The effects of aging on visual contour and shape perception

Abstract

<p>Human vision has an incredible ability to translate light reaching the retinae into a coherent, three-dimensional representation of the outside world in a fraction of a second. Much research has been devoted to understanding how local orientation information is integrated to form global contours and shapes -– a crucial step in visual processing. This dissertation describes experiments examining how contour and shape perception are affected in healthy aging.</p> <p>Chapter 2 examined contour grouping at low contrast and in the absence of distracters. Unlike younger subjects, older subjects did not benefit from co-alignment of local orientations with the contour’s outline, suggesting that grouping by orientation co-alignment is impaired in older age in low contrast. Chapters 3 and 4 examined the effects of aging on the ability to detect and discriminate high-contrast contours embedded in a dense field of distracters, as real life situations often require detecting objects among clutter, such as a snake hiding among tall grass. Results showed that older adults require significantly more time to discriminate contours in clutter, especially for less salient contours. Moreover, increasing the relative density of background clutter had a greater detrimental effect on older, compared to younger, subjects. However, aging did not seem to affect the ability to group contours across a range of spatial distances, or the sensitivity of contour integration to orientation misalignment. Lastly, Chapter 5 examined the influence of local orientation information on the perception of a contour's shape. Results revealed that older and younger subjects perceived the shape of a sampled contour in the same way, even when the contour's orientation and position information were in conflict. These findings indicated that the integration of orientation and position information in shape perception does not change with age.</p>