372 John R. Platt 



I. MOSAIC RECEPTORS 



Single-element and Multiple-element Receptor Systems 



A feedback mechanism or a neural network or a social organization is a 

 decision network connecting sensory-receptor inputs with motor-effector outputs. 

 The system may have single-element receptors or multiple-element receptors. An 

 example of a single-element receptor is a phototube. Another is a proprioceptive 

 muscle spindle cell. In the simplest case each of these might actuate a single- 

 channel feedback loop or reflex arc leading to a one-coordinate output function 

 of time. There may be non-linear circuit elements in the loop that pulse or 

 chop or clip or average or stabilize the input or otherwise transform it. Never- 

 theless, each feedback signal from a single-element receptor remains a one- 

 dimensional time signal except as it may be trivially or artificially split into 

 several components. 



Multiple-element receptors consist of many functionally similar single- 

 element receptors acting simultaneously. If each of these has its own private 

 reflex arc, independent of the others, to its private motor output, the system is 

 merely an additive system of single-element receptors. But to avoid conflict 

 in the motor responses, it is desirable to reduce their independence. In this case, 

 the simultaneous inputs can be combined in a decision network which selects a 

 single complex response from the output field, with suppression of conflicting 

 alternatives. Some of the physical and mathematical relationships in such a 

 network were discussed earlier (1). 



The receptor organ of such a system becomes a mosaic receptor with a 

 pattern and hierarchy of connections to the decision network. It is an advantage 

 if the network is concentrated into a compact central switchboard where 

 extensive interconnections can be made quickly and cheaply. 



Examples of mosaic receptors are the 10^-element retina of the human eye, 

 the basilar membrane of the ear, and the olfactory membrane. The retina will 

 be treated as the prototype of such systems. Mechanical mosaic receptors have 

 also been constructed such as the lO^-element assembly of sensory pins in the 

 reading head of a punch-card sorter or reader. A social mosaic receptor would 

 be the 10- traveling salesmen sent out by a business organization. The relatively 

 low complexity of these man-made systems means that they are inferior to their 

 biological counterparts by more orders of magnitude than almost any other 

 man-made devices. 



It is true that some artificial receptor systems are more elaborate than the two 

 mentioned. A television camera iconoscope tube with its 1 0^ separate resolvable 

 spots is an example. But at present, the iconoscope signals are scanned and 

 sent in sequence into a single output channel, undergoing only the most rudi- 

 mentary inter-comparisons or decisions, such as stabilization, contrast or color 

 balance. Likewise the 10^ grains of a photographic emulsion, although they form 

 a very fine-grained system, do not feed into any decision network until they are 

 transduced onto the human retina. 



Pre-addressed and Non-addressed Mosaics 



An address, in computer nomenclature, designates a point in the network at 

 which a signal may be located. But in a mosaic receptor, the address of an 



