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Localization of tones by horses: use of binaural cues and the role of the superior olivary complex.

The ability of horses to use binaural time and intensity difference cues to localize sound was assessed in free-field localization tests by using pure tones. The animals were required to discriminate the locus of a single tone pip ranging in frequency from 250 Hz to 25 kHz emitted by loudspeakers located 30 degrees to the left and right of the animals' midline (60 degrees total separation). Three animals were tested with a two-choice procedure; 2 additional animals were tested with a conditioned avoidance procedure. All 5 animals were able to localize 250 Hz, 500 Hz, and 1 kHz but were completely unable to localize 2 kHz and above. Because the frequency of ambiguity for the binaural phase cue delta phi for horses in this test was calculated to be 1.5 kHz, these results indicate that horses can use binaural time differences in the form of delta phi but are unable to use binaural intensity differences. This finding was supported by an unconditioned orientation test involving 4 additional horses, which showed that horses correctly orient to a 500-Hz tone pip but not to an 8-kHz tone pip. Analysis of the superior olivary complex, the brain stem nucleus at which binaural interactions first take place, reveals that the lateral superior olive (LSO) is relatively small in the horse and lacks the laminar arrangement of bipolar cells characteristic of the LSO of most mammals that can use binaural delta I.

Animals↗

Children's implicit knowledge of harmony in Western music.

Three experiments examined children's knowledge of harmony in Western music. The children heard a series of chords followed by a final, target chord. In Experiment 1, French 6- and 11-year-olds judged whether the target was sung with the vowel /i/ or /u/. In Experiment 2, Australian 8- and 11-year-olds judged whether the target was played on a piano or a trumpet. In Experiment 3, Canadian 8- and 11-year-olds judged whether the target sounded good (i.e. consonant) or bad (dissonant). The target was either the most stable chord in the established musical key (i.e. the tonic, based on do, the first note of the scale) or a less stable chord. Performance was faster (Experiments 1, 2 and 3) and more accurate (Experiment 3) when the target was the tonic chord. The findings confirm that children have implicit knowledge of syntactic functions that typify Western harmony.

Analysis of Variance↗

Patterns of organization in auditory cortex.

Previous work has described recently developed techniques that are contributing to advances in the study of the auditory system; some of these techniques have been used to make significant progress in this field. This paper includes a discussion of the tonotopic and binaural organizations of the auditory cortex (especially area AI), the neuronal connections between auditory cortical fields, the relationships between the functional maps and the connectivity patterns, the nature of binaural processing within AI, and the techniques used to assess the structural and functional properties of this portion of the central auditory pathway.

Animals↗

Sound localization, use of binaural cues and the superior olivary complex in pigs.

Noise localization thresholds and the ability to localize pure tones at 60 degrees separation were determined for three domestic pigs using a conditioned avoidance procedure. The average threshold for localizing a brief noise burst was 4.5 degrees which is much more accurate than the thresholds of other hoofed mammals, such as horses, cattle and goats. The ability of pigs to localize low-frequency tones indicates that they can use the binaural phase-difference cue. However, they were unable to localize tones of 4 kHz and higher, indicating that, like other hoofed mammals, their ability to use binaural intensity cues is greatly restricted if not completely absent. An examination of the superior olivary complex of pigs revealed that in relative size, shape and cell density it is more like that of cats than that of other hoofed mammals.

Animals↗

Neural encoding and retrieval of sound sequences.

Although considerable progress has been made recently in our understanding of the coding of complex sounds in the cerebral cortex, the processing and storage of tone sequences is still poorly understood. We have used functional magnetic resonance imaging to identify brain mechanisms involved in the encoding and retrieval of melodies by studying the anticipation of familiar music. The results suggest a specific role for each of the following brain structures: the anterior part of the right superior temporal cortex, the right inferior frontal cortex and anterior insula, the left anterior prefrontal cortex, the lateral cerebellum, and the anterior cingulate. In a separate study, we investigated single-neuron responses in the auditory cortex of awake behaving monkeys to alternating tone sequences that in humans evoke the perception of "streaming." Depending on the frequency separation between the tones, an initial single stream may segregate into two streams after a build-up period of several seconds. The neural responses in the monkeys' primary auditory cortex (A1) mirror the psychophysical time course extremely well, suggesting that habituation within A1 may be one reason for stream segregation. However, the higher auditory and prefrontal areas found to be activated by musical melodies are expected to interact with primary areas in both bottom-up and top-down fashion to bring about the perceptual organization of sound sequences.

