Journal of Psychosomarir Pmwd I” meat Brltal”
Research.
Vol.
35.
No.
415,
pp.
509-514.
1991. 0
HABITUATION
0530-3999/91 1991 Pergamo”
AND TINNITUS: AN EXPERIMENTAL
53.00+.00 Press
plc
STUDY
SVEN G. CARLSSON and SOLY I. ERLANDSSON (Received
29 May
1990; accepted
in original form
12 December
1990)
Abstract-The study is an experimental test of Hallam’s habituation theory of tin&us; this theory implies that the huge variation in suffering among individuals with about the same amount of tinnitus is due to differences in habituation to the perceived sound. Fourteen patients, seven ‘complainers’ and seven ‘noncomplainers’, participated in an experiment where we studied changes in skin conductance and heart rate responses to a series of tinnitus-like sound stimuli. No group differences in habituation were observed. We suggest that facilitatory processes, like disinhibition, may be more important than deficient habituation for the inability, in some individuals, to adapt to their tinnitus. INTRODUCTION DISCREPANCY, observed for several disorders, between objective pathology and subjective suffering is a challenging problem which requires new models guiding the search for psychosomatic causation. Among the most thoroughly discussed examples are certain chronic pain states, like long-standing low back pain. Fordyce [ll has proposed that important #determinants of pain maintenance are to be found at a behavioral, rather than a somatic level: for many pain patients, by learning processes, psychological and social changes occur which tend to maintain the illness, regardless of somatic pathology. Tinnitus, a condition where the affected individual experiences sounds which have no external source, seems to be another excellent example: the variation in suffering can hardly be accounted for by physical or somatic factors. While clinical investigations of tinnitus patients have described them as generally affected, epidemiological studies have disclosed a significant proportion of individuals who do not seek help for it, and do not seem to suffer 121. Again, the clinically important question remains: what makes some tinnitus patients plagued and handicapped, while others are left quite undisturbed? Richard Hallam, an English psychologist, has proposed an interesting and unusually detailed theory, based on the concept of habituation [31.Habituation is the successive reduction of reactions and awareness in relation to a repetitive, non-signal stimulus. Hallam has adopted the concept in order to account for the long-term adaptation which he has observed in many tinnitus patients. In others, however, the perceived sound sensations remain unhabituated. In Hallam’s model, possible causes of such incomplete or inhibited response decline may be found in the experimental literature concerning habituation of the orienting reaction (OR). The OR, according to Sokolov [41,is a wide-spread preparatory physiological change in response to a stimulus; the change is believed to promote the organism’s need to analyse new and potentially important environmental events. Prerequisites for optimal habituation are non-signal stimulus properties and low THE
Department of Psychology, University Correspondence to Sven G. Carlason, 14158. S-400 20 Griteborg, Sweden.
of GBteborg, Sweden. University of Giiteborg,
Department
of Psychology,
Box
510
S.
G.
