500 THE BELL SYSTEM TECHNICAL JOURXAL, MARCH 1957 



Experiment 2: Effect of Word Length and Familiarity 



It was not clear from Experiment 1 how much of the drop in word 

 rate for the dictionarj^ hst was affected bj' decreased familiarity and how 

 much by increased word length. 



These two variables were then untangled in a separate experiment. 

 Word lists were prepared which kept both length and familiarity rela- 

 tively constant for a given list. The words were chosen from a list of the 

 20,000 most frequently encountered words in the language.^ Reading 

 rates were measured for the thousand most familiar words, for the ninth 

 to tenth thousand most familiar, and for the nineteenth to twentieth 

 thousand most familiar words. 



The results are shown in Figs. 3(a), (b), and (c). There is considerable 

 consistency among readers as to the relative effect of length and famili- 

 arity. The most familiar trisyllable words, for example, are read about 

 as rapidly as the least familiar monosjdlables, 



A confirmatory demonstration of the effect of familiarity upon reading 

 rate is shown in Fig. 4. This shows reading rates for randomized lists of 

 eight nonsense words averaging 1.5 syllables/word (e.g., jevhin, tosp) 

 which are necessarily totally unfamiliar when the reader first encounters 

 them. As the reader becomes more familiar with the words on successi^'e 

 readings, his word rate increases until he approaches the rates of familiar 

 words in Fig. 2. 



Experiment 3: Preferred Vocahidary for Increasing Transmission Rate 



The transmission rate is the product of the reading rate and the 

 logarithm to the base 2 of the vocabulary size. To maximize the rate we 



Fig. 1 — Parts of tj'pical lists for vocabulary sizes. 



grew foot 



action tomorrow 



grew count 



grew issue 



action rain 



action month 



grew earth 



grew cook 



action build 



action corner 



grew j-ard 



action historj- 



grew forest 



action pleasant 



grew wrong 

 (a) (b) 



