The material-weight illusion revisited

Experiment 1 documents modality effects on the material-weight illusion for a low-mass object set (58.5 g). These modality effects indicate that the m aterial-weight illusion is principally a haptically derived phenomenon: Hap tically accessed material cues were both sufficient and necessary for full- strength illusions, whereas visually accessed material cues were only suffi cient to generate moderate-strength illusions. In contrast, when a high-mas s object set (357 g) was presented under the same modality conditions, no i llusions were generated. The mass-dependent characteristic of this illusion is considered to be a consequence of differing grip forces. Experiment 2 d emonstrates that the enforcement of a firm grip abolishes the low-mass mate rial-weight illusion. Experiment 3 documents that a firm grip also diminish es perceptual differentiation of actual mass differences. Several possible explanations of the consequences of increasing grip force are considered.