Perception of weight and volume of functional objects as judged by the sighted and blind

Summary The manner in which sighted, sighted-but-blindfolded, late-blind (subsequent to 7 years of age), and congenitally blind (blind since birth) persons employ physical parameters in determining weight and volume of functional objects was studied. Eight stimuli each having a unique combination of physical specifications were judged, using both a match and estimate procedure. The results indicated that information derived from mass, displacement, and density provides the basis for volumetric and weight judgements of sighted persons. Non-sighted individuals employ this information differently than do sighted persons. Likewise, individuals after 7 years of age retain information provided by early visual experience and thus may employ a combination of kinesthetic and visual cues. The results also show that sighted and late-blind groups may employ visual perception or memory in determining volume, whereas sighted-but-blindfolded persons and the congenitally blind may employ mass in volumetric tasks. All groups may employ mass (and perhaps density) in determining weight, and although the weight judgements of non-sighted groups correlate highly with mass, sighted subjects are more accurate in judgement (i.e. have the smaller constant error). Sighted subjects apparently employ a complex system in determining weight. Age at which blindness occurred and the number of years of blindness had no effect for the late-blind group.