Effects of Pavlovian conditioning procedures in which CS follows US were demonstrated in dogs. In Experiment 1, tone onset occurred 1 sec. before (cessation-conditioning group) or 1 sec. after (backward-conditioning group) shock termination; presentation of CSs during Sidman avoidance responding in the shuttle box resulted in decreased rates. In Experiment 2, tone following shock termination by 15 sec. produced similar effects, while CS which followed shock termination by 1 sec., but was not reliably followed by a long ITI, was ineffective. Thus, although these procedures produce inhibition of fear, this result is not due to a backward associational process, but to the fact that, when CS follows US and the ITI is long, the CS signals safety.
Th e extent of novelty reactions and of disruption of a running response, brought about by stimulus changes made at cue-pos iti ons located a t different distances from the reward, were me asured in 12 rats. Both measures showed higher values for the cue-pos iti on closer to the reward. The results support the idea of a gen eral attentiveness factor that is distinct from obs erving responses which might emerge as a consequence of differential responding. Problem The conc ept of' 'observing responses " was introduced by Wyckoff (1952) a s a variable responsible for some perceptual s electivity in discrimination tasks. The dev elopment of observing r esponses is considered by Wyckoff to be a fun ction of the extent to which S responds differently to discriminative stimuli; differential res ponding is a ssum ed to be ne cessary for reinforcing observing r esponses. Thus he r egards the eme r gence of any specific set of observing responses to be linked to particular di scriminative s ti muli. However, it seems reasonable to suppose that some additi onal , nonsp ecific a tt enti onal fa ctor m ight also pl ay a part in the early stages of discrimination learning. In the present study we investigated the possible existen ce of such a general a ttentional factor th at might precede the eme r gence of differentiated observing r esponses. Raskin (1965) has shown th at succ essive discrimination learning in a runway is inversely r el ated to the degree of cue-rewar d separation. On the a s sum pti on of a general attentional fa ctor, one would expect Ra skin's Ss to have attended differentially to stimuli at the two cue-position areas r egardless of the su ccess or fa ilure of discrimination le arning and of the presence or absence of discriminative stimuli. In the present expe r ime nt we examined this possibility by studying "novelty r ea ctions" (rearing, sniffing, etc.) made by rats in r esponse to stimulus change s introduced at the two cue-pos itions in th e same discrimination apparatus a s was us ed by Raskin. Th e exte nt of increase in novelty r eactions following a stimulus change a t a cue-pos ition would indicate th e de gree to which the animals had atte nde d to th e original stimuli at th at position. We exp ected a stimulus change in the ne ar cue-position to evoke novelty r eactions and inter fe re with th e r unning r e s ponse eve n when Ss had been given di scrimination training (unsu cce s sfully) with cues in th e po s ition fa r from the goal. Ie.hod Th e Ss were 12 naive mal e hood ed r ats, about 100 days old. They wer e maintained on a 23-hr water
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