Newly learned shape-colour associations show signatures of reliability-weighted averaging without forced fusion or a memory colour effect

Reliability-weighted averaging of multiple perceptual estimates (or cues) can improve precision. Research suggests that newly-learned statistical associations can be rapidly integrated in this way for efficient decision-making. Yet, it remains unclear if integration of newly-learned statistics into decision-making can directly influence perception, rather than taking place only at a decision stage. In two experiments, we implicitly taught observers novel associations between shape and colour. Observers made colour matches by adjusting the colour of an oval to match a simultaneously presented reference. As the colour of the oval changed across trials, so did its shape according to a novel mapping of axis ratio to colour. Observers showed signatures of reliability-weighted averaging – a precision-improvement in both experiments and reweighting of the newly-learned shape cue with changes in uncertainty in Experiment 2. To ask whether this was accompanied by perceptual effects, Experiment 1 tested for “forced fusion” by measuring colour discrimination thresholds with and without incongruent novel cues. Experiment 2 tested for a “memory colour effect”, observers adjusting the colour of ovals with different axis ratios until they appeared grey. There was no evidence for forced fusion and the opposite of a memory colour effect. Overall, our results suggest that the ability to quickly learn novel cues and integrate them with familiar cues is not immediately (within the short duration of our experiments, and in the domain of colour and shape) accompanied by common perceptual effects