Contour Detectability Threshold as a Function of Chronological Age

Abstract

Evidence from various areas of investigation was cited to support the view that an aging process in the visual receptor mechanism might be expected to bring about a rise in contour detectability thresholds. Support was also garnered for the view that certain geometrical illusions which decline with chronological age are determined by the degree of figure-ground contrast (or contour strength) of their inducing lines. Two experiments were carried out, the first to measure contour detectability thresholds at 5 age levels (8 yr. to 12 yr.), and the second to measure the magnitude of a modified Mueller-Lyer illusion at these age levels. Both experiments yielded significant results in the expected directions. Correlation of the results based on common Ss yielded a significant negative r. Intelligence correlated negatively to a significant degree with contour detectability threshold, but not with magnitude of illusion. Possible implications were discussed.

The effect of simulated receptor aging on two types of visual illusions

“…Furthermore, Pollack (1963) discovered that sensitivity to brightness contrast declines as age increases from 8 to 12 years. The increasing contour detectability thresholds were also found (Pollack, 1963) to be negatively c orrelated (r = ,49, P < .01) with magnitude of the Müller-Lyer illusion, a Type I phcnomenon.…”

Illusion magnitude as a function of visual field exposure

“…the change in Type I phenomena is not viewed as developmental; instead. the data (Pollack, 1963(Pollack, . 1964 suggest that it is due to a decline in the sensitivity of the visual receptor as it ages.…”

Visual acuity in children as a function of hue

“…Dispensa (1939) and Slaton and Jorgenson (1958) likewise found no correlation between intellectual ability and visual acuity. In contrast, Loranger and Misiak (1959) report that acuity can be related to intelligence, and Pollack (1963) reports a correlation (r = -.33, P < .05) between contour detectability thresholds and IQ. Weale (1963) points out that relationships between intelligence or age and visual sensitivity must be interpreted with caution since these relationships may be due to some other common source.…”

“…Wilson's distribution-free analysis of variance was computed Since contour detection ability based on brightness contrast decreases with age (Pollack, 1963), it would be expected that acuity would also decrease with age. In the present study, there was no discernible age trend.…”

“…Based on research by Brody (1955) and Weale (1961 a, b), Pollack (1963) demonstrated that contour detectability as a function of light intensity decreases with age; however, hue detection thresholds (Pollack, 1965a) did not follow anticipated ontogenetic trends. Pollack, therefore, concluded that contour detection and hue detection processes are underlain by different receptor systems with different ontogenetic trends.…”