On the efficiency of psychophysical measurement.

A previously proposed upper bound on the performance of psychophysical techniques that attempt to determine points on psychometric functions is shown to be a least upper bound. The existence of a realizable technique (the Robbins‐Monro process) which asymptotically attains the performance of the proposed ideal shows that this ideal provides an appropriate basis from which to calculate the absolute as opposed to relative efficiency of real psychophysical measurement techniques. The concept of incremental efficiency is introduced. It is shown to be useful in analyzing the performance of measurement techniques when the initial uncertainty of the estimate, often ignored in simulation studies, is neither infinite nor zero, and to permit independent assessment of the efficiency of separate portions of a measurement process.