Visual Perception and Aging

Article excerpt

Abstract A series of studies performed in our laboratory on aging and its effect on perceptual processing and working memory capacity for visual stimuli are reviewed. Specifically, studies on luminance, colour, motion, texture, and symmetry processing are reported. Furthermore, experiments on the capacity to retain size and spatial frequency information are also discussed. The general conclusion is that there are a number of perceptual abilities that diminish with age. However, the extent of these deficits will depend on the complexity of the neural circuitry involved for processing a given task. This is also true for visual working memory where no evidence of loss due to aging is demonstrated for processing low-level visual information, when individual differences in sensory input are compensated for. It is concluded that perceptual processing deficits due to aging (like working memory) will become evident when the computational load reaches a certain level of complexity (larger or more complex network) even if the tasks remain cognitively simple.

Throughout life humans interact with the environment in response to their perception of the world. In the early stages of development, the world as we perceive it changes rapidly. We are born with rudimentary preset abilities that are refined in early life by maturation and interaction with the environment. The capacity to perceive the world correctly reaches a high level of sophistication that is unparalleled by any artificial system. Regardless of the very complex processing required to adequately represent the external world, our abilities become so refined and automatic that we are unaware of the immense computation required to perceive it. During adulthood, our sensory and perceptual abilities also change but these changes are usually subtle, often gradual, so they are seldom noticed. However, under controlled laboratory conditions, it is possible to isolate perceptual functions that are clearly affected by aging.

Until recently, there has been little emphasis in the scientific literature on the consequences of aging on visual perception, although there has been a substantial amount of work on higher cognitive abilities. The work on visual perception has been somewhat contradictory because some perceptual abilities appear relatively spared while others are affected by aging. In the present paper, I will report studies performed in our laboratory that attempt to determine what perceptual abilities are or are not affected by aging, and why performance of the elderly may differ in different contexts.

Anatomical and Physiological Effects of Aging

Although individuals over 65 years of age currently make up more than 10% of the population and represent the fastest growing segment of the population (U.S. Administration on Aging, 1991), our understanding of the nature and cause of visual changes in the elderly remains limited. The risk of visual impairment is elevated in elderly individuals: Each of the four leading causes of blindness in North America has a higher incidence in the elderly (macular degeneration, glaucoma, diabetic retinopathy, and cataracts). Some elderly individuals suffer profound visual loss and blindness, but many others exhibit less severe visual dysfunction, which nevertheless impairs their ability to function efficiently (Kosnik, Winslow, Kline, Rasinski, & Sekuler, 1988; Spear, 1993). The extent to which particular anatomical and physiological changes contribute to specific visual deficits in the healthy elderly remains unresolved. In addition, it is not known whether all visual capacities deteriorate at the same rate.

Virtually every structure in the primary visual pathway undergoes some degree of nonpathological agerelated change (for a review, see Spear, 1993). At the photoreceptor level, rods seem to be more vulnerable than cones as rod numbers decrease and cone numbers remain stable with age (Curcio, 2001). …