Haptic perception of volume and surface area of 3-D objects

Abstract

Haptic perception of volume (Experiment 1) and surface area (Experiment 2) was studied with tetrahedrons, cubes, and spheres as stimuli (2-14 cm 3 ). The results of Experiment 1 showed that subjects perceived a tetrahedron to be larger in volume than either a cube or a sphere of the same physical volume and that they perceived a cube to be larger than a sphere. This pattern was independent of object size. The biases were smaller in conditions with mass information than in those without. The average biases in the different conditions ranged from 7% to 67%. Analyses revealed that the subjects apparently based their volume judgments on the surface area of objects. Experiment 2 showed that surface area itself could be perceived accurately, almost independently of the objects' shape. Experiment 3 investigated volume perception of objects in the absence of surface area (wire-frame objects) and showed larger biases than those observed with solid objects. With wire-frame objects, the maximal distance between two vertex points was probably the dimension on which the volume judgment was based. In conclusion, haptic volume perception of geometric objects has to be inferred from other object properties, but surface area can be perceived unbiased.

Characterization of the Haptic Shape-Weight Illusion with 3D Objects

“…Kahrimanovic et al [6] demonstrated that a tetrahedron was perceived as being larger in volume than a cube or a sphere of the same physical volume, and that a cube was perceived as larger than a sphere. The biases measured in that study are shown in Table 1.…”

“…From this, we can predict that a sphere will be perceived as heavier than a cube or a tetrahedron of the same physical mass, and that a cube will be perceived as heavier than a tetrahedron. The magnitude of these biases can be predicted by substituting the biases found in [6] for the ratio V 2 =V 1 in (1). The predicted direction and magnitude of these biases are shown in Table 1.…”

“…The stimuli were sets of tetrahedrons, cubes, and spheres, which were the same as those from our previous study on volume perception [6]. The weight of these brass stimuli ranged from 16.8 to 117.6 g, in steps of 8.4 g (i.e., 1 cm 3 ).…”

“…The weight and volume of these references are presented in Table 2. These references were the same as in our previous study on haptic volume perception [6]. In that study, the selection of the reference stimuli was based on pilot studies showing that a tetrahedron was matched to both a larger cube and a larger sphere and that a cube was matched to a larger sphere.…”

“…During the experiments, vision was not allowed in order to study a purely haptic shape-weight illusion. The nature of this illusion could be predicted from the haptic size-weight [5] and shape-size [6] illusions. Ellis and Lederman [5] showed that a physically smaller object is perceived as being heavier: a doubling of the volume of cubes with the same physical weight resulted in a 26 percent decrease of their estimated weight.…”