Mengting Fang¹ (mtfang@sas.upenn.edu), Alan Stocker; ¹University of Pennsylvania

Perceptual decision making often involves integrating evidence over time. Our prior work showed that this process is governed by a resource-rational principle where the brain actively balances task performance with cognitive effort. For a fixed level of evidence reliability, participants maintained a stable trade-off strategy. However, our previous study did not test whether participants adapt their strategy when evidence reliability changes. Given the brain’s ability to actively control the accumulation process, we considered two competing hypotheses: (1) the system increases encoding precision when evidence is reliable and reduces it when evidence is less reliable, or (2) the opposite, the system increases encoding precision to compensate for low-quality evidence and lowers it when reliability is high. To test these hypotheses, we conducted a visual estimation task where participants inferred the angular position of an unknown source from 8 sequentially presented, normally distributed stimulus samples. We manipulated sampling noise across three levels. The testing phase included 9 blocks across 3 visits in a balanced Latin square design, with trial-by-trial feedback and a performance-dependent bonus. Noise levels were not disclosed in each block. Results showed that participants' estimation performance decreased as sampling noise increased. Fits with our normative resource-rational model showed that encoding precision scaled with sampling noise, supporting our first hypothesis that the brain actively adjusts encoding precision to match external sensory reliability. Circular regression analysis further revealed that the variance of normalized temporal weights decreased as noise increased, reflecting shifts in temporal weighting strategies (e.g., from recency to uniform/primacy). Changes in trade-off parameters also showed greater tolerance for effort costs under higher noise, partly offsetting the reduced encoding precision. Together, these findings demonstrate that evidence accumulation is governed by a performance-effort trade-off strategy that adapts sensory encoding precision to the reliability of the evidence.

Acknowledgements: This work was supported by the NSF CRCNS grant IIS-1912232 to A.A.S