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This investigation studies the changes produced in the electroencephalogram during the course of conditioning, i.e., from the beginning of conditioning to the end of extinction. Pure tone (1, 000 cps and about 70 db) and light were used as conditioned and unconditioned stimuli respectively. The conditioned response Could be traced in EEG in almost all the subjects.
The characteristics of the changes in EEG found in this experiment may be summarized as follows :
(1) Under tone stimulation alpha waves do not show any tendency to increase with the progress of conditioning.
(2) In the early stage of conditioning and also at the end of extinction, alpha waves gradually increase during tone stimulation, but this tendency to increase takes a different form in each case.
(3) On the other hand, when the conditioning is well advanced and comes to be nearly completed, alpha waves appear very much in the begining of tone stimulation and decrease gradually with its continuance. This decrease may be considered as the manifestation of the expectant reflex and perhaps is characteristic of the conditioned response in EEG.
(4) With respect to the duration of the disappearance of alpha waves, the extinction process seems to have a special pattern of its own.
(5) There is a limit to the duration of the disappearance of alpha waves. even if the number of conditioning is increased ; the duration is limited by the duration of light stimulation.
(6) In the first extinction trial, after the cessation of tone stimulus alpha waves increase in inverse ratio to the number of conditioning. Alpha waves disappear, however, after ten trials of conditioning.
(7) The number of appearance of the conditioned response is approximately proportional to that of conditioning.
From (6) and (7), it may be inferred that the greater the number of conditioning is, the greater will be the strength of conditioning.
(8) The changes in EEG produced after light stimulation in conditioning bear a resemblance to those that appear after the conditioned response in extinction. In both cases, alpha waves disappear for the first one or two seconds and increase rapidiy for the next five to seven seconds, and then they decrease again. The process continues for sometime in a smaller scale.