Aging, visual intermittency, and variability in isometric force output.

We tested the hypothesis that increases in minimal visual motor processing (VMP) time in older adults contribute to age-related increases in force variability. We manipulated the intermittency rate of visual information feedback over a 100-fold range as young (20-29 years old) and old (60-79 years old) participants produced isometric force output to a visually presented target. The force output of the old adults was more variable and more structured, and the old adults had an increase in minimal VMP time compared with the young adults. However, there was no significant relation between VMP time and force variability. We propose that the age-related changes in variability are a reflection of information-processing capacity limitations and not a decrement in minimal VMP time.