lixil) 



II \M)Bl M 'k l 'I I'HYM' ILI >G"S 



NEUROPHYSIOLOGV III 



fig. 4 A configuration illustrating assimilation, contrast and the role of boundaries in structuring 

 .1 visual field. Bisecl the gray ring by placing a pencil across it, vertically, and note the abrupt 

 darkening of the right half of the ring, and the increase in brightness of the left half, by moving the 

 pencil to the left or right, contrast can be "drawn" from one side to the other. [Based on Koffka (284). 



Rubin himself and others Mich as Wertheimer (537) 

 and Musatti (356) to define the stimulus determi- 

 nants which decide what pan of a pattern will become 

 figure and whal part ground. It is often, but not al- 

 ways, the enclosed portion that assumes figure 

 character, but ,1 complete enumeration of factors has 

 never heen achieved. 



Ii is possible to make the stimulus situation am- 

 biguous so that what is figure can also be seen as 

 ground and conversely fig . . ii is under these con- 



1 greater or lesser ambiguity that subjective 



determinants (attitudes, past history) on the part of 

 the perceivcr can pla\ their role in determining whal 

 is seen Although the figure-ground principle was 

 in 1 developed foi the somewhat artificial situation ol 



bidimensional patterns on paper, ii probably holds 

 for iridiinension.il visual objects and seems to have its 

 analogues in other sensor} modalities (250, 553). The 

 era! importance of the figure-ground principle is 

 underscored I >y the observation that ambiguous figures 

 are apparently not rccouni/cd by most subjects if on 

 second presentation their figure-ground articulation 

 has become reversed 1 41 >l i 



principles of grouping. What determines figure 

 formation in a stimulus array? Wertheimei (537) has 

 derived a scries of principles of grouping or phe- 

 nomenal laws, the most important being those ol 

 proximity, similarity and 'good figure.' These 'laws' 

 of grouping have heen severely criticized. For one. 



