Does Confidence Use a Common Currency Across Two Visual Tasks?

Observers typically know about their own uncertainty during simple perceptual decisions: Better performance is linked to greater confidence in being correct (e.g., Fleming, Dolan, & Frith, 2012; Peirce & Jastrow, 1884; Yeung & Summerfield, 2012). However, there are many outstanding issues concerning how observers evaluate their confidence, an ability we refer to here as metacognition. At the processing level, computation of confidence could take place early (Baranski & Petrusic, 1994; Zylberberg, Barttfeld, & Sigman, 2012) or late (Pleskac & Busemeyer, 2010) during the decision process. Here, we focus on the representation level of confidence. More specifically, we report an experiment in which we investigated whether confidence is represented in a taskspecific or a generic (task-independent) format. Although conceptually very different, these two possibilities (task-specific vs. generic format) are not easily distinguishable via confidence ratings. Consider an orientation discrimination task: Observers judge the tilt of a bar as clockwise or counterclockwise relative to vertical and then rate their confidence in that judgment. The confidence rating could reflect the absolute tilt estimated in degrees (task-specific format) or, alternatively, the probability of success given this estimate (task-independent confidence). Critically, however, according to traditional signal detection theory (Green & Swets, 1966), these two quantities are perfectly correlated and indistinguishable (see Mathematical Appendix in the Supplemental Material available online). We therefore took another approach to address this question. In a computerized experiment, observers (N = 35) performed two visual tasks (orientation and spatialfrequency discrimination) on Gabor stimuli (for details on the method, see Supplementary Methods in the Supplemental Material). On each trial, two Gabor stimuli were presented in succession, and observers judged the second orientation as clockwise or counterclockwise relative to the first orientation, or judged the spatial frequency of the second stimulus as higher or lower than the spatial frequency of the first stimulus. The tasks were known in advance and manipulated across blocks. After every pair of trials, observers made a comparative judgment of their confidence (Barthelmé & Mamassian, 2009, 2010), indicating the trial on which they felt they were more likely to have been correct. In two blocks, the same task was performed on all trials, so that confidence comparisons were for the same task (within-task condition); in the other two blocks, the task alternated between trials, so that confidence comparisons were for pairs of trials involving different tasks (across-task condition). If confidence is task-specific, then comparing confidence across two different tasks should be harder (i.e., observers should be less able to separate high-performance from low-performance trials) than comparing confidence across two instances of the same task. Alternatively, if confidence is accessed as an abstract and task-independent quantity (e.g., success probability), then comparing confidence in two decisions should not depend on whether the same task was performed. We constructed psychometric curves describing the proportion of responses indicating counterclockwise rotations in the orientation task or increase in spatial frequency in the frequency task, as a function of the angular difference between the two orientations or the log-ratio of the two spatial frequencies. We quantified performance via sensitivity (i.e., the slope of the psychometric curve; see Psychometric Analyses in the Supplemental Material). We measured metacognitive ability as the change in sensitivity from low-confidence to high-confidence trials, by using the observers’ confidence-comparison response for each trial pair to classify one trial as high confidence and the other as low confidence. As expected, sensitivity increased with 528956 PSSXXX10.1177/0956797614528956de Gardelle, MamassianConfidence Comparison Across Tasks research-article2014