Similarities and differences in the effects of different stimulus manipulations on accuracy and confidence

Visual stimuli can vary in multiple dimensions that affect accuracy and confidence in a perceptual decision-making task. However, previous studies have typically included just one or at most two manipulations, leaving it unclear how a wider set of manipulations may relate to each other. Here, we examine the similarities and differences between five different stimulus manipulations across two experiments. Subjects indicated whether a tilted Gabor patch was oriented clockwise or counterclockwise from 45°. In Experiment 1, we independently manipulated the size, duration, noise level, and tilt offset of the stimuli. In Experiment 2, we employed a 2x2x2x2 design jointly manipulating size, spatial frequency, noise level, and tilt offset of the stimuli. We found that manipulations of size, duration, noise level, and spatial frequency had remarkably similar effects on accuracy and confidence. In contrast, the tilt offset manipulation stood out by affecting accuracy more strongly than confidence. In addition, tilt offset exhibited supraadditive interaction with all other manipulations for both accuracy and confidence, whereas the remaining manipulations exhibited either no interactions or subadditive interactions with each other. Furthermore, tilt offset was also the only manipulation for which confidence in incorrect trials decreased with increasing difficulty, while all other manipulations exhibited the opposite trend. Overall, our results reveal a startling similarity between the effects of four very different stimulus manipulations and a prominent difference with a fifth manipulation. These results open the door for a priori predictions of how novel manipulations would affect accuracy and confidence.