Heart rate, recall, and reaction-time measures of levels of processing.

A problem of circularity emerges in any attempt to index depth by retention alone. In the present study, reaction time (RT), and heart-rate response were used to index the three qualitatively distinct levels of physical, phonemic, and semantic processing. An additional objective was to distinguish between the three levels under incidental vs intentional learning conditions. Subjects were 46 male undergraduates who were given 30 trials. A trial consisted of the presentation of an orienting question and an imperative word-stimulus separated by a 6-sec. interval. There were three types of questions in order to induce processing to one of the three target levels. The results indicated that recall as well as heart-rate acceleration distinguished between two (physical vs phonemic and semantic) rather than three levels of processing in the incidental condition. Heart-rate change differentiated between incidental and intentional, the intentional condition showing a smaller change. Semantic and phonemic RTs were faster than physical RT, but there were no differences between semantic and phonemic RTs. Intentional recall was superior to incidental recall. It is suggested that psychophysiological indices can provide independent evidence for 'levels of processing.'