Monitored heart rate and suppression of bar pressing concurrently in 24 male hooded rats during the W. Estes and B. Skinner (see pa, vol. 16:534) cer situation. Variations in ucs intensity and type of cs were found to affect changes in these responses differentially. When white noise interrupted at a low frequency was used as the cs, there was no difference in the rate of acquisition of a decelerative heart-rate response and of suppression of bar pressing. When the cs consisted of white noise interrupted at a high frequency, increases in shock intensity retarded the acquisition of the decelerative heart-rate response, but not of suppression of bar pressing. (23 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)