PERCEPTION 



r 597 



long as one's efforts are concentrated on reflex mecha- 

 nisms of the spinal cord, the problems of patterning 

 of skilled movements seem residual and nearly in- 

 soluble questions, relegated to some 'highest inte- 

 grating activity' of the central nervous system. The 

 very fact, however, that patterning should thus re- 

 main unexplained casts serious doubts on the ade- 

 quacy of current theories of coordination on spinal as 

 well as supraspinal levels (531 ). 



The distinction between sensory and perceptual 

 processes, and the preoccupation with the former at 

 the expense of the latter has historical rather than 

 logical reasons. We can trace the origin of this dis- 

 tinction by considering, first, a problem which cuts 

 across individual modalities of sensation, the problem 

 of measurement of sensory intensity and quality (psy- 

 chophysics). 



PSYCHOPHYSICS 



Reduction of Sensory Qualities 



The traditional distinction between sensation and 

 perception and the resulting difficulties have a long 

 history [admirably treated by Boring (53)]. Empiri- 

 cism has always been sensationism; experience could 

 not be acquired except through the senses, and the 

 senses could not err except for erroneous interpreta- 

 tion of their unequivocal message. Sensations were 

 elementary conditions of learning, while perceptions 

 were complex and learned; they were considered as 

 compounds in which present sensations gained their 

 meaning through related residues, 'images,' 'ideas' of 

 previous sensory events [see Berkeley (38)]. Yet the 

 sensations, so conceived, were actually postulates of 

 classical physics. 



From its renaissance beginnings, physics has sys- 

 tematically restricted its data by reducing the quali- 

 tative richness of everyday sensory experience to 

 certain quantifiable aspects of matter and of matter- 

 in-motion. Galileo established physical acoustics by 

 suggesting that perceived pitch might be reducible 

 to frequencies of vibration in a medium such as air 

 or water. [See Galileo Galilei (141); the Galilean 

 discovery was communicated two years earlier by 

 his correspondent Mersenne (344)] Newton analo- 

 gously referred perceived differences in hue to corre- 

 sponding differences in vibrations of the ether, 

 likening these to vibrations of air which "according 

 to their several bignesses, make(s) several tones in 

 sound." He did so in spite of his increasing prefer- 



ence for a corpuscular theory of light; in fact, his 

 curious insistence on seven primary colors was based 

 on an explicit analogy to the seven tones within the 

 octave (361). The progressive elimination of sensory 

 qualities in physics culminated in the nineteenth 

 century, 2 and it was at that time that 'psychophysics' 

 arose as a systematic effort to reintroduce the 'lost' 

 qualities through a special form of experimentation. 

 The very form of these experiments at first reinforced 

 the distinction of sensation and perception. 



Attempted Restitution 0/ Qualities in Psychopfq 



In the typical psychophysical procedures of the 

 nineteenth century, as formulated by Weber (523), 

 Fechner (122), von Helmholtz (501) and Wundt 

 (551), attributes of sensation, such as pitch, were ex- 

 plored by systematic \ariation of a single physical 

 dimension, such as frequency , as if pitch were the per- 

 ception of the frequency of a tone. Thus, a one-to-one 

 correspondent!' between physical and sensory dimen- 

 sions was assumed, although Weber I 523) had already 

 established that such a correspondence was not 

 linear: for anv given intensity of stimulation, /, the 

 just noticeable difference, A/, was known to vary with 

 the intensity of stimulation, where / was small, SI 

 tended to be small, where / was larije, A/ tended to 

 be lame, in fact, Weber believed that one might 

 formulate a law : A/ / = constant (Weber's law I. 



For instance, in judging differences of weights 

 placed successively on the finger, the just-discrimi- 

 nable difference (or, as we now say, the Weber frac- 

 tion) was thought to be approximately constant at 

 1 30. From Weber's law, Fechner derived, by inte- 

 grating, the expression .V = A' log / (Fechner's law) 

 where S is the magnitude of sensation, measured in 

 some appropriate unit, and / the stimulus measured 

 in terms of physical units defining the absolute 

 threshold. 



This simple logarithmic relation between stimulus 

 and sensation cannot be valid if just-discriminable 

 differences of sensation are unequal, i.e. Fechner's 

 law cannot hold if Weber's law is incorrect. The 

 evidence, available for many sensory dimensions, 



- It could be argued that classic physics, by eliminating most 

 aspects of everyday experience from its primary data, elevated 

 somatic sensation to the status of prototype of all sensation; 

 mechanics implies action and reaction through contact, 

 especially if forces acting at a distance are denied. The much 

 greater abstractness of modern physics is accomplished by 

 abandoning any attempt at reconciling the structure of physical 

 reality with that of perceptual phenomena. 



