THE ROLE OF HAPTIC VERSUS VISUAL VOLUME CUES IN THE SIZE WEIGHT ILLUSION

Three experiments establish the size-weight illusion as a primarily ha ptic phenomenon, despite its having been more traditionally considered an example of vision influencing haptic processing. Experiment 1 docu ments, across a broad range of stimulus weights and volumes, the exist ence of a purely haptic size-weight illusion, equal in strength to the traditional illusion. Experiment 2 demonstrates that haptic volume cu es are both sufficient and necessary for a full-strength illusion. In contrast, visual volume cues are merely sufficient, and produce a rela tively weaker effect. Experiment 3 establishes that congenitally blind subjects experience an effect as powerful as that of blindfolded sigh ted observers, thus demonstrating that visual imagery is also unnecess ary for a robust size-weight illusion. The results are discussed in te rms of their implications for both sensory and cognitive theories of t he size-weight illusion. Applications of this work to a human factors design and to sensor-based systems for robotic manipulation are also b riefly considered.