Visual Salience Controls the Speed of Evidence Accumulation in Value-Based Decisions by Rats.

Studies of visual discrimination learning decision making in rodents, particularly those using visual cues, can confound the effects of cue salience with reward value, making it difficult to determine which factor guides choice behavior. We addressed this issue using a two-alternative forced-choice task in which rats chose between visual cues associated with high or low sucrose rewards. After initial training with high (16 LEDs) and low (1 LED) luminance cues, we introduced a novel cue of intermediate luminance (4 LEDs) in a "luminance shift" test, keeping the associated reward values constant. We found that while rats maintained a preference for the higher-value option, the introduction of a perceptually more similar cue consistently reduced choice preference and eliminated latency differences compared to baseline. Using drift diffusion modeling, we determined that the luminance shifts primarily caused a reduction in the drift rate (the speed of evidence accumulation), reflecting increased difficulty in cue discrimination. This finding suggests that the visual salience of the options dictates the efficiency of evidence accumulation in value-based decisions. Furthermore, this effect on drift rate is notable because it shows a dissociation from our previous work (Palmer et al., 2024), where prefrontal cortex inactivation specifically affected the decision threshold but not the drift rate. Our results demonstrate that the relative salience of visual stimuli influences deliberation, with low-level perceptual features shaping the computational dynamics of value-based choice. Our findings clarify the distinct contributions of sensory input and prefrontal function in the decision process. Significance Statement: This study reveals that visual perception plays a crucial role in an animal's value-based decisions. We trained rats to make visually guided choices and found that relative differences in the brightness of the stimuli affects how quickly the rats made decisions and how often they chose a higher-value option. Our findings, together with a recent study on the role of the prefrontal cortex in value-guided decisions (Palmer et al., 2024), suggest that separate factors influence choice dynamics in rodents: visual salience affects the speed of deliberation, while prefrontal activity regulates caution. This study helps clarify how sensory and higher cognitive variables relate to the distinct computational components of the decision process.