Cross-modal adaptive matching for global psychophysics

This exploratory study investigates the effect of the elimination of stimulus role-based influences on cross-modal PSEs. In cross-modal matching of brightness and loudness, traditionally a "global" psychophysical paradigm is used, called magnitude production. One stimulus serves as the standard and the target stimulus’ intensity is adjusted by the subject to match the standard’s perceived intensity. This introduces an asymmetry in the experimental roles of the stimuli. The well-replicated regression effect shows a tendency of the adjustments/matches towards a mean magnitude of the presented stimulus range of the target. The theory of global psychophysics (Luce et al., 2010) assumes that the perceived intensities of the stimuli are judged against internal (respondent-generated) references, and that these references potentially depend on the role of the stimulus in the experiment (standard or target; Heller, 2021). By employing a 2AFC paired comparison task embedded in an adaptive staircase procedure, the adjustment of the comparison stimulus’ intensity are not performed by the participants but are instead implemented dynamically by the experimental program and remain obscured from the participants. Hence, stimulus roles are eliminated, and therefore role-independent reference intensities can be assumed in the model. With this experimental manipulation, the global psychophysics model (Heller 2021) will be fitted to the cross-modal PSE data to examine the resulting matching curves under role-independent reference intensities. A nonetheless occurring regression effect could be unambiguously attributed to another parameter of the model, the cognitive representation of the task W(1). A regression effect-like pattern would indicate a biased representation of the task, i.e. W(1) != 1. Furthermore, an estimation of the global psychophysics model from data collected with methods from local psychophysics, i.e. paired comparisons (Fechner, 1860) complements previous empirical approaches (Naumann, in preparation).