Vision and touch interact in spatial perception. How vision exerts online influences on tactile spatial perception is well-appreciated, but far less is known about how vision modulates tactile perception offline. Here, we investigated how visual cues exert both online and offline biases in bimanual tactile spatial perception. In a series of experiments, participants performed a 4-alternative forced-choice tactile detection task in which they reported the perception of peri-threshold taps on the left hand, right hand, both hands, or no touch (LRBN). Participants initially performed the LRBN task in the absence of visual cues. Subsequently, participants performed the LRBN task in blocks comprising non-informative visual cues that were presented on the left and right hands. To explore the effect of distractor salience on the visuo-tactile spatial interactions, we varied the brightness of the visual cues such that visual stimuli associated with one hand were consistently brighter than visual stimuli associated with the other hand. We found that participants performed the tactile detection task in an unbiased manner in the absence of visual distractors. Visual cues biased tactile performance, despite an instruction to ignore vision, and these online effects tended to be larger with brighter distractors. Moreover, tactile performance was biased toward the side of the brighter visual cues even on trials when no visual cues were presented during the visuo-tactile block. Using a modeling framework based on signal detection theory, we compared a number of alternative models to recapitulate the behavioral results and to link the visual influences on touch to sensitivity and criterion changes. Our collective results reveal the obligatory and systematic influences of vision on both online and offline tactile spatial perception. The nervous system appears to automatically leverage multiple sensory modalities to build representations and calibrate decision processes for bimanual tactile spatial perception.
The Right Hand Draws the Trees, But the Left Draws the Forest?
