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Lindsay E. Farber, Allison B. Sekuler, Patrick J. Bennett; Evidence for no increased surround modulation in the aging visual system. Journal of Vision 2009;9(8):1064. doi: 10.1167/9.8.1064.
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Age-related changes in perceptual performance are thought to be due, in part, to a degradation in intracortical inhibition for older observers (Leventhal et al., 2003). Although decreased inhibition can sometimes lead to improved performance (e.g., Betts et al., 2005), inhibitory mechanisms are necessary for focusing on central targets in the receptive field while ignoring surrounding patterns. Saarela and Herzog (2008) investigated the effect of surround masking on visual suppression in young observers, and found that the presence of a surround annulus does not modulate central target detection. If inhibitory mechanisms are impaired in older observers, we would expect a larger effect of surround masking as a function of age. Six younger (mean age 27 years) and six older (mean age 73 years) observers detected a target within the centre of an iso-oriented centre-surround pattern in a 2-IFC task. Stimuli consisted of Gabor gratings at six different base contrast levels (0, 0.0025, 0.005, 0.01, 0.02, 0.08). The diameter of the centre of the stimuli (3.6 deg) was half the size as the surrounding mask (7.2 deg). Two interleaved staircases varied the contrast of the central target to obtain target discrimination thresholds. Consistent with previous findings, surround masking did not produce an effect for young observers. Although higher thresholds for target detection were observed for older adults, there was no significant effect of the surrounding mask across age (F(1,10) = 0.0919, p = 0.77). In addition, the extent of the modulation did not vary as a function of mask contrast (F(4,40) = 0.2603, p = 0.75). These results are not consistent with the hypothesis that intracortical inhibitory mechanisms are less effective in elderly observers. Future research will extend this result by investigating the effects of time-course, orientation, and surround mask configuration as a function of age-related changes in inhibitory mechanisms.
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