PSVGHO PHYSIOLOGY
Vol. 13, No. 1 Printed in U.S.A.
Ctipyrighl ® 1976 by The Society for Psychophysiological Research
Effects of "Below-Zero" Habituation on the Electrodermal Orienting Response to a Test Stimulus DAVID STEPHENSON AND DAVID A. T. SIDDLE Department of Psychology, University of Southampton
ABSTRACT Two experiments were designed to investigate the effect of below-zero habituation training on skin conductance response (SCR) amplitude to a change in auditory stimulus frequency. In both experiments, subjects were trained with a 1000 Hz tone until zero responding and then received 5, 10, or IS further training trials. In Experiment 1 (N =45), subjects then received 1 presentation of a test stimulus of 1400 Hz, while in Experiment 2 (N=4S), tbe test stimulus was a tone of 670 Hz. On the basis of dual-process theory, it was hypothesized that response amplitude to the test stimulus would be inversely related to amount of below-zero training. However, the results of botb experiments indicate that SCR amplitude was positively related to amount of below-zero training. These results suggest that in situations of extended habituation training, an expectancy or subjective probability of stimulus occurrence gradient is important in determining response amplitude to a test stimulus. DESCRIPTORS: Below-zero habituation, Electrodermal orienting response. Stimulus change. Response recovery. (D. Stepbenson) In proposing their dual-process theory of habituation, Groves and Thompson (1970) have argued that the theory can account for all the characteristics of habituation outlined by Thompson and Spencer (1966). One of these has been termed "belowzero" habituation. Essentially, this refers to a continuation of the inferred habituation process beyond the point at which zero responding has occurred. This would seem to be a logical necessity in any theory of habituation, since the point of response habituation (zero responding) is somewhat arbitrarily determined, at least in the case of autonomic responses, by the sensitivity of the recording apparatus used. Thompson and Spencer (1966) have suggested that additional habituation training beyond the point of "zero'' responding will result in less spontaneous recovery of the response, after a recovery interval, than will no additional training. The evidetice tor a below-zero habituation effect is, however, meagre and somewhat equivocal. Humphrey (1933) reported that below-zero training of a defensive withdrawal response in snails proPart of this research was performed while the first author was in receipt of a Science Research Council postgraduate award. Address requests for reprints to: David Stephenson, Department of Psychology, University ot Southampton, Southampton, U.K.
10
duced a delay in the spontaneous recovery of the response, while Prosser and Hunter (1936) reported a positive relationship between the stimulus strength required to produce dishabituation of the startle response in rats and amount of below-zero training. Thompson and Spencer (1966) themselves presented evidence indicating that the flexion response to shock in decerebrate cats took longer to display spontaneous recovery following below-zero training. On the other hand, Gardner (1968) failed to demonstrate any below-zero training effect on the spontaneous recovery of hooking and withdrawal responses in earthworms. However, her recovery interval of 24 hrs may have been inappropriately long since habituation could have dissipated in all groups during this time. Studies investigating human orienting responses (ORs) have provided little evidence to support Thompson and Spencer's (1966) predictions conceming the effect of below-zero habituation training. Indirect evidence for the effect was obtained by Gorman (1967) in an investigation of generalization of habituation to changes in auditory stimulus frequency. Gorman (1967) reported an inverse relationship between the number of consecutive zero responses immediately prior to the end of training and amount of skin conductance response (SGR) recovery to test stimuli. However, since examina-
January, 1976
EFFECTS OF "BELOW-ZERO" HABfTUATION
tion of this part of the data was post-hoc, the effect of below-zero training was necessarily confounded with the speed with which the subjects had habituated to the training stimulus, i.e. only those subjects who displayed relatively rapid habituation during the 10 presentations of the training stimulus could have undergone below-zero training. JaEnes, Daniels, and Hanson (1974) investigated the effects of below-zero training with an auditory stimulus and length of recovery interval on spontaneous recovery of the SCR. The below-zero training consisted of either 2 or 5 consecutive trials which produced no measurable responses. In view of the small absolute amount of below-zero training and the small difference in below-zero training between groups, it is hardly surprising that no significant training effect was obtained. However, Waters and McDonald (1974) also reported no difference in spontaneous recovery of the auditoryevoked SCR following 2 or 12 below-zero training trials. In fact, when responses