64 BRAIN MECHANISMS AND LEARNING 



appeared unchanged in the animal reared in a deprivation situation, used 

 hke a ready-made tool by the inexperienced animal. Conditioning deter- 

 mined the way of their application only (see also Eibl-Eibesfeldt, 1956b 

 and Eibl-Eibesteldt and Kramer, 1958). 



Fixed patterns or instinctive movements as defined by Hcinroth and 

 Lorenz are therefore not a fiction as implied by the 'anti-instinctivists', but 

 something real, and the distinction between innate and acquired is of 

 analytical value. The learning psychologist who docs not know what is 

 genetically determined is in a position equivalent to a geneticist perform- 

 ing modification experiments on genetically unanalyscd material. We 

 know, of course, that we abbreviate, when we say a behaviour pattern is 

 inherited or innate instead of saying that its anatomical and physiological 

 conditions are. But there is no reason for not using the term this way, as 

 long as we remain aware of the fact that characters always develop on the 

 basis of an inherited range of variation, all the more if the range of 

 modifiability is practically nil. 



Although we do not know yet what a fixed pattern is, a number of 

 investigations have made it highly probable that they share a common 

 physiological basis. Besides the peculiarities already mentioned, the fixed 

 pattern is characterized by a specific spontaneity (Lorenz, 1937), which 

 may be hypothetically explained by, the assumption of neural centres 

 creating impulses. The spontaneous activity of the central nervous 

 system has been demonstrated by von Hoist (1935, 1936, 1937), first in the 

 earthworm in which he discovered in the isolated ventral nerve cord salvos 

 of rhythmical impulses, corresponding exactly to the contraction of 

 segments in the normal creeping movements. Later von Hoist found that 

 even such highly complicated inborn motor patterns like swimming in 

 fishes are based on a central nervous system automatism. Von Hoist 

 explains this spontaneity by the hypothesis that there are groups of cells in 

 the CNS creating impulses. These groups of cells influence each other, 

 leading to certain forms of co-ordinated movements. 



Very little is known about the neuroanatomical basis for fixed patterns 

 but the experiments of Hess (1948), Hess and Brugger (1943) and the 

 recent investigations of von Hoist and von St. Paul (1959) strongly 

 indicate that fixed patterns are based on an inherited neurophysiological 

 mechanism. 



Experiments have shown that fixed patterns are released by certain key 

 stimuli which characterize simply but unmistakably the biologically 

 adequate situation, and release the behaviour pattern even in an in- 

 experienced animal. In other words, besides the innate ability to perform 



