Mice learned to perform a visual decision-making task where they detected the presence of a visual grating to their left or right, and reported the perceived location by turning a steering wheel (The International Brain Laboratory et al., 2020). The stimulus moved with the wheel rotation, remaining on the screen until feedback. For each correct response, mice received 1.5 μl of 10% sucrose water. Trial duration was estimated from stimulus onset to the delivery of feedback (either the water reward or a white noise indicating an error). Visual stimuli were presented at variable contrast (0–100%), allowing us to fit psychometric functions to quantify each animal’s behavior. The duration of each session was dependent on the engagement of the animal, which was determined through automated criteria (The International Brain Laboratory et al., 2020; see their Fig. 1e and Supplemental Table 3). Early in training, animals were supplemented toward the institutional minimum of 1 ml/d or 40 μl/g of body after the experimental session. After they became proficient at the behavioral task, they usually performed enough trials to fully earn their water requirement in the rig on weekdays.

A mouse was considered proficient at this basic task once its behavior met a set of prespecified criteria: >400 trials performed in each of the last three sessions; accuracy >80% correct on easy trials in each of the last three sessions; and on a psychometric function fit on those three sessions combined, a threshold of <19, absolute bias of <16, and lapses <0.2 (The International Brain Laboratory et al., 2020; Appendix 2). Extended Data Figure 3-1E–I shows behavioral data and psychometric function fits from the 3 d leading up to the animal being trained. The psychometric function has the following form:

where x is the signed visual contrast, μ is a stimulus-independent bias term, σ is the steepness of the psychometric function, and γ and λ are lapse rates. After reaching task proficiency, animals proceeded to a more complex full task, where they combined visual information with an asymmetric stimulus prior that switched between blocks (The International Brain Laboratory et al., 2020).

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