Twenty cats were classically conditioned using electric shock as the unconditional stimulus (US). A 1000 cps tone served as the reinforced conditional stimulus (CS+) and a 500 cps tone as the non‐reinforced conditional stimulus (CS–). The CS–US interval was 10 seconds. Data collected show a heart rate deceleration to the CS+ which is accompanied by a drop in blood pressure, respiratory apnea, a negative baseline shift of the galvanic skin potential (GSP), pupillary dilatation, a decrease of the electromyographic (EMG) activity of the muscles of the shocked foreleg, and a low voltage fast pattern of the electroencephalographic (EEG) activity of the sigmoid gyrus of the cerebral cortex and olfactory bulb. The heart rate deceleration is present after muscle paralysis with succinyl choline and it is blocked by atropine. It is presumed to be of vagal origin. Difference in CS+ and US responsivity is discussed.

This study tested twelve hypotheses derived from psychophysiological theory underlying the systematic desensitization method of reducing phobic anxiety. Subjects with phobias imagined threatening scenes and neutral scenes under relaxed or non‐relaxed conditions while cardiac, respiratory, digital vasomotor, and skin conductance activity was recorded. Seven hypotheses were confirmed for one or more response measures. The results indicated that (a) imagining threatening scenes produces autonomic arousal in direct proportion to degree of subjective threat associated with the scenes, (b) autonomic reactions do not extinguish and countercondition faster to weak stimuli than to strong stimuli, and (c) muscle relaxation has a demonstrable but limited effect on counteracting autonomic fear reactions. Desensitization theory was partially supported.

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A factor analysis methodology for the study of individual differences in response functions developed by Tucker (1958, 1966) was illustrated by analysis of conditional cardiac responses. Three cardiac (factor) responses were found: one acceleratory‐deceleratory, a second monophasic, and a third deceleratory‐acceleratory, over the CS–UCS interval. Individual conditional responses were composed of the acceleratory‐deceleratory component plus either positive or negative parts of the second and third components. Individual differences in conditional cardiac response forms were substantial. The factor model provided a better fit of observed responses than the average response model provided. The advantages of determining psychophysiological functions (laws) having explicit parameters for individuals were discussed.