CHAPTER LX 



Sensory discrimination 



WILLIAM D. N E F F Laboratory of Physiological Psychology,* University of Chicago, Chicago, Illinois, 



CHAPTER CONTENTS 



Historical Summary 



The Beginning of Scientific Inquiry 

 The Modern Period 

 Neurophysiological Basis of Sensory Discrimination 

 The Primary Sense Modalities 

 Discriminate Dimensions of Sensation 

 Intensity discrimination 

 Quality discrimination 

 Space discrimination 

 Pattern discrimination 

 Relation of the Primary Sensory Systems to Other Systems 



to report verbally when a stimulus change occurs; 

 often he is asked to respond by pushing a button or 

 by making some other nonverbal response. When a 

 lower animal is used as an experimental subject, it is 

 usually trained to indicate the stimulus change by 

 in. iking a movement, such as Hexing a leg, pressing .1 

 lever with its foot or moving from one position to 

 another in the test apparatus. In each case, the dis- 

 crimination consists simply of a motor response to a 

 change in some aspect of a physical stimulus which 

 acts upon the sensory end organs. 



in other chapters, the function of each of the 

 sensory systems has been discussed in detail. It is 

 the purpose of this chapter to consider the informa- 

 tion we have for all the senses in a less specific fashion 

 and to look for common principles which may have 

 emerged in the search for neurophysiological ex- 

 planations of sensory discrimination. 



To the sensory physiologist or psychologist, the 

 meaning of the phrase 'sensory discrimination" 

 needs no explanation. To others, its meaning may 

 not be clear immediately. Therefore, a brief ex- 

 planation is in order. The living organism makes a 

 sensory discrimination when it shows by its behavior 

 that it has made a response to a change in a physical 

 stimulus applied to one of its sense organs. It may re- 

 spond to the presence or absence of a particular 

 stimulus or may make a choice between two or more 

 stimuli. When man is used as a subject in an experi- 

 ment on sensory discrimination, he may be instructed 



1 The Laboratory of Physiological Psychology is supported 

 by the Office of Naval Research and the Air Force Office of 

 Scientific Research. 



HISTORICAL SUMMARY 2 



The nature of the questions asked and of the ap- 

 proaches taken in current research on sensory dis- 

 crimination can best be understood after a brief 

 consideration of the history of scientific investigation 

 of the sensory systems. 



The Beginning of Scientific Inquiry 



There is no evidence to indicate that learned men 

 of pre-Hellenic times attempted to account for how 

 man perceives the world by making careful observa- 

 tions and logical speculations; they were inclined to 

 account for natural phenomena in terms of the super- 

 stitions and religious dogmas of their particular 

 civilizations. 



Greek scholars did observe carefully and specu- 

 lated wisely. Handicapped by lack of knowledge — 



2 This historical summary is based for the most part on 

 secondary sources. For more complete accounts of the history 

 of the neurophysiology of sensation, the reader is referred to the 

 works of Boring and others (26, 28, 30, 46, 50, 63, 64 



'447 



