498 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1957 



information, as contrasted A\-ith, for example, typing, playing the piano, 

 or tracking.* 



The work presented here, while undertaken independently, is in 

 general similar to and in agreement with that reported for reading rate 

 experiments by Licklider, Stevens and Hayes,- and by Quastler and 

 Wulff.^ However, we have considered some factors in more detail than 

 these workers, and also, contrary to the former group, we find that, 

 under optimal conditions, reading with tracking has a lower information 

 rate than reading alone. 



The chief problem investigated was: 



(1) Taking people as they are, ^\'ith no additional training, how fast, 

 in bits per second, can they transmit information by reading? 



(2) What principal factors control this limiting rate? 



The experimental procedure consisted simply of people reading aloud 

 as rapidly as they could typed lists of words. Each list was composed of 

 a single vertical row of 12 groups of 5 words, giving a total of GO words 

 per page. In each instance, the words were chosen at random from a 

 given vocabulary of words. If n is the number of words in the vocabularj' 

 and if the words are chosen ^^dth equal probabilities, and if all words are 

 read correctly,! the amount of information which is conveyed or trans- 

 mitted through the human being measured in bits is^ 



log2 n bits/word 



When the vocabularj^ for a particular experiment has much fewer 

 than 60 words, certain words must necessarilj^ be repeated several times 

 within a list. When the vocabulary is much greater than 60 words, repe- 

 titions are necessarily few and differences in reading rate among different 

 vocabularies would be expected onlj^ if the vocabularies differed in 

 nature, as in sjdlable length or familiarity of words. 



Unless otherwise specified, each result quoted below is the average 

 reading speed for two lists for each of three readers, chosen as repre- 

 senting fast, medium and slow readers for people mth at least a high 

 school education. The results on these three readers are substantially 

 similar to those on ten similar readers used in preliminary experiments. 

 The chief experiments performed, and some interpretations of them, 

 follow under numbered headings. Some supplementar}' experiments are 

 then described briefly and the over-all results are commented on. 



* Here tracking means successively pointing to a series of marks. 

 t In preliminary experiments the reader's voice was recorded, and it was found 

 that errors in reading aloud occur very seldom if ever. 



