University of Groningen
An ethological approach of interpersonal theories of depression
Geerts, Erwin Adrianus Henricus Maria
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CHAPTER 5
NONVERBAL INTERPERSONAL ATTUNEMENT AND EXTRAVERT
PERSONALITY PREDICT OUTCOME OF LIGHT TREATMENT IN SEASONAL
AFFECTIVE DISORDER
Erwin Geerts, Ester Kouwert, Netty Bouhuys, Ybe Meesters, and Jaap Jansen.
ABSTRACT
Nonverbal interpersonal behaviour and personality may play a role in the response to
light treatment in seasonal affective disorder. We investigated whether the response to
light treatment can be predicted by 1) the (time course of the) nonverbal attunement
between the patients' support seeking behaviour and an interviewer's support giving
behaviour (reflecting interpersonal satisfaction in normals) during a pre-treatment
interview and 2) the pre-treatment levels of the patients' personality traits Neuroticism
and Extraversion.
Nonverbal behavioural elements of 60 patients and of 3 interviewers was
registered from videotaped pre-treatment interviews. The elements were pooled into
behavioural factors. The nonverbal attunement was assessed by calculating the absolute
difference between the patients' and the interviewers' behavioural factors.
The more the patients and the interviewers became attunened over the interview
and the higher Extraversion was, the more favourable the outcome of light treatment
was. There were no relationships between the change of the nonverbal attunement, on
the one hand, and the patients' Neuroticism and Extraversion scores, on the other. Our
results support the involvement of psycho-social factors in seasonal affective disorder.
59
Submitted
60
INTRODUCTION
Seasonal affective disorder (SAD, winter-type) is a recurrent depression type that is
characterized by the seasonal pattern in the onset (autumn or winter) and the remission
(following spring or summer) of the depressive episodes (Rosenthal et al., 1984; DSMIV, American Psychiatric Association, 1994). Exposure to bright light has been proven a
successful treatment of SAD (up to 70% successful responses; Terman et al., 1989;
Wirz-Justice et al., 1993; Meesters et al., 1995). However, the mechanism of action of
bright light is yet unknown. SAD may shift into non-seasonal recurrent depression
(Leonhardt et al., 1994; Sakamoto, 1995; Thompson et al., 1995). Thus, factors
involved in the course of non-seasonal depression may also underlie the outcome of
light treatment in SAD. In the present study factors from two different domains will be
investigated: interpersonal behavioural processes (nonverbal attunement) and
personality traits (Neuroticism (N) and Extraversion (E)).
Interactions between depression-prone subjects and their social environment are
considered to play a causal role in depression-onset and -persistence (e.g. Libet and
Lewinsohn, 1973; Youngren and Lewinsohn, 1980; Coyne et al., 1990). In particular
interpersonal satisfaction and the relation between support seeking behaviour by
depression-prone subjects and support giving behaviour by others have received much
attention (e.g. Coyne et al., 1990; Veiel et al., 1992; Brown et al., 1994; Paykel et al.,
1996). In SAD high pre-treatment levels of patients' nonverbal manifestations of
"support seeking behaviour" are related to poor outcome of light treatment (Geerts et
al., 1995). Also, high pre-treatment levels of an interviewer's nonverbal "support giving
behaviour" predict poor outcome of light treatment (Geerts et al., 1995). Geerts et al.
(1997) demonstrated that depressed patients attune their "support seeking behaviour"
to experimentally controlled levels of an interviewer's "support giving behaviour".
Moreover, in naturalistic interactions between hospitalized, severely depressed patients
and an interviewer, the time-course of such attunement predicts subsequent
improvement: the more the patients and the interviewers become attuned over the
interview, the more favourable the outcome of the depression will turn out to be (Geerts
et al., 1996). In non-depressed subjects, nonverbal attunement is related to
interpersonal satisfaction and rapport (Cappella and Palmer, 1990; Hall et al., 1995).
Hence, the results by Geerts et al. (1996) underscore the suggestion that interpersonal
satisfaction plays a causal role in depression.
61
Hypothesis 1: We hypothesized that the (time-course of the) attunement between
patients' nonverbal "support seeking behaviour" and an interviewer's nonverbal
"support giving behaviour" also predicts the outcome of light treatment in SAD.
Personality characteristics may also play a role in the outcome of light treatment.
