ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pPP33. Referential coding and the ``severe departure'' from Weber's law.

Christopher J. Plack

Dept. of Exp. Psychol., Univ. of Sussex, Brighton BN1 9QG, UK

The Weber fraction for intensity discrimination for a 30-ms, 6.5-kHz sinusoidal pedestal is greater at medium pedestal levels that a low or high pedestal levels, particularly when the pedestal is gated with notched noise [R. P. Carlyon and B. C. J. Moore, 1369--1376 (1984)]. In the present experiments, Weber fractions were measured for a 30-ms, 6-kHz pedestal, at a range of levels between 40 and 70 dB SPL. Measurements were made in quiet and in the presence of a 110-ms notched noise with an onset 40 ms before the onset of the pedestal. The bandstop portion of the noise was 1-kHz wide, centered on 6 kHz, and the noise had a fixed spectrum level of 20 dB. In contrast to the earlier results, at pedestal levels of around 50 dB SPL the notched noise caused a reduction in the Weber fraction. It is suggested that the noise might improve performance by providing a proximal reference for coding the intensity of the pedestal. [Work supported by The Royal Society.]