BiologicalPsychology 7 (1978) 167-168
© North-Holland Publishing Company
CLASSICAL CONDITIONING OF HEART RATE IN INFANTS: METHODOLOGY OR MATURATION? LEIGHTON E. STAMPS * Department o f Psychology, University o f New Orleans, New Orleans, Louisiana, U.S.A.
Accepted for publication 1 October 1978
In examining classical conditioning of heart rate in adults, most researchers have reported conditioned heart rate decelerations in anticipation of the unconditioned stimulus (UCS), and in the absence of the UCS when it is omitted on test and extinction trials (Obrist, Webb, and Sutterer, 1970; Wilson, 1969). Studies of infant heart rate conditioning have also consistently reported decelerations in the absence of the UCS. The findings with regard to anticipatory responses in infants have been less uniform. In looking closely at the methodologies used, it appears that a generalization can be drawn in relation to the presence or absence of anticipatory responding. In both studies which failed to find this type of response, the infants were given presentations of the conditional stimulus (CS) before starting the conditioning procedure. Clifton (1974) used a tone as the CS and glucose presented through a nipple as the UCS in a delayed paradigm. Subjects in her study received 'pre-conditioning trials' consisting of three presentations of the UCS alone, and six presentations of the CS alone with three UCSs randomly interspersed. Forbes and Porges (1973) used auditory stimuli for both the CS and UCS in a trace procedure. They presented the CS alone on 'desensitization trials' a minimum of eight times or until heart rate changes to the stimulus failed to occur. The purpose of pre-conditioning trials is to eliminate the spontaneous orienting response (OR), as characterized by heart rate deceleration, to the CS. In this way, the authors were attempting to focus on a conditioned anticipatory deceleration resulting exclusively from the conditioning procedure. Gormezano (1966) has pointed out, however, that one CS-UCS pairing may reinstate the spontaneous response to the CS. Thus, in some cases the procedure may not produce the desired results. In the remaining studies of infant heart rate conditioning, pre-conditioning trials were not used, and all reported the presence of anticipatory responding. Stamps and Porges (1975) used an auditory CS and a visual UCS in a trace paradigm,
* Address requests for reprints to: Leighton E. Stamps, Department of Psychology, University of New Orleans, Lake Front New Orleans, LA 70122, U.S.A. 167
L.E. Stamps / Classical conditioning of heart rate in infants
Stamps (1977) used an auditory UCS with a temporal procedure, and finally, Turco and Stamps (in preparation) used a visual CS and an auditory UCS with a trace procedure. Clifton (1974) has suggested that the presence o f anticipatory cardiac CRs may be a function o f the infant's maturationat stage. The research discussed above, however, seems to indicate that the responses may be more closely tied to the methodology used. When the OR to the CS has habituated during pre-conditioning trials, the infant has learned 'not to respond' or attend to the stimulus. If the infant is not attending to the CS during the conditioning procedure, it would seem to be rather difficult to make the associations necessary for classical conditioning. If pre-conditioning trials are not used, the heart rate deceleration seen in anticipation o f the UCS may very well be a combination o f the spontaneous OR to the CS and the conditioned deceleration. Conditioning can then be evaluated by comparing the decelerations seen in experimental and control groups. The spontaneous OR found in the control subjects should habituate across trials. The magnitude o f the deceleration seen in the experimental subjects should increase across trials as the anticipatory response is acquired. Most o f the research dealing with classical conditioning o f heart rate in infants seems to indicate that CRs are more difficult to establish and less stable than responses seen in adults. By eliminating pre-conditioning trials, the probability of forming the necessary associations needed for classical conditioning would appear to be maximized.
References Clifton, R.K. (1974). Heart rate conditioning in the newborn infant. Journal of Experimental Child Psychology, 18, 9-21. Forbes, E.J. and Porges, S.W. (1973). Heart rate classical conditioning with a noxious auditory stimulus in human newborns. Psychophysiology, 10, 192. Obrist, P., Webb, R., Sutterer, J. and Howard, J. (1970). Cardiac deceleration and reaction time: An evaluation of two hypotheses. Psychophysiology, 6, 695-706. Wilson, R.S. (1969). Cardiac response: Determinants of conditioning. Journal of Comparitive an~l Physiological Psychology Monographs, 68, 1-23. Stamps, L.E. and Porgos, S.W. (1975). Heart rate conditioning in newborn infants: Relationships among conditionability, heart rate variability, and sex. Developmental Psychology, 11, 424-431. Stamps, L.E. (1977). Temporal conditioning of heart rate responses in newborn infants. Developmental Psychology, 13, 624-629. Turco, T.L. and Stamps, L.E. (in preparation). Heart rate conditioning in young infants using a visual CS.