WHAT D' SCORES CAN HIDE AND WHAT DECISION SPACE REPRESENTATIONS SHOULD REVEAL: AN ACCOUNT ON ASYMMETRIES IN VOWEL PERCEPTION

  • Charalampos Karypidis

Abstract

The introduction of the signal detection theory has been a significant step in psychophysics,and d' score estimations have helped us understand cognitive processing to a significantdegree. However, researchers in the field of speech perception have been using this sensitivitymeasure while assuming that the decision spaces are symmetrical, neglecting thus theinternal structure of categories. In a two-interval ‘same-different’ paradigm, for example, theareas covered by the S1S1, S1S2, S2S1 and S2S2 distributions are not necessarily equivalent.In this paper, we will contest the assumption of symmetry by revisiting some papers whichprovide evidence in favour of asymmetrical vowel perception. Perceptual distance isdependent on the salience of the acoustic properties of the stimuli, with salient stimuli eitherdecaying slower or interfering more with the processing of adjacent stimuli. We will thenattempt to provide a hypothetical decision space for a ‘same-different’ task implementing twovowels, <i> and <e> and will discuss the usefulness of decision spaces as tools forunderstanding the perceptual robustness of stimuli.
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