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

## 2pPP38. On measuring psychometric functions.

**Huanping Dai
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*Psychoacoust. Lab., Dept. of Psychol., Univ. of Florida, Gainesville, FL
32611
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Psychometric functions of simulated observers were obtained using the
conventional constant-stimulus method and an adaptive up--down method through a
post-hoc analysis of the track. The form of the psychometric functions was
assumed to be Pc=(Psi)(d'/2[sup 1/2]), where (Psi) is the cumulative Gaussian
probability function. The detectability d', is related to the signal level x by
d'=ax[sup k], where a and k are the two parameters to be estimated. Among the
factors considered in the simulation were step size and number of trials. For
small number of trials (n(less than or equal to)120), and particularly when the
step size was also small, the slope values (k) estimated using the adaptive
method were systematically greater than the true slopes. Such biases were
smaller with the constant-stimulus method. When the number of trials was
reasonably large (n(greater than or equal to)300), the constant-stimulus method
showed no clear advantage over the adaptive method. The only a priori
information required in the adaptive method is the starting stimulus level,
whereas the constant-stimulus method requires pilot measurements in order to
set all the stimulus levels properly. Thus the adaptive method is reasonably
efficient for measuring psychometric functions. [Work supported by NIH.]