CARLETON
and S. I. ERLANDSSON
general arousal level; in other words, habituation is slow or absent when stimuli have acquired some significance, and/or when the stimulated organism’s arousal level is high. Dishabituation, the reappearance of reactivity after habituation has occurred, can be observed as the consequence of the appearance of a new stimulus; the effect is not only a response to that stimulus, but a recovery of responses to the original one. In his habituation model of tinnitus, Hallam [31 makes use of what is known about the prerequisites for habituation and dishabituation of the OR. For instance, if the patient has negative beliefs, attitudes or feelings in regard to his tinnitus, habituation may not occur; if habituation has occurred, intrusive stimulation may heighten the arousal level and induce awareness due to dishabituation. This study represents an attempt to subject the habituation model to a direct experimental test. Two groups of tinnitus patients, one highly disturbed and the other relatively unbothered by their symptom, were to be compared in an OR habituation type of experiment, with a repetitive tinnitus-like sound as stimulus; we chose as a response measure the skin conductance response, which is one of the most widely used in human OR habituation research, and heart rate pre- to post-stimulus change, because of its presumed relationship to OR as well as reactions of the defence type [51. METHOD
Patient5 Two groups of patients, after informed consent, entered the study. Group A (complainers) were seven patients (four male, three female) with bothersome tinnitus; they were recruited among patienta who had sought medical help hecause of their symptom, and after examination. they were found to he severely distressed by their disorder. and in need of treatment. Group B (noncomplainers) were seven patients (all male) who had not consulted medical expertise for their tinnitus; their tinnitus had been noticed in connection with medical examination of their hearing impairment. They were found to he non-distressed by their tinnitus, and not in need of treatment for it. Mean age was 61 yr for both groups. Mean pure tone average (0.5, 1.0, 2.0 and 2.0 Hz) were, for left/right ear, 32133 (SD = 11113) and 38140 (SD = 1019) for complainers and noncomplainers. respectively. For eight of the patients the hearing loss was noise induced; one had a neurogenic etiology; for the remaining five patients. the etiology was unknown. The general symptom attitude, negative for the complainers versus neutral for non-complainers, wa\ verified in an initial interview. Meusurrments For each individual. the tinnitus character and loudness level were explored with a tinnitus analyzer (Watic. Model TA 3). The individually shaped tinnitus-like sound was used as experimental stimulus; the tlnnitus analyscr was used as stimulus source. The stimulus intensity level was well above the individual hearing threshold for the sound, and well below the discomfort threshold. There were 30 stimuli, stimulus duration was 0.4 s, and intervals between stimuli were 20, 2.5 or 30 s, in a fixed random order. The stimulus configuration was monitored by a tape recorder, with a tape carrying signals corresponding to stimuli; these signals activated a frequency decoder with a reed relay, closing the stimulus circuit. Stimuli were administered via head phones, according to localization: patients with unilateral tinnitus heard the stimuli through the ear where they localized tinnitus, others were stimulated binaurally. Skin conductance was recorded with silver-silver chloride electrodes (diameter 10 mm), attached to the medial phalanx of the fore and middle fingers ot. the non-preferred hand. Parker electrode gel was used as contact medium. Two GRASS 7Pl preamplifiers were used for recording of skin conductance level and skin conductance responses (SCR). Heart rate was recorded with standard EKG methodology; the signal was fed into a GRASS 7P4 preamplifier, giving a tachographic beat-by-heat record. A questionnaire *as used to explore the frequencies of negative reactions to environmental sounds, and sleep problems like insomnia. Both aspects were covered by three items, ranging from I -never to 4.very often.
Habituation
511
and tinnitus
State and trait anxiety was assessed with the Stait Trait Anxiety Inventory (STAI, Form Y) [61.We used, also, a shortened version of The Geer Fear Scale [71;it is a 18 item self-rating scale where the degree of fears (of e.g. sharp objects, spiders. blood and heights) are estimated on 1 through 7 scales (1 is no fear, 7 is ‘terror’). Data reduction Skin Conductance Responses amplitudes were estimated according to the guidelines given by Edelberg [81. For heart rate responses, mean heart rate 10 set before and 10 set following each stimulus was estimated with a planimetric method: the area for a 10 set period under the tachographic trace was measured with a digitizer feeding into a computer program transforming the area into mean heart rate. The reliability of this methodology was found to be quite good (the test-retest error is within + - 1%). Individual habituation tendencies were estimated by means of a habituation index, based on comparisons between each consecutive response magnitude and the average of all preceding ones. Given the null hypothesis that no systematic response magnitude trend exists, there is an equal probability for a response to be larger or smaller than the mean of the preceding ones; this mean represents an estimate of the individual’s reactivity to the given stimulation. The number of instances, for an individual, where a response is smaller, represents the habituation index for that individual; with 30 stimuli, the index varies, accordingly, between 0 and 29. The normal approximation of a binomial distribution, with p = q = 0.5 and N = 29, is used to identify the significance limits for rejection of the null hypothesis L91. For a two-sided, p = 0.05 test the upper limit is 20.28; consequently, a habituation index 21 and above indicates significant habituation; towards the other end of the index range, a value of 8 or lower would indicate a significant sensitization. All group comparisons were made with the Mann-Whitney U test 1101.
