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IIWDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



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fic- 41 Reversals of the Necker cube sliown in figure 40 as a 

 function of brain injury. Average number of reversals {ordinal,) 

 are plotted for each of six successive 15-sec. observation periods 

 Normal adults (controls) show reversal rates which 

 increase up to the middle of the total 1 ' j min. -period and then 

 level off. Patients with unilateral frontal lesions show fewer 

 reversals than those with lesions elsewhere in the brain (uni- 

 lateral or bilateral nonfrontal brain lesions). Patients with 

 unilateral lesions of the right hemisphere show fewer reversals 

 than those with unilateral lesions of the left hemisphere. 

 Patients with bilateral frontal lesions (upper left), however, 

 show significantly higher reversal rates than controls and all 

 other groups with brain injury. [From Cohen (go) 



pretation of the changes observed will continue to 

 elude us, until we are able to devise a more adequate 



perceptual theory (<)i I. 



CtiNCl I SHIN 



The forms that a theory of perception may have 

 in lake can perhaps lie sketched. The theory would 

 have lo (leal with the basic facts of perception thai 

 have recurred in this review: responses to patterned 

 fields, to gradients and ratios of stimulation, trans- 

 position ol p. uterus (and its limits), and orderly 

 response i" sequentially patterned stimuli. There is 

 little hope of understanding the underlying processes 

 il we continue to restrict investigation to such un- 

 natural stimuli as single points of light, pure tones 

 (or even clicks) and punctate pressure. NT 111.111 made 



hi il. 1 01 the nervous swem would he able to 



start with such sensations and arrive .it the percep- 



ol which so many species seem to he capable. 



\"i 1. hi we expect 10 understand the essentia] 



central :lates ol perceiving by adhering to those 



conceptions of the nervous system which view it as a 

 passive receiver of sensory information. The nervous 

 s\ stem must operate upon its inputs, not only by 

 selecting them, but by providing the essential "con- 

 stancies' without which the information would be 

 chaotic. Neither field theories [such as that of Kohler 

 (273)], nor scanning theories of perception can thus 

 far deal with these problems. The field theory has 

 difficulties (which we have described) and disre- 

 gards much of the intricacy and orderliness of the 

 neural substrate. The scanning notions were spe- 

 cifically devised to deal with perceptual constancies 

 [see Pitts & McCulloch (381), Deutsch (103) and 

 Sutherland (461)], but they too conflict with facts 

 [e.g. MacKay (334) and Teuber el at. (469)], and 

 none can explain even the limited readjustment of 

 constancies as seen in rearrangement experiments. 



Throughout this chapter we have stressed the 

 potential role of a central corollary discharge which 

 is postulated as coordinating efferent and afferent 

 processes. This corollary discharge presumably travels 

 from motor into sensory systems at the onset of ever) 

 bodily movement and thus permits anticipatory 

 adjustment of the perceptual process. These dis- 

 charges are pure conjecture; if they exist, they would 

 enable the organism to distinguish ordinary afferent 

 stimulation (due to changes in the environment) from 

 reafferent stimulation due to his self-produced move- 

 ments. If modifiable (in higher species 1, these corollary 

 discharges might serve as carriers of perceptual 

 adaptation to altered sensory environments; they can, 

 as we have shown, account for certain illusions, and 

 they may be important in building up classes of 

 responses to equivalent Stimuli in a normally pat- 

 terned environment. Malfunctioning of this internal 

 activity would be evidenl in highly redundant (336), 

 or in 'empty 1 or noisy environments (as in isolation 

 and deprivation studies), and in some of the Strange 

 but patterned abnormalities of perception after 

 cerebral lesions. 



I hese fragmentary notions may raise the hope for a 

 theory, but they are far from constituting one It can 

 be seen that these concepts are closely related to the 



earlier neurologic postulates of 'schemata' as the 



neural basis for awareness o| posture and spatial 

 orientation advanced by Tick (378, 379), Head (186), 

 Lhermitte 1 |2o) .md Okllickl & Z.mgwill (366, 367). 

 These neural schemata appear in a new and different 

 guise in MacKay's concept ol the matching responses 

 within die nervous system ( ; 35 1, The central cor- 

 relates ol perception may nun out to be activities 

 thai organize "'an outwardly directed internal match- 



