J. p. SEGUNDO, C. GALEANO, J. A. SOMMER-SMITH AND ). A. ROIG 28 1 



but, in spite of having clear-cut 'dcsynchronizing' abilities (when applied 

 alone) was incapable (when applied during SS) of affecting evoked 

 potentials in a manner comparable to that of T (Fig. 6 — fourth line). 

 Resemblance of effects of T on the one hand and of EEG 'arousal' — 

 inducmg influences on the other, did not go beyond the electrographic 

 sphere. Separation could be established in the behavioural held: MRF 

 excitation was inoperant (sub-threshold) ; novel T and intense sounds were 

 either ineffective or produced 'surprise' effects (investigation reflex, 

 startle) : conditioned tones (CT) produced slight or no changes when 

 applied during SS. 



'OPPOSITE' EFFECTS OF DIFFERENTIATED TONES 

 I leOO'x.f-CESS SS) II leO^(DIFF) 



sil 





Fig. 12 

 'opposite' effects of differentiated tones, a tone of 1600 c.p.s. (but not one of 160 c.p.s.) 

 was reinforced by cessation of SS. Eventually, differentiation ensued (see te.xt and Fig. 11). 

 Reinforced tones (1600 — CESS. SS) masked large control evoked potentials; non-reinforced 

 tones (160 DIFF.) augmented small control potentials. 



Specificity of effects described above was explored from different points 

 of view. 



I. Frequency specificity. When a cat had been trained to respond to a tone 

 of a given frequency (e.g. 1.600 c.p.s.) habitually 'reinforced' by cessation 

 of SS, the first applications of a different frec]ucncy (e.g. 160 c.p.s.) 

 provoked a smiilar effect (generalization) (Fig. 11 — I, and A). After a 

 number of sessions in which one tone (1600 c.p.s.) but not the other 

 (160 c.p.s.) was reinforced by substraction of SS, three cats out of four, 

 reached a point in which effects were produced consistently by 1600 

 c.p.s. and exceptionally by 160 c.p.s. (differentiation) (Fig. 11 — I-b, B). 

 In this situation, it occurred frequently that small cortical responses (not 

 modified by the 'positive' tone) were augmented by application of the 

 'negative' tone (Fig. 12). 



