The relation between action and perception in older adults 

Healthy aging is associated with a decline in various aspects of cognitive, perceptual and motor abilities. There is also evidence that aging is manifested by interactions between functional and neural processing mechanisms, which operate in a separate and efficient fashion at young age. This blending of functions is termed 'dedifferentiation'. In particular, the loss of differentiation between two major visual systems – vison for perception and vision for action – can lead to a decrease in the efficiency of grasping at old age. At young age, the two systems are proposed to operate by separate rules of processing: vision for perception is proposed to be context-bound and relativistic, whereas vision for action is proposed to be selective, analytic, and absolute. Thus, in young adults, perception but not grasping obeys Weber’s Law, perception but not grasping exhibits Garner interference, and perception but not grasping is affected by context. And, for young adults, the Ponzo illusion is recorded in perception, but it is present to a lesser extent (if at all) in grasping. The behavioral dissociations between grasping and perceptual estimates indicate that perception is shaped by and benefits from relative and contextual cues in the neighborhood of the object, but grasping is performed best by ignoring context and concentrating exclusively on the to-be-reached object -- its size, orientation, and momentary position with respect to the hand that intends to pick it up. However, once this separation of functions is compromised (at old age), the same relativistic rules and contextual cues that help perception can intrude on action and impair grasping performance. To test for possible dedifferentiation and its consequences in old age, we plan to compare performance by young (20-35 years of age) and older (65-80 years of age) adults in grasping and in perceptual estimates in several cognitive domains, each tapping a unique, different aspect of information processing. This comprehensive mapping of visual functions is bound to reveal age-dependent changes in the nature of perception-action relation as well as age-depended changes along different aspects of perceptual processing and visuomotor control. Beyond the insights to-be-gained on perception and grasping at old age, the results carry practical implications, too. They will help to specify the optimal conditions for effective visuomotor action in older adults and to develop diagnostic tools to quantify grasping control and perceptual processing in aging.