Predictions from a model of global psychophysics about differences between perceptual and physical matches

Abstract

A well-known phenomenon is that "matched" successive signals do not result in physical identity. This phenomenon has mostly been studied in terms of how much the second of two signals varies from the first, which is called the time-order error (TOE). Here, theoretical predictions led us to study the more general question of how much the matching signal differs from the standard signal, independent of the position of the matching signal as the first or second in a presentation. This we call non-equal matches (NEM). Using Luce's (Psychological Review, 109, 520-532, 2002, Psychological Review, 111, 446-454, 2004, Psychological Review, 115, 601, 2008, Psychological Review, 119, 373-387, 2012) global psychophysical theory, we predicted NEM when an intensity z is perceived to be "1 times a standard signal x." The theory predicts two different types of individual behaviors for the NEM, and these predictions were evaluated and confirmed in an experiment. We showed that the traditional definition of TOE precludes the observation, and thus the study, of the NEM phenomenon, and that the NEM effect is substantial enough to alter conclusions based on data that it affects. Furthermore, we demonstrated that the custom of averaging data over individuals clearly leads to quite misleading results. An important parameter in this modeling is a reference point that plays a central role in creating variability in the data, so that the key to obtaining regular data from respondents is to stabilize the reference point. © 2012 Psychonomic Society, Inc.