Abstract
In the study of perceptual decision making, it has been widely assumed that random fluctuations of motion stimuli are irrelevant for a participant’s choice. Recently, evidence was presented that these random fluctuations have a measurable effect on the relationship between neuronal and behavioral variability, the so-called choice probability. Here, we test, in a behavioral experiment, whether stochastic motion stimuli influence the choices of human participants. Our results show that for specific stochastic motion stimuli, participants indeed make biased choices, where the bias is consistent over participants. Using a computational model, we show that this consistent choice bias is caused by subtle motion information contained in the motion noise. We discuss the implications of this finding for future studies of perceptual decision making. Specifically, we suggest that future experiments should be complemented with a stimulus-informed modeling approach to control for the effects of apparent decision evidence in random stimuli.
Highlights
A key question in perceptual decision making is how the brain rapidly makes decisions to categorize sensory input
The random-dot motion (RDM) task is a motion direction discrimination task, usually applied in two-alternative forced choice settings, where participants must decide about the net motion direction of a cloud of seemingly randomly moving dots presented on the screen
Model Comparison (Exact Input Model vs. Drift Diffusion Model) Here, we focus on a model comparison question: does equipping a drift diffusion model (DDM)-like model with the motion cues makes it a better model to explain the behavioral data? In other words, is the EXaM a better model to explain the participants’ responses at the 0% coherence level than the DDM? To address this question, we formally compared the two models using a two-way Bayesian model comparison (Penny et al, 2010)
Summary
A key question in perceptual decision making is how the brain rapidly makes decisions to categorize sensory input. The 0% coherence condition is typically used for specific experimental reasons, e.g., to control for the effect of trial-to-trial stimulus variation on neural measurements (Britten et al, 1992, 1996; Bair and Koch, 1996; Cohen and Newsome, 2009) and Stochastic Stimuli Influence Perceptual Choices has been used in theoretical studies to model neural or behavioral responses when there is no net motion evidence (Wang, 2002; Wong et al, 2007; Wimmer et al, 2015). In these studies, one typically implicit assumption about 0% coherence stimuli, by way of their construction, was that the expected net motion over stimulus presentation time, i.e., the accumulated motion cues, is zero across the presentation time of the stimulus (Britten et al, 1993, 1996). When using this implicit assumption, the concrete random instantiation of a RDM stimulus in a single trial is considered uninformative about the choice made by the participant, because the stimulus on average does not contribute decision-relevant information and should not influence decisions
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