Biomedical subjects

A J van Hessen

Publications and source records attributed to A J van Hessen.

4 recordsLinked to original sources

PubMed1998

Response distributions in intensity resolution and speech discrimination.

In this paper the assumption of an equal, Gaussian distribution of the response to each stimulus in an experiment, an assumption which has to be met if d' is to be estimated by calculating the difference between z(H) and z(FA), is tested for two different sets of stimuli: 1000-Hz tones differing in level only, and a continuum of stop consonants, obtained by full spectral interpolation between /p/, /t/, and /k/. Response distributions were measured directly by means of a form of non-numerical magnitude estimation, in which subjects had to indicate the position of each stimulus on a quasi-continuous rating scale. It could be shown that, in general, all distributions were sufficiently unimodal, but that their variances differed. The consequences for the calculation of d' are unlikely to be serious.

Female↗

PubMed1992

Modeling phoneme perception. I: Categorical perception.

On the basis of a number of vowel and stop-consonant discrimination experiments (AX and 2IFC fixed and roving) with natural stimuli, it is concluded that stop-consonant perception is highly categorical: there were few significant differences between the discrimination results and the phoneme identification results. Moreover, the discrimination and identification response maxima differed significantly from the other data points. Vowel perception was much less categorical: the maxima in the functions were much less significant, and there were significant differences between the various paradigms. Consonant discrimination was much less (if at all) subject to range effects than vowel discrimination. All these results point to different memory types for stop consonants and vowels, and, consequently, to a combination of two different theories of speech sound discrimination: dual-process theory (DPT) for consonants, and trace-context theory (TCT) for vowels.

Adult↗

PubMed1992

Modeling phoneme perception. II: A model of stop consonant discrimination.

Combining elements from two existing theories of speech sound discrimination, dual process theory (DPT) and trace context theory (TCT), a new theory, called phoneme perception theory, is proposed, consisting of a long-term phoneme memory, a context-coding memory, and a trace memory, each with its own time constants. This theory is tested by means of stop-consonant discrimination data in which interstimulus interval (ISI; values of 100, 300, and 2000 ms) is an important variable. It is shown that discrimination in which labeling plays an important part (2IFC and AX between category) benefits from increased ISI, whereas discrimination in which only sensory traces are compared (AX within category), decreases with increasing ISI. The theory is also tested on speech discrimination data from the literature in which ISI is a variable [Pisoni, J. Acoust. Soc. Am. 36, 277-282 (1964); Cowan and Morse, J. Acoust. Soc. Am. 79, 500-507 (1986)]. It is concluded that the number of parameters in trace context theory is not sufficient to account for most speech-sound discrimination data and that a few additional assumptions are needed, such as a form of sublabeling, in which subjects encode the quality of a stimulus as a member of a category, and which requires processing time.

Adult↗

PubMedDate not supplied

Categorical perception as a function of stimulus quality.

A number of experiments were carried out in order to test the hypothesis that categorical perception of speech stimuli is a function of synthesis quality - specifically, that the greater complexity of more natural speech stimuli makes it difficult for listeners to focus on particular stimulus parameters as psychoacoustic cues. The results show that there is an increase in categorical perception as synthesis quality improves from a simple synthesis by rule, via LPC synthesis, to a much more complex type called sinewave generation.

Adult↗