In order to examine the ability of native Japanese speakers to distinguish between English voiceless fricatives, a five-alternative, forced-choice (5AFC) test was administered to 104 Japanese students of English. The stimuli consisted of 75 nonsense syllables in which five fricatives (/f/, /s/, /∫/, /θ/, /h/) were presented in five vowel environments (/i ε a o u/) and in three different consonant contexts, and were spoken by three native speakers of English. The identification rates were submitted to signal-detection-theoretic (SDT) analysis (measured by d^′), multidimensional-scaling (MDS) analysis, and cluster analysis. Overall, identification rates ranged from a maximum of 88% for the /∫/ stimuli to 55% for the /θ/ stimuli. The results showed that both vowel environment and consonant context had an effect on the listeners’ perception of the stimuli in this study. A control group of six native English subjects took the same identification test using the same procedure. All of the control listeners had no difficulty in identifying the target fricatives except in the case of the /f/–/θ/ contrast.

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For the loss factor measurement, the half-power-width method and curve fitting method are used. In this paper, two curve fitting methods based on pole-zero models are proposed. The first method is to express the measured and model frequency response functions in decibels and the parameters of the model are changed so that the model response gets close enough to the measured response by the differential iteration method. The second method is to take the distance of the two responses on the complex plane and normalize it to the amplitude of the measured frequency response function. Then, the normalized distance is minimized by the differential iteration method. These two methods have the following features: (1) They can fit the resonance and anti-resonance characteristics simultaneously. (2) They can fit frequency response functions with large loss factors to which the half-power-width method are not applicable. (3) The minimum required numbers of measurement points within the half-power-width for these methods are roughly 1/30 of the number necessary for the half-power-width method.

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In this paper, the thresholds of detection and laterality are explored using a tone signal with interaural time difference (ITD) and a diotic tone masker in the three stimulus configurations: in simultaneous, forward and backward masking paradigms. The inter-stimulus intervals (ISIs) between the signal and the masker are 2, 5, 10, 20 and 50 ms. The results show that both of the thresholds decrease with increasing ISI. Characteristics of the laterality thresholds is similar to the well-known pattern of temporal masking, which means that we measured the temporal masking pattern on laterality. As the frequency difference between the tonal masker and the signal tone becomes smaller, the detection threshold increases due to masking. The laterality thresholds with an interferer, however, are higher than those without an interferer at a wider frequency range around the frequency of an interfering tone.

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In the actual sound environment, the objective system often exhibits the non-Gaussian property, owing to physical, social and psychological factors. Many kinds of probability distributions have been proposed from various viewpoints to describe the probabilistic property of complicated random phenomena. Sometimes, a probability distribution of orthogonal series expansion type, which takes the well-known probability distribution (e.g., Gaussian, binomial distributions, etc.) as the first term and reflects the lower and higher order statistics in the expansion terms is also utilized. This paper describes a practical trial to choose the permissible order of series expansion, especially by introducing a pre-established tolerance range for the deviation of the theoretical cumulative probability from the experimental one. The minimal number of expansion terms can be rationally determined so as to satisfy the tolerance range. Finally, the effectiveness of this method is experimentally confirmed by applying it to the environmental noise.

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