When in Doubt, Touch Is More Convincing Than Vision.

We sometimes feel compelled to touch objects after having looked at them. Is this because touch gives us more accurate information, or is it simply because we tend to trust what we feel more than what we see? To disentangle these possibilities, participants were subjected to a variant of the 'Vertical-Horizontal' illusion where the length of a vertical bar is consistently overestimated relative to the length of a horizontal bar. Our variant focuses on points of subjective equality where the bars almost look the same, and possesses two key characteristics: it creates ambiguity as stimuli can be subjectively similar yet objectively distinct and operates both in vision and touch. In a forced resampling bimodal experiment, participants inspected the stimuli using both vision and touch, judged which bar appeared longer, and rated their confidence. They then re-examined the same objects using either vision or touch, as instructed, and provided a second judgement with another confidence rating. Resampling did not significantly improve the overall accuracy, but participants were more likely to change their mind when using touch. In a second, free resampling bimodal experiment, participants chose their preferred modality for reinspection. Neither modality led to more accurate responses, but participants chose to resample by touch increasingly more frequently when the vertical and horizontal bars' lengths were closer in perceived size, leading to higher ambiguity. Additionally, they were more likely to change their mind under these ambiguous conditions. These findings suggest a selective bias toward touch in case of ambiguity, even when it offers no objective advantage over vision.