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Abstract

A common task in psychophysics is to measure the psychometric function. A psychometric function can be described by its shape and four parameters: offset or threshold, slope or width, false alarm rate
or chance level and miss or lapse rate. Depending on the parameters of interest some points on the
psychometric function may be more informative than others. Adaptive methods attempt to place trials
on the most informative points based on the data collected in previous trials. A new Bayesian adaptive
psychometric method placing trials by minimising the expected entropy of the posterior probabilty dis-
tribution over a set of possible stimuli is introduced. The method is more flexible, faster and at least as efficient as the established method (Kontsevich and Tyler, 1999). Comparably accurate (2dB) threshold and slope estimates can be obtained after about 30 and 500 trials, respectively. By using a dynamic
termination criterion the efficiency can be further improved. The method can be applied to all experimental designs including yes/no designs and allows acquisition of any set of free parameters. By weighting
the importance of parameters one can include nuisance parameters and adjust the relative expected
errors. Use of nuisance parameters may lead to more accurate estimates than assuming a guessed
fixed value. Block designs are supported and do not harm the performance if a sufficient number of trials are performed. The method was evaluated by computer simulations in which the role of parametric assumptions, its robustness, the quality of different point estimates, the effect of dynamic termination criteria and many other settings were investigated.