May 1, 2000

lthough scientists have documented many age-related changes, little has been done to examine how aging affects a person's sense of touch.

In a recent study, a team of UConn researchers examined dynamic touch - involved when an object is grasped firmly and then swung or wielded - in elderly volunteers by testing their ability to perceive a tennis racket's "sweet spot." The sweet spot, or center of percussion, is defined as the point on the racket at which contact with a ball would produce the best results.

In an article on "Aging and the Perception of the Racket's Sweet Spot," published recently in the journal Human Movement Science, Claudia Carello, a professor of psychology, and her colleagues report that, like young people, the elderly are able to determine an object's sweet spot and length simply by holding it.

In the first of two experiments, eight volunteers, aged 62 to 89, who were not recreational tennis players, were seated at a desk and had a tennis racket placed in their right hand. With their hand and the racket obscured by a curtain, each volunteer was asked to indicate the length of the racket and the spot on the racket at which they would like to hit a ball.

For each of six different-sized rackets, the participants were within 10 centimeters of the actual sweet spot and 15 centimeters of the actual lengths, Carello and her colleagues write. These values are comparable to those obtained with younger participants.

In the second experiment, eight volunteers between 63 and 79 years old were asked to perceive the length and sweet spot of a rod with a metal ring attached to it. The purpose of attaching the ring was to manipulate the distribution of the object's mass without altering its actual mass and length. As in the first experiment, the volunteers indicated the characteristics while they held the hidden object.

According to the study's findings, the rod's perceived length depended on whether the ring was attached near the participant's hand or far from it. Perception of the sweet spot closely tracked the actual sweet spot. Given the similar results for both age groups, it is apparent that, as among the young, the elderly's perception is constrained by an object's resistance to being rotated.

The study's results "confirm that the two distances can be perceived by dynamic touch with reasonable accuracy and reliability, even when the objects in question are unfamiliar in structure and size," Carello and her colleagues write.

The two experiments' findings show that simply by holding an object, elderly people obtain enough information to determine the distance to the object's sweet spot and its tip.

"Elderly participants without foreknowledge of the actual dimensions of wielded rackets and rods seem able to register these two lengths with reasonable (and, perhaps, surprising) accuracy," Carello and her colleagues write. "Furthermore, this ability of our group of elderly participants is fairly comparable to that of participants younger than them by 40-50 years."

However, performance by the two groups is not identical, the researchers find. The elderly people tended to perceive the object's length to be smaller than the young people's perceptions. This difference in perception increased as the objects increased in size.

The difference in the two groups' performance may be due to age-related declines in muscle strength, Carello and her colleagues conjecture. If the elderly felt they couldn't control an object when it was fully extended then their report of how far they could reach or strike with it ought to be correspondingly shorter.

"Despite dramatic changes in the sensory machinery with age," Carello says, "the difference lies not in perception but in the potential for action.

Allison Thompson