Animals↗

Dynamics of spontaneous and evoked activities of the substructures within the cat inferior colliculus.

The spontaneous EEG and evoked electrical activities (EP) recorded simultaneously and bilaterally from different depths below the dorsal surface of the inferior colliculus (IC), have been systematically analyzed in freely moving cats. Power spectral analysis techniques were employed for evaluating the frequency characteristics of the EEG and EP which were recorded from substructures of the IC. The changes in the electrical activities following local lesions further helped us to understand whether these frequencies represent volume conducted field potentials or local neural activity. It was found that in the IC, high frequency electrical activities up to 1000 Hz are generated locally and recorded with maximal amplitudes in the ventral and ventralmost parts. Following the stimulation, strong amplitude enhancement and frequency stabilization were obtained in 70-80 Hz, 350-400 Hz, and 850-950 Hz frequency ranges.

Animals↗

Evaluation of interaural signal differences.

A model of binaural signal processing is discussed which is based on a running interaural cross-correlation mechanism in frequency bands. A pattern of a hypothetical "binaural neural activity distribution" is derived from the ear signals. It is assumed that the binaural activity patterns are evaluated by a central pattern-recognition processor, which extracts certain cues to form the spatial attributes of the auditory events. The model is applied to sound fields in rooms to explain a special kind of spatial impression on the listener which can be described as "spaciousness".

Auditory Pathways↗

An auditory Stroop effect for pitch, loudness, and time.

Increased reaction time to pitch, loudness, or duration of an auditorily presented word whose meaning is in conflict with the response label (i.e., high/low, loud/soft, or fast/slow) demonstrates an auditory Stroop effect. Fifteen normal adults participated in an auditory Stroop test. Analysis of reaction time data supports the existence of an auditory Stroop effect for pitch and loudness, but not duration. The interaction between psychoacoustic and semantic attributes of speech stimuli is discussed.

Adult↗

The effect of amplitude comodulation on auditory object formation in sentence perception.

To comprehend speech in most environments, listeners must combine some but not all sounds from across a wide range of frequencies. Three experiments were conducted to examine the role of amplitude comodulation in performing an essential part of this function: the grouping together of the simultaneous components of a speech signal. Each of the experiments used time-varying sinusoidal (TVS) sentences (Remez, Rubin, Pisoni, & Carrell, 1981) as base stimuli because their component tones are acoustically unrelated. The independence of the three tones reduced the number of confounding grouping cues available compared with those found in natural or computer-synthesized speech (e.g., fundamental frequency and simultaneity of harmonic onset). In each of the experiments, the TVS base stimuli were amplitude modulated to determine whether this modulation would lead to appropriate grouping of the three tones as reflected by sentence intelligibility. Experiment 1 demonstrated that amplitude comodulation at 100 Hz did improve the intelligibility of TVS sentences. Experiment 2 showed that the component tones of a TVS sentence must be comodulated (as opposed to independently modulated) for improvements in intelligibility to be found. Experiment 3 showed that the comodulation rates that led to intelligibility improvements were consistent with the effective rates found in experiments that examined the grouping of complex nonspeech sounds by common temporal envelopes (e.g., comodulation masking release; Hall, Haggard, & Fernandes, 1984). The results of these experiments support the claim that certain basic temporal-envelope processing capabilities of the human auditory system contribute to the perception of fluent speech.

Adult↗

Preliminary study of improved perception of words with the same sound but different intonation in tinnitus patients following electrical stimulation of the ear.

The present study aimed to explain how tinnitus relief following electrical promontory stimulation affects detection of changes in pitch frequency. To determine the effects of tinnitus relief on the auditory system. Japanese words with the same sound but different intonation were used to verify the effects of tinnitus relief on pitch detection in tinnitus patients Eight out of 11 patients experienced relief of tinnitus following treatment. The averaged number of the ratio in 8 patients with relief of tinnitus, 0.58, was significantly higher (p < 0.02) than that in 3 patients without relief, 0.15. In comparison with averaged hearing level, there was no significant difference in averaged hearing level between 8 patients with relief of tinnitus (52.4 dBSL; SD: 11.4) and 3 without relief of tinnitus (58.0 dBSL; SD: 14.7) (p > 0.68). No significant difference in age between patients with and without relief of tinnitus was observed.