In non-seasonal depression, agreement exists on N as a risk factor for depression-onset
(e.g. Ormel and Wohlfarth, 1991; Bagby et al., 1995). Some studies also have found a
relationship between N and persistence of depression (e.g. Hirschfeld et al., 1986;
Duggan et al., 1995), although others did not (e.g. Bagby et al., 1995; see also Clark et
al.,1994). In addition, E has been found to be related to a favourable course of
depression (e.g. Bagby et al., 1995; see also Clark et al., 1994). With respect to
patients with SAD it has been found that personality scores lie between normal scores
and the scores of patients with non-seasonal depression (Schulz et al., 1988; Lilie et al.,
1990). However, Bagby et al. (1996) found no significant differences between N and Escores of patients with SAD and patients with non-seasonal depression. Moreover, N is
positively correlated with seasonality and SAD (Murray et al., 1995). ReichbornKjennerud and Lingjærde (1996) demonstrated that the presence of personality
disorders in SAD may hamper the response to light treatment. To our knowledge, the
relationship between personality traits and the outcome of light treatment in SAD has
not yet been addressed by other investigators.
Hypothesis 2: We hypothesized that pre-treatment levels of N are negatively related to
the outcome of light treatment in SAD and that high pre-treatment levels of E predict a
favourable outcome.
It is assumed that the relationship between N and E on the one hand and mental
health on the other is effected via interpersonal events (N: Ormel and Wohlfarth, 1991;
Poulton and Andrews, 1992; E: Lu and Argyle, 1991). Personality is manifested via
interpersonal behaviour (Gifford, 1991; Gilbert, 1991; Clark et al., 1994). Wiens et al.
(1980) experimentally demonstrated that interviewees' N and E scores are each related
to their nonverbal responses to an interviewer's speech behaviour.
Hypothesis 3: We hypothesized that the (time-course of the) attunement between
patients' nonverbal "support seeking behaviour" and interviewers' nonverbal "support
giving behaviour" is related to the patients' N and E. A 3-way relationship between 1)
interpersonal behaviour, 2) personality-scores, and 3) outcome of light treatment, if
found, may suggest that the relation between personality and outcome of light
62
treatment in SAD is effected via interpersonal processes.
METHODS
Subjects and experimental design
Sixty patients with the diagnosis SAD (Rosenthal et al.,1984; DSM-III-R, American
Psychiatric Association, 1987) participated in the study. They were a subgroup of the
68 patients who participated in an experiment that has been described previously by
Meesters et al. (1995). There were 46 females and 14 males (mean age=27 years ,
range 17 - 68). Patients were included if they 1) had a pre-treatment severity of the
depression > 13 on the Beck Depression Inventory (BDI; Beck et al., 1988), 2) had not
participated in our previous studies on the relationship between observed behaviour and
the course of depression, and 3) had given written informed consent. Seven patients
had experience with light treatment. All patients had been drug free for at least 3 weeks
before the light treatment and remained so during the experimental period.
The experimental period lasted 19 days: a baseline period (days 1-4), a treatment
period (days 5-9) and a 10-days post-treatment period (days 10-19). Treatment
consisted of 30-minutes exposure to 10.000 lux for 4 consecutive days. There were 5
different treatment conditions, varying with respect to the timing of the light treatment
(4 days of morning light: 8:00-8:30 am (ML); 4 days of evening light: 8:00-8:30 pm
(EL); 2 days of ML followed by 2 days of EL; 2 days of EL followed by 2 days of ML;
and 4 days of afternoon light: 1:00-1:30 pm, see Meesters et al. (1995) for a more
precise description of the treatment protocol). The patients were, balanced for gender,
randomly assigned to one of the 5 treatment-conditions. Meesters et al. (1995) already
demonstrated that timing of light did not affect the outcome of the light treatment. This
was corroborated in the present study (see results). Therefore, in the present study the
data for the different treatment-conditions were pooled for further analyses.
A Hamilton interview (HRSD, 17 item version; Hamilton, 1967) was conducted 3
days prior to light treatment. The interviews were videotaped for the registration of
behaviour. Fifty-one patients were interviewed by a male therapist (age=41), 9 patients
were interviewed by one of the 2 participating male research assistants (age 30 and 31
years). The patients were informed about their treatment-condition after the interview.
All interviews took place between 8:00 and 12:00 am. The severity of the baseline
depression was assessed on day 5 (prior to light treatment) by the use of the BDI.
