Date of Award

Winter 1986

Project Type


Program or Major

Experimental Psychology

Degree Name

Doctor of Philosophy


Although a number of studies have suggested that the phases of the alpha cycle and the cardiac cycle reflect temporal relationships in cortical processing, these studies are not conclusive. The reason is that almost all of these suggestions have been based upon the demonstration that a measure of visual processing varies with the phase of the alpha cycle or the cardiac cycle at which stimuli are presented. These visual effects could have been caused by a peripheral mechanism involving the tremor of the eyes. Because of this, this dissertation was interested in the effect of these physiological cycles on auditory performance. It was reasoned that if it could be shown that auditory performance is also influenced by these physiological cycles, then it would suggest that the cause is due to a central mechanism involving cortical processing, rather than to a peripheral mechanism.

Through two psychophysical experiments, auditory performance effects were observed as a function of the phase of the alpha cycle and the cardiac cycle at which stimuli were presented. The major effect was that signal detection varied as a function of the alpha cycle. Also, post hoc analysis suggested that the cardiac cycle also influence signal detection, with performance being poorer at carotid systole. These effects were explained by assuming that the alpha cycle reflects a "neuronic input shutter" which is closed for a longer duration at carotid systole due to baroreceptor induced cortical inhibition. In addition to these primary findings, further post hoc analyses indicated that the alpha cycle and/or the cardiac cycle had an effect on the difference between target and non-target reaction times and the probability that the initial target category would be indicated. These secondary effects were speculatively explained by suggesting that the onsets of processes which perform response selection and stimulus evaluation are locked in time to these physiological cycles. The conclusion is that the temporal rhythm of cortical operation is reflected by these physiological cycles.