RESULTS
Mean tinnitus loudness level above threshold was 14.3 dB (range 5-20) for complainers and 15.4 dB (range 5-25) for noncomplainers; the difference is nonsignificant. TABLE
I.-MEDIANS
(AND RANGES)• F PSYCHOMETRIC QUESTIONNAIRE DATA
Complainers Trait State Fears Noise Sleep
anxiety anxiety sensitivity problems
38 33 31 7 6
(31-61) (25-53) (20-67) (3-12) (4-l I)
AND
Noncomplainers 36 29 23 5 4
(20-39) (20-35) (18-35) (3-6) (3-6)
NS NS NS NS LJ = 0.013
Table I shows the results of the psychometric tests and the questionnaire. There are consistent, although not significant, differences between the groups in state and trait anxiety, in fear as assessed with the Geer Fear Scale, and in sensitivity to environmental sounds. Problems with sleep are significantly greater among complainers. Figure 1 gives group means of individual, relative SCR amplitudes (responses 2-30 expressed as percent of the amplitude of the SCR to the first stimulus). There are no significant differences between groups in relative SCR’s to stimuli 2-30. Medians (and ranges) of the habituation index were 23 (20-29) and 24 (21-29) for complainers and noncomplainers, respectively. Individual binomial tests of response magnitude trend, as described above, showed significant habituation in all noncomplainers, and in all but one of the complainers. The group difference is nonsignificant.
512
S. G. CARLSSON and S. I.
ERLANDSSON
20
IO
3G
Stimulus no. FIG.
1.
Mean
amplitudes of skin conductance responses, expressed as percentages Open squares, complainers; filled squares, noncomplainers.
of first response.
Table II gives group means for HR during pre- and post-stimulus periods for stimuli l-3 and 28-30, together with differences between pre- and post-values, indicating HR responses to stimuli. While there are no group differences in HR responses, groups differ significantly in the way HR pre-stimulus and HR poststimulus levels change from the first to the last three observations: complainers. compared to non-complainers, increase their HR. ‘GABLE
II.-MEAN
THREE
AND
LAST
HR FOR 10 SEC THREE
STIMULI,
PERIODS
AND
POST-STIMULUS
Stimuli
Complainers Noncomplainers
P=
post
65.7 67.4
65.0 67.8
PRECEDING
MEAN
FOLLOWING
BETWEEN
FIRST
PRE-
AND
PERIODS
1. 2, 3 difference 0.69 -0.40
AND
DIFFERENCE
Stimuli we
post
70.5 66.7
69.8 61.3
28, 29, 30 difference 0.71 -0.S5
DISCUSSION
In this study, we have attempted to contrast two groups of patients, with the same type of physical symptom but with different types of orientation towards the symptom. The first question to be discussed concerns the validity of our selection. All patients entering the study unequivocally confirmed the background information concerning their way of coping with their tinnitus. The complainers scored higher on questionnaire data indicating sleep disturbances, and their subjective sound sensitivity tended to be greater. Also, the two groups tended to differ in anxiety and amount of fears. Based on all these observations, it seems justified to conclude that the two groups differ in their way of coping with their tinnitus, and that the
Habituation
and tinnitus
513
complainers are more psychologically vulnerable than their more sanguine fellowpatients among the noncomplainers. The psychophysiological data, in large, did not differentiate between the two groups. An exception was the tendency for complainers to increase their HR during the course of exposure to the sound stimulus; hypothetically, this may reflect a greater psychological impact, among complainers, of the experimental situation. Our basic question pertains to a differential mode of habituation to tinnitus-like sound stimulation. With our experimental paradigm, which was intended to reflect a common way of studying OR habituation, no