E. GRASTYAN 245 



reflex disappear. In this stage the significance of the stnnuhis becomes 

 'certain' and as a consequence the 'what is it reflex' loses its biological 

 usefulness. 



It is very easy, however, to regain the orientation reflex after this stage 

 also, if we make a slight change in the learning situation. This happens 

 for example, if we introduce a differentiating stimulus or during extinction. 

 As a consequence of the application of the unreintorced stimulus, the effect 

 of the positive stimulus transicndy regresses, i.e. it elicits again the charac- 

 teristic slow waves in the hippocampus and the orientation reflex. 



At the time of stabilization of differentiation, the slow potentials again 

 disappear and desynchronization will be elicited by both kinds of stimuli; 

 however, in some cases when the differentiation proves to be too difficult, 

 remnants of the slow potentials can be observed to the very last. 



The conception that the orientation reflex corresponds to a conditioned 

 phenomenon seems to be contradicted by the common experience that 

 every new and unfamiliar stimulus is capable of eliciting the orientation 

 reflex if it is strong enough. However, I believe that the problem of 

 intensity of the stimulus requires special consideration. It seems probable 

 that with strong stimuli the conditioned factor is represented by the 

 intensity in itself, which is independent of the quality or the modality of 

 the stimulus. The animal in natural conditions often meets strong stimuli 

 signalling danger. The unknown amount of natural conditioned reflexes, 

 however, makes it difficult to decide in every case whether a stimulus is 

 new or not. By means of the tendency towards generalization, probably 

 considerable numbers of stimuli become more or less familiar to the 

 animal m natural conditions. As a consequence, it is sometimes very 

 difficult to find a completely indifferent stimulus for a mature animal. 



In asserting that the orientation reflex represents a conditioned mani- 

 festation, I have no intention of implying that the unfaimliar stimulus has 

 no effects at all at its very first application. Disregarding the well known 

 electrical reactions, marked somatic reactions can often be observed too. 

 These reactions, however, are not orientation movements, or at least are 

 not identical with those observed following the reinforcement of the 

 stimulus. 



The most common effect elicited by a new stimulus is the well-known 

 startle response, or a transitory form between the startle and orientation, 

 a quick, phasic movement of the head towards the stimulus. The startle 

 reaction has aroused the attention of several researchers in the past, and its 

 significance m relation to the temporary connection has recendy been 

 reviewed by Gastaut (1957). Let me give a short account of some of our 



