Abstract
The contribution of non-sensory information processing to perceptual decision making is not fully understood. Choice biases have been described for mice and humans and are highly prevalent even if they decrease rewarding outcomes. Choice biases are usually reduced by discriminability because stimulus strength directly enables the adjustments in the decision strategies used by decision-makers. However, choice biases could also derive from functional asymmetries in sensory processing, decision making, or both. Here, we tested how particular experimental contingencies influenced the production of choice biases in mice and humans. Our main goal was to establish the tasks and methods to jointly characterize psychometric performance and innate side-choice behavior in mice and humans. We implemented forced and un-forced visual tasks and found that both species displayed stable levels of side-choice biases, forming continuous distributions from low to high levels of choice stereotypy. Interestingly, stimulus discriminability reduced the side-choice biases in forced-choice, but not in free-choice tasks. Choice biases were stable in appearance and intensity across experimental days and could be employed to identify mice and human participants. Additionally, side- and alternating choices could be reinforced for both mice and humans, implying that choice biases were adaptable to non-visual manipulations. Our results highlight the fact that internal and external elements can influence the production of choice biases. Adaptations of our tasks could become a helpful diagnostic tool to detect aberrant levels of choice variability.
Highlights
Through psychophysics, experimenters can estimate perceptual thresholds of detection and how changes in stimulus strength lead to perceptual changes
We found that increasing contrast and decreasing stimulus similarity led to a robust increase in visual performance of the mice (SSIM, F = 35.3, P < 0.01, n = 8; center panel, Figure 1C) and humans (k, F = 273, P < 0.001, n = 10; dark cyan dots, right panel, Figure 1C)
Despite the fact that structural similarity among them (SSIM) strongly controlled the visual discrimination performance in this task, we found that choice bias (Kolmogorov–Smirnov test, P > 0.12 for all cases; RM ANOVA test, F = 0.05, P > 0.5) and alternation (Kolmogorov-Smirnov test, P > 0.14 for all cases; RM ANOVA test, prob. alternation: F = 0.16, P > 0.5) probabilities were similar across all SSIM values (Figures 3C,D)
Summary
Experimenters can estimate perceptual thresholds of detection and how changes in stimulus strength lead to perceptual changes. The exact contribution of nonsensory information processing to perceptual decision making is not fully understood (Ahissar et al, 2009; Resnik et al, 2011; Trevino et al, 2013). Observers can present sensory and non-sensory biases in their choices (Linares et al, 2019). Throughout this work, we will refer to the term choice bias as the (rational or irrational) tendency to choose one alternative over another. Stereotypical choice behavior exhibits low variability from trial to trial and has no apparent goal or function (Langen et al, 2011; Novak et al, 2016). Choice biases can be identified as a horizontal shift in the psychometric function
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