282 BELL SYSTEM TECHNICAL JOURNAL 



Nature of the Problem 



In the simplest case of conversational interchange each party speaks 

 for a short time, pauses, and the other party replies. The time intervals 

 are then simply the lengths of time each party speaks and the lengths 

 of the pauses between speeches. The period during which there is 

 speech may be called a talk-spurt, and the length of the pause may be 

 called the response-time. These two quantities would then suffice to 

 describe this simple type of interchange. 



In many instances, however, the process is not so orderly; for 

 example one speaker may pause and then resume speaking, or the 

 listener may begin to reply without waiting for the end of the talker's 

 speech. The possible, and indeed frequently encountered, variations 

 of the simple cycle of which the preceding examples constitute only a 

 fraction make it necessary to carefully define and delimit the elements 

 into which a conversation may be resolved. It is believed that any 

 telephonic conversation between two persons can be completely de- 

 scribed in terms of the presence or absence of energy by the following 

 time elements: 



A talkspurt is speech by one party, including his pauses, which 

 is preceded and followed, with or without intervening pauses, by 

 speech from the other party perceptible to the one producing the 

 talkspurt. Obvious exceptions to this definition are the initial 

 and final talkspurts in a conversation. There may be simul- 

 taneous talkspurts by the two talkers; if one party is speaking 

 and at the same time hears speech from the other double talking 

 is said to occur. 



Resumption time is the length of the pause intervening between 

 two periods of speech within a talkspurt. 



Response time is the length of the interval between the beginning 

 of a pause as heard by the listener and the beginning of his reply. 

 It may be positive or negative. The pause to which reference is 

 made ordinarily occurs at the end of a talkspurt but may be a 

 pause followed by a resumption of speech by the first talker. 



In the terms of these definitions a telephone subscriber "hears" or 

 "perceives" when voice currents flow in his receiver; a possible lack 

 of attention or other failure to appreciate what is "heard" is not 

 considered. Likewise, it should be stressed that pauses are not con- 

 fined to the intervals between words or sentences but may occur within 

 words; in the measurements described herein they are determined 

 solely by the absence of voice energy on the circuit. 



In addition to these natural conversational elements there is a fourth 



