Cognitive decline with aging is a patchwork of scores of progressive failures in different systems in the brain, all proceeding at their own pace. The research noted here is a good example of the way in which researchers try to pick apart the whole into comprehensible pieces, a necessary part of the much lengthier process of mapping specific declines to specific damage and change in the brain:
Staying on topic may be more difficult for older adults than it is for younger people because older adults begin to experience a decline in what is known as inhibition - the ability to inhibit other thoughts in order to pursue the storyline. Evidence for inhibition deficits in older adults has appeared in studies that task participants with completing a familiar phrase with an unfamiliar word. For example, when asked to complete out loud the sentence "I take my coffee milk and ..." with the word "pajamas" instead of "sugar," older adults are more likely to first respond with "sugar" than young participants because they have a harder time inhibiting the high-probability word to complete the sentence. Decline in inhibition also can affect visual perception, as is demonstrated by new research. Inhibition is an important part of neural processing throughout the brain, and it plays a significant role in visual perception. For example, evidence suggests that when we look at an object or a scene, our brain unconsciously considers alternative possibilities. These competing alternatives inhibit one another, with the brain effectively weeding out the competition before perceiving what is there. With regard to vision, age-related declines in the efficiency of inhibitory processes have been demonstrated in research involving simple perception tasks, such as the ability to detect symmetry and discriminate between shapes.
In this study, the researchers were interested specifically in what is known as figure-ground perception, in which two areas in a person's visual field share a border. If you imagine a white heart on a black background, for example, the heart is the "figure" - with its definitive shape - and the black background is the "ground," which seems to simply continue behind the figure. In the lab, researchers showed on a screen a series of small, symmetrical white-on-black silhouettes to two different groups: young participants with an average age of about 20 and older participants with an average age of about 66. Participants were asked to determine whether each white "figure" depicted a familiar object, such as an apple, or a novel object - a meaningless shape.
"For a long time my students and I have been investigating how we see the world. Our work has suggested that the brain first detects all the borders in a scene and then for every border, accesses object properties - essentially different interpretations - on both sides. These two interpretations compete by inhibiting each other, and whichever one has more evidence in favor of it is going to exert more inhibition on the other one to win the competition." In the end, younger and older participants both came to the same conclusions about whether the white objects were familiar. However, it took longer overall for older adults to come to that conclusion, especially when images presented more inhibitory competition. The findings support and further evidence that older adults experience age-related deficits in inhibition related to vision.