were expressed as ratios of the first response in the training series, there was a tendency for greater recovery to occur following below-zero training. Moreover, the below-zero training group displayed larger SCRs to a dishabituating stimulus, and more dishabituation to a subsequent presentation of the training stimulus. The present study reports two experiments, carried out several months apart, which were designed to investigate further the phenomenon of belowzero habituation of the SCR component of the OR. In both experiments, subjects received 5, 10, or 15 below-zero training trials, followed by presentation of a test stimulus which differed from the training stimulus along one dimension (frequency). Dualprocess theory (Thompson & Spencer, 1966; Groves & Thompson, 1970) views response to a test stimulus as an example of incomplete generalization of habituation. Moreover, there is some evidence (Thompson & Spencer, 1966; Voronin & Sokolov, 1960) that stimulus generalization of habituation increases as a positive function of number of training trials. It seems reasonable to suppose, therefore, that the amount and extent of generalization of habituation varies as a positive function of the amount of below-zero training. On this basis, it was predicted that response amplitude to the test stimulus would be inversely related to the amount of below-zero training. Method Subjects The subjects in Experiment 1 were 45 undergraduate volunteers (age I ange 17-31 yrs) who were allocated randomly io one of three groups, with the restriction that all groups contained the
11
same proportion of males and females (7 males and 8 females in each group). The records of 4 subjects who failed to display any evoked SCRs were discarded, and 4 more subjects recruited from the same population. In Experiment 2, the subjects were 45 undergraduate volunteers (age range 18-27 yrs) Who were allocated to one of three groups in the same manner as in Experiment 1. The records of 3 subjects who failed to display any evoked SCRs were discarded and replaced by subjects from the same population. Apparatus and Procedure In both experiments, the training stimulus consi.sted of a 1000 Hz tone of 3 sec duration, presented at randomly ordered intervals of 20, 25, 30, 35, and 40 sec (mean interstimulus interval = 30 sec). TotK intensity was 70 dB (re: .0002 dyne/cm^) as rated by a Dawe's sound level meter at the headrest of the chair in which the subjects sat. The test stimulus in Experiment 1 was a 70 dB, 3 sec tone of 1400 Hz (increase of 250 meis), while in Experitnent 2, it was a 70 dB, 3 sec tone of 670 Hz (decrease of 250 mels). Ail stimuli were produced by an Advance A.F. signal generator (Model HIB) and delivered through a speaker 100 cm directly behind the subject. Stimulus duration was controlled by a Birkbeck timer. Bipolar recording of skin conductance was made using domed Ag-AgCl electrodes filled with 0.05M NaCl electrolyte and attached to masked areas on the index and second fingers of the subject's left hand. The masking collars were placed over the whorls of the fingerprints on the distal phalanges.. A constant voltage of 0.5V (Lykken & Venables, 1971) was applied across the electrode.* and conductance recorded on a Grass Model 7 polygraph with a 7P! B preamplifier sensitivity of 1 mm of pen deflection equal to 0.02 Mmhos. The total area from which conductance was recorded was 0.35 cm". Respiration was recorded via a Grass nasal thermocouple to detect SCRs arising from coughs, deep breaths, and other respiratory irregularities. The subjects were seated in a semi-reclining padded chair in a sound-proofed room with an ambient illumination of 2 lux, a temperature range of 19-*24°C, and a relative humidity within the range 49-56''^. The stimulus equipment and recording apparatus were monitored from an adjoining room. The subjects were informed that, after a short rest period, some tones would be heard from time to lime and that no responses were required. They were asked to relax with their eyes closed, to avoid movement as much as possible, but not to goto sleep. After a 5 min resi period, the stimulus programme commenced without prior warning. All subjects were pre.sented with the training stimulus until the criterion of habituation was reached (3 consecutive lesponscs ofiess than 0.02 jtimhos). In both ex[x;riments, those subjects in condition 1 (Group I) then received 2 furtherpresentations of the training stimulus, those in condition 2 (Group 2) received 7 further presentations, and those in condition 3 (Group 3Vreceived 12 additional presentations. Thus, Group 1 received 5 belowzero training trials. Group 2 received 10 below-zero training trials, and Group 3 received 15 below-/ero training trials, In Experiment 1, Groups 1,2, and 3 received an avera,t;e of 17, 21, and 26 training trials respectively, while in Expciimcnt 2. Groups !, 2, and 3 received an average of 15, 19, and 26 training trials. All subjects then received. 25 sec later, I presentation of the test stimulus (1400 Hz in Experiment 1 and 670 Hz in Experiment 2), followed, 30 .sec later, by I further presentation of the training stimulus.
