PubMed2001

Hearing and looking.

Explore the source record for details and available documents.

Acoustic Stimulation↗
PubMed2001

Eye position influences auditory responses in primate inferior colliculus.

We examined the frame of reference of auditory responses in the inferior colliculus in monkeys fixating visual stimuli at different locations. Eye position modulated the level of auditory responses in 33% of the neurons we encountered, but it did not appear to shift their spatial tuning. The effect of eye position on auditory responses was substantial-comparable in magnitude to that of sound location. The eye position signal appeared to interact with the auditory responses in at least a partly multiplicative fashion. We conclude that the representation of sound location in primate IC is distributed and that the frame of reference is intermediate between head- and eye-centered coordinates. The information contained in these neurons appears to be sufficient for later neural stages to calculate the positions of sounds with respect to the eyes.

Acoustic Stimulation↗
PubMed2002

Perception of sound-source motion by the human brain.

We assessed the human brain network for sound-motion processing using the same virtual stimulus in three independent functional imaging experiments. All experiments show a bilateral posterior network of activation, including planum temporale (PT) and parieto-temporal operculum (PTO). This was demonstrated in contrasts between sound movement and two control conditions: externalized stationary stimuli (in the midline or to the side of the head) and midline sounds within the head with similar spectro-temporal structure. We suggest specific computational mechanisms in PT for disambiguation of the intrinsic spectro-temporal features of a sound and the spectro-temporal effect of sound movement. The results support the existence of a posteriorly directed temporo-parietal pathway for obligatory perceptual processing of sound-source motion.

Adult↗
PubMed2002

Cortical processing of speech sounds and their analogues in a spatial auditory environment.

We used magnetoencephalographic (MEG) measurements to study how speech sounds presented in a realistic spatial sound environment are processed in human cortex. A spatial sound environment was created by utilizing head-related transfer functions (HRTFs), and using a vowel, a pseudo-vowel, and a wide-band noise burst as stimuli. The behaviour of the most prominent auditory response, the cortically generated N1m, was investigated above the left and right hemisphere. We found that the N1m responses elicited by the vowel and by the pseudo-vowel were much larger in amplitude than those evoked by the noise burst. Corroborating previous observations, we also found that cortical activity reflecting the processing of spatial sound was more pronounced in the right than in the left hemisphere for all of the stimulus types and that both hemispheres exhibited contralateral tuning to sound direction.

Acoustic Stimulation↗
PubMed2003

Effects of same- and different-modality cues in a Posner task: extinction-type, spatial, and non-spatial deficits after right-hemispheric stroke.

The response delay to left target stimuli preceded by right-side cues, first described by Posner et al. [J. Neurosci. 4 (1984) 1863-1874] appears to be a stable marker of right-parietal injury. However, only few studies compared patients' performance to age-matched controls. Furthermore, only few studies compared visual and auditory stimuli in this task. Therefore, two groups of right-hemisphere stroke patients, with and without left visual hemineglect, and a healthy control group were studied in three versions of Posner's paradigm. Visual or auditory target stimuli were presented to the subject's left or right, following a visual or auditory cue by 150 ms. The classical 'extinction-type' effect, an increase in missing responses for right visual cue/left visual target, was specifically observed in neglect patients. In the same condition, an 'extinction-type' response delay was present in patients with neglect and in those without neglect. No such delay occurred in any group when cues were auditory. Specifically in neglect patients, response times were generally longer for left than for right visual targets, regardless of cue side and of cue modality. Response times were generally prolonged in neglect patients regardless of target modality. This suggests that three components impair neglect patients' performance in this paradigm: a non-spatial, supramodal deficit, a global, neglect-type deficit of the contralesional hemi-field, and the extinction-type impairment. The latter two deficits appear to be most marked within the visual domain.

Acoustic Stimulation↗
PubMed2003

Cross-modal perceptual integration of spatially and temporally disparate auditory and visual stimuli.

Under certain conditions, auditory and visual information are integrated into a single unified percept even when they originate in different locations in space. The present study shows how this illusion, known as the ventriloquism effect, depends on spatial, temporal and cognitive factors. A method of psychophysical scaling was employed in combination with simple auditory-visual stimuli (tone bursts and flashing light spots) that were presented with various spatiotemporal disparities. Participants either judged their impression of the likelihood of a common cause (Experiment 1) or spatial alignment (Experiment 2) or synchrony of sound and light (Experiment 3). In all three experiments the participants' judgements depended significantly on temporal disparity whereas influences of spatial disparity were significant in Experiments 1 and 2. Optimum scores were always obtained when auditory stimuli were presented with a delay of 50-100 ms after the visual stimuli. These results demonstrate that both temporal and spatial proximity of the two stimuli are critical for the experience of phenomenal causality. On the other hand, spatio-temporal ranges for optimal perception of phenomenal causality in Experiment 1 were significantly larger than predicted by simultaneous detection of spatial and temporal disparities. This finding suggests that auditory-visual binding was further facilitated by additional, cognitive, factors, associated with the specific instruction to judge the likelihood of a common cause. Obviously, these instructional influences may reflect similar perceptual effects, as have been shown previously by increasing the complexity or cognitive compellingness of auditory-visual stimuli.

