Date created: | Last Updated:

Category: Project

Description: _ 2AFC is recommended as to “use 2AFC whenever possible (Brady et al., 2023).” But, in 2AFC task, equal variance is assumed (Brady et al., 2023). Distribution of sensation of a signal stimulus is determined by its mean and variance (or standard deviation). Without the equal variance assumption, distribution for a signal stimulus cannot be determined. If your sensitivity measure d' was estimated by the well-known formula (7.2) in Hautus et al. (2022) in the case of unequal variance , it may be contaminated. For the indeterminacy, check the file Est_Mu_Sgm.pdf in the Files box below. Probability of correct response Pc in 2AFC task depends strongly on both the mean and variance for a signal stimulus, which is shown by a contour graph in the file PcContour.pdf in the Files box below. It is said that unequal variance signal detection models provide a good account of ROC curves (Brady et al., 2023). To apply an unequal variance model to 2AFC task, two pairs of stimuli, (noise, noise) and (signal, signal), were added to the pairs, (noise, signal) and (signal,noise) , of the standard 2AFC task, and rating of judgment was introduced. From rating data of the pair (noise,noise) , boundaries of categories of rating can be estimated. From rating data of the pair (signal, signal) and estimates of category boundaries, variance of sensation of the signal stimulus can be estimated. From these estimates and data of pairs of (noise, signal) and (signal, noise), mean of sensation of the signal stimulus can be estimated. This is an intuitive explanation. Statistical analysis of the data by the extended 2AFC rating task is done by Bayesian method based on a stochastic model. A model of the extended 2AFC rating task is presented in the file Model.pdf in the Files box below. Program files for Bayesian analysis of data from the extended 2AFC rating task are archived in the file prgs_doc.zip in the Files box below. The program is explained in the pdf file Program.pdf in the Files box below. The script files are also presented at the website http://y-okamoto-psy1949.la.coocan.jp/Python/en2/Ex2AFCR/ _ Reference Brady, T. F., Robinson, M. M., Williams, J. R., & Wixted, J. T. (2023). Measuring memory is harder than you think: How to avoid problematic measurement practices in memory research. Psychonomic Bulletin & Review, 30, 421-449. Hautus, M. J., Macmillan, N. A., & Creelman, C. D. (2022). Detection theory: A user's guide, third edition. Routledge. _