The Individual as an Information Processing System 307 



power function of the stimulus magnitude. The exponent of this 

 function for loudness is about 0.3, while it is about 3.5 for the 

 apparent intensity of electric current applied to the fingers. 

 Stevens (5) notes that: "In three modalities investigated . . . 

 transducers . . . have three radically different operating charac- 

 teristics. The slow growth of loudness (exponent less than one) 

 suggests that the ear behaves as a 'compressor' . . . This com- 

 pressor action probably helps to make it possible for the ear to 

 respond to an enormous range of sound pressures — range of 

 millions to one. The apparent intensity of vibration on the finger 

 tip grows almost linearly with vibration amplitude — as though 

 the transducer were approximately linear. The effective range of 

 vibration amplitudes to which the finger is sensitive is of the order 

 of hundreds to one. (Incidentally, vibration on the arm does not 

 follow a simple power law.) The steep operating characteristic 

 for electric shock suggests the action of an 'expander' of some 

 sort; doubling the current increases the sensation about tenfold. 

 And correlated with this rapid expansion is a narrow operating 

 range of stimuli of the order of only tens to one." 



In input transducers the output signal usually differs from the 

 input signal in bandwidth characteristics. For instance, light of 

 different wave lengths and sound of different frequencies are 

 subjectively reported as various colors and pitches. Sensitivity 

 over the range of light waves and sound waves is not uniform. 



Also input transducers are active over only a limited range. 

 There are light waves above and below the visible spectrum and 

 sounds which the human ear cannot hear. 



Phase shift refers to the lag in phase of the output signal over 

 the input signal. Input transducers differ in speed of transmission. 

 For example, sound waves travel through the atmosphere quite 

 slowly but are transmitted rapidly through the auditory organ, 

 while light waves, which reach the eye very speedily, are processed 

 through a slow input transducer. Input transducers also differ in 

 the amounts and kinds of noise they insert into the signal. 



Channel and Net 



Broadbent (6) suggests that the whole individual may be re- 

 garded as a single channel which performs a selective operation 



