Abstract
Detecting Gabor-defined contours in cluttered backgrounds requires integrating local orientation information across space. Older adults require longer stimulus durations than younger adults to integrate contours in dense clutter, although both groups are similarly affected by changes in contour element collinearity, with performance declining as collinearity decreases (Roudaia et al., 2013). Several EEG studies with younger adults have shown that contour grouping requires top-down information from parietal cortex and LOC to early visual areas (e.g., Volberg & Greenlee, 2014). Here, we examined EEG activity during a contour integration task in 12 younger and 12 older adults (mean ages 22.8 and 66.4 years) under single- and dual-task conditions. Stimuli comprised spiral-shaped Gabor contours embedded within an array of randomly-oriented Gabors, and contour salience was manipulated with 5 levels of collinearity. On each trial in the single-task condition, participants reported the quadrant containing the spiral contour's tail; in the dual-task condition, participants also reported the quadrant of a high-contrast element among background Gabors. As expected, contour discrimination performance varied with collinearity in both groups. The addition of a secondary task did not affect contour discrimination in the younger group, but significantly reduced performance in the older group. The pattern of event-related potentials did not differ between the single- and dual-task conditions, but differed across groups: Younger, but not older adults, showed an occipital positivity ~120 ms post stimulus-onset; both groups showed a strong occipital negativity at ~170 ms, with significantly greater amplitude for older adults; younger adults then showed a large positivity at ~300 ms, which was not apparent in older adults. The groups also differed in scalp distribution during the pre-stimulus interval, with younger adults showing a frontal positivity and occipital negativity, and older adults showing the reverse. Results suggest that the neural processes underlying contour integration change with age.
Meeting abstract presented at VSS 2018