63
Patients still improve after the actual days of treatment (Meesters, 1995). Therefore, we
did not assess outcome at the stop of the treatment period, but at day 19 (i.e. 10 days
after the last exposure to bright light, BDI). The severity of the atypical symptoms was
assessed on day 5 and day 19 by the use of the BDI-addendum (BDI-add) for seasonal
affective disorder (Meesters and Jansen, 1993). A criterium for a successful response
was defined analogue to the joined HRSD criteria by Terman et al. (1989): patients were
judged as responder if the change of the BDI (day 5 - day 19) > 50% and the BDI (day
19)<10; BDI<10 is considered as not depressed (Beck et al., 1988).
Behavioural analyses and assessment of attunement
We applied the methods that have been described previously by Bouhuys et al. (1991),
Bouhuys and van den Hoofdakker (1991), Geerts et al. (1995), and Geerts et al, (1996).
For the first 15 minutes of the Hamilton-interview the occurrence of different nonverbal
elements of behaviour of the patients and of the interviewers (e.g. speaking, looking,
yes-nodding, and hand movements) was continuously registered. Speaking and listening
affect the occurrence of the different elements of behaviour. Therefore, durations and
frequencies of the behavioural elements were analysed with respect to occurrence
during speaking and occurrence during listening. Bouhuys et al. (1991) demonstrated
that, on the basis of statistical arguments, different behavioural elements that are
interpreted as the patients' nonverbal "support seeking behaviour" can be pooled into a
factor. This factor is called Speaking Effort and consists of the durations and
frequencies of looking at the interviewer, of gesticulating, and of general head
movements, all during the patients' speaking, and of the duration of looking at the
interviewer during speaking of the interviewer. Likewise, elements of the interviewers'
nonverbal "support giving behaviour" can be pooled into a factor, called Encouragement
(Bouhuys and van den Hoofdakker, 1991). This factor is constructed by the durations
and frequencies of yes-nodding and of verbal backchannel ("hmm hmm, yes yes,"
emitted to ensure one is listening and to encourage the other to continue speaking)
during speaking of the patients. Appendix 1 presents how the different behavioural
elements constitute the patients' Speaking Effort and the interviewers' Encouragement.
All behaviour was registered by one observer who was blind to both the outcome of the
light treatment and the patients' personality scores (inter-rater reliability compared to
previous reportings on observable interpersonal behaviour in depression kappa (Cohen,
64
1968): mean=0.90, standard deviation (SD)=0.08, range 0.76 - 1.00).
Attunement is defined as equalizing durations and frequencies of elements of
behaviour between participants of an interaction (Cappella and Palmer, 1990). Thus,
attunement will result into relatively small absolute differences between the elements of
behaviour of the participants (Cappella and Palmer, 1990; Geerts et al., 1996). We
assessed the attunement between the patients' nonverbal "support seeking behaviour"
and the interviewers' nonverbal "support giving behaviour" by calculating the absolute
difference between the patients' Speaking Effort and the interviewers' Encouragement.
Hence, low absolute differences represent high levels of attunement. The time-course of
the attunement was assessed per 3-minutes epoch. Z-scores of the different behavioural
elements were calculated over the patients and over time (hence over 60 x 5 cases).
Then, per epoch the behavioural factors were calculated. The change in the attunement
over the interview was assessed as the attunement during the first 3 minutes of the
interview minus the attunement during the last 3 minutes (Geerts et al., 1996). Hence,
a positive change reflects an increase of the attunement. In addition, Speaking Effort
and Encouragement were calculated over the 15 minutes period (Z-scores calculated
over 60 cases).
Personality
Two for the Dutch language validated personality questionnaires were used: the Dutch
Personality Questionnaire (DPQ, 132 items, Luteijn et al., 1985) and the Dutch Short
Form of the Minnesota Multiphasic Personality Inventory (DSM, 83 items, Luteijn and
Kok, 1985). For the Dutch' language the short version of the MMPI has been found to
have better psychometric qualities compared to the translation of the original version
(Luteijn and Kok, 1985). The DPQ and the DSM cover in combination the personality
traits N and E (Luteijn et al., 1985): N is assessed as the average Z-scores of the
subscales inadequacy (DPQ) and negativism (DSM); E is calculated as the average Zscores of the subscales dominance (DPQ), self-esteem (DPQ), and E (DSM), and the
mirrored Z-scores of social anxiety (DPQ) and shyness (DSM). N and E were assessed
between day 2 and day 5 of the experimental period.
