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When do haptic estimates of discordant visual-haptic size capture vision? Observers looked at a square through a minifying lens (50%) whilst they simultaneously touched the square from below through a hand-concealing cloth. Their subsequent match of the square's size, rendered by touching a set of comparison squares, was haptically biased when they practised estimating the square's size (Experiment 1, N = 72), when they actively explored rather than passively touched the square (Experiment 2, N = 24), but not when they were uninformed before inspecting the square that they would estimate its size (Experiment 3, N = 36). Evidently, the haptic exploratory strategies occasioned by the practise influenced the integration of the felt size and the seen size by weighing the haptic input more than the visual input, and this weight shifting manifested itself by strengthening haptic capture.
Keywords: visual perception, tactual perception, sensory integration, perceptual distortion
Often multiple sensory modalities are available for perceiving some attributes of physical objects. An object's size, for instance, can be estimated using either touch or vision. When simultaneously touched and seen, however, what is the object's perceived size? Does the visual size, the haptic size, or the combination of both determine the perceived size? Can repeated haptic estimates, haptic exploratory strategies, and prior knowledge of the response demands influence the relative merging of vision and touch? The present experiments investigated these factors (1) to explain opposing findings in the "size-conflict" paradigm pioneered by Rock and Victor (1964) and (2) to incorporate those findings into recent developments in understanding intersensory integration (Bresciani, Dammeier, & Ernst, 2006; Ernst & Biilthoff, 2004; Hillis, Ernst, Banks, & Landy, 2002).
A common procedure for examining intersensory relations involves producing discordant sensations about the very same physical property. Rock and Victor (1964; see also Rock, 1966; Rock & Harris, 1967), for example, had observers manually grasp a square from below through a hand-concealing cloth and view the same square from above through a lens that halved its visual size. After visually and haptically inspecting the square for 5s, observers selected, either by sight or by touch, a matching square from amongst a set of comparison squares. Because the haptic comparison matched the square's illusory visual size, Rock and Victor concluded that the felt...