How important are changes in body weight for mass perception?

It is often assumed that weight judgements depend primarily on the effort experienced in lifting an object against a 1-G force. Changes in effort and in other weight-cues certainly alter apparent heaviness; but there is a tendency towards mass-constancy when such changes are unrelated to mass. Under water or altered G, both the observer's body and other objects change their effective weight: the change in the former probably provides a cue to the latter. Mass-constancy increases with opportunity for adaptation to the change, leaving a negative aftereffect on return to normal circumstances. The discrimination of weight or mass also deteriorates with sudden changes in arm weight, just as it does with other types of maladaptation and with a reduction in sensory cues. The relative importance of arm weight and other factors has not been precisely measured, but experiments in prolonged spaceflight should help to elucidate the issue.