Effects of surrounding sensory evidence on central visual confidence

During the generation of visual confidence, the metacognitive system evaluates sensory evidence available in the stimulus and task. Typically, the stimulus is a small image within central vision. In the present study, we report a novel "contextual effect" of surrounding sensory evidence, despite being irrelevant to the central stimulus and task, on central confidence judgments. Experiments were conducted online with participants being recruited on CloudResearch and Amazon MTurk. On each trial, observers performed an orientation-discrimination task on a central stimulus (sine-wave gratings tilted -30 or +30 degrees from vertical), and then rated their confidence on the task using an on-screen slidebar. Surrounding the central stimulus was an annulus with horizontal gratings. We manipulated sensory evidence strength in this surrounding stimulus by varying the grating contrast (.30 or .01) against a fixed noise contrast (1.00). Participants were explicitly told to ignore the surrounding stimulus and focus on performing the perceptual and metacognitive tasks on the central stimulus only. In Experiment 1 (n=100, 4 between-subjects difficulty levels), perceptual accuracy remained constant between strong and weak surrounding sensory evidence. Interestingly, at the difficulty level resulting in around .82 of perceptual accuracy (n=25), central confidence ratings were higher when surrounding sensory evidence was strong than when it was weak (p=.0005, Cohen’s d=0.73). In Experiment 2 (n=23), we replicated this contextual effect (p=.0008, Cohen’s d=0.81) when participants reported both confidence and visibility on the central stimulus. In Experiment 3 (n=21), when participants rated central visibility only instead of confidence, visibility was constant between weak and strong surrounding evidence (Cohen’s d=0.12 , BF10=0.26), suggesting that the contextual effect cannot be explained by changes in central visibility. Our findings suggest that the metacognitive system could generalize sensory evidence in a task-irrelevant stimulus in the surrounding to the central stimulus when producing confidence judgments for the central task.