Citation

Betts LR, Sekuler AB, Bennett PJ. Vision Res. 2007; 47(13): 1769-1780.

Affiliation

Department of Psychology, Neuroscience, and Behaviour, McMaster University, Hamilton, Ont., Canada.

Copyright

(Copyright © 2007, Elsevier Publishing)

DOI

10.1016/j.visres.2007.02.016

PMID

17466355

Abstract

The current experiments measured orientation discrimination thresholds in younger (mean age approximately 23 years) and older (mean age approximately 66 years) subjects. In Experiment 1, the contrast needed to discriminate Gabor patterns (0.75, 1.5, and 3c/deg) that differed in orientation by 12deg was measured for different levels of external noise. At all three spatial frequencies, discrimination thresholds were significantly higher in older than younger subjects when external noise was low, but not when external noise was high. In Experiment 2, discrimination thresholds were measured as a function of stimulus contrast by varying orientation while contrast was fixed. The resulting threshold-vs-contrast curves had very similar shapes in the two age groups, although the curve obtained from older subjects was shifted to slightly higher contrasts. At contrasts greater than 0.05, thresholds in both older and younger subjects were approximately constant at 0.5deg. The results from Experiments 1 and 2 suggest that age differences in orientation discrimination are due solely to differences in equivalent input noise. Using the same methods as Experiment 1, Experiment 3 measured thresholds in 6 younger observers as a function of external noise and retinal illuminance. Although reducing retinal illumination increased equivalent input noise, the effect was much smaller than the age difference found in Experiment 1. Therefore, it is unlikely that differences in orientation discrimination were due solely to differences in retinal illumination. Our findings are consistent with recent physiological experiments that have found elevated spontaneous activity and reduced orientation tuning on visual cortical neurons in senescent cats.

Language: en