Statistical analyses
We applied an Analysis of Variance (ANOVA) to investigate whether the (time course of
65
the) nonverbal attunement between the patients' Speaking Effort and the interviewers'
Encouragement differed between the interviews with responders and those with nonresponders. The grouping of patients has some major disadvantages. Therefore also a
correlational approach was applied. To avoid confounding effects of regression to the
mean (see Lord, 1963), correlations with the change of the depression were assessed
by calculating partial correlations (partial r) with the BDI on day 19 while severity of the
baseline depression was statistically controlled for.
RESULTS
Clinical outcome
Two patients had failed to complete the BDI at day 19. The group as a whole
significantly improved due to the light treatment (mean BDI day 5=21.78, SD=6.49,
range 13 - 37; mean BDI day 19=10.05, SD=7.82, range 0 - 35, n=58; main effect
before after: ANOVA F(1,57)=86.27, p<0.001). The timing of the light did not affect
the outcome (interaction-effect treatment-condition x time: 2-way ANOVA
F(4,53)=1.38, not significant (ns)). Twenty-five patients (43 %) were judged as a
responder (mean BDI day 5=22.00, SD=6.11, range 13 - 37; mean BDI day 19=2.80,
SD=2.65, range 0 - 8 ), 33 patients (57 %) were judged as non-responders (mean BDI
day 5=21.6, SD=6.85, range 13 - 34; mean BDI day 19=15.55, SD=5.60, range 7 35). The severity of the atypical symptoms also decreased over time (mean BDI-add day
5=5.26, SD=2.04, range 2 - 10; mean BDI-add day 19=2.84, SD=2.25, range 0 - 8
main effect before after: ANOVA F(1,57)=3.39, p <0.001.
There was no relationship between severity of the baseline depression and the
severity of the depression after light treatment (Pearson's r=0.11, ns, n=58).
Furthermore, the change of the depression could not be explained by either the baseline
severity of the atypical symptoms (partial r=-0.01, ns, n=58) or by the ratio between
the typical and atypical symptoms at baseline (BDI-add/(BID-add + BDI) x 100) (partial
r=-0.06, ns, n=58). Also, there was no relationship between change of the depression
and the patients' age (partial r=0.16, ns, n=58) . Responders did not differ from nonresponders with respect to gender (P2=0.41, df=1, ns) , experience with light
treatment (P2=0.46, df=1, ns), or interviewer condition (P2=1.84, df=2, ns).
66
Hypothesis 1: Nonverbal attunement predicts outcome of the light treatment
Table 1 and figure 1 present the attunement per 3-minutes epoch of the pre-treatment
interview for the interviews with patients who responded to the light treatment and the
interviews with patients who did not respond to light treatment. For two patients the
total interview-duration was shorter than 15 minutes. These patients were excluded
from this part of the analyses. The mean level of the attunement did not differ between
the 2 groups (ANOVA [main effect on groups]: F(1,54)=0.07, ns). However, the timecourse of the attunement did differ between the interviews with patients who would
respond to the light treatment and those with patients who would not respond
(interaction-effect: 2-way ANOVA [between groups, repeated measures on time]
F(4,216)=3,10, p=0.017): the patients and the interviewers became better attuned in
the interviews with the patients who responded (ANOVA first versus last epoch:
F(1,54)=9.60, p=0.003, n=25). The attunement did not change in the interviews with
non-responders (ANOVA first versus last epoch: F(1,54)=2.03, ns, n=31).
Table 1:
Mean levels of attunement (±SD) between Speaking Effort of patients with seasonal
affective disorder and interviewers' Encouragement per 3-minutes epoch for the first
15 minutes of a pre-treatment interview with responders (n=25) and non-responders
(n=31) to subsequent light treatment. Attunement=*Speaking Effort Encouragement*(high absolute differences reflect poor attunement). Interaction effect
group x time: ANOVA F(4,216)=3.10, p=0.02.
time (min)
0-3
3-6
6-9
9-12
12-15
responders
2.28 (2.26)
1.81 (1.68)
2.06 (1.51)
1.67 (1.46)
1.34 (1.53)
non-responders
1.52 (1.24)
2.11 (1.39)
1.87 (1.73)
2.19 (1.89)
1.90 (1.16)
67
Figure 1: Time-course of the attunement between patients' Speaking Effort and interviewers'
Encouragement for the interviews with responders and non-responders to light treatment.
