This study was concerned with the role of visual experience on identity perception. Hooded rats were used; 10 reared in darkness and 10 normally reared. As adult animals they were compared on learning to discriminate vertical and horizontal striations. No difference in performance was found. These findings are contrary to those predicted by Hebb (1949) and in agreement with those found by Woodruff (1951). It is concluded that prolonged visual experience is not a necessary requirement for simple identity visual perc)eption. IntroductionHebb (1949) presented a basis for a "revision of perceptual theory" in which, among other things, he attempted to point out the respective roles of inherited behavioral tendencies and learning in relatively simple visual discrimination tasks. He utilized two concepts, "primitive unity" and "identity." Primitive unity referred "to that unity and segregation from the background which seems to be a direct product of the pattern of senso:r-y excitation and the inherited characteristics of the nervous system on which it acts" (Hebb, 1949, p. 19). This was demonstrated by a study (Hebb, 1937) in which albino rats, reared in darkness, oriented themselves in the direction of a figure against a ground the first time they received any visual stimulation. Identity is defined as "referring to the properties of association inherent in perception" (Hebb, 1949, p. 26) and "is dependent on a prolonged experience" (p. 28). This concept was illustrated by another aspect of his above mentioned study (Hebb, 1937) in which white rats, reared in darkness, learned to discriminate between vertical and horizontal striations using a Lashley jumping apparatus. These data were compared with those of normally reared animals in a study by Lashley (1938). Hebb's dark reared Sstook six times as many trials to learn this discrimination. Hebb (1958) and Riesen (1961) pointed out that experience is fundamental to the perception of "identity."Woodruff (1951) reared 24 hooded rats in complete darkness until they were 150 days old and compared their performance in learning a vertical-horizontal striations discrimination with a normally reared group of rats. The apparatus was a Lashley jumping box, modified by an elevated Y-maze set up to the openings. A correction method of running was used and the criterion of learning was two consecutive blocks of at least 9 correct trials out of 10. contrary to the above prediction, no difference was found between the two .groups.Psyclwn. Sci., 1965, VoL 2. A. B. Woodruff and M. L Slovak NORTHERN ILUNOIS UNIVERSITYThe discriminanda used in these studies were the same, but they do show some methodological differences.(1) Hebb-Lashley used a jumping response and Woodruff a running response. (2) The Hebb-Lashley Ss were first taught a black-white discrimination before they were introduced to the striations, but Woodruff's were not.(3) Hebb-Lashley used a noncorrection method and Woodruff used a correction method. (4) Most important Woodruff's Ss were hooded rats, Hebb us...