32 K. S. LASHLEY 



the cortex abolish the visual habit. We must conclude, there- 

 fore, that the cerebral mechanism of the visual habit is largely 

 confined to this occipital region. 



Within this region the experiments show that the various 

 parts are equipotential for the performance of the habit. 

 As was brought out in the preceding section, animals making 

 thirty or more errors in retention tests showed a distribu- 

 tion of lesions such that only a small dorsal region (text fig. 4) 

 was common to all. The range of destruction in these animals 

 is from 15.8 to 29.1 per cent of the neopallium. The average 

 destruction was 22.4 per cent. Thus, except for the small 

 dorsal region, every possible part of the visual area escaped 

 destruction in one or another animal, which nevertheless 

 showed serious disturbance of the habit. In contrast to this, 

 the combinations of lesions in animals which showed little 

 disturbance covers every part of the occipital region (text 

 fig. 5). Thus, the habit of brightness discrimination survives 

 the destruction of any part of the occipital region, provided 

 that the lesion is small, whereas it is abolished by larger 

 lesions irrespective of their location within the occipital areas. 

 This can only mean that the cerebral mechanism of the habit, 

 whatever its physiological character may be, is diffused 

 throughout the occipital region. Any part of the mechanism 

 can perform the functions of the whole, in the absence of 

 other parts, provided only that a suflficient quantity of tissue 

 remains intact. The evidence opposed to the view that this 

 is the result of scotoma seems conclusive and leaves only 

 the hypothesis that the lesions produce an amnesia, as con- 

 sistent with all the results of the experiment. The quantita- 

 tive data point to the conclusion that the efficiency of the 

 memory trace is proportional to the amount of functional 

 tissue, irrespective of its locus, and this in turn suggests 

 that the function of the memory trace must in some way be 

 additive, efficiency increasing as a simple function of the mass 

 irrespective of the neural patterns involved. 



