Shinobu Masaki

Learning-induced neural plasticity associated with improved identification performance after training of a difficult second-language phonetic contrast.

Adult native Japanese speakers have difficulty perceiving the English /r-l/ phonetic contrast even after years of exposure. However, after extensive perceptual identification training, long-lasting improvement in identification performance can be attained. This fMRI study investigates localized changes in brain activity associated with 1 month of extensive feedback-based perceptual identification training by native Japanese speakers learning the English /r-l/ phonetic contrast. Before and after training, separate functional brain imaging sessions were conducted for identification of the English /r-l/ contrast (difficult for Japanese speakers), /b-g/ contrast (easy), and /b-v/ contrast (difficult), in which signal-correlated noise served as the reference control condition. Neural plasticity, denoted by exclusive enhancement in brain activity for the /r-l/ contrast, does not involve only reorganization in brain regions concerned with acoustic-phonetic processing (superior and medial temporal areas) but also the recruitment of additional bilateral cortical (supramarginal gyrus, planum temporale, Brocas area, premotor cortex, supplementary motor area) and subcortical regions (cerebellum, basal ganglia, substantia nigra) involved with auditory-articulatory (perceptual-motor) mappings related to verbal speech processing and learning. Contrary to what one may expect, brain activity for perception of a difficult contrast does not come to resemble that of an easy contrast as learning proceeds. Rather, the results support the hypothesis that improved identification performance may be due to the acquisition of auditory-articulatory mappings allowing for perception to be made in reference to potential action.

When meaningless symbols become letters: neural activity change in learning new phonograms.

Left fusiform gyrus and left angular gyrus are considered to be respectively involved with visual form processing and associating visual and auditory (phonological) information in reading. However, there are a number of studies that fail to show the contribution of these regions in carrying out these aspects of reading. Considerable differences in the type of stimuli and tasks used in the various studies may account for the discrepancy in results. This functional magnetic resonance imaging (fMRI) study attempts to control aspects of experimental stimuli and tasks to specifically investigate brain regions involved with visual form processing and character-to-phonological (i.e., simple grapheme-to-phonological) conversion processing for single letters. Subjects performed a two-back identification task using known Japanese, and previously unknown Korean, and Thai phonograms before and after training on one of the unknown language orthographies. Japanese subjects learned either five Korean or five Thai phonograms. Brain regions related to visual form processing were assessed by comparing activity related to native (Japanese) phonograms with that of non-native (Korean and Thai) phonograms. There was no significant differential brain activity for visual form processing. Brain regions related to character-to-phonological conversion processing were assessed by comparing pre- and post-tests of trained non-native phonograms with that of native phonograms and non-trained non-native phonograms. Significant differential activation post-relative to pre-training exclusively for the trained non-native phonograms was found in left angular gyrus. In addition, psychophysiologic interaction (PPI) analysis revealed greater integration of left angular gyrus with primary visual cortex as well as with superior temporal gyrus for the trained phonograms post-relative to pre-training. The results suggest that left angular gyrus is involved with character-to-phonological conversion in letter perception.

An estimation of the production process for fricative consonants

Voiceless fricatives, / s / , / f / , / h / , and / f / , are produced by the turbulent noise which is generated at or after constriction in the vocal tract, and their acoustical characteristics are determined mainly by the configuration of vocal tract area functions. Many investigations have been performed not only from acoustical but also physio; logical points of view [1-5]. The extraction of the characteristics of these consonants is important for the recognition and synthesis of speech. The effective extraction of the characteristics is performed in the frequency domain. Some researchers have used poles and zeroes of spectra to describe the characteristics of these consonants. We attempt to extract the characteristics of fricative consonants by the estimation of area function using a simplified vocal tract model which simulates the production process of these consonants. The overall spectrum including slope is taken into account to obtain more minute features of these consonants than when the pole-zero model is used. Pn U r

Extraction of vocal tract area function from three‐dimensional magnetic resonance images using digital waveguide mesh

A method is proposed in this paper to extract the vocal tract area function from the three‐dimensional magnetic resonance images. The proposed method uses the digital waveguide mesh, an implementation of the finite‐difference time‐domain (FDTD) method, to simulate wave propagation in the vocal tract from the glottis to the lips. The dimensions of the vocal tract areas are then calculated along the traveling wavefront that emerges from the simulation. Formant analysis has been conducted for Japanese vowels to show the validity of the proposed method. The calculated formant frequencies of the area functions obtained by the proposed method and other existing methods have been compared to those measured from the acoustic utterance of the imaged person.

Foreword to the special issue on "the ASA-ASJ joint meeting"

It is my great pleasure to introduce this special issue on ‘‘the ASA-ASJ joint meeting,’’ which was held from November 28th to December 2nd, 2006 in Honolulu, Hawaii. There have been three previous ASA-ASJ joint meetings’’ in 1978, 1988 and 1996 in Hawaii. As a symbol of the continuous friendship between the ASA (Acoustical Society of America) and the ASJ (Acoustical Society of Japan), this fourth meeting was held at the same place as the previous meeting in 1996. In this joint meeting, 1616 papers were presented in more than one hundred sessions covering the entire range of acoustical fields, including acoustical oceanography, animal bioacoustics, architectural acoustics biomedical ultrasound, bioresponse to vibration, engineering acoustics, musical acoustics, noise, physical acoustics, psychological and physiological acoustics, speech communication, signal processing, underwater acoustics, structural acoustics and vibration, and education in acoustics. This special issue was planned so that some of the papers presented at the joint meeting could be rapidly circulated. In order to minimize the ‘‘review period,’’ a working group on the publication of the special issue was set up, which was directed by Kentaro Nakamura, Head of the Journal Committee of the Editorial Board, and supported by Masato Akagi, the former Editor-in-Chief. In response to the announcement of the publication of the special issue on the joint meeting, eighteen Papers and six Letters were submitted. All of these articles were peer reviewed by reviewers on a strict schedule overseen by the working group. As a result, twelve Papers and six Letters were accepted and published in this issue. The eighteen articles herein cover a wide range of the acoustical fields such as structural acoustics (two Papers and one Letter), ultrasound and underwater acoustics (two Papers and one Letter), noise (one Paper and one Letter), physiological acoustics (one Paper), musical acoustics (three Papers and one Letter), speech communication (two Papers and one Letter), and signal processing (one Paper and one Letter). It is hoped that even readers who did not attend the joint meeting in Honolulu will be able to sense the atmosphere of the sessions at the conference while reading the articles. I wish to express my deep gratitude to all the reviewers and the members of the working group for their contribution to the reviewing process. I also would like to thank the Secretariat of the Acoustical Society of Japan from the bottom of my heart for their prompt correspondence.

Effects of tempo and context on jaw openings for vowel in vowel sequence words

Jaw movements were observed using a system which was composed of infrared light emitting diodes and an optical position sensitive detector. The jaw opening for each vowel was measured in the production of vowel sequences at slow and fast speaking rates. The influence of (1) the speaking rate and (2) the context on the jaw opening for each vowel were observed for open vowels; (1) the jaw opening for each vowel at the fast speaking rate was less than that at the slow rate, and (2) the jaw opening for the word-final vowel followed by /d/ in the carrier phrase /desu/ was less than that for the vowel in any other word-internal position. The mechanism of these variations in jaw openings were investigated in terms of the duration and the target of the jaw opening for each vowel. The results suggest that the variations in the jaw opening for the same vowel were caused not only by the under-shoot due to the shortness of the duration, but also by the variation in the target of the jaw opening.