KAO LIANG CHOW 515 



Beck, Doty and Kooi, 1958; Galambos, 1959). The present study empha- 

 sizes this point. The problem of functional localization is not of primary 

 interest. The search here centres on detecting systematic EEG alterations 

 in cortical areas known to be concerned with visual discrimination 

 learning in the monkey. 



Records have been obtained to date on six young monkeys. Each 

 animal lived continuously in a monkey chair throughout the 5 to 6 months 

 experimental period. The first 2 months were used to tame the animal 

 which was held loosely in the chair so that it could turn around, scratch 

 its head, lift the leg to scratch the back, etc. The animals continued to 

 grow and remained in excellent health. They were adapted to the testing 

 situation and trained to be quiet before each trial so that a relaxed, waking 

 EEG baseline could be obtained. Eight pairs of bipolar electrodes made 

 with 30 gauge nichrome wire, insulated except for the tip, were implanted 

 in the temporal and visual areas. Additional placements of electrodes in 

 the lateral geniculate body, the midbrain reticular formation, and the 

 hippocampus will not be reported here. After the completion of the 

 experiment, the brains were studied histologically. The electrodes were in 

 the middle and inferior temporal gyrus, and the lateral surface of the 

 visual areas. The electrode sites showed either slight cortical depression or 

 some scarring of the tissue, caused by direct injury or by the repeated 

 electric shocks (see next section). 



The test situation is shown 111 Fig. 4. Either two or three successive, 

 two-choice visual discriminations (red v. green; black triangle v. circle 

 on grey background; black and grey vertical i>. horizontal striations) 

 were presented to the animals. The training was conducted in a-dark- 

 room with a specially constructed photic stimulator as the light source. 

 The light was continuous between trials but changed to flashes (5-10 

 c.p.s.) before each trial. Thus, the animal saw the visual stimuli only 

 through the flickering light, which may serve as a 'tracer stimulus' 

 (Galambos, 1959, p. 334). Each trial consisted of presenting one visual 

 stimulus. If it was a positive stimulus, the moiikey was required to push 

 open the door of the stimulus box to get a food reward within 5 seconds. 

 For a trial with the negative stimulus, the door was locked and the animal 

 was required not to push the door within 5 seconds. A piece of food was 

 handed to the animal if it did not push the door when the negative stimulus 

 was presented three times in succession. A trial was given in the following 

 way: the opaque screen was in front of the monkey to conceal the stimulus 

 box. The EEG machine was turned on, continuous light was changed to 

 flashes, the opaque screen was removed and the stimulus was exposed 



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