Abstract
The role of changes of mind and multiple choices has recently received increased attention in the study of perceptual decision-making. Previously, these extensions to standard two-alternative tasks have been studied separately. Here we explored how changes of mind depend on the number of choice-alternatives. To this end, we tested 14 human subjects on a 2- and 4-alternative direction-discrimination task. Changes of mind in the participants' movement trajectories could be observed for two and for four choice alternatives. With fewer alternatives, participants responded faster and more accurately. The frequency of changes of mind, however, did not significantly differ for the different numbers of choice alternatives. Nevertheless, mind-changing improved the participants' final performance, particularly for intermediate difficulty levels, in both experimental conditions. Moreover, the mean reaction times of individual participants were negatively correlated with their overall tendency to make changes of mind. We further reproduced these findings with a multi-alternative attractor model for decision-making, while a simple race model could not account for the experimental data. Our experiment, combined with the theoretical models allowed us to shed light on: (1) the differences in choice behavior between two and four alternatives, (2) the differences between the data of our human subjects and previous monkey data, (3) individual differences between participants, and (4) the inhibitory interaction between neural representations of choice alternatives.
Highlights
Compared to the decisions we are faced with every day, for instance what to choose for lunch in the cafeteria, or which shirt to wear, decision-making in psychophysical experiments is typically reduced to the highly simplified conditions of two-alternative forced-choice (2AFC) tasks [1,2]
A lower threshold in the model caused faster reaction times and more changes of mind. This corresponds to the strong negative correlation we found between the mean reaction times of individual participants and the tendency to change their mind
Experimental data To study the relation of changes of mind to the number of choice alternatives, we asked naive human subjects to perform a random-dot motion (RDM) discrimination task with two and four possible directions of motion (Fig. 1)
Summary
Compared to the decisions we are faced with every day, for instance what to choose for lunch in the cafeteria, or which shirt to wear, decision-making in psychophysical experiments is typically reduced to the highly simplified conditions of two-alternative forced-choice (2AFC) tasks [1,2]. One classic example for such a 2AFC task is the random-dot motion (RDM) reaction-time paradigm, which allows investigating the temporal accumulation of evidence in order to reach a decision [3,4,5]. By definition, 2AFC tasks neglect important features of real-life decision-making such as: (1) choices between multiple alternatives and (2) choice reevaluation after an initial decision. Churchland et al [9] and Niwa and Ditterich [10] augmented the RDM task from binary to multiple choices. Churchland et al [9] tested monkeys on a 4-alternative RDM discrimination task and compared their behavioral and neurophysiological responses to the standard binary task. Participants occasionally switched from one direction to the other, ‘‘changing their mind’’
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