Research on the contributions of the human nervous system to language processing and learning has generally been focused on the association regions of the brain without considering the possible contribution of primary and adjacent sensory areas. We report a study examining the relationship between the anatomy of Heschl's Gyrus (HG), which includes predominately primary auditory areas and is often found to be associated with nonlinguistic pitch processing and language learning. Unlike English, most languages of the world use pitch patterns to signal word meaning. In the present study, native English-speaking adult subjects learned to incorporate foreign pitch patterns in word identification. Subjects who were less successful in learning showed a smaller HG volume on the left (especially gray matter volume), but not on the right, relative to learners who were successful. These results suggest that HG, typically shown to be associated with the processing of acoustic cues in nonspeech processing, is also involved in speech learning. These results also suggest that primary auditory regions may be important for encoding basic acoustic cues during the course of spoken language learning.
The way in which normal variations in human neuroanatomy relate to brain function remains largely uninvestigated. This study addresses the question by relating anatomical measurements of Heschl’s gyrus (HG), the structure containing human primary auditory cortex, to how this region processes temporal and spectral acoustic information. In this study, subjects’ right and left HG were identified and manually indicated on anatomical MRI scans. Volumes of gray matter, white matter and total gyrus were recorded, and asymmetry indices were calculated. Additionally, cortical auditory activity in response to noise stimuli varying orthogonally in temporal and spectral dimensions was assessed and related to the volumetric measurements. A high degree of anatomical variability was seen, consistent with other reports in the literature. The auditory cortical responses showed the expected leftward lateralization to varying rates of stimulus change and rightward lateralization of increasing spectral information. However, the present data are the first to explicitly link anatomical variability of auditory cortex to individual differences in the way that cortex processes acoustic information. Specifically, larger volumes of left HG were associated with larger extents of rate-related cortex on the left, and larger volumes of right HG related to larger extents of spectral-related cortex on the right. This finding is discussed in relation to known microanatomical asymmetries of HG, including increased myelination of its fibers, and implications for language learning are considered.
Pitch and timbre are two of the building blocks of music. Variations in pitch lead to a melodic line, whereas variations of timbre are usually heard as different instrumentations. Do pitch and timbre interact? Listening to an orchestra, one can hear a continuous melody being played when different instruments switch off playing separate parts of this melody, even if each note of the melody is played by a different instrument, a compositional style called klangfarbenmelodieor hocket. A more striking demonstrationof this phenomenon occurs with sung melodies, in which the changing vocal timbres associated with speech do not alter perception of the melody. This implies that one can follow the fundamental frequency (F0) of a series of tones, even when their spectral shapes differ, which argues for the separability of pitch and timbre. However, since both pitch and spectral timbre are rooted in the frequency dimension of sound, it should not be surprising if they interact under some circumstances. To test this idea, one could look at people's perceptions of pitch and/or timbre when both the F0 and the spectral shape of the tones differ. This paper investigates the interaction between pitch and timbre, focusing on spectral timbre's influence on pitch perception as a function of context.The literature in which interactions between pitch and timbre are examined has yielded contradictory results. Some researchers have found that the timbre of a tone affects its perceived pitch (e.g., Krumhansl & Iverson, 1992, Experiment 1;Melara & Marks, 1990a, 1990b, 1990cPlatt & Racine, 1985;Singh & Hirsh, 1992;Wapnick & Freeman, 1980), whereas others have found no effect of timbre on pitch perception (e.g., Krumhansl & Iverson, 1992, Experiments 2 and 3;Semal & Demany 1991, 1993. It seems that those studies presenting tones in the absence of other tones tend to find an interaction between pitch and timbre, whereas studies presenting tones within the context of other tones find no such interaction (but see also , in which pitch and timbre difference thresholds for isolated tones were not affected by variation in the irrelevant dimension).A same-different paradigm was used by Singh and Hirsh (1992) to determine the perceived pitch of isolated residue tones, tones having no component at F0. Six timbres were synthesized, each containing four consecutive harmonics, the lowest of which could be the second, third, fourth, or up to the seventh harmonic. Each pair of tones could differ in F0, spectral composition, or both. Subjects indicated whether timbre was the same or different, and whether pitch stayed the same, went up, or went down. When the harmonic numbers and F0 moved in the same direction, subjects correctly reported the direction of pitch change. However, when harmonic number and F0 moved in opposite directions, this created a conflict. If the change in F0 was 4% or greater, the direction of F0 change dominated pitch judgments. However, when the change in F0 was less than 4%, the direction of harmonic change dominated pitch judgmen...
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