Vol. 13, No. I
STEPHEN.SON AND SIDDLE
12 Scoring
Any artifact-free SCR greater than 0.02 /xmhos, occurring from 1-5 sec after stimulus onset, was considered a change evoked by the stimulus. All SCRs elicited by test stimuli were artifact-free. Where between subjects comparisons were made in terms of SCR amplitude to test .stimuli, the responses were range-corrected (Lykken & Venables, !97!) in terms of each subject'.s maximum SCR displayed during the experimental session, in Experiment I, 43 subjects displayed their maximum SCR in response to the first training stimulus, while for the remaining 2 .subjects, it occurred in response to the test .stimulus. In Experiment 2, 42 subjects displayed maximum SCR amplitude on the first training trial and the remaining 3 subjects on the test trial. Tonic skin conductance level (SCL) and spontaneous activity were as.sessed during the rest period. SCL was measured at each min, and the mean rest period SCL range-corrected in terms of the minimum and maximum SCL displayed by each subject during testing (Lykken & Venable.s, 1971). However, since the subjects did not go to sleep, it is possible that the minimum SCL values were not sufficiently accurate to employ range-correction. Accordingly, rest period SCL was also measured in terms of non-range-conected ^tmhos. Spontaneous activity was measured by counting the number of artifact-free fluctuations greater than 0.02 /limhos.
Results Experiment I Initially, the groups were compared in terms of spontaneous activity and SCL during the prestimuius period, SCR amplitude to the first training stimu-ius, and number of stimulus presentations required to reach the criterion of habituation. In order to satisfy the assumptions underlying analysis of variance, the data concerning tonic SCL, trials to habituation, and response amplitude to the first training stimulus were subjected to a logarithmic transformation and the SCR amplitude data from the test trial to a square root transformation (Edwards, 1960, pp. 125-132). The spontaneous activity data were analyzed using a Kruskal-Wallis nonparametric analysis of variance. There were no group differences in terms of spontaneous activity {H(2)=\ .64), amplitude of first response (F(2/ 42)
Vol. 13, No. 1 Printed in U.S.A.
Ctipyrighl ® 1976 by The Society for Psychophysiological Research
Effects of "Below-Zero" Habituation on the Electrodermal Orienting Response to a Test Stimulus DAVID STEPHENSON AND DAVID A. T. SIDDLE Department of Psychology, University of Southampton
ABSTRACT Two experiments were designed to investigate the effect of below-zero habituation training on skin conductance response (SCR) amplitude to a change in auditory stimulus frequency. In both experiments, subjects were trained with a 1000 Hz tone until zero responding and then received 5, 10, or IS further training trials. In Experiment 1 (N =45), subjects then received 1 presentation of a test stimulus of 1400 Hz, while in Experiment 2 (N=4S), tbe test stimulus was a tone of 670 Hz. On the basis of dual-process theory, it was hypothesized that response amplitude to the test stimulus would be inversely related to amount of below-zero training. However, the results of botb experiments indicate that SCR amplitude was positively related to amount of below-zero training. These results suggest that in situations of extended habituation training, an expectancy or subjective probability of stimulus occurrence gradient is important in determining response amplitude to a test stimulus. DESCRIPTORS: Below-zero habituation, Electrodermal orienting response. Stimulus change. Response recovery. (D. Stepbenson) In proposing their dual-process theory of habituation, Groves and Thompson (1970) have argued that the theory can account for all the characteristics of habituation outlined by Thompson and Spencer (1966). One of these has been termed "belowzero" habituation. Essentially, this refers to a continuation of the inferred habituation process beyond the point at which zero responding has occurred. This would seem to be a logical necessity in any theory of habituation, since the point of response habituation (zero responding) is somewhat arbitrarily determined, at least in the case of autonomic responses, by the sensitivity of the recording apparatus used. Thompson and Spencer (1966) have suggested that additional habituation training beyond the point of "zero'' responding will result in less spontaneous recovery of the response, after a recovery interval, than will no additional training. The evidetice tor a below-zero habituation effect is, however, meagre and somewhat equivocal. Humphrey (1933) reported that below-zero training of a defensive withdrawal response in snails proPart of this research was performed while the first author was in receipt of a Science Research Council postgraduate award. Address requests for reprints to: David Stephenson, Department of Psychology, University ot Southampton, Southampton, U.K.
