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PubMed1981

Evidence for auditory localization ability in the turtle.

Evidence is presented that the semiaquatic turtle Chrysemys scripta and the terrestrial turtle Terrapene carolina major can detect the direction of a tone within their sensitive area of hearing. It is further suggested that not only can these species respond behaviorally to sound without extensive manipulation but can use limited hearing in a problem-solving situation of maze learning. Adult emydid turtles (5 C. scripta, 3 T. carolina) learned a Y-maze with a 500-c/s signal to an invisible open goal box to avoid bright light. All animals performed above chance levels, but it required over 240 trials on the average to reach 60%-correct performance. Computations suggest that binaural cues used by mammals would not be adequately encoded by the primitive auditory systems of the species studied. It is further suggested that these turtles use bone conduction by coupling their ears to the substrate to hear vibrations in the immediate area. This would appear to be a carryover from the ancient reptile stem stock. The poor middle-ear impedance system relegates air-borne sound processing to be a somewhat insensitive limited low-pass system, depending heavily on monaural cues derived from head scanning. vocal output in these species appears to be spectrally imbalanced with their auditory sensitivity. The role of species-specific vocal signalling is unclear from the present data.

Animals↗
PubMed1983

The effect of head movements on visual and auditory dominance.

Two experiments were performed to determine the effect of active auditory exploration (head movement) on visual and auditory dominance. In each experiment subjects located a small audio speaker unimodally or bimodally. On the bimodal trials a modality discordance was created by requiring prismatic viewing. Half the subjects in each experiment remained unaware of the discordance while the other half were informed that a prism was used, and its refracting properties were demonstrated. The second experiment differed from the first by allowing observers free head movement during target localization which was transduced and recorded electromechanically. The results indicated that knowledge of modality discordance greatly reduced visual bias of audition for observers with heads immobilized, but did not affect auditory bias of vision significantly. Observers permitted head movement but not provided with knowledge of discordance demonstrated visual bias which was substantially reduced from that found in the first experiment for no-knowledge subjects. Observers who were permitted head movement and provided with knowledge of discordance demonstrated no visual bias or auditory bias. Head movements were executed systematically, when permitted, and resulted in an increase in the precision of auditory localizations and a reduction in the biasing effect of vision. In contrast, head movement did not affect the precision of visual localizations. Results are discussed in terms of current hypotheses regarding perceptual dominance.

Attention↗
PubMed1969

Auditory and vibratory responses in the midbrains of snakes.

Airborne sound and substrate vibration each elicit electrical responses below the surface of the tectum in species of three families of snakes. Tones of 50 to 1000 hertz evoke responses independently of substrate vibration. Sensitivity to locally applied sound is present over much of the body surface. This sensitivity is attributed to the auditory nerve, because it is not altered by spinal section but is eliminated by destruction of the inner ear.

Animals↗
PubMed2005

Encoding of virtual acoustic space stimuli by neurons in ferret primary auditory cortex.

Recent studies from our laboratory have indicated that the spatial response fields (SRFs) of neurons in the ferret primary auditory cortex (A1) with best frequencies > or =4 kHz may arise from a largely linear processing of binaural level and spectral localization cues. Here we extend this analysis to investigate how well the linear model can predict the SRFs of neurons with different binaural response properties and the manner in which SRFs change with increases in sound level. We also consider whether temporal features of the response (e.g., response latency) vary with sound direction and whether such variations can be explained by linear processing. In keeping with previous studies, we show that A1 SRFs, which we measured with individualized virtual acoustic space stimuli, expand and shift in direction with increasing sound level. We found that these changes are, in most cases, in good agreement with predictions from a linear threshold model. However, changes in spatial tuning with increasing sound level were generally less well predicted for neurons whose binaural frequency-time receptive field (FTRF) exhibited strong excitatory inputs from both ears than for those in which the binaural FTRF revealed either a predominantly inhibitory effect or no clear contribution from the ipsilateral ear. Finally, we found (in agreement with other authors) that many A1 neurons exhibit systematic response latency shifts as a function of sound-source direction, although these temporal details could usually not be predicted from the neuron's binaural FTRF.

