Testing a new theory of Fechnerian scaling: The case of auditory intensity discrimination

Abstract

Recently, Dzhafarov and Colonius [Psych. Bull. Rev. 6, 239–268 (1999)] proposed a theory that refines Fechner’s ideas of deriving the perceptual distance between stimuli from discriminability measures in the unidimensional case, and generalizes it to multidimensional stimulus domains. In this theory, the existence of a Fechnerian metric is based on testable assumptions about the shape of the psychometric functions. Thus, ‘‘same–different’’ psychometric functions: (1) have to attain a single minimum at some point; (2) must be locally symmetric around their minima; and (3) must show the same degree of cuspidness, or flatness, along the stimulus continuum. In the present investigation, these assumptions were evaluated experimentally employing acoustical stimuli differing along one stimulus dimension, intensity. In a ‘‘same–different’’ paradigm, using the method of constant stimuli, seven 1000-Hz tones deviating from 0 to 2.1 dB with respect to a standard were presented diotically to five observers. For every participant, psychometric functions were assessed at five hearing levels ranging from 40- to 80-dB HL. The outcome of the ‘‘same–different’’ experiments generally supports the assumptions of the theory. Therefore, data such as these are, in principle, suitable for deriving a global loudness scale from local discriminability measures.