Speech sounds are said to be perceived categorically. This notion is usually operationalized as the extent to which discrimination of stimuli is predictable from phoneme classification of the same stimuli. In this article, vowel continua were presented to listeners in a four-interval discrimination task (2IFC with flankers, or 4I2AFC) and a classification task. The results showed that there was no indication of categorical perception at all, since observed discrimination was found not to be predictable from the classification data. Variation in design, such as different step sizes or longer interstimulus intervals, did not affect this outcome, but a 2IFC experiment (without flankers, or 2I2AFC) involving the same stimuli elicited the traditional categorical results. These results indicate that the four-interval task made it difficult for listeners to use phonetic information and, hence, that categorical perception may be a function of the type of task used for discrimination.

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.

In Experiment 1, subjects were asked to identify the direction (up or down) of sweep tones centered around frequencies of 400, 1300, and 2700 Hz. Durations were 20, 30, 40, or 50 msec, and the rates of the (unidirectional) sweeps were 0, 5,10,20,40, and 60 octaves/sec. The main result was that, on the whole, stimuli with zero-or low-sweep rates were judged to move "down," irrespective of the actual direction. Experiment 2 was a discrimination experiment, in which subjects had to discriminate between falling, rising, and level sweep tones centered around 1300 Hz.

Listeners discriminate acoustic differences between phoneme categories at a higher level than similarly sized differences within phoneme categories. The question this paper aims to answer is how this pattern in perceptual sensitivity develops along an acoustic dimension that contrasts two non-native speech sounds: through acquired distinctiveness, through acquired similarity, or through a combination of the two. A pretest-training-post-test experiment was designed to study perceptual development directly, i.e., by including (i) a discrimination task to measure perceptual sensitivity, (ii) a transfer test to ensure language learning instead of stimulus learning, and (iii) a control group to exclude task repetition as an explanation of improvement. It is shown that the typical peak in perceptual sensitivity near a phoneme boundary that native listeners show is not found in relatively inexperienced language learners, despite their ability to classify a continuum in a nativelike way after short laboratory training. Experiment II indicates that a discrimination peak may be achieved by language learners, but only after much more language experience than short-term laboratory training can offer. Furthermore, reasons are given why classification improvement in the laboratory should not be taken as evidence for (i) increased discrimination of the newly learned phonemes and (ii) learning of phoneme representations.

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