The threshold for the detection of the dark interval between two flashes of light (DIT) was investigated for 240 school children aged [6][7][8][9][10][11][12][13][14][15][16][17] Pollack (1969) has put forth a two-process theory to explain age changes in visual perception. One of these processes, nondevelopmental in nature. involves a progressive loss in receptor sensitivity due to physiological aging. Within the framework of this theory those phenomena which show nondevelopmental age changes (Type I) are not correlated with intellectual ability, but appear to be related directly to receptor efficiency and such stimulus variables as intensity, duration, contrast, and orientation. The operation of all these variables depends on the sensitivity and efficiency of the visual receptor system. Weale (1963) has shown that lenticular density and pigmentation, as well as retinal pigmentation, increase with age, while pupil size decreases. The pinpointing of the precise mechanisms involved, however, requires further physiological investigation. Some behavioral research exists that tends to confmn the above notions. Polla<:k's investigation of contour detectability thresholds in childhood (I963c) supports the above. Both sensitivity to contour as produced by brightness contrast and the magnitude of the Mueller-Lyer illusion were found to decline between ages 8 and 12, and intelligence played no significant role. Two experiments by Pollack (1965a. b) on backward figural masking showed that figure-grounu contrast of the target and contour orientation of the target and mask were significant variables in producing the masking effect with adults. Those conditions that produced the maximal amount of backward masking in adults were presented to children ranging in age from 7 to 10 years. The interstimulus interval permitting masking declined steadily as a function of increasing chronological age. Adult Ss exhibited masking with even shorter intervals than the l()..year-olds. There was no correlation with IQ. Again, stimulus variables interacting with the declining sensitivity of the visual receptor system were believed to be the factors responsible for the decline in masking with age.The other process put forth by Pollack ( 1969) is "developmental" in that age changes seem to be related to central cognitive functions and abilities that are hierarchically organized. Those phenomena showing developmental age changes (Type II) are correlated with intellectual ability and do not depend as much upon classical stimulus variation. Presentation of such phenomena usually involves a sequence of discrete stimulus events, registered by the S as traces, which are then centrally compared and contrasted. Pollack (1964) demonstrated this by converting a Type I illusion (MuellerLyer) into a Type II illusion, by altering the mode of presentation from simultaneous to successive. This was done by presenting the oblique inducing lines before presenting the main line. The classical illusion reversed its usual direction; the new iUusion increased in ma...

The threshold for the dark interval between two flaslles was illl'estigated ill 100 elementary school children, age 6-IU. It was foulld that Ille threshold decreased with chrollological age, 'a findillg altribllted to physiological agillg of Ille I'isual receptor system producillg diminished persistence of tile illitial stimulus.Pollack (\ 968) has put forth a two-process theory to ex plain age changrs in visual perception_ One of these processes. nondevelopmental in nature. involves a progressive loss in receptor sensitivity due to physiological aging_ The other process is "developmental" in that age changes are related to central cognitive functions and abilities which are hierarchically organized. Within the framework of this theory, those phenomena which show non developmental age changes (Type I) are not correlated with intellectual ability. but appear to be related directly to receptor efficiency and various stimulus variables such as intensity, duration, contrast, and orientation. Those phenomena showing developmental age changes (Type II) are correlated with intellectual ability and do not depend as much upon classical stimulus variation. Presentation of such phenomena usually involves a sequence of discrete stimulus events, registered by the S as traces, which are then centrally compared and contrasted.It is assumed that in making judgments about two stimuli presented in rapid succession, the individual early in life makes use of the physical persistence of the initial stimulus to make what is virtually a simultaneous comparison. As this stimulus persistence weakens as a function of aging in the receptor system, comparison comes to be based upon the higher-order cognitive function of comparing the trace of the vanished initial stimulus ...,ith the second stimulus. This transition was demonstrated by Pollack (1966) in a study dealing with apparent movement. The temporal range of apparent movement decreased between the ages of 6 and 9, but increased again beyond the age of 9. Correlation with IQ was nonsignificant for the 6-to 9-year-olds, but positive and significant for the 10-and Il-year-olds. The pattern of results obtained in this experiment was very similar to that obtained in an earlier study by Pollack (1960), concerning the frequency of occurrence of figural aftereffects following brief inspection.The present experiment was designed to test further the hypothesis that stimulus persistence declines with age. The dark-interval threshold (Din can be thought of as a simplified version of the critical flicker frequency (CFF), in which two flashes of light are presented in quick temporal succession with a varying interflash interval. The S is simply asked to report whether he can detect a dark interval between the flashes. At the present time, data on the DIT are very scarce. In general, results from studies of CFF have shown a decrease in CFF (poorer performance) beyond the age of 14. Cross (1963) performed a study of CFF with an age range of 6 to 12 years. She found a significant increase in CFF (bet...