Acoustic Stimulation↗
PubMedDate not supplied

[Role of the temporal neocortex in the mechanisms of spatial hearing at different stages in the ontogenesis of cats].

Significance of the temporal (AI, AII, Ep, IT) cortical areas for localization of acoustic stimuli sources of various parameters (tones 0.25-5 kHz, polytonal signals, clicks) was studied in acute and chronic experiments on kittens in the age of 15-90 days and on adult cats. The temporal areas were shown to take part in localization of tones beginning from third week, in that of polytonal signals from the second month, and in that of clicks from the third month of life. The degree of the corticalization of the mechanisms of stimuli localization is not the same in adult animals as well, the most corticalized being the mechanisms of tone localization, the least corticalized--that of clicks. Heterofunctionality of the right and the left temporal areas in the mechanisms of the spatial hearing has been revealed. In ontogeny the right temporal area functionally forestalls the left one. The role of the callosal body in the spatial orientation becomes apparent from the second month of life and consists mainly in ability to localize the sources of monotonal signals.

Acoustic Stimulation↗
PubMed1983

[Multichannel infant reflex audiometry (MIRA)].

A new method for evaluation of hearing threshold in babies is presented. The method does not require much time, cost or personnel and is practicable for infants up to about 12 months. It is based on synchronous electrical registration of sucking and breathing activities as well as of eye movements evoked by acoustic stimuli. Sucking and breathing are reduced by supra-threshold stimuli, preparing the baby for attentive listening. Eye movements are directed towards localizing the site of the stimulus.

Acoustic Stimulation↗
PubMedDate not supplied

[Specific features of lateralization of a stationary auditory image by a human under condition of stimulation without interaural differences: a neurophysiological analysis].

Analysis of the lateralization phenomena of a fused auditory image (FAI) was performed on the basis of the previously developed model of the binaural directional hearing. It was found earlier that, under conditions of auditory stimulation without interaural differences, the FAI was localized at the head midline only in about a quarter of subjects. In a greater part of the listeners, the FAI was lateralized within the range of -4.6 ... +11.2 degrees from the midline. It was shown that FAI localization with reference to the head midline may be determined by the extent of asymmetry and spatial contrast between the "active" neural zones in the left and right halves of the subjective auditory space. In turn, the asymmetry (or its absence) of these "active" zones fully depends on a distribution of neurons by characteristic time delays in the left and right halves of the subjective auditory field. The model also explains the fact of a decrease in localization precision with the FAI position just at the midline.

Acoustic Stimulation↗
PubMed1979

Spatial localization under conflict conditions: is there a single explanation?

Visual--auditory (VA) and visual--proprioceptive (VP) localization conflict paradigms were varied to explore the comparability of the conflict situations. In experiment 1 various attempts were made to decrease the dominance of visual information over proprioceptive and auditory target information. Pairing auditory with proprioceptive information against conflicting visual information did not lessen the visual dominance, nor did dimming the visual field. A 'cognitive' manipulation, in which the subject was led to doubt the reliability of the visual information, reduced visual dominance over audition but not visual dominance over proprioception. This difference between the two conflict situations was further explored and corroborated in experiment 2. In experiment 3 no attempt was made to lead the subject to believe that paired discrepant targets were related, and the visual dominance of audition was strong while the visual dominance of proprioception did not occur. The apparent differences between the VA and VP conflict situations are discussed with regard to the feability of generating a unitary explanation of localization conflict results. Several further factors are discussed that must be explored before undertaking such a unitary formulation.

Cognition↗
PubMed1989

Minimum audible angle thresholds obtained under conditions in which the precedence effect is assumed to operate.

