Abstract
The current study evaluated the ability of 17 younger (mean age = 20.4) and older adults (mean age = 76.7) to discriminate shapes depicted by Glass patterns (Glass, 1969). On any given trial, observers identified a particular pattern as either possessing a radial or concentric (i.e., circular) organization. Detecting a shape defined by a Glass pattern requires the successful detection of the orientations of its constituent local dipoles. In addition, long-range processes (e.g., the Boundary Contour System of Grossberg & Mingolla, 1985) are needed to integrate the spatially separated dipoles into perceivable contours that have a particular (e.g., radial or concentric) organization. In the current experiment, the shapes were defined by either 40 or 200 oriented dipoles spread over an area with a diameter of either 6 or 25 degrees visual angle. Three amounts of visual noise were added to the patterns to manipulate task difficulty: 1) no added noise points, 2) moderate amounts of noise (a 1:1 ratio of randomly-placed noise points and signal dipoles), and 3) large amounts of noise (a 5:1 ratio of randomly-placed noise points and signal dipoles). The results showed that the addition of noise greatly affected the observers’ ability to discriminate global shape (F(2, 30) = 141.8, p < .000001, partial eta squared = .90). Interestingly, there was no effect of the change in size of the pattern (F(1, 15) = 1.35, p = .26). Both younger and older adults were able to effectively discriminate shape even when the size of the pattern was increased more than 400 percent to 25 degrees visual angle (i.e., no age × size interaction: F(1, 15) = 0.5, p = .49). The current results demonstrate that older observers maintain an impressive ability to integrate local spatial information over large distances to perceive global shape.