D. O. HEBB 49 



As far as L)r Hcbb's experimental data are concerned, I hnd them very interesting 

 and possibly requiring further elucidaton. They show that the d}-namic memory 

 trace, produced by presentation ot a given series of numbers, is not totally oblite- 

 rated by the subsequent scries. It would be interesting to know what will be the 

 rate of memorizing of the repeated series if it recurs less frequently than in Dr 

 Hebb's experiments, and whether it is possible in this way to prevent memorizing 

 of tliis series at all. 



I realize the difficulty connected with the understanding of transient memory of 

 series of items in terms of reverberating circuits. May be that the place of a given 

 item in the sequence is determined, among other things, by the strength of the 

 retroactive inliibition produced b}' the following items. I also agree with Dr Hebb 

 that all the series he used in his expermients are in a greater or lesser degree already 

 included in our stable memory repertory and one has only to remember that this 

 and not that sequence was presented at the given moment. 



Hebb. I should make clear that Milner did not develop liis conception to account 

 for those results. On the contrary, I was still struggling to find some intelligibility 

 in the data when I saw Milner's paper. 



If I have given the impression of thinking that Dr Eccles's position was pure 

 dogma I should like to get that corrected right away. It seems to me that it is dogma 

 to maintain the negative proposition that something like electrical fiicilitalion 

 cannot happen. The positive side ot chemical transmission has been established well 

 beyond anv questioning bv me, but there is still the possibility that you might have 

 some ancillary mechanism. 



I can find no way, to come to Dr Konorski's second question, of accounting for 

 the ordering in that series. I remind you that the same digits are used trial after 

 trial, and that the essence of the successful response is in the proper ordering. 

 Suppose that each one of these systems is firing and reverberating. What deter- 

 mines the order in which the)' cause the motor sequence? I would only say that as 

 nearly as I can determine there must be in addition to reverberation, some sort of 

 connection between the separate reverberation systems, so that A fires its motor 

 paths and then causes B to do so — and not vice versa. There is some short-term, 

 essentially structural, modification which with repetition may turn into something 

 more lasting. 



Gerard. Dr Konorski, I was not for one moment objecting to going down to 

 the synapse; you will remember I went all the way down to the molecule in the 

 first paper. I simply said that whatever specific mechanism one assumes at the 

 synapse is irrelevant to the problem Dr Hebb is facing. The problem is whether or 

 not a message gets to the synapse, not how it produces a change there. The questions 

 are at different levels. 



Thorpe. With reference to the one trial learning experiments with the insects 

 Philaiitliiis and Auiuiophila bv Tinbergen and Baerends I would like to say first that I 

 don't think there is the slightest doubt about the facts. It is quite easy to observe the 

 orientation flights of these insects. Secondly I would like to point out that the task 

 learned on these flights is in itself a very complex one. Moreover it is a kind of 

 serial learning since, because of its very nature, the insect's eye cannot be getting a 

 unitary vision of the whole field; on the contrary it is flying around picking up the 

 various landmarks one after the other — and they may be numerous. So it seems to 

 me to be a decidedly complex piece of learning; not as complex a task perhaps as 



