The dispersions of estimates of sensitivity obtained from four psychophysical procedures: Implications for experimental design

The dispersions of estimates of sensitivity obtained from the yes-no, two-alternative forced-choice (2AFC), matching-to-sample, and same-different tasks were examined to determine which task would be more appropriate to use in a given experimental context. Consideration was given to the effects of corrections for extreme sampled proportions. These corrections result in biased estimators, and hence the mean square deviation of the sampled values about the population mean [MSD((d) over cap')], rather than that about the mean of the estimates [VAR((d) over cap')], indicates more completely the extent of the error in the estimator. For barely discriminable events (d' similar or equal to 0.5), the yes-no and BAFC tasks had the lowest values of MSD(d'). However, for very discriminable events (d' > 3), the same-different and matching-to-sample tasks had lower values of MSD((d) over cap').