The Individual as an Information Processing System 309 



of letters, playing cards, scales, or dials. His research was designed 

 to establish the principal factors limiting performance. 



With these experimental conditions, the performances which 

 were obtained were at peak rates which could have been achieved 

 only under favorable conditions. Quastler (10) says: "We find 

 that people can make up to five to six successful associations per 

 second, can transmit about twenty-five bits per second, can operate 

 efficiently over a range of about thirty possible values and can 

 assimilate some fifteen bits at a glance. We do not expect that 

 they will reach such perfonnance levels with every kind of activity; 

 in fact, we know that they usually do not.'' In bits per second, he 

 and his colleagues found peak performances for piano playing of 

 twenty-two bits; for reading aloud, twenty-four bits; and for 

 mental arithmetic, twenty-four bits. They concluded that the 

 peripheral input mechanisms were not responsible for limitations 

 upon information processing. Quastler (11) notes: "The capacity 

 of the optic nerve is many orders of magnitude higher than twenty 

 or forty bits per second ; a much wider range of symbols could be 

 accommodated with the resolving power of the retina. As to speed 

 limitations, it is known that about three symbols are grouped in 

 the act of reading, and that about four such groups can be assimi- 

 lated in a second; this gives twelve syinbols per second, con- 

 siderably more than the highest useful speed in typing or piano 

 playing. On the output side, it is easy to see that the limitations 

 of the actual speed, both alone and in combination with precision, 

 cannot be attributed to mechanical difficulties. In all tests, ob- 

 served speeds would have been much improved by rehearsing. 

 Thus the mechanisms which limit the observed performance must 

 be connected with the speed of processing information." 



Signal-to-noise ratio can be important in the specification of 

 channels where minimal energies are involved. Barlow (12) has 

 shown that the limiting factor in the absolute threshold for vision 

 is fluctuation in the noise in the visual pathways. 



The Decoder 



If information is to be used by the individual, it must be suitably 

 coded. That is, it must be in a language or signal system which 

 he can understand. Deininger and Fitts (13) have experimented 



