326 Information Storage and Neural Control 



This decrease of information output rate in living systems is 

 not the result of destruction of the system by an overload of the 

 energy which conveys the information because 1) the process is 

 reversible — decrease of input rate immediately raising output rate 

 back to channel capacity, and 2) final irreversible change of such 

 systems by energy input undoubtedly occurs when the energy is 

 orders of magnitude greater than that involved in informational 

 overload. 



b) There is a hierarchical, cross-level difference in maximum 

 channel capacity. Assuming pulse-interval coding, we found this 

 to be of the order of 4,000 bits per second for neurons in the 

 frog sciatic nerve, and about fifty bits per second for a single 

 channel in the visual nervous system of the rat. It was six bits 

 per second for the individual, three bits per second for a single- 

 channel group, and three to four bits per second per channel in 

 a small social institution with about the same number of com- 

 ponents in each channel as there were in the group. 



Apparently the more components there are in an information 

 processing system, the lower is its channel capacity. There are 

 several reasons for this. Two of the most obvious are that recoding 

 of information is necessary at the border between each component 

 and the next, and that such recoding always results in loss of a 

 certain amount of information. Moreover, if there are n com- 

 ponents in any system, one must have a lower channel capacity 

 than the others, and the statistical probability of there being such 

 a slow component is always greater as n increases. This sluggish 

 component constitutes a bottleneck, since no channel is faster than 

 its slowest component. 



c) Several of the adjustment processes are used by all of these 

 systems, the use increasing as input rate rises. 



d) Fewer adjustment processes seem to be available to the 

 systems at the lower levels. Those employed at the higher levels 

 appear to be more complex as well as more numerous, although 

 their fundamental similarity to the lower level processes is clear. 



Of course the findings for other types of systems at each of the 

 levels might be difTerent in significant ways from our findings in 

 the particular systems we chose to study. The goal of these projects 



