Visual backward masking in retardates and normals

Abstract

DOWhen the onset of a visual stimulus (S, ) follows immediately or shortly after the offset of another visual stimulus (SI ) at the same point in space, and when S, (the masking stimulus) has appropriate contours, duration, and illumination relative to SI, then SI will be inhibited. The blanking of SI by S, is one instance of a phenomenon labelled "backward masking" (see Raab, 1963, for a review). That perception of SI can be voided by an ensuing stimulus indicates that SI requires a period of time after offset for visual processing. As the interstimulus interval (lSI) between SI and S, lengthens, the masking effect of S, weakens. At some point S, no longer interferes with the perception of S\ .Backward masking allows for a comparative test of the speed of visual processing by retardates and normals. If retardates take a longer period of time to process a visual stimulus than do normals of equal chronological age (Spitz, 1963), the presentation of S, to retardates must be delayed for a longer interval to prevent its interference with the visual processing of S\. The present experiment tests this hypothesis. Of additional interest is the relationship of backward masking to chronological age in normal Ss (Pollack, 1965). SubjectsThe Ss, all males, were 20 retardates (R) (mean CA = 15.78, SD =.73; mean IQ =63.85, SD =6.60), residents of a state training school for educable retardates; 20 equal-MA normals (MA) (mean CA = 9.92, SD = .66); and 20 equal-Ca normals (CA) (mean CA =15.18, SD =.84). The normals were volunteers from a local military institute and from local cub scout packs. No IQs were available for the normals, who were assumed to have approximately average or slightly above average intelligence. Apparatus and StimuliStimuli were presented in a three-channel Scientific Prototype Model GB tachistoscope allowing three consecutive presentation times with accuracy of better than ±2%. The test figures (SI) were the letter D or the letter O. Black Deca-Dry transfer letters were used (Venus Medium style typeface of 60-pt size), and each letter was placed on its own white card. The D was 15 mm high and 12 mm wide, the 0 was 15.5 mm high and 13 mm wide. When placed in one channel of the tachistoscope a letter was approximately 121.92 em from S's eyes and subtended a visual angle of approximately 43 min in height and 35 min in width. The dimensions varied slightly, depending on the letter (Fig. I).The masking figure (S,), placed in the second channel of the tachistoscope, was a copy of the pattern that Schiller and Wiener (1963, Fig. 2, Pattern 3) found to be efficient in masking letters. It consisted of a 21 mm outline square enclosing four parallel diagonal lines that cross-hatched the area enclosed by the square (see Fig. I). All lines were made by applying matte black 1/32 in. pressure sensitive tape (Chart-Pak) on a white card. The visual angle of the masking pattern was approximately 59 min. The cards were so placed that when the slide holders were seated in the tachistoscope the letter was approximately cen...

Automatic processing in mildly retarded and nonretarded persons

“…First, the mean individually determined SOA for e^ch of the five groups in the study was comparable. The nonretarded adult groups did not differ fi-om the mildly retarded and child groups, a finding that is inconsistent with some earlier masking studies which have indicated that nonretarded adults are better (more accurate at shorter SOAs) than mentally retarded and equal-MA matched subjects in their ability to identify a masked stimulus (Mosley 1980;Saccuzzo et al 1979;Spitz & Thor 1968;Welsandt & Meyer 1974). Second, the present findings revealed that the experimental SOA remained stable across the 120 experimental trials for all subjects in each of the groups.…”

Observations on the visual-perceptual abilities and adaptive behavior in adults with Down syndrome

“…Often we find a transfer of the same methods and observation procedures from a study on normal subjects to a study with mentally retarded children or adults, although a qualitative difference in their performances has not been demonstrated. It is well established that mentally retarded subjects tend to show a quantitatively lower ability in the assumption and elaboration of information [Spitz and Thor, 1968;Olson, 19711, but many researchers suggest the existence also of qualitative differences [Abercrombie, 1964;Crosby, 1972;Miranda and Fantz, 1973;Morozas and May, 19851. An early and specific diagnosis of perceptual and cognitive abilities of DS persons may contribute to our knowledge of the evolution of these aspects of their aging. In a previous study [Saviolo-Negrin and lkevisan, 19881, visual-perceptual abilities, which present a particularly significant decline in the first stage of Alzheimer disease [Wisniewski et al, 19851, were tested in 52 DS adults using the Development Test of Visual Perception (DTVP) of Frostig et al [1963].…”

Visual Masking and Developmental Differences in Information Processing

“…Apparatus and procedure.-The target stimuli were the letters "D," "O," and "S," and the mask a crosshatched rectangular box similar to that used by Spitz and Thor (1965). For the simultaneous condition, the mask and letters were placed upon the same card.…”

“…Finally, previous developmental studies of visual masking have either reported monotonic decreases in masking strength as the interval between the onset of the mask and target increases (Spitz & Thor 1965) or have used measures which tend to assume such a relation (e.g., Pollack 1965). Among adults, however, the relation between stimulus onset asynchrony (SOA) and masking effectiveness is frequently curvilinear rather than monotonic (Weisstein 1968).…”