differences emerged; the course of SCR decline is practically identical in the two groups, and stimulus-induced HR change was also similar both in the beginning and in the end of the stimulus sequence. In summary, our attempt to find an OR habituation correlate to the independent variable difference was not met with success. The number of patients in our groups are small, and it would be presumptuous to claim that we have proven the null hypothesis. However, by the way we selected our patients, they probably represent rather extreme segments of our independent variable, and the similarity between the groups in the habituation measures we used is quite striking. Therefore, it seems reasonable to conclude that it is unlikely that a pronounced difference in individual OR habituation tendencies can explain the group differences in tinnitus suffering. An obvious threat to the validity of our experiment has to do with the time-scale: can a short-term response decline observed over an experimental session reflect adaptations taking place over years after an individual has started experiencing tinnitus sounds? The answer may depend upon the variability of tinnitus; while some experience a more or less constant sound, others report of huge variations both in intensity and quality. In the latter case, long-term adaptation may be dependent upon repeated, short-term habituation episodes, bearing some resemblance to an experiment of the type presented in this study; speculatively, the adaptation outcome in individuals with less variable tinnitus becomes more influenced by response facilitation, rather than by deficient inhibition. Groves and Thompson [ 11 I, in their dual-process theory of habituation, suggest that the strength of behavioral responses to repetitive stimulation is the resultant of two independent processes, one inhibitory (habituation) and one facilitatory (sensitization). According to the theory, dishabituation reflects sensitization. It is quite possible that the difference between tinnitus complainers and noncomplainers may be related more to dishabituation than to lack of habituation; this issue could be addressed experimentally. Recently, Watson and Pennebaker 1121 discussed the relationships between subjective health state and negative affectivity (NA). Negative affectivity is a tendency to describe one’s mood and emotional state in negative terms. Watson and Pennebaker 1121 have discussed possible mechanisms for the impact of NA upon subjective health. According to Watson and Pennebaker, high NA individuals are vigilantly scanning and ‘checking’ stimuli, e.g. bodily sensations; they are more likely to observe minor aches and pains. The ‘scanning’ is anxiety-provoking, which increases the risk of negative labelings of the sensations noted. Although somewhat circular, these ideas are of some interest here because they indicate the importance of facilitation, rather than mere lack of inhibition, as a core element in the etiology of non-adaptation.
514
S. G. CARLSSON
and S. I. ERLANDSSON
The habituation theory of tinnitus adaptation is an intriguing attempt to explain individual variations in sickness impact. The theory seems to be relevant for a wide array of conditions, where somatic pathology does not fully account for the degree of suffering. The failure in this study to find a short-term OR habituation correlate does not, in our opinion, nullify the theory; however, it may indicate the necessity to relate it to other, maybe more complex, processes than can be studied within an OR habituation paradigm. Acknowledgemenrs-This Tercentenary Foundation.
study was supported by a grant to Dr Carlsson from the Bank of Sweden The technical assistance by Sven-ejvind Swahn is thankfully acknowledged.