Acoustic Stimulation↗
PubMed2003

Auditory capture of vision: examining temporal ventriloquism.

Four experiments investigated whether irrelevant sounds can influence the perception of lights in a visual temporal order judgment task, where participants judged which of two lights appeared first. In Experiment 1, presenting a sound before the first light and after the second light improved performance relative to baseline (sounds appearing simultaneously with the lights), as if the sounds pulled the perception of lights further apart in time. Experiment 2 ruled out an alerting explanation for this effect and indicated that the performance improvement resulted from the second sound trailing the second light. Experiment 3 excluded the possibility that leading or simultaneous sounds were interfering with performance and revealed that only the second sound had an effect within the temporal window known to support multisensory integration. Experiment 4 demonstrated that sounds intervening between the two lights led to a decline in performance, as if the sounds pulled the lights closer together. The results suggest a 'temporal ventriloquism' phenomenon analogous to spatial ventriloquism.

Acoustic Stimulation↗
PubMed2003

Auditory distraction by duration and location deviants: a behavioral and event-related potential study.

Auditory distractibility was investigated using four noise stimuli that differed in their duration and/or sound source. In the duration-task/location-deviant condition, participants were asked to discriminate between equiprobable short and long stimuli. Mostly, stimuli were presented from one location (Standards), but, infrequently, a stimulus was presented from another location (Deviant). In the location-task/duration-deviant condition, participants had to discriminate between stimuli presented equiprobably from the speaker in front of them or to their left. Here, most stimuli were of equal duration (Standards), but, infrequently, a stimulus duration changed (Deviant). The rare deviations in location and duration were irrelevant for the actual task. Whether they affected processes related to the actual task was assessed with performance- and event-related potential (ERP) measures. In both conditions, responses to Deviants were slowed compared to responses to Standards. Deviants elicited ERP components mismatch negativity (MMN), P3a and reorienting negativity (RON). These results show that the processing of both a sound's duration and a sound's location can be distracted by rare, but irrelevant, changes in its location and duration, respectively. Behavioral distraction effects were markedly smaller with duration Deviants. It is suggested that duration Deviants interfere with task-related processing at later stages than location Deviants, as the processing of task-relevant information (i.e. stimulus location) commences before deviation in the location-task/duration-deviant condition occurs. Interestingly, distraction effects also prevail in the first Standard stimulus after a Deviant, as indicated by the prolonged response times and late negativity in the ERPs.

Acoustic Stimulation↗
PubMed2003

Dynamics of sensorimotor cortex activation to spatial sounds precueing ipsi- versus contralateral manual responses.

Spatially informative visual precues give rise to event-related potential asymmetries with higher negativities over the contralateral hemisphere. However the attribution of these potentials to sensorimotor areas is still unclear. The present magnetoencephalography study assessed movement preparation processes to auditory spatial precues. Event-related desynchronization (ERD) was measured to test the hypothesis that lateralized sounds would give rise to a fast, stimulus-driven activation of motor networks independent of the precued response side. The lateralized vowels /a/ and /e/ served as precues for either ipsi- or contralateral responses, respectively, which had to be executed when an imperative stimulus was presented 1 s after precue onset. Two separate experiments were conducted with either blocked or mixed presentation of ipsi- and contralateral precues. Beta ERD over sensorimotor regions representing the stimulus side was elicited by both types of precues approximately 200 ms after their onset. For contralateral precues, a switch of beta ERD to the response hemisphere took place approximately 400 ms after trial-onset, peaking prior to the imperative stimulus (approximately 800 ms post trial-onset). Signal subspace projection demonstrated a high topographical correspondence between the early precue-related ERD and the pattern immediately preceding the response, suggesting that both were generated in similar motor networks. Apparently lateralized sounds give rise to an early activation of contralateral motor networks independent of the precued response. This suggests strong associations between space processing and action preparation networks, with fast activations preceding a detailed cortical analysis of stimulus meaning.

Adult↗
PubMed1999

Selective tuning of the left and right auditory cortices during spatially directed attention.

Effects of spatially directed auditory attention on human brain activity, as indicated by changes in regional cerebral blood flow (rCBF), were measured with positron emission tomography (PET). Subjects attended to left-ear tones, right-ear tones, or foveal visual stimuli presented at rapid rates in three concurrent stimulus sequences. It was found that attending selectively to the right-ear input activated the auditory cortex predominantly in the left hemisphere and vice versa. This selective tuning of the left and right auditory cortices according to the direction of attention was presumably controlled by executive attention mechanisms of the frontal cortex, where enhanced activation during auditory attention was also observed.

Acoustic Stimulation↗