10
duced a delay in the spontaneous recovery of the response, while Prosser and Hunter (1936) reported a positive relationship between the stimulus strength required to produce dishabituation of the startle response in rats and amount of below-zero training. Thompson and Spencer (1966) themselves presented evidence indicating that the flexion response to shock in decerebrate cats took longer to display spontaneous recovery following below-zero training. On the other hand, Gardner (1968) failed to demonstrate any below-zero training effect on the spontaneous recovery of hooking and withdrawal responses in earthworms. However, her recovery interval of 24 hrs may have been inappropriately long since habituation could have dissipated in all groups during this time. Studies investigating human orienting responses (ORs) have provided little evidence to support Thompson and Spencer's (1966) predictions conceming the effect of below-zero habituation training. Indirect evidence for the effect was obtained by Gorman (1967) in an investigation of generalization of habituation to changes in auditory stimulus frequency. Gorman (1967) reported an inverse relationship between the number of consecutive zero responses immediately prior to the end of training and amount of skin conductance response (SGR) recovery to test stimuli. However, since examina-
January, 1976
EFFECTS OF "BELOW-ZERO" HABfTUATION
tion of this part of the data was post-hoc, the effect of below-zero training was necessarily confounded with the speed with which the subjects had habituated to the training stimulus, i.e. only those subjects who displayed relatively rapid habituation during the 10 presentations of the training stimulus could have undergone below-zero training. JaEnes, Daniels, and Hanson (1974) investigated the effects of below-zero training with an auditory stimulus and length of recovery interval on spontaneous recovery of the SCR. The below-zero training consisted of either 2 or 5 consecutive trials which produced no measurable responses. In view of the small absolute amount of below-zero training and the small difference in below-zero training between groups, it is hardly surprising that no significant training effect was obtained. However, Waters and McDonald (1974) also reported no difference in spontaneous recovery of the auditoryevoked SCR following 2 or 12 below-zero training trials. In fact, when responses were expressed as ratios of the first response in the training series, there was a tendency for greater recovery to occur following below-zero training. Moreover, the below-zero training group displayed larger SCRs to a dishabituating stimulus, and more dishabituation to a subsequent presentation of the training stimulus. The present study reports two experiments, carried out several months apart, which were designed to investigate further the phenomenon of belowzero habituation of the SCR component of the OR. In both experiments, subjects received 5, 10, or 15 below-zero training trials, followed by presentation of a test stimulus which differed from the training stimulus along one dimension (frequency). Dualprocess theory (Thompson & Spencer, 1966; Groves & Thompson, 1970) views response to a test stimulus as an example of incomplete generalization of habituation. Moreover, there is some evidence (Thompson & Spencer, 1966; Voronin & Sokolov, 1960) that stimulus generalization of habituation increases as a positive function of number of training trials. It seems reasonable to suppose, therefore, that the amount and extent of generalization of habituation varies as a positive function of the amount of below-zero training. On this basis, it was predicted that response amplitude to the test stimulus would be inversely related to the amount of below-zero training. Method Subjects The subjects in Experiment 1 were 45 undergraduate volunteers (age I ange 17-31 yrs) who were allocated randomly io one of three groups, with the restriction that all groups contained the
11
same proportion of males and females (7 males and 8 females in each group). The records of 4 subjects who failed to display any evoked SCRs were discarded, and 4 more subjects recruited from the same population. In Experiment 2, the subjects were 45 undergraduate volunteers (age range 18-27 yrs) Who were allocated to one of three groups in the same manner as in Experiment 1. The records of 3 subjects who failed to display any evoked SCRs were discarded and replaced by subjects from the same population. Apparatus and Procedure In both experiments, the training stimulus consi.sted of a 1000 Hz tone of 3 sec duration, presented at randomly ordered intervals of 20, 25, 30, 35, and 40 sec (mean interstimulus interval = 30 sec). TotK intensity was 70 dB (re: .0002 dyne/cm^) as rated by a Dawe's sound level meter at the headrest of the chair in which the subjects sat. The test stimulus in Experiment 1 was a 70 dB, 3 sec tone of 1400 Hz (increase of 250 meis), while in Experitnent 2, it was a 70 dB, 3 sec tone of 670 Hz (decrease of 250 mels). Ail stimuli were produced by an Advance A.F. signal generator (Model HIB) and delivered through a speaker 100 cm directly behind the subject. Stimulus duration was controlled by a Birkbeck timer. Bipolar recording of skin conductance was made using domed Ag-AgCl electrodes filled with 0.05M NaCl electrolyte and attached to masked areas on the index and second fingers of the subject's left hand. The masking collars were placed over the whorls of the fingerprints on the distal phalanges.. A constant voltage of 0.5V (Lykken & Venables, 1971) was applied across the electrode.