Effects of aging on face perception: Exploring efficiency, noise & orientation

Abstract

Face perception is impaired in a variety of ways in older adults, but the mechanisms underlying these changes remain unclear. A central theme of this dissertation is that task performance is constrained by two factors intrinsic to the observer: sources of random variability -- internal noise -- and the efficiency with which task-relevant stimulus information is utilized. This thesis uses several behavioural, psychophysical methods to examine how age-related changes in one or both of these factors affect face processing. Chapter 2 used the classification image (CI) method to characterize the spatial sampling patterns of younger and older observers performing a face discrimination task. Compared to younger adults, older adults used information in the eye/brow region less consistently and instead relied on relatively less informative regions such as the forehead. The differences in CIs accounted for the lower absolute efficiency that was found in older observers. Chapter 3 estimated internal noise and calculation efficiency by measuring threshold-vs.-noise (TvN) curves and response consistency in a face discrimination task. Compared to younger observers, older observers had higher additive internal noise and lower calculation efficiency, but the magnitude of multiplicative internal noise did not differ between age groups. Previous studies have shown that younger adults have a bias to rely on horizontal structure to discriminate and identify faces, and the magnitude of this so-called horizontal bias is correlated with identification accuracy. The experiments in Chapter 4 measured horizontal bias in younger and older adults, and found that age differences in horizontal bias account for some, but not all, of the age difference in face identification accuracy. In summary, my work demonstrates that additive (but not multiplicative) internal noise is greater in older adults, and that they are less efficient at sampling information that is conveyed by structure at different locations and orientations in a face.