Two experiments were conducted to examine the ability of human listeners to localize the "lag" or "echo" source in a precedence effect paradigm. A 5-ms noise burst was presented from a source located between 554-279 cm from the subject. This "lead" source was always located at 0 degrees azimuth. At the same time, one of two sources located at a distance of 610 cm from the subject was also activated with the same 5-ms noise burst. The subject's task was to identify which lag source had been active. Across sessions, the angular distance between the lag sources was varied, so as to allow a determination of the minimum audible angle (MAA) that could be resolved. Tests were run in a room designed to minimize reflections and in a hallway that was acoustically quite complex. No systematic differences in MAA thresholds were observed as a function of the environment employed. MAA thresholds obtained without the signal from the lead speaker were less than 1 degree for four of the five subjects tested. The precedence effect, as measured by the change in the MAA threshold, appears to have only a modest influence on localization performance. Under conditions in which the lead source was concurrently active, the thresholds were generally elevated by only 2 degrees-4 degrees. A reduction of this magnitude in the ability to resolve the position of the lag source does not seem to be sufficient, in itself, to account for the excellent localization performance frequently observed in reflective environments.

Acoustic Stimulation↗
PubMed1961

Psychomotor coordination of auditory and visual space at birth.

Before it was 10 minutes old, a human neonate was able to turn its eyes in the direction of an auditory stimulus. This demonstrates that learning is not essential for a crude form of auditory localization, directional oculomotor response, and coordination of auditory and visual functioning.

Auditory Perception↗
PubMed1984

Binaural phase differences and binaural auditory adaptation.

In order to determine the relationship between binaural phase localization and auditory adaptation, subjects were asked to perform a series of phase-based localization tasks, as well as an SDLB adaptation task. A binaurally presented 400 Hz tone was used for midplane localization tasks, and adaptation balances. The tone was presented monaurally during adaptation after binaural localization and the SDLB pre-test. Following 7 min exposure, subjects readjusted phase to centre the binaural stimulus in the midline, and then adjusted intensity to determine dB of adaptation. No consistent or statistically significant change in phase settings occurred. There was a significant decline in the balance intensity as a function of adaptation. A further re-establishment of the midline by phase manipulation also showed no localization effect. For the stimulus values used in the present study, there was no inter-effect of binaural phase localization, and SDLB auditory adaptation.

Adaptation, Physiological↗
PubMed1994

Bilateral digital hearing aids for binaural hearing.

The rehabilitation of binaural hearing performance in hearing impaired listeners has received relatively little attention to date. Both localization ability and speech-understanding-in noise are affected in the impaired listener. When localization performance is tested in impaired ears with conventional hearing aid fittings it is found to be worse than the unaided condition. Advances in electronic design now permit speculation about the implementation of complex digital filters within the confines of an in-the-ear hearing aid. We have begun exploring strategies to enhance the localization performance of impaired listeners with bilateral digital signal processing. We are examining three strategies in bilateral hearing aid design to improve localization performance in hearing impaired listeners, namely 1) more accurate fitting of individual ear losses, 2) equalization of the effect of the hearing aid itself on the acoustics within the ear canal, and 3) binaural fitting strategies which in effect modify individual ear fittings to enhance localization performance. The results of early psychophysical testing suggests that localization performance can be improved with these strategies.

Amplifiers, Electronic↗
PubMed1985

Influence of monaural spectral cues on binaural localization.

Seven subjects located, monaurally and binaurally, narrow bands of noise originating in the horizontal plane. The stimuli were 1.0 kHz wide and centered at 4.0-14.0 kHz in steps of 0.5 kHz. The loudspeakers, 15 deg apart, were arranged in a semicircle (0-270-180 deg, azimuth). In the first part of the experiment all sounds emanated from the loudspeaker at 270 deg, but their apparent locations varied widely as a function of their center frequency. For each subject, the pattern of location judgments under the binaural listening condition corresponded to that recorded for the monaural condition. In the second part of the experiment the loudspeaker from which each of the same narrow bands of noise emanated was varied in irregular order. Again, monaural location judgments were governed by the frequency content of the noise bands. Binaural location judgments were strongly influenced by the sounds' frequency composition when the stimuli originated from 315-225 deg, notwithstanding the presence of interaural differences in time and intensity. For narrow bands of noise emanating off midline, monaural spectral cues significantly override binaural difference cues, and they also determine the resolution of front-back ambiguities.

Auditory Perception↗