### ASA 125th Meeting Ottawa 1993 May

## 4aPP9. Predicting intensity discrimination from power-law modifications of
the loudness function.

**William S. Hellman
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*Dept. of Phys., Boston Univ., Boston, MA 02215
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**Rhona P. Hellman
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*Dept. of Psychol., Northeastern Univ., Boston, MA 02115
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Several modifications of Stevens' power law have been introduced to
account for the steepening of the loudness function below about 40 dB SPL. The
relation between intensity discrimination ((Delta)I/I) and loudness is
determined for three proposed modifications: (a) L[sub s]=K(I-I[sub 0])[sup n],
(b) L[sub s]=K(I[sup n]-I[sub 0][sup n]), and (c) L[sub s]=k([I+cI[sub 0]][sup
n]-[cI[sub 0]][sup n]), where I[sub 0] is the sound intensity at threshold.
Below 15 dB SPL Eqs. (a) and (b) generate a rapidly decreasing function for
intensity discrimination, whereas the function derived from Eq. (c) rises with
a slope of -1 in log--log coordinates. The slope of the measured
intensity-discrimination function is compatible with results predicted for pure
tones from Eq. (c) but not with those predicted from Eqs. (a) and (b). [Work
supported in part by NIH.]