X 



INTERCONNECTED CHAINS: MULTIDIMENSIONAL 

 PSYCHOPHYSICAL ANALYSIS 



In some cases, for example in the making of aesthetic judgments, 

 the stimulus-objects are complex and may provide stimulation in any 

 number of distinct modes. Then if a statement of preference is called 

 for — one of two incompatible responses — the sequence of stimulus and 

 response may be regarded as a discriminal sequence as defined in the 

 preceding chapter provided we regard each of the two stimuli as a 

 resultant of the components in the various modes. The composition, 

 we may suppose, is effected in some way within the organism through 

 the concurrence at some point of the afferent chains leading from the 

 several receptors. 



The simplest scheme for representing the neural processes which 

 mediate a discriminal sequence of this type is the following. Suppose 

 that each complex stimulus-object, C P (p = 1 , 2), provides stimuli of 

 intensities C P ;(i = 1 , ■■• , n) in the n modalities, and that these stim- 

 uli send impulses independently along discrete afferent chains to the 

 synapse Si where they occasion the production of o- = S P i , the S P i for 

 each p combining additively to yield the S P hitherto employed: 



s P = zs 



Pi 



Each S pi is then some function of C pi alone; still regarding only the 

 near-threshold range we may take these functions to be all linear, 



S P = ^LiC pi -M. (1) 



We may now use either of the procedures introduced in the previous 

 chapter, with a = /5 , according to the choice of location for the ran- 

 dom element. In either case there are but three, or, with more special 

 assumptions, only two, functions P . The functions remain, however, 

 functions of the S P ; for any pair of stimuli d and C 2 , which provide 

 some (unknown, since the L, are unknown) <S X and S 2 , it is possible 

 to determine experimentally the relative frequencies P , and those 

 stimulus-pairs which yield the same values of the P's will be those 

 which yield a fixed difference 



Si-s;=2£i(Cn-&i). (2) 



The same result follows if we assume crossing inhibition connecting 

 also the pair of afferents affected by the two stimuli for each modal- 

 ity. This would justify extending the assumption of linearity to a 



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