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Thirty pictures, rated on 22 scales, were shown to 34 males, while pupillary diameters and heart rates were recorded, to test the prediction that attention to the environment leads to sympathetic‐like dilatation and parasympathetic‐like cardiac slowing, and to study the relationships of the responses to stimulus‐attributes. The prediction was satisfied, demonstrating directional fractionation and situational stereotypy. Tonic levels changed significantly during the experiment and also showed directional fractionation. A few individuals and stimuli, however, yielded reliable pupillary constriction, demonstrating intra‐stressor stereotypy. Four factors characterized the ratings, two of which were associated with the autonomic responses. Pupillary dilatation and cardiac slowing increased as the Attention‐Interest value increased. Pupillary dilatation was greatest to pictures midway on the Pleasantness‐Evaluation factor, and greater to unpleasant than to pleasant stimuli. Cardiac slowing was linearly related to pleasantness, with unpleasant stimuli provoking the greatest slowing. The two responses were correlated less than measurement reliability would have allowed, demonstrating quantitative dissociation. When base‐corrected scores were used the correlations again were low and highly variable among subjects and stimuli, even in direction.

Results oj earlier and ongoing research dealing with time within the cardiac cycle as an experimental variable are summarized. In a variety oj different experiments, meaningful sensorimotor events produced changes in heart rate that were systematically related to where in the cardiac cycle the events occurred. This junction is proposed as a noninvasive measure in intact humans oj cortically mediated ejects on vagal control oj the heart. Time within the cardiac cycle is also a dependent variable: Self-initiated responses are postponed to increasingly later times as momentary heart rate increases. It is hypothesized that this may result from visceral afferent feedback to the central nervous system via the baroreceptor nerves. Preliminary results are presented from acute cat experiments showing that changes in frequency oj carotid sinus stimulation, and differences in the direction oj change, affect the temporal pattern of discharge of the carotid sinus nerve.Since prehistoric times it has been known that the heart has the characteristic of autorhythmicity. A heart removed from the chest of a slaughtered animal, or from the chest of a human in preparation for a transplant, continues to beat at its own pace. The reason is that the origin of the heartbeat lies within the heart itself. In the normal heart, the beat is initiated at the sinoatrial node. Here, a series of biochemical processes, of repetitive membrane depolarization and repolarization, results in repetitive transmission along the heart's own conductive tissue system, which, in turn, results in cyclic contraction and relaxation of the cardiac muscle.In situ, within the chest cavity, the heart's autorhythmicity is modified by both neural and humoral factors. The heart is slowed and speeded by the vagal and sympathetic cardiac efferents. But action at the effector organ does not end the process: Sensitive interoceptors feed back to the central nervous system information about the timing, force, volume, and pressure of each, heartbeat. This feedback loop provides an oscillatory input to the central nervous system.We are concerned in this article with limited aspects of the significance for behavioral science of these efferent and afferent connections. We will deal with a relatively novel variable: time within the cardiac cycle. In our studies of efferent mechanisms affecting the heart, time within the cardiac cycle is an independent variable, and we discuss, in an elementary way, the biochemical processes at the sinoatrial node. In our studies of presumably afferent mechanisms, time is a dependent variable.Our presentation is limited to bare essentials, since space does not permit an exposition of the statistical and experimental controls we employed to provide assurance of the validity of our general statements. Nor have we time to discuss other than main effects. On the Efferent PathWe have spoken in the past of the "bradycardia of attention," for one general formulation that emerged from our early work was that the intention to note and detect external stim...

In one experiment, 60 male college students counted silently the number of rarely presented tones embedded in a sequence of “standard” tones. The tones differed by 50 Hz. Both rare and standard tones produced a primary bradycardia which exhibited time‐dependency: Stimuli which happened to fall relatively early in the cardiac cycle prolonged the duration of that very cycle more than late‐occurring stimuli. The latter slowed the subsequent cardiac cycle. These effects are identical qualitatively with those found in acute animal experiments upon direct electrical stimulation of the vagus, and they verified and extended results from previous experiments with human subjects in response to other sensorimotor events. The effects of expectancy, evaluated by serial positional effects on the magnitude and slope of time‐dependent cardiac slowing, were different for standard and for rare tones. Comparisons with P300, the late positive component of the average evoked potential, suggest that while P300 is most strongly associated with poststimulus decisional processes, primary bradycardia and its time‐dependent aspects reflect both early stimulus registration and later decision making. The results suggest limbic and neocortical modulation of primary bradycardia. In a second experiment with 20 male college students, in which tones were presented at experimentally controlled times within the cardiac cycle, the basic effects obtained with post hoc separation of tones into relative cycle time of occurrence were verified.