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

Studies of visual discrimination in rodents can confound the effects of cue salience with reward value, making it difficult to determine which factor guides choice behavior. We examined this issue by testing how changes in relative salience affect decision dynamics in rats performing 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 and low luminance cues, we introduced a novel cue of intermediate luminance as a "luminance shift" test. The intermediate luminance cue substituted for either the brighter or dimmer cue and had the same reward value as the cue that it replaced. 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 relative salience of the options determines the efficiency of evidence accumulation in value-based decisions. Furthermore, this effect on drift rate shows a dissociation from our previous work (Palmer et al., 2024), where prefrontal cortex inactivation specifically affected only the decision threshold. Our results demonstrate that relative salience 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 StatementThis study reveals that changes in the relative salience of visual stimuli shape the computational dynamics of value-based decisions. We trained rats to make visually guided choices and found that relative differences in the brightness of the stimuli affect 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.