SECTIONAL TRANSACTIONS.— J. 487 



types of employment and indicate the importance, from the point of view of 

 industry, of social development as well as intellectual. 



Mr. J. G. W. Davies. — The place of interests in vocational adjustment (4.15). 



Friday, August 19. 



Presidential Address by Dr. R. H. Thouless on Eye and brain as factors 

 in visual perception (lo.o). (See p. 197.) 



Prof. A. Michotte. — Motor learning and morphology of the responses 

 (ii.o). 



Mr. F. B. KiRKMAN. — Recent field experiments on birds [1937-38) (12.0). 



Subject of experiments : the black-headed gull {Larus ridibundus) in its 

 breeding place. 



1. Recapitulation of previous experiments : what a gull will incubate 

 as functional equivalents of its eggs ; the range of equivalence ; the re- 

 sponse-determining factor common to the equivalents. 



2. What a gull will retrieve ("i.e. get back into the nest from outside) as 

 functional equivalents of its eggs ; the range of equivalence ; the response- 

 determining factor common to the equivalents. 



3. The gull's response when presented with an object that serves two 

 conflicting needs, e.g., hunger, broodiness. 



4. The relative strength of two selected opposing needs or drives : 

 broodiness and the territorial impulse. 



5. Conclusions. 

 Illustrated by lantern slides. 



Afternoon. 



Dr. F. W. Edridge- Green, C.B.E. — Acquired colour-blindness (2.0). 



Acquired colour-blindness, which may be temporary or permanent, 

 may be in every respect similar to congenital colour-blindness. A person 

 suffering from a septicaemic condition may become partially colour-blind. 

 When examined a year afterwards he may have recovered or become much 

 worse and become a very bad dichromic. Acquired colour-blindness 

 throws light on the nature of the colour sensations in congenital colour- 

 blindness. Red and violet are the two sensations of the dichromic, they 

 are the last to go and the first to reappear on recovery from total colour- 

 blindness. 



Mr. K. J. W. Craik. — Sensory adaptation in vision (2.45). 



It is well known that dark adaptation lowers, and that bright adaptation 

 raises, the absolute brightness threshold of the eye. The present paper 

 describes some investigations into the effect of such adaptation upon bright- 

 ness discrimination, visual acuity, and the subjective brightness of a uniform 

 field. The eye was adapted by prolonged exposures to fields ranging from 

 darkness to 5,000 or 10,000 equivalent foot candles in brightness, and its 

 acuity and brightness discrimination tested by brief exposures to equal or 

 different illuminations. It was found that brightness discrimination was 

 keenest, and acuity highest, when the eye was adapted to the same illumina- 

 tion at which it was tested ; testing at illuminations far above or below 