REFERENCES Adv Neural 1974; 4: 415-422. 1. FORDYCE WE. Pain viewed as learned behavior. of tinnitus. In Tinnitus, Ciba Foundation 2. COLES HR, DAVIS AC, HAGGARD MP. Epidemiology Symposium No. 85. London: Pitman Books, 1981. aspects of tinnitus. In Contriburions fo 3. HALLAM R, RACC~MANS, HINCHCLIFFE R. Psychological Medical Psychology, (Edited by RACHMAN S), Vol. 3. Oxford: Pergamon Press, 1984. models and the orienting reflex. In The Cenrru[ Nervous Sysrem and 4. SOKOLOV EN. Neuronal Behavior. (Edited by BRAZIER MAB). New York: Josiah Macy, Jr. Foundation, 1960. and dishabituation of responses innervated by the autonomic nervous 5. GRAHAM FK. Habituation system. In Habituation. (Edited by HARMAN HVS, HERZ MJ) Vol. 1. New York: Academic Press, 1973. Anxiety Inventory (Form Y). Palo Alto, CA: 6. SPIELBERGER CD. Manual for the State-Trait Consulting Psychologists Press, 1983. of a scale to measure fear. Behav Res Ther 1965; 4: 45-53. 7. GEER JH. The development (Edited by BROWN 8. EDELBERG R. Electrical properties of the skin. In Methods in Psychophysiology. CC). Baltimore: The Williams and Wilkins Co., 1967. 9. LINDGREN BW, MCELRATH GW. Introduction to Probability and Statistics. New York: Macmillans, 1959. Statistics for rhe Behavioral Sciences. New York: McGraw-Hill, 1956. 10. SIEGEL S. Nonparametric A dual-process theory. Psychol Rev 1970; 77: 419-450. 11. GROVES PM, THOMPSON RF. Habituation: stress, and distress: Exploring the central role 12. WATSON D, PENNEBAKER JW. Health complaints, of negative affectivity. Psycho! Rev 1989; 96: 234-254.
Research.
Vol.
35.
No.
415,
pp.
509-514.
1991. 0
HABITUATION
0530-3999/91 1991 Pergamo”
AND TINNITUS: AN EXPERIMENTAL
53.00+.00 Press
plc
STUDY
SVEN G. CARLSSON and SOLY I. ERLANDSSON (Received
29 May
1990; accepted
in original form
12 December
1990)
Abstract-The study is an experimental test of Hallam’s habituation theory of tin&us; this theory implies that the huge variation in suffering among individuals with about the same amount of tinnitus is due to differences in habituation to the perceived sound. Fourteen patients, seven ‘complainers’ and seven ‘noncomplainers’, participated in an experiment where we studied changes in skin conductance and heart rate responses to a series of tinnitus-like sound stimuli. No group differences in habituation were observed. We suggest that facilitatory processes, like disinhibition, may be more important than deficient habituation for the inability, in some individuals, to adapt to their tinnitus. INTRODUCTION DISCREPANCY, observed for several disorders, between objective pathology and subjective suffering is a challenging problem which requires new models guiding the search for psychosomatic causation. Among the most thoroughly discussed examples are certain chronic pain states, like long-standing low back pain. Fordyce [ll has proposed that important #determinants of pain maintenance are to be found at a behavioral, rather than a somatic level: for many pain patients, by learning processes, psychological and social changes occur which tend to maintain the illness, regardless of somatic pathology. Tinnitus, a condition where the affected individual experiences sounds which have no external source, seems to be another excellent example: the variation in suffering can hardly be accounted for by physical or somatic factors. While clinical investigations of tinnitus patients have described them as generally affected, epidemiological studies have disclosed a significant proportion of individuals who do not seek help for it, and do not seem to suffer 121. Again, the clinically important question remains: what makes some tinnitus patients plagued and handicapped, while others are left quite undisturbed? Richard Hallam, an English psychologist, has proposed an interesting and unusually detailed theory, based on the concept of habituation [31.Habituation is the successive reduction of reactions and awareness in relation to a repetitive, non-signal stimulus. Hallam has adopted the concept in order to account for the long-term adaptation which he has observed in many tinnitus patients. In others, however, the perceived sound sensations remain unhabituated. In Hallam’s model, possible causes of such incomplete or inhibited response decline may be found in the experimental literature concerning habituation of the orienting reaction (OR). The OR, according to Sokolov [41,is a wide-spread preparatory physiological change in response to a stimulus; the change is believed to promote the organism’s need to analyse new and potentially important environmental events. Prerequisites for optimal habituation are non-signal stimulus properties and low THE
Department of Psychology, University Correspondence to Sven G. Carlason, 14158. S-400 20 Griteborg, Sweden.
of GBteborg, Sweden. University of Giiteborg,
Department
of Psychology,
Box
510
S.
G.
