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bioRxiv · 10.1101/2025.11.02.686051

Perceptual Decoys Do Not Reliably Bias Choice: Boundary-Condition Evidence

Ibarra, D.·Suri, G.
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Abstract

The decoy effect occurs when adding an inferior third option biases choice between two others, even though the decoy is rarely chosen. While robust in value-based decisions, evidence in perceptual tasks is mixed. Using the rhesus-macaque paradigm from Parrish et al. (2015), we tested whether a perceptual decoy effect generalizes to humans. Participants (n = 50) completed 400 trials. Contrary to our preregistered prediction, we found no reliable decoy effect. Accuracy improved on the hardest trials (Level 1) when a decoy was present, response times were slower in decoy conditions than baseline, and accuracy was higher for tall versus wide rectangles, consistent with the vertical-horizontal asymmetry. The relatively wide spacing of stimuli may have reduced grouping and attentional clustering; because spacing was not manipulated, this remains a hypothesis for future tests. Results suggest that context effects in perceptual choice operate under narrower boundary conditions than in value-based domains.

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Ibarra, D., Suri, G.. 2025-11-04. Perceptual Decoys Do Not Reliably Bias Choice: Boundary-Condition Evidence. https://doi.org/10.1101/2025.11.02.686051

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