TACTILE IMPAIRMENTS CANNOT EXPLAIN THE EFFECT OF AGE ON A GRASP AND LIFT TASK

This experiment addressed the often-posed theory that age-related decl ines in manual dexterity result from diminished tactile function. We m easured the time 'young' subjects (n=33; mean=45 years) and 'old' subj ects (n=33; mean=74 years) needed to grip (thumb and index finger), li ft, and transport a small metal sphere when vision was permitted and w hen blindfolded. Subjects began each trial by reaching for the sphere and were instructed to complete the entire task quickly. In the absenc e of visual information, placement of the finger and thumb for a secur e grip and lift cannot be performed efficiently without tactile inform ation. If age-related tactile changes are functionally significant for this task, then without visual information the 'old' group should sho w a disproportionate increase in the duration of the grip and lift pha se of the task compared to the 'young' group. Perceptual thresholds fo r tactile pressure stimuli (Semmes-Weinstein filaments) confirmed well -known age-related changes. Age and vision effects were manifest mainl y during the grip-lift phase (time from object contact to lift-off fro m its support surface), with the expected finding that the 'old' group required more time than 'young' group, regardless of visual condition . The main finding was that the 'grip-lift' duration in the 'no-vision ' condition was about twice the duration observed in the 'vision' cond ition for both age groups (ratios of 2.1 and 2.3 for 'young' and 'old' , respectively). This similar relative slowing for the two groups fail s to support the hypothesis that old adults' ability to grip and lift the object was limited by changes in the availability or use of tactil e information.