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Abstract

Perceptual decisions not only depend on the incoming information from sensory systems but constitute a combination of
current sensory evidence and internally accumulated information from past encounters. Although recent evidence
emphasizes the fundamental role of prior knowledge for perceptual decision making, only few studies have quantified the
relevance of such priors on perceptual decisions and examined their interplay with other decision-relevant factors, such as
the stimulus properties. In the present study we asked whether hysteresis, describing the stability of a percept despite a
change in stimulus property and known to occur at perceptual thresholds, also acts as a form of an implicit prior in tactile
spatial decision making, supporting the stability of a decision across successively presented random stimuli (i.e., decision
hysteresis). We applied a variant of the classical 2-point discrimination task and found that hysteresis influenced perceptual
decision making: Participants were more likely to decide ‘same’ rather than ‘different’ on successively presented pin
distances. In a direct comparison between the influence of applied pin distances (explicit stimulus property) and hysteresis,
we found that on average, stimulus property explained significantly more variance of participants’ decisions than hysteresis.
However, when focusing on pin distances at threshold, we found a trend for hysteresis to explain more variance.
Furthermore, the less variance was explained by the pin distance on a given decision, the more variance was explained by
hysteresis, and vice versa. Our findings suggest that hysteresis acts as an implicit prior in tactile spatial decision making that
becomes increasingly important when explicit stimulus properties provide decreasing evidence.