Vowel Quality Decay and Perceptual Asymmetries in Light of the Neutralisation Hypothesis

The present paper consists in replicating Repp and Crowder’s (1990) neutralisation hypothesis according to which the auditory trace left by the first vowel in a pair decays toward a central point in the acoustic space, triggering order effects in perception. Two ‘same-different’ tasks were undertaken by French listeners. A prototype and four satellite tokens were synthesized for ten vowel categories of French; satellites were paired with the prototype in both orders of presentation. The focus of the two tasks undertaken was the possibility of [ǝ] being a target of decay for auditory traces on the F1/F2 and F2/F3 acoustic space. Results from both tasks failed to validate the initial hypothesis. In his seminal work Elemente der Psychophysik, Fechner (1860) introduces the concept of ‘time-order error’ which consists in the fact that subjects often overor under-estimate the magnitude of a stimulus’s properties depending on its order of presentation in a sequence of tokens. Albeit the growing literature on this topic, the mechanisms behind it remain obscure. Using an /i/-/ɪ/ continuum, Cowan and Morse (1986) claim that discrimination was easier when the second vowel in a pair was closer to the /i/ endpoint. They suggest that the asymmetry in the perceived distance between two stimuli is triggered by a change in quality toward the centre of the vowel space corresponding to the region occupied by the vowel /ǝ/. The mechanism of this change in quality is presented in Figure 1. Figure 1. The vowel shift model, adapted from Cowan and Morse (1986). On the left is illustrated the auditory trace that the stimulus has left in memory 250 ms after its presentation. The dashed line indicates the vowel’s ‘confidence region’. In the middle of this region lies the centre of the mental representation that the listener has created for the stimulus. At moment 2, 2000 ms after the presentation of the stimulus, the confidence ha ls hs -0 06 75 87 3, v er si on 1 2 M ar 2 01 2 Author manuscript, published in "Fechner Day 2010, Padova : Italy (2010)"