M. E. H. Schouten
A. J. van Hessen
Res. Inst. for Language and Speech, Utrecht Univ., Trans 10, 3512 JK Utrecht, The Netherlands
One of the assumptions underlying the calculation of almost every d' in the literature is that the distribution of sensations resulting from repeated presentation of a stimulus is normal and is equal to the distributions produced by the other stimuli in an experiment. This could be a reasonable approximation for pure tones, but it is doubtful whether it applies to more complex stimuli such as speech. A series of magnitude-estimation experiments was carried out, in which subjects were asked to indicate the position of each stimulus on a line on a monitor screen, which ran either from ``soft'' to ``loud'' or from /p/ to /t/. The stimuli were practically identical to those used by [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483--502 (1972), and by M. E. H. Schouten and A. J. van Hessen, J. Acoust. Soc. Am. 92, 1841--1855 (1992)]. Training was done by means of identification of the same stimuli on a similar line, but now subdivided into segments. Each stimulus was presented for magnitude estimation 400 times before and 400 times after training; as a result, the shape and size of each distribution could be traced out.