Abstract
Humans often have to use different decision criteria in different tasks such as when detecting a mosquito against a white versus a patterned wall. However, it is debated whether people can maintain independent criteria for different tasks. Early work uncovered suboptimal biases when multiple tasks are performed simultaneously, and concluded that in such situations people inadvertently use the same decision criteria across different perceptual tasks. On the other hand, these studies could not measure the criterion location directly and more recent work has questioned whether the same criteria are indeed used across different tasks. To resolve this debate, here we develop a new external noise paradigm that can objectively quantify criterion location across two tasks that optimally require very different criteria. Twenty-eight participants judged which of two overlapping distributions generated full-contrast stimuli of varying orientations. Critically, we included two different experimental conditions. In the Low Variability condition, the two distributions had similar means and low standard deviations (SDs), whereas in the High Variability condition, the distributions had dissimilar means and high SDs. The means and SDs in the two conditions were proportionate so that the tasks were equally difficult. Participants indicated the confidence in their responses and we examined whether the criteria for confidence were independent in the two conditions. We found strong evidence of “criterion attraction” where the criteria across the two conditions moved towards each other but did not become identical. On average, the criteria in each condition shifted by 24% with this effect appearing in every single participant. The criterion attraction led to a large and consistent confidence-accuracy dissociation in the absence of reaction time differences between the conditions. These results unify the seemingly disparate findings in the literature and establish a robust way of inducing dissociations between subjective and objective performance.