CARLETON
and S. I. ERLANDSSON
general arousal level; in other words, habituation is slow or absent when stimuli have acquired some significance, and/or when the stimulated organism’s arousal level is high. Dishabituation, the reappearance of reactivity after habituation has occurred, can be observed as the consequence of the appearance of a new stimulus; the effect is not only a response to that stimulus, but a recovery of responses to the original one. In his habituation model of tinnitus, Hallam [31 makes use of what is known about the prerequisites for habituation and dishabituation of the OR. For instance, if the patient has negative beliefs, attitudes or feelings in regard to his tinnitus, habituation may not occur; if habituation has occurred, intrusive stimulation may heighten the arousal level and induce awareness due to dishabituation. This study represents an attempt to subject the habituation model to a direct experimental test. Two groups of tinnitus patients, one highly disturbed and the other relatively unbothered by their symptom, were to be compared in an OR habituation type of experiment, with a repetitive tinnitus-like sound as stimulus; we chose as a response measure the skin conductance response, which is one of the most widely used in human OR habituation research, and heart rate pre- to post-stimulus change, because of its presumed relationship to OR as well as reactions of the defence type [51. METHOD
Patient5 Two groups of patients, after informed consent, entered the study. Group A (complainers) were seven patients (four male, three female) with bothersome tinnitus; they were recruited among patienta who had sought medical help hecause of their symptom, and after examination. they were found to he severely distressed by their disorder. and in need of treatment. Group B (noncomplainers) were seven patients (all male) who had not consulted medical expertise for their tinnitus; their tinnitus had been noticed in connection with medical examination of their hearing impairment. They were found to he non-distressed by their tinnitus, and not in need of treatment for it. Mean age was 61 yr for both groups. Mean pure tone average (0.5, 1.0, 2.0 and 2.0 Hz) were, for left/right ear, 32133 (SD = 11113) and 38140 (SD = 1019) for complainers and noncomplainers. respectively. For eight of the patients the hearing loss was noise induced; one had a neurogenic etiology; for the remaining five patients. the etiology was unknown. The general symptom attitude, negative for the complainers versus neutral for non-complainers, wa\ verified in an initial interview. Meusurrments For each individual. the tinnitus character and loudness level were explored with a tinnitus analyzer (Watic. Model TA 3). The individually shaped tinnitus-like sound was used as experimental stimulus; the tlnnitus analyscr was used as stimulus source. The stimulus intensity level was well above the individual hearing threshold for the sound, and well below the discomfort threshold. There were 30 stimuli, stimulus duration was 0.4 s, and intervals between stimuli were 20, 2.5 or 30 s, in a fixed random order. The stimulus configuration was monitored by a tape recorder, with a tape carrying signals corresponding to stimuli; these signals activated a frequency decoder with a reed relay, closing the stimulus circuit. Stimuli were administered via head phones, according to localization: patients with unilateral tinnitus heard the stimuli through the ear where they localized tinnitus, others were stimulated binaurally. Skin conductance was recorded with silver-silver chloride electrodes (diameter 10 mm), attached to the medial phalanx of the fore and middle fingers ot. the non-preferred hand. Parker electrode gel was used as contact medium. Two GRASS 7Pl preamplifiers were used for recording of skin conductance level and skin conductance responses (SCR). Heart rate was recorded with standard EKG methodology; the signal was fed into a GRASS 7P4 preamplifier, giving a tachographic beat-by-heat record. A questionnaire *as used to explore the frequencies of negative reactions to environmental sounds, and sleep problems like insomnia. Both aspects were covered by three items, ranging from I -never to 4.very often.