* and conductance recorded on a Grass Model 7 polygraph with a 7P! B preamplifier sensitivity of 1 mm of pen deflection equal to 0.02 Mmhos. The total area from which conductance was recorded was 0.35 cm". Respiration was recorded via a Grass nasal thermocouple to detect SCRs arising from coughs, deep breaths, and other respiratory irregularities. The subjects were seated in a semi-reclining padded chair in a sound-proofed room with an ambient illumination of 2 lux, a temperature range of 19-*24°C, and a relative humidity within the range 49-56''^. The stimulus equipment and recording apparatus were monitored from an adjoining room. The subjects were informed that, after a short rest period, some tones would be heard from time to lime and that no responses were required. They were asked to relax with their eyes closed, to avoid movement as much as possible, but not to goto sleep. After a 5 min resi period, the stimulus programme commenced without prior warning. All subjects were pre.sented with the training stimulus until the criterion of habituation was reached (3 consecutive lesponscs ofiess than 0.02 jtimhos). In both ex[x;riments, those subjects in condition 1 (Group I) then received 2 furtherpresentations of the training stimulus, those in condition 2 (Group 2) received 7 further presentations, and those in condition 3 (Group 3Vreceived 12 additional presentations. Thus, Group 1 received 5 belowzero training trials. Group 2 received 10 below-zero training trials, and Group 3 received 15 below-/ero training trials, In Experiment 1, Groups 1,2, and 3 received an avera,t;e of 17, 21, and 26 training trials respectively, while in Expciimcnt 2. Groups !, 2, and 3 received an average of 15, 19, and 26 training trials. All subjects then received. 25 sec later, I presentation of the test stimulus (1400 Hz in Experiment 1 and 670 Hz in Experiment 2), followed, 30 .sec later, by I further presentation of the training stimulus.
Vol. 13, No. I
STEPHEN.SON AND SIDDLE
12 Scoring
Any artifact-free SCR greater than 0.02 /xmhos, occurring from 1-5 sec after stimulus onset, was considered a change evoked by the stimulus. All SCRs elicited by test stimuli were artifact-free. Where between subjects comparisons were made in terms of SCR amplitude to test .stimuli, the responses were range-corrected (Lykken & Venables, !97!) in terms of each subject'.s maximum SCR displayed during the experimental session, in Experiment I, 43 subjects displayed their maximum SCR in response to the first training stimulus, while for the remaining 2 .subjects, it occurred in response to the test .stimulus. In Experiment 2, 42 subjects displayed maximum SCR amplitude on the first training trial and the remaining 3 subjects on the test trial. Tonic skin conductance level (SCL) and spontaneous activity were as.sessed during the rest period. SCL was measured at each min, and the mean rest period SCL range-corrected in terms of the minimum and maximum SCL displayed by each subject during testing (Lykken & Venable.s, 1971). However, since the subjects did not go to sleep, it is possible that the minimum SCL values were not sufficiently accurate to employ range-correction. Accordingly, rest period SCL was also measured in terms of non-range-conected ^tmhos. Spontaneous activity was measured by counting the number of artifact-free fluctuations greater than 0.02 /limhos.
Results Experiment I Initially, the groups were compared in terms of spontaneous activity and SCL during the prestimuius period, SCR amplitude to the first training stimu-ius, and number of stimulus presentations required to reach the criterion of habituation. In order to satisfy the assumptions underlying analysis of variance, the data concerning tonic SCL, trials to habituation, and response amplitude to the first training stimulus were subjected to a logarithmic transformation and the SCR amplitude data from the test trial to a square root transformation (Edwards, 1960, pp. 125-132). The spontaneous activity data were analyzed using a Kruskal-Wallis nonparametric analysis of variance. There were no group differences in terms of spontaneous activity {H(2)=\ .64), amplitude of first response (F(2/ 42)
