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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 





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fic. 8. Drawings' produced by a chimpanzee. The experimenter provided the animal with the 

 regular outlines shown, and the animal scribbled over them, filling interspaces and 'completing' 

 designs which the experimenter had deliberately left unfinished. [From von Schiller (510).] 



human forms, as has been done by Riissel (409) and 

 Gellcrman (147). 



An obvious, but again, little explored difference 

 between children and adults is the marked difficulty 

 children have with apprehension of peripherally ex- 

 posed figures and with tachistoscopy. That children 

 require a much longer exposure time for the percep- 

 tion of patterns has been adduced in favor of the view 

 that pattern perception is learned (188), but alterna- 

 tive interpretations are possible. Apparently, the two 

 sources of difficulty, limited peripheral span and in- 

 creased time requirements, interact in some complex 

 fashion. It is known thai even with unlimited exposure 

 children take much longer than adults in surveying an 

 array of patterns, and brain lesions in children pro- 

 duce disproportionate slowing in searching time, 

 according to Tcuber et al. (468). Piagct has sii'-mested 

 that children may have virtually a tubular field, and 

 some of the peculiarities of their perceptions can 

 perhaps lie understood in these terms (148). 



- netu Considerations 



Discover) of neural correlates of pattern perception 



will be made e likcK if we can define some of the 



essential similarities and differences that exist between 

 pattern perception in man and various other species. 

 We ate verv far from such a goal. 



VERTEBRATES. Work on subhuman primates bv 

 Kohler (j;oi and KJiiver (259) has disclosed puzzling 

 resemblances among the perceptions of monkeys, 



anthropoid apes and man Most revealing in this 



respect is Kluver's systematic snrvev (259) of equiva- 



lent responses in monkeys. Kluver's method involves 

 presenting the animal with a pair of discriminanda 

 (e.g. a triangle vs. a circle), and then varying these 

 stimuli until the learned choice breaks down. This 

 method thus defines ranges of similarity or equiva- 

 lence of stimuli; it reveals that all of the patterns which 

 are functionally equivalent (i.e. elicit the same 

 response) in the monkey look similar to man. 



Analogous conclusions are suggested by the analy- 

 sis of figural preferences in the scribbling of chimpan- 

 zees studied by von Schiller (510). These scribblings, 

 to be sure, are never representational drawings, but 

 they can be influenced by the figural properties of 

 visual patterns placed on the paper by the experi- 

 menter prior to letting the animal scribble over it 

 (see fig. 8). 



Lashley (1501) has extended Kluver's technique of 

 'equivalent and nonequivalcnt stimuli' to the study of 

 pattern perception in the rat. Apparently, rodents as 

 well as primates tend to group stimulus arrays into 

 figure and ground. Figures that are easilv discrimi- 

 nated by man are also 'easy 3 for monkey and rat, and 

 stimuli lacking identiiiabilitv lor one species are also 

 readily confused by the other, as shown in figure 9 

 (301). These similarities (of perceived figural simi- 

 laritv ) were si. surprising that Lashle) considered but 

 rejected the possibility that results might have been 

 different if rat and not man had constructed the test 

 patterns. Comparable data on lower vertebrates are 

 scant [sec, however, Pache I ;; 3) for frogs and Herter 

 (jot.) for Itsh 1 but oiler no support lor assuming any 

 abrupt changes in the evolution of vertebrate pattern 

 vision. 



