Heaviness perception. IV. Weight x aperture -1 as a heaviness model in finger-grasp perception.

The present study verified that a simple division of Weight/Aperture (W/A) from information obtained from the individual cubes could describe perceived heaviness when pairs of cubic objects were haptically held one-by-one for comparison utilizing a thumb/index finger grasp. To test the effect of W/A, 15 subjects judged the heaviness between a pair of cubes in three experimental conditions with all visual and material input blocked: (1) cubes with similar ratios, but different weights; (2) cubes with different ratios, but of the same weight; and (3) cubes with dissimilar ratios and weights. The largest percentage of errors (67.4%) was made when objects with similar ratios but different weights were presented, because subjects tended to perceive these objects as being of equal weight. In the condition "equal weight and different ratio", the percentage of correct responses (17.7%) was relatively small, as the subjects tended to perceive the objects as being of different weights. These results strongly suggest that the W/A ratio is an authoritative model to explain human performance in the process of discriminating heaviness. The division model is proposed as Weight x Aperture(-1) on the basis of a recently expounded concept of multiplicative neural circuits.