Attunement=*Speaking Effort - Encouragement*(high absolute differences reflect poor attunement).
The y-axis presents the inversed absolute differences. Interaction effect group x time: ANOVA
F(4,216)=3.10, p=0.017.
Figure 2-a presents the relationship between the change in the attunement over the
interview and the change of the depression. The correlational approach revealed similar
results: the change in the attunement was significantly correlated with the patients'
outcome of the treatment. The more the attunement increased over the interview, the
more favourable the outcome of the light treatment turned out to be (partial r=-0.37,
p=0.005, n=56). The relationship between the change of the attunement and the
change of the depression could not be ascribed to the levels of either the patients'
Speaking Effort (partial correlation with correction for baseline depression and Speaking
Effort: partial r=-0.40, p=0.002, n=56) or the interviewers' Encouragement (partial
correlation with correction for baseline depression and Encouragement: partial r=-0.38,
p=0.004, n=56). One may argue that the change in nonverbal attunement depends on
the initial levels of attunement during the interview. However, when the level of
attunement during the first 3 minutes of the interview was statistically corrected for,
the change in the attunement over the interview was still significantly related with the
patients' response to the light treatment (partial correlation with correction for baseline
depression and for the levels of attunement during the first 3 minutes of the interview:
68
partial r=-0.36, p=0.008, n=56).
It is also unlikely that our results should be ascribed to interviewer effects. When
only the interviews by the medical attendant were investigated, the relationship
between the change in the attunement and outcome of light treatment remained
significant (partial r=-0.35, p=0.018, n=47).
Our previous results on the relationship between Speaking Effort, Encouragement,
and the outcome of light treatment could only be partially replicated: high levels of the
interviewers' Encouragement tended to be correlated with poor outcome of light
treatment (partial r=0.25, p=0.062, n=58). However, the patients' Speaking Effort
was not correlated with the outcome of light treatment (partial r <0.01, ns, n=58).
Hypothesis 2: Personality predicts outcome of light treatment
Fifty-eight patients completed the personality questionnaires. We investigated whether
N and E are related to the outcome of light treatment. It was found that the higher the
levels of E were, the more the patients would benefit from light treatment (partial r=0.27, p=0.050, n=56). The relationship between pre-treatment levels of E and the
outcome of light treatment is presented in figure 2-b. There was no relationship
between pre-treatment levels of N and the outcome of the light treatment (partial
r=0.03, ns, n=56).
Hypothesis 3: The relationship between personality and outcome of light treatment is
effected via nonverbal attunement
We investigated whether the patients' E was related to the levels of the patients'
Speaking Effort and to the change in the attunement over the interview. Eventual
69
Figure 2: a) Relationship between the change of the attunement over the interview and the
outcome of the light treatment. The change in the attunement was assessed as *Speaking
Effort
-Encouragement*during
the
first
3
minutes
minus*Speaking
Effort
-
Encouragement*during the last 3 minutes (a positive change reflects an increase of the
attunement). Partial correlation (when baseline depression is statistically controlled for): partial
r=-0.37, p=0.005. b) Relationship between pre-treatment levels of Extraversion and the
outcome of the light treatment. Partial correlation (when baseline depression is statistically
controlled for): partial r=- 0.27, p=0.050.
relationships may be masked by the severity of the depression. Therefore, we calculated
both Pearson's r and partial correlations (with baseline depression statistically controlled
for). However, no significant correlations were found between E and Speaking Effort
(Pearson's r=-0.05, ns; partial r=-0.02, ns, n=56) or between E and the change of the
attunement over the interview (Pearson's r=0.17, ns; partial r=0.20, ns, n=56). We
also investigated whether the change in the attunement, N, and E could predict the
change in the atypical symptoms or the change in the ratio between atypical and typical
symptoms. However, none of the calculated partial correlations reached statistical
significance.
DISCUSSION
Main results
We hypothesized that nonverbal interpersonal behavioural processes and personalty
traits predict the outcome of light treatment in seasonal affective disorder (SAD). Our
70
first hypothesis was confirmed by the present study: the more the patients and the
interviewers became attuned over the interview, the more favourable the patients'
outcome of the light treatment was. Hypothesis 2 was partially confirmed: high levels of
Extraversion (E) were related to a favourable outcome of the light treatment, however,
Neuroticism (N) was not related to the outcome of the light treatment. These findings
are independent of the severity of the baseline depression. The third hypothesis could
not be confirmed: E was not related to the change of the attunement or to Speaking
Effort.
