AN EXPERIMENTAL ANATOMICAL STUDY OF 



SENSORY MASKING* 



Introduction 



THE TEMPORARY local "benumbing" effects of stimulating nerves with certain 

 electric currents have been known for a long time— certainly since 1858, 

 when Robert^ suggested that this diminished perception results not from 

 anesthesia in the ordinary sense, but from diversion of attention, or confusion 

 of consciousness, by the sensation springing from the electrical stimulus. This 

 type of diminished sensibility, the mechanism of which he attributed to the 

 central nervous system (though the electric current was applied peripherally), 

 Robert designated "anesthesie de diversion," or "masking." Detailed reference 

 to the nunrerous subsequent observations of this phenomenon (for example 

 by Peterson, Leduc, and others) seems unnecessary; an experimental study was 

 published by Thompson, Banks, Barron, Fratis and Mattison in 1934." Think- 

 ing, with Robert, that the diminished sensibility was central in nature, I pro- 

 posed^ in 1933, upon the basis of purely subjective experience, to follow him 

 in calling it "masking." In 1934 my assistants (L. W. Denny and J. C. Luce) 

 and I performed a series of experiments upon ourselves, designed to prove or 

 disprove Robert's suggestion that this type of ciiminished perception is a 

 central phenomenon. I gave a preliminary account' of these experiments before 

 the Association foi' Research in Nervous and Mental Disease on December 27, 

 1934. In 1935 Davis and Derbyshire" advanced evidence that auditory masking 

 is a peripheral phenomenon, dependent upon the refractory period of nerve 

 fibers. Thereupon, in a note to Science,''' I gave another preliminary (illustrated) 

 account of our experiments; concluded that they confirmed Robert's sugges- 

 tion that this type of electrical masking is a central phenomenon, and suggested 

 that the term "masking" be restricted to Robert's original usage. Stevens' and 

 Henry^ objected to this suggestion, mainly on the ground that in the literature 

 of audition the term "masking" has been employed in a purely phenomenologi- 

 cal way, withoiu reference to suggested underlying mechanisms; they urged the 

 continuance of this practice. Though not convinced that it is wholly justified, 

 I prefer adopting their contention to arguing about it. 



Observations and Discussion 



This contribution is mainly a detailed account of the experiments referred to 

 above, now published for the first time. Many of these experiments involved 



* From the Departments of Anatomy of the Universities of California and Manitoba. Tliis 

 investigation was aided by grants from the Board of Rcsearcli of the University of California, 

 and from the Uni\ersity of California Chapter of the Society of Sigma Xi, to whom appre- 

 ciative acknowledgments are tendered. The procaine used was kindly donated by Ely Lilly 

 and Company. All the injections (save one) were skillfully performed by Dr. A. A. Koneff. 



L 555 J 