Aged↗

Cerebral lateralization of familiar and unfamiliar music perception in nonmusicians: a dual task approach.

In a dual task procedure that controls for attentional trade-off effects, asymmetrical interference effects were observed in dual task conditions of finger tapping and concurrent processing of familiar and unfamiliar music. Laterality effects suggested that perception of orchestral presentations is largely lateralized to the left hemisphere in both males and females. In a second dual task condition of vocalization and music processing, both males and females displayed interference in speech production during concurrent music processing. Males showed greater left hemispheric interference effects during simultaneous vocalization and music processing.

Adult↗

Memory prerequisites of mismatch negativity in the auditory event-related potential (ERP).

The mismatch negativity (MMN) is a component of the auditory event-related brain potential that occurs in response to infrequent changes in the physical properties of homogeneous series of sounds, even when subjects are instructed to ignore the auditory channel of stimulation. It has been proposed (e.g., Näätänen, 1990) that the MMN is generated by an automatic process in which a difference between the deviant sound and the previous, standard sound is detected by the brain. However, it is unclear how the form of memory involved is related to the rest of the memory system. The present study indicates that, for an MMN to be elicited in response to a change in tone frequency, the representation of the standard tone must be both (a) well-established as a standard in memory, and (b) in a currently active state. The relation between physiological and psychological aspects of memory representation is discussed.

Acoustic Stimulation↗

Relations between auditory functions in impaired hearing.

Relations between auditory functions, as expressed by coefficients of correlation, were studied for a group of 22 sensorineurally hearing-impaired subjects with moderate losses. In addition to the audiogram, we measured frequency resolution, temporal resolution, and speech reception in quiet and in noise. Frequency resolution was derived from masking with comb-filtered noise and from the psychophysical tuning curve, for both paradigms in simultaneous and in nonsimultaneous masking. The critical ratio was also determined. Temporal resolution was determined with intensity-modulated noise and from backward and forward masking. All tests were performed at 1000 Hz. Correlations among tests were gathered in a matrix and subjected to a principal-components analysis. It turned out that tests on frequency resolution form a cluster, and are approximately independent of audiometric loss. Furthermore, hearing loss for speech in noise is closely allied to frequency resolution, whereas hearing loss for speech in quiet is governed by audiometric loss.

Adult↗

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. I. Responses to wideband noise.

We examined the responses of low-frequency neurons in the central nucleus of the inferior colliculus (ICC) of the cat to interaurally delayed, wideband noise stimuli. The stimuli were pseudorandom noise signals that were generated digitally with a nominal bandwidth of 60-4,000 Hz. We also compared the responses to noise with those obtained from interaural phase differences of pure tones. We studied 144 neurons with characteristic frequencies below 2.5 kHz. Eighty-five percent (85%) of these were sensitive to changes in both interaural time differences (ITDs) of noise and interaural phase differences of pure tones, only 2% were sensitive to one stimulus but not the other, and the remainder were insensitive to both stimuli. For most cells the discharge rate was modulated in an approximately cyclic fashion by changes in ITDs of the wideband noise stimuli. The maximal spike counts often occurred near zero ITD, and there was considerable variability in the nature of the cycling, though it usually disappeared for ITDs greater than +/- 4,000 microseconds. The position of the central peak was usually (65%) within the physiologically relevant range of +/- 400 microseconds, and most (80%) occurred at positive ITDs, which corresponded to delays to the ipsilateral stimulus. In general, the shapes of the responses were not affected by changes in stimulus level above threshold. As long as identical noises were delivered to both ears, the responses were not sensitive to the particular noise stimulus used. When uncorrelated noises were delivered to the two ears, there was no sensitivity to ITDs. Composite curves were computed by linear summation of the responses to ITDs of pure tones at frequencies spaced at equal intervals throughout each cell's response area. The shapes of composite curves were similar to the responses of the same cell to ITDs of wideband noise stimuli. The positions of the central peaks of these two functions were highly correlated (r = 0.91, slope = 0.97). The values of characteristic delay and characteristic phase computed from the tonal responses were found to be good indicators of the shapes of the noise delay curves. Characteristic phases (CPs) near zero were associated with noise delay curves symmetric about the central peak, CPs near 0.5 cycles with those symmetric about the trough, while CPs between 0 and 0.5 or between 0.5 and 1.0 had noise delay curves that were asymmetric with a prominent trough to the left or right, respectively, of the central peak.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