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')], rather than that about the mean of the estimates [VAR(d')], indicates more completely the extent of the error in the estimator. For barely discriminable events (d' approximately equal to 0.5), the yes-no and 2AFC 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').