1. The Social Use of Space 71 



rary store. Storage here is in terms of seconds only. From this short-term 

 store, signals must pass through a hmited capacity channel before they 

 can serve to initiate immediate responses or reach a long-term store where 

 the signal can be preserved to affect later action. Signals passing through 

 the limited capacity channel from the temporary store may be passed 

 back through another circuit and reenter the temporary store. Likewise, 

 responses made to a stimulus or a sequence of stimuli, in turn, serve as 

 stimuli which generate signals entering the temporary store. Furthermore, 

 several signals may arrive simultaneously at the temporary store through 

 separate sensory channels. Only a portion of these signals in the tempo- 

 rary store can get through the limited capacity channel. 



There has evolved a neural mechanism which Broadbent calls a "filter," 

 intervening between the temporary store and the limited capacity channel. 

 This filter "selects" which signals may get through the limited capacity 

 channel and thus be available for (a) recirculation into the temporary 

 store, (b) inducing immediate response, or (c) entering the long-term 

 store. 



The following conditions affect the probability of signals passing through 

 the filter: 



1. The signal is of the same class as that of the prior signal. That is, 

 the related stimulus has similar characteristics in terms of frequency, in- 

 tensity, pattern, or location of origin. In other words, the filter tends to 

 pass in sequence several signals from stimuli with related characteristics. 



2. However, the longer a given category of signals has been passing the 

 filter, the more likely the filter will switch to signals arriving from a differ- 

 ent sensory channel. 



3. Signals generated by intense or infreciuent (novel) stimuli e.xhibit a 

 high probability of passing through the filter. 



4. Given any three signals in the temporary store and one is passed 

 through the filter, the one of the remaining two most likely to follow it is 

 the one which followed it most frequently on prior occasions. 



A special case will particularly concern us. An animal may exhibit both 

 bodily response and vocalization to a given external stimulus. Each of 

 these responses also becomes a stimulus with a high probability of associa- 

 tion, each with the other, and each with the external stimulus. As the ex- 

 ternal stimulus becomes weaker, only the bodily response is preserved. 

 Presumably the reason for this is that the bodily response represents 

 a more intense stimulus and for this reason develops a higher conditional 

 probability of association with the external stimulus. That is, the signal 

 from the bodily response stimulus is more likely to pass through the filter 

 immediately after the signal from the external stimulus. 



