## QuestTest

##### >Psychtoolbox>PsychTests

Created by hacking a copy of QuestDemo.m, in order to

do some simulations for Beau Watson.

128 repetitions of each condition

Quest assumes LogWeibull psychometric function with parameters:

beta = {1.5, 2., 2.5, 3., 3.5, 4., 4.5, 5., 5.5} (in separate conditions)

gamma = 0.03

delta = .01

sample range = {-30,30} dB

sample step size 0.5 dB

Prior is always Gaussian, sd=12 dB, centered on guess.

Initial guess drawn from Normal distribution with mean 0 and sd=6 dB.

Quest uses mode of posterior density.

Simulated observer has LogWeibull psychometric function with parameters:

{beta=3.5,gamma=.03,delta=.01}

By commenting and uncommenting five lines below, you can use

this file to implement three QUEST-related procedures for measuring

threshold.

QuestMode: In the original algorithm of Watson & Pelli (1983)

each trial and the final estimate are at the MODE of the posterior pdf.

QuestMean: In the improved algorithm of King-Smith et al. (1994).

each trial and the final estimate are at the MEAN of the posterior pdf.

QuestQuantile & QuestMean: In the ideal algorithm of Pelli (1987)

each trial is at the best QUANTILE, and the final estimate is at

the MEAN of the posterior pdf.

King-Smith, P. E., Grigsby, S. S., Vingrys, A. J., Benes, S. C., and Supowit, A.

(1994) Efficient and unbiased modifications of the QUEST threshold method: theory,

simulations, experimental evaluation and practical implementation.

Vision Res, 34 (7), 885-912.

Pelli, D. G. (1987) The ideal psychometric procedure. Investigative Ophthalmology

& Visual Science, 28 (Suppl), 366.

Watson, A. B. and Pelli, D. G. (1983) QUEST: a Bayesian adaptive psychometric

method. Percept Psychophys, 33 (2), 113-20.

Copyright (c) 1996-1997 Denis G. Pelli

6/24/97 dgp wrote it, based on QuestDemo.m

`Psychtoolbox/PsychTests/QuestTest.m`