[Binaural diplacusis, new accuracy in cases of a lesion of Corti's organ].
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The purpose of this research was to investigate a set of factors that may influence the perceived rate of an auditory event. In a paired-comparison task, subjects were presented with a set of music-like patterns that differed in their relative number of contour changes and in the magnitude of pitch skips (Experiment 1) as well as in the compatibility of rhythmic accent structure with the arrangement of pitch relations (Experiment 2) Results indicated that, relative to their standard referents, comparison melodies were judged to unfold more slowly when they displayed more changes in pitch direction, greater pitch distances, and an incompatible rhythmic accent structure. These findings are suggested to stem from an imputed velocity hypothesis, in which people overgeneralize certain invariant relations that typically occur between melodic and temporal accent structure within Western music.
A detailed clinical and psychophysical study of a woman who had developed pure word deafness associated with amusia after bilateral temporoparietal destructions is reported. The patient had a defect in temporal resolution encompassing auditory, visual and somatosensory modalities, but the clinical defect was limited to the auditory sphere. Auditory comprehension did not improve even if she was spoken to slowly, although marked improvement of temporal resolution was observed as the duration of a nonlinguistic sound was extended. Also, she exhibited a supramodal defect in the perception and reproduction of rhythm, which was rate-dependent. These and other findings led to the following conclusions: the auditory modality is much more dependent on temporal resolution than other sensory modalities; for a full understanding of the mechanism of pure word deafness, not only the defect of temporal resolution but also many other factors, for example, defective discrimination of loudness, pitch or tone duration have to be taken into consideration; and rhythm sense strongly depends on a supramodal capacity of temporal resolution.
It remains a matter of controversy precisely what kind of neural mechanisms underlie functional asymmetries in speech processing. Whereas some studies support speech-specific circuits, others suggest that lateralization is dictated by relative computational demands of complex auditory signals in the spectral or time domains. To examine how the brain processes linguistically relevant spectral and temporal information, a functional magnetic resonance imaging study was conducted using Thai speech, in which spectral processing associated with lexical tones and temporal processing associated with vowel length can be differentiated. Ten Thai and 10 Chinese subjects were asked to perform discrimination judgments of pitch and timing patterns presented in the same auditory stimuli under two different conditions: speech (Thai) and nonspeech (hums). In the speech condition, tasks required judging Thai tones (T) and vowel length (VL); in the nonspeech condition, homologous pitch contours (P) and duration patterns (D). A remaining task required listening passively to nonspeech hums (L). Only the Thai group showed activation in the left inferior prefrontal cortex in speech minus nonspeech contrasts for spectral (T vs. P) and temporal (VL vs. D) cues. Thai and Chinese groups, however, exhibited similar fronto-parietal activation patterns in nonspeech hums minus passive listening contrasts for spectral (P vs. L) and temporal (D vs. L) cues. It appears that lower level specialization for acoustic cues in the spectral and temporal domains cannot be generalized to abstract higher order levels of phonological processing. Regardless of the neural mechanisms underlying low-level auditory processing, our findings clearly indicate that hemispheric specialization is sensitive to language-specific factors.
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Carlyon and Shackleton [J. Acoust. Soc. Am. 95, 3541-3554 (1994)] presented an influential study supporting the existence of two pitch mechanisms, one for complex tones containing resolved and one for complex tones containing only unresolved components. The current experiments provide an alternative explanation for their finding, namely the existence of across-frequency interference in fundamental frequency (F0) discrimination. Sensitivity (d') was measured for F0 discrimination between two sequentially presented 400 ms complex (target) tones containing only unresolved components. In experiment 1, the target was filtered between 1375 and 15,000 Hz, had a nominal F0 of 88 Hz, and was presented either alone or with an additional complex tone ("interferer"). The interferer was filtered between 125-625 Hz, and its F0 varied between 88 and 114.4 Hz across blocks. Sensitivity was significantly reduced in the presence of the interferer, and this effect decreased as its F0 was moved progressively further from that of the target. Experiment 2 showed that increasing the level of a synchronously gated lowpass noise that spectrally overlapped with the interferer reduced this "pitch discrimination interference (PDI)". In experiment 3A, the target was filtered between 3900 and 5400 Hz and had an F0 of either 88 or 250 Hz. It was presented either alone or with an interferer, filtered between 1375 and 1875 Hz with an F0 corresponding to the nominal target F0. PDI was larger in the presence of the resolved (250 Hz F0) than in the presence of the unresolved (88 Hz F0) interferer, presumably because the pitch of the former was more salient than that of the latter. Experiments 4A and 4B showed that PDI was reduced but not eliminated when the interferer was gated on 200 ms before and off 200 ms after the target, and that some PDI was observed with a continuous interferer. The current findings provide an alternative interpretation of a study supposedly providing strong evidence for the existence of two pitch mechanisms.
Event-related brain potentials (ERPs) elicited by multidimensional auditory stimuli were recorded from the scalp in a selective-attention task. Subjects listened to tone pips varying orthogonally between two levels each of pitch, location, and duration and responded to longer duration target stimuli having specific values of pitch and location. The discriminability of the pitch and location attributes was varied between groups. By examining the ERPs to tones that shared pitch and/or locational cues with the designated target, we inferred interrelationships among the processing of these attributes. In all groups, stimuli that failed to match the target tone in an easily discriminable cue elicited only transitory ERP signs of selective processing. Tones sharing the "easy" but not the "hard" cue with the target elicited ERPs that indicated more extensive processing, but not as extensive as stimuli sharing both cues. In addition, reaction times and ERP latencies to the designated targets were not influenced by variations in the discriminability of pitch and location. This pattern of results is consistent with parallel, self-terminating models and holistic models of processing and contradicts models specifying either serial or exhaustive parallel processing of these dimensions. Both the parallel, self-terminating models and the holistic models provide a generalized mechanism for hierarchical stimulus selections that achieve an economy of processing, an underlying goal of classic, multiple-stage theories of selective attention.
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Cardiac responses of 36- to 39-week-old (GA) fetuses were tested with a no-delay pulsed stimulation paradigm while exhibiting a low heart rate (HR) variability (the HR pattern recorded when fetuses are in the 1f behavioral state). We examined whether fetuses could discriminate between two low-pitched piano notes, D4 (F(0) = 292 Hz/292-1800 Hz) and C5 (F(0) = 518 Hz/518-300 Hz). Seventy percent of all fetuses reacted to the onset of the first note (D4 or C5) with the expected cardiac deceleration. After heart rate returned to baseline, the note was changed (to C5 or D4, respectively). Ninety percent of the fetuses who reacted to the note switch did it with another cardiac deceleration. Control fetuses, for whom the first note did not change, displayed few cardiac decelerations. Thus, fetuses detected and responded to the pulsed presentation of a note and its subsequent change regardless of which note was presented first. Because perceived loudness (for adults) of the notes was controlled, it seems that the note's differences in F(0) and frequency band were relevant for detecting the change. Fetuses' ability to discriminate between spectra that lay within the narrow range of voice F(0) and F(1) formants may play an important role in the earliest developmental stages of speech perception.