Correspondence Between Haptic and Visual Perception of Stand-on-ability: Do Hills Look as Steep as they Feel?

Vision and haptics play a central role in perceiving environmental layout to guide action. Hajnal, Wagman, Doyon, and Clark (2016) demonstrated that visual perception of stand-on-ability is accurate compared to action capabilities, whereas haptic perception of stand-on-ability reliably underestimates action capabilities. This finding contradicts Gibson’s (1979) theory of equivalence in perceptual systems, which suggests that perception should be equivalent regardless of modality. Previous comparisons of visual and haptic perception tested the modalities in isolation. The current experiment directly compares visual to haptic perception of stand-on-ability by using one perceptual system to estimate the other. Observers viewed a surface set to a discrete angle and attempted to match it haptically with a continuously adjustable surface occluded by a curtain, or felt an occluded surface set to a discrete angle then matched it visually with a continuously adjustable visible surface. Results indicated that visual and haptic perceptions of stand-on-ability are equivalent across some measures and analyses: no differences were found between visual, haptic, and action boundaries. Additionally, matching judgments were scaled similarly across conditions. However, some differences do exist and are modulated by action measures of body posture. Such differences demand a recasting of the question regarding equivalence. The correspondence of perceptual systems and the complex intertwining in the perception-action cycle are discussed