Habituation
511
and tinnitus
State and trait anxiety was assessed with the Stait Trait Anxiety Inventory (STAI, Form Y) [61.We used, also, a shortened version of The Geer Fear Scale [71;it is a 18 item self-rating scale where the degree of fears (of e.g. sharp objects, spiders. blood and heights) are estimated on 1 through 7 scales (1 is no fear, 7 is ‘terror’). Data reduction Skin Conductance Responses amplitudes were estimated according to the guidelines given by Edelberg [81. For heart rate responses, mean heart rate 10 set before and 10 set following each stimulus was estimated with a planimetric method: the area for a 10 set period under the tachographic trace was measured with a digitizer feeding into a computer program transforming the area into mean heart rate. The reliability of this methodology was found to be quite good (the test-retest error is within + - 1%). Individual habituation tendencies were estimated by means of a habituation index, based on comparisons between each consecutive response magnitude and the average of all preceding ones. Given the null hypothesis that no systematic response magnitude trend exists, there is an equal probability for a response to be larger or smaller than the mean of the preceding ones; this mean represents an estimate of the individual’s reactivity to the given stimulation. The number of instances, for an individual, where a response is smaller, represents the habituation index for that individual; with 30 stimuli, the index varies, accordingly, between 0 and 29. The normal approximation of a binomial distribution, with p = q = 0.5 and N = 29, is used to identify the significance limits for rejection of the null hypothesis L91. For a two-sided, p = 0.05 test the upper limit is 20.28; consequently, a habituation index 21 and above indicates significant habituation; towards the other end of the index range, a value of 8 or lower would indicate a significant sensitization. All group comparisons were made with the Mann-Whitney U test 1101.
RESULTS
Mean tinnitus loudness level above threshold was 14.3 dB (range 5-20) for complainers and 15.4 dB (range 5-25) for noncomplainers; the difference is nonsignificant. TABLE
I.-MEDIANS
(AND RANGES)• F PSYCHOMETRIC QUESTIONNAIRE DATA
Complainers Trait State Fears Noise Sleep
anxiety anxiety sensitivity problems
38 33 31 7 6
(31-61) (25-53) (20-67) (3-12) (4-l I)
AND
Noncomplainers 36 29 23 5 4
(20-39) (20-35) (18-35) (3-6) (3-6)
NS NS NS NS LJ = 0.013
Table I shows the results of the psychometric tests and the questionnaire. There are consistent, although not significant, differences between the groups in state and trait anxiety, in fear as assessed with the Geer Fear Scale, and in sensitivity to environmental sounds. Problems with sleep are significantly greater among complainers. Figure 1 gives group means of individual, relative SCR amplitudes (responses 2-30 expressed as percent of the amplitude of the SCR to the first stimulus). There are no significant differences between groups in relative SCR’s to stimuli 2-30. Medians (and ranges) of the habituation index were 23 (20-29) and 24 (21-29) for complainers and noncomplainers, respectively. Individual binomial tests of response magnitude trend, as described above, showed significant habituation in all noncomplainers, and in all but one of the complainers. The group difference is nonsignificant.
512
S. G. CARLSSON and S. I.
ERLANDSSON
20
IO
3G
Stimulus no. FIG.
1.
Mean
amplitudes of skin conductance responses, expressed as percentages Open squares, complainers; filled squares, noncomplainers.
of first response.
