Magnitude-sensitive reaction times reveal non-linear time costs in multi-alternative decision-making

Abstract

Optimality analysis of value-based decisions in binary and multi-alternative choice settings predicts that reaction times should be sensitive only to differences in stimulus magnitudes, but not to overall absolute stimulus magnitude. Yet experimental work in the binary case has shown magnitude sensitive reaction times, and theory shows that this can be explained by switching from linear to multiplicative time costs, but also by nonlinear subjective utility. Thus disentangling explanations for observed magnitude sensitive reaction times is difficult. Here for the first time we extend the theoretical analysis of geometric time-discounting to ternary choices, and present novel experimental evidence for magnitude-sensitivity in such decisions, in both humans and slime moulds. We consider the optimal policies for all possible combinations of linear and geometric time costs, and linear and nonlinear utility; interestingly, geometric discounting emerges as the predominant explanation for magnitude sensitivity.

Thoughts from the forest floor: a review of cognition in the slime mould Physarum polycephalum

“…Few studies examine ternary or higher-order decision-making. In a notable exception, Physarum plasmodia were given a choice between 3 food sources that were all identical in value (Marshall et al 2022 ). When the sum of the quality of all the food sources was low (low ‘magnitude’), plasmodia took significantly longer to make a decision than when the options had high magnitude; an identical result was recorded by Dussutour and colleagues ( 2019 ) in a binary-choice scenario.…”

Heuristic Search of Heuristics

“…We consider a typical decision-making task [17,22,13]; participants need to decide which of two gray patches presented on a computer screen is brighter, Figure 1. Specifically, during each trial, participants are presented with a fixation cross at the centre of the screen, and, equidistant from the fixation cross, two stimuli, in the form of homogeneous, round, grey patches on a black background.…”