Biomedical subjects

Tomohiro Nakatani

Publications and source records attributed to Tomohiro Nakatani.

4 recordsLinked to original sources

PubMed2006

Fundamental frequency of infants' and parents' utterances in longitudinal recordings.

The fundamental frequencies (F0) of daily life utterances of Japanese infants and their parents from the infant's birth until about 5 years of age were longitudinally analyzed. The analysis revealed that an infant's F0 mean decreases as a function of month of age. It also showed that within- and between-utterance variability in infant F0 is different before and after the onset of two-word utterances, probably reflecting the difference between linguistic and nonlinguistic utterances. Parents' F0 mean is high in infant-directed speech (IDS) before the onset of two-word utterances, but it gradually decreases and reaches almost the same value as in adult-directed speech after the onset of two-word utterances. The between-utterance variability of parents' F0 in IDS is large before the onset of two-word utterances and it subsequently becomes smaller. It is suggested that these changes of parents' F0 are closely related to the feasibility of communication between infants and parents.

Adult↗

PubMed2006

Speech feature extraction method using subband-based periodicity and nonperiodicity decomposition.

This paper proposes a speech feature extraction method that utilizes periodicity and nonperiodicity for robust automatic speech recognition. The method was motivated by the auditory comb filtering hypothesis proposed in speech perception research. The method divides input signals into subband signals, which it then decomposes into their periodic and nonperiodic components using comb filters independently designed in each subband. Both features are used as feature parameters. This representation exploits the robustness of periodicity measurements as regards noise while preserving the overall speech information content. In addition, periodicity is estimated independently in each subband, providing robustness as regards noise spectrum bias. The framework is similar to that of a previous study [Jackson et al., Proc. of Eurospeech. (2003), pp. 2321-2324], which is based on cascade processing motivated by speech production. However, the proposed method differs in its design philosophy, which is based on parallel distributed processing motivated by speech perception. Continuous digit speech recognition experiments in the presence of noise confirmed that the proposed method performs better than conventional methods when the noise in the training and test data sets differs.

Algorithms↗

PubMed2004

Robust and accurate fundamental frequency estimation based on dominant harmonic components.

This paper presents a new method for robust and accurate fundamental frequency (F0) estimation in the presence of background noise and spectral distortion. Degree of dominance and dominance spectrum are defined based on instantaneous frequencies. The degree of dominance allows one to evaluate the magnitude of individual harmonic components of the speech signals relative to background noise while reducing the influence of spectral distortion. The fundamental frequency is more accurately estimated from reliable harmonic components which are easy to select given the dominance spectra. Experiments are performed using white and babble background noise with and without spectral distortion as produced by a SRAEN filter. The results show that the present method is better than previously reported methods in terms of both gross and fine F0 errors.

Adult↗

PubMed2003

Prediction of invasive activities in hepatocellular carcinomas with special reference to alpha-fetoprotein and des-gamma-carboxyprothrombin.

BACKGROUND: Hepatocellular carcinoma (HCC) is one of the world's major malignancies, especially in Asian countries. To improve the prognosis of HCC, it is essential to predict its invasive behavior in both intra- and extra-hepatic modalities. For this purpose, we examined the predictive values of two tumor markers, alpha-fetoprotein (AFP) and des-gamma-carboxyprothrombin (DCP). METHODS: 194 HCC cases at the National Cancer Center Hospital were selected from the Pathology Records. Detailed information regarding the existence of extra-hepatic venous invasion (EHVI) at the portal vein and intra-hepatic multiple malignant tumors (IHMTs) were collected and combined with the preoperative AFP and DCP testing results. Furthermore, information about the viral infection status such as HBs antigen positive or HCV antibody positive or no viral hepatitis was obtained. The information was analyzed by the ROC (Receiver Operating Characteristic Curve) method. RESULTS: and CONCLUSIONS: In both the EHVI group and the IHMT group, all the combinations except the HCV-positive group of IHMT revealed a tendency for DCP to offer better diagnostic accuracies, although this was statistically significant only in the HBs-positive group of IHMT. This result indicates either (1). that in a strict sense, DCP is not necessarily better than AFP at predicting the invasive characteristics or (2). that DCP is better than AFP at reflecting the invasive characteristics of HCC although not statistically significant. In either situation, from a long-term viewpoint, it is advisable to find a new marker or to re-evaluate the existing markers in order to predict the invasive characteristics more accurately.

Biomarkers↗