Table II gives group means for HR during pre- and post-stimulus periods for stimuli l-3 and 28-30, together with differences between pre- and post-values, indicating HR responses to stimuli. While there are no group differences in HR responses, groups differ significantly in the way HR pre-stimulus and HR poststimulus levels change from the first to the last three observations: complainers. compared to non-complainers, increase their HR. ‘GABLE
II.-MEAN
THREE
AND
LAST
HR FOR 10 SEC THREE
STIMULI,
PERIODS
AND
POST-STIMULUS
Stimuli
Complainers Noncomplainers
P=
post
65.7 67.4
65.0 67.8
PRECEDING
MEAN
FOLLOWING
BETWEEN
FIRST
PRE-
AND
PERIODS
1. 2, 3 difference 0.69 -0.40
AND
DIFFERENCE
Stimuli we
post
70.5 66.7
69.8 61.3
28, 29, 30 difference 0.71 -0.S5
DISCUSSION
In this study, we have attempted to contrast two groups of patients, with the same type of physical symptom but with different types of orientation towards the symptom. The first question to be discussed concerns the validity of our selection. All patients entering the study unequivocally confirmed the background information concerning their way of coping with their tinnitus. The complainers scored higher on questionnaire data indicating sleep disturbances, and their subjective sound sensitivity tended to be greater. Also, the two groups tended to differ in anxiety and amount of fears. Based on all these observations, it seems justified to conclude that the two groups differ in their way of coping with their tinnitus, and that the
Habituation
and tinnitus
513
complainers are more psychologically vulnerable than their more sanguine fellowpatients among the noncomplainers. The psychophysiological data, in large, did not differentiate between the two groups. An exception was the tendency for complainers to increase their HR during the course of exposure to the sound stimulus; hypothetically, this may reflect a greater psychological impact, among complainers, of the experimental situation. Our basic question pertains to a differential mode of habituation to tinnitus-like sound stimulation. With our experimental paradigm, which was intended to reflect a common way of studying OR habituation, no differences emerged; the course of SCR decline is practically identical in the two groups, and stimulus-induced HR change was also similar both in the beginning and in the end of the stimulus sequence. In summary, our attempt to find an OR habituation correlate to the independent variable difference was not met with success. The number of patients in our groups are small, and it would be presumptuous to claim that we have proven the null hypothesis. However, by the way we selected our patients, they probably represent rather extreme segments of our independent variable, and the similarity between the groups in the habituation measures we used is quite striking. Therefore, it seems reasonable to conclude that it is unlikely that a pronounced difference in individual OR habituation tendencies can explain the group differences in tinnitus suffering. An obvious threat to the validity of our experiment has to do with the time-scale: can a short-term response decline observed over an experimental session reflect adaptations taking place over years after an individual has started experiencing tinnitus sounds? The answer may depend upon the variability of tinnitus; while some experience a more or less constant sound, others report of huge variations both in intensity and quality. In the latter case, long-term adaptation may be dependent upon repeated, short-term habituation episodes, bearing some resemblance to an experiment of the type presented in this study; speculatively, the adaptation outcome in individuals with less variable tinnitus becomes more influenced by response facilitation, rather than by deficient inhibition. Groves and Thompson [ 11 I, in their dual-process theory of habituation, suggest that the strength of behavioral responses to repetitive stimulation is the resultant of two independent processes, one inhibitory (habituation) and one facilitatory (sensitization). According to the theory, dishabituation reflects sensitization. It is quite possible that the difference between tinnitus complainers and noncomplainers may be related more to dishabituation than to lack of habituation; this issue could be addressed experimentally. Recently, Watson and Pennebaker 1121 discussed the relationships between subjective health state and negative affectivity (NA). Negative affectivity is a tendency to describe one’s mood and emotional state in negative terms. Watson and Pennebaker 1121 have discussed possible mechanisms for the impact of NA upon subjective health. According to Watson and Pennebaker, high NA individuals are vigilantly scanning and ‘checking’ stimuli, e.g. bodily sensations; they are more likely to observe minor aches and pains. The ‘scanning’ is anxiety-provoking, which increases the risk of negative labelings of the sensations noted. Although somewhat circular, these ideas are of some interest here because they indicate the importance of facilitation, rather than mere lack of inhibition, as a core element in the etiology of non-adaptation.
514
S. G. CARLSSON
and S. I. ERLANDSSON
The habituation theory of tinnitus adaptation is an intriguing attempt to explain individual variations in sickness impact. The theory seems to be relevant for a wide array of conditions, where somatic pathology does not fully account for the degree of suffering. The failure in this study to find a short-term OR habituation correlate does not, in our opinion, nullify the theory; however, it may indicate the necessity to relate it to other, maybe more complex, processes than can be studied within an OR habituation paradigm. Acknowledgemenrs-This Tercentenary Foundation.
study was supported by a grant to Dr Carlsson from the Bank of Sweden The technical assistance by Sven-ejvind Swahn is thankfully acknowledged.
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