Yi Y, Merfeld DM. A quantitative confidence signal detection model: 1. Fitting psychometric functions. J Neurophysiol 115: 1932J Neurophysiol 115: -1945J Neurophysiol 115: , 2016. First published January 13, 2016; doi:10.1152/jn.00318.2015.-Perceptual thresholds are commonly assayed in the laboratory and clinic. When precision and accuracy are required, thresholds are quantified by fitting a psychometric function to forced-choice data. The primary shortcoming of this approach is that it typically requires 100 trials or more to yield accurate (i.e., small bias) and precise (i.e., small variance) psychometric parameter estimates. We show that confidence probability judgments combined with a model of confidence can yield psychometric parameter estimates that are markedly more precise and/or markedly more efficient than conventional methods. Specifically, both human data and simulations show that including confidence probability judgments for just 20 trials can yield psychometric parameter estimates that match the precision of those obtained from 100 trials using conventional analyses. Such an efficiency advantage would be especially beneficial for tasks (e.g., taste, smell, and vestibular assays) that require more than a few seconds for each trial, but this potential benefit could accrue for many other tasks.thresholds; decision-making; confidence rating; confidence calibration MEASURING THRESHOLDS IS PROBABLY the most common psychophysical procedure in use today; applications range from experimental psychology to neuroscience to economics to engineering. Fitting psychometric functions using categorical data analyses (Agresti 1996) that describe the relationship between a stimulus characteristic (e.g., amplitude) and a subject's forced-choice categorical responses provides a standard approach used to estimate thresholds (Green and Swets 1966; Macmillan and Creelman 2005).A recent comprehensive analysis (Garcia-Perez and AlcalaQuintana 2005) concluded that only maximum likelihood methods should be used when accuracy and precision of psychometric function fit parameters is important and, furthermore, showed that more than 100 forced-choice trials are generally required to yield acceptable fit parameter estimates. Because such perceptual threshold tests are common and because many trials are needed to yield accurate and precise psychometric fits, studies spanning 50 yr (Garcia