Different stimulus manipulations produce dissociable confidence-accuracy relationships

A central goal in visual metacognition is to uncover the underlying computations that give rise to our sense of subjective confidence. Achieving this goal necessitates an understanding of how confidence changes in response to various manipulations. However, existing studies have predominately relied on a single stimulus manipulation under the tacit assumption that different manipulations are likely to have equivalent effects on confidence. Here, we test this assumption by including four distinct stimulus manipulations within a single experiment. Subjects judged the orientation (clockwise vs. counterclockwise from 45°) of Gabor patches. The stimuli varied in (1) size (2.5, 5, and 7.5° visual angle), (2) duration (33, 100, and 500 ms), (3) noise contrast (.1, .75, and .9), and (4) orientation (T/2, T, 2T, where T is the individualized threshold obtained by a staircase procedure). We found that the four manipulations produced vastly different effects on accuracy and confidence. Specifically, the size and noise contrast manipulations had a small effect on accuracy but a substantial effect on confidence. Conversely, the orientation manipulation greatly affected accuracy but had only a modest influence on confidence. The orientation manipulation stood out in yet another aspect: it was the only manipulation for which confidence for incorrect trials was higher for the more difficult compared to the easier conditions. The remaining three manipulations exhibited the opposite pattern. We speculate that these effects were driven by orientation being the only manipulation not immediately obvious to the observers. These results clearly demonstrate that different stimulus manipulations yield extensive differences in the confidence-accuracy relationship. Our findings challenge prominent models of confidence that assume a single, stereotypical relationship between confidence and accuracy.