The effect of senescence on orientation discrimination and mechanism tuning

Abstract

Accurately processing orientation information is a fundamental component of visual performance. Single-unit recordings have shown that the orientation tuning of individual neurons in macaque cortical areas V1 and V2 is reduced dramatically with age (M. T. Schmolesky, Y. Wang, M. Pu, & A. G. Leventhal, 2000; S. Yu, Y. Wang, X. Li, Y. Zhou, & A. G. Leventhal, 2006). These researchers suggest that losses in single-unit orientation selectivity result in declines in orientation discrimination and object recognition in older humans. Three experiments were conducted to determine whether human performance is affected by putative age-related changes in tuning of cortical neurons. Ten younger and ten older observers participated in this study. Experiment 1 demonstrated significant differences in the contrast sensitivity of the two age groups. Experiment 2 showed significant differences in orientation discrimination thresholds. However, when thresholds were plotted in terms of multiples of detection threshold, age-related differences were not observed. In Experiment 3, perceptual orientation tuning curves did not significantly differ in shape for younger and older subjects. As in Experiment 2, at any given contrast, there is a large difference in sensitivity between younger and older adults. This implies a model of orientation processing that allows the adult visual system to maintain consistent and reliable orientation information at the network and ultimately the perceptual level.

Face Processing Changes in Normal Aging Revealed by fMRI Adaptation

“…Stimulus contrast was held at 100% for all faces used. For these reasons, synthetic faces are optimal for testing older adults whose face perception and recognition are affected by age differences in aspects of spatial vision such as contrast and spatial frequency (Lott et al, 2005;Owsley, Sekuler, & Boldt, 1981; also see Delahunt, Hardy, & Werner, 2008;Owsley, Sekuler, & Siemsen, 1983). The synthetic faces were used to examine older adults in Habak et al (2008): Older adults performed as well as young adults in matching the same facial identity when there was no viewpoint change, but they were poor at matching the same face across different viewpoints.…”

Shape Perception Is Altered by Normal Aging

“…Both types of intermediate form-perception task require the correct encoding of component orientation and position information (presumably in pathways from retina through to V1) prior to integration of the global shape. Given that closed-shape discrimination has been previously shown to be intact with aging, and that aging minimally impairs orientation discrimination [20][21][22] and the ability to perform spatial position judgments, 23,24 both intermediate form-perception tasks might predictably be minimally affected by age. However, it is also possible that aging may differentially alter task performance.…”

Visual Form Perception from Age 20 through 80 Years

“…Numerous recent studies have measured the effects of aging on visual tasks designed to assess the function of various features of the early through intermediate object perception pathway. Human perceptual studies show small changes to orientation discrimination 11 and intact orientation tuning 12,13 with advancing age. The ability to encode local position also is maintained largely in the elderly 14,15 ; hence, the ability to encode local form features seems fairly robust to aging.…”

“…[21][22][23] Age-related differences exist in the perception of shapes defined by texture, 24 and for higher levels of form processing, such as facial matching when faces are displayed from different viewpoints. 25 Previous studies that have documented age-related changes to form perception generally have included two age groups: younger adults (usually below ages 35 to 40 years) and older adults (typically over the age of 60 years), and have conducted detailed experiments on a specific aspect of form perception (e.g., orientation discrimination, 12 center-surround suppression of perceived contrast, 18,19 contour integration, 22 shape discrimination 26 ). Differing experimental designs among studies limit the ability to compare the relative magnitude of agerelated change across the many different aspects of form perception.…”