Humans exhibit substantial biases in their decision making even in simple 2-choice tasks but the origin of these biases remains unclear. We hypothesized that one source of bias could be individual differences in sensory encoding. Specifically, if one stimulus category gives rise to an internal evidence distribution with higher variability, then responses should optimally be biased against that stimulus category. Therefore, response bias may reflect a previously unappreciated subject-to-subject difference in the shape of the internal evidence distributions. We tested this possibility by analyzing data from three different 2-choice tasks (N = 443, 443, 498). We found that, for all three tasks, response bias moved in the direction of the optimal criterion determined by each subject’s idiosyncratic internal evidence variability. These results demonstrate that seemingly random variations in response bias can be driven by individual differences in sensory encoding and are thus partly explained by normative strategies.
Response bias reflects individual differences in sensory encoding