Our findings are in line with the results in non-seasonal depression on nonverbal
attunement (Geerts et al., 1996) and E (Clark et al., 1994; Bagby et al., 1995). Hence,
our results underscore the suggestion that mechanism that are involved in the course of
non-seasonal depression may also underlie the outcome of light treatment in SAD. The
lack of a relationship between N and outcome of light treatment is in line with some
studies on non-seasonal depression (e.g. Bagby et al., 1995) but in contrast with others
(e.g. Hirschfeld et al., 1986; Duggan et al., 1995; see also Clark et al., 1994).
Interpersonal theories of depression
There is substantial support for a causal role of interpersonal processes in the onset and
persistence of non-seasonal depression (e.g. Coyne, 1976b; Hickie et al., 1991; Veiel et
al., 1992; Brown et al., 1994; Segrin and Abramson, 1994) although some authors find
no relationship between interpersonal factors and the course of depression (e.g. Paykel
et al., 1996). However, little is known on the role of interpersonal processes in the
etiology and course of SAD. According to Bagby et al. (1996) patients with SAD are
less sensitive to rejection and are less likely to be impaired in their capability to maintain
close relationships compared to patients with non-seasonal depression. This may
suggest that interpersonal processes are less likely to be involved in SAD compared to
non-seasonal depression. However, on the level of nonverbal behaviour it has been
found that high levels of Speaking Effort and of Encouragement are related to an
unfavourable outcome of subsequent light treatment in SAD (Geerts et al., 1995). We
could only partially corroborate these findings. High levels of Encouragement tended to
be related to poor outcome, however, the level of Speaking Effort was not related to the
outcome of the light treatment. Nonetheless, the present study underscores the
involvement of interpersonal processes in the response to light treatment in SAD in two
71
ways. In normals nonverbal attunement is related to interpersonal satisfaction (Cappella
and Palmer, 1990; Hall et al., 1995). Thus, the observed relationship between poor
nonverbal attunement and an unfavourable outcome of the light treatment indicates that
lack of interpersonal satisfaction may play a role in the persistence of SAD. Further
support for the involvement of interpersonal processes in SAD is provided by the
positive relationship between the personality trait E and outcome of light treatment.
Extraverted subjects are characterized by high levels of social involvement and interest
and of cooperation (e.g. Lu and Argyle, 1994; Clark et al., 1994). Also, the assessment
of E in the present study (low levels of social anxiety and of shyness and high levels of
dominance, of self-esteem, and of extraversion) refers to interpersonal behaviour.
Hence, the results on E suggest that in particular those patients with SAD who report
relatively high "social functioning" may benefit from light treatment.
Extraverts are considered more alert and more sensitive to reward signals (Clark et
al., 1994). However, our hypothesis that the relationship between E and outcome of
light treatment was effected via nonverbal attunement was not confirmed. The lack of
interrelatedness between E and nonverbal interpersonal behaviour may be explained in
various ways. The relationship between E and outcome of the light treatment may be
mediated via (attunement of) other behaviour. Furthermore, some authors have found
that depressed subjects are impaired in the ability to decode social cues compared to
normal controls (e.g. Zuroff and Colussy, 1986; Gur et al., 1992; Wexler et al., 1994).
Therefore, a relationship between E and attunement as observed in healthy subjects
(e.g. Wiens et al., 1980) may have been affected or even annulled by the depression.
On the mechanisms of action of bright light
Some authors suggest that light treatment may be a placebo (e.g. Eastman et al., 1992;
Eastman et al., 1993). This is supported by Terman et al. (1996) who found that high
baseline expectations of the treatment-effects are related to a favourable outcome of
the light treatment. Pre-treatment interactions between patients and a therapist may
play a role in these processes (Eastman et al., 1992; Hall et al., 1995). Our results
underscore such an explanation for the beneficial effects of bright light by
demonstrating that variables that are related to interpersonal satisfaction are positively
related to the outcome of light treatment. However, alternative explanations may be
possible. According to Terman et al. (1987), bright light has an energizing effect, apart
72
from the possible anti-depressogenic effects. One may speculate that increased levels of
energy may improve the patients' capabilities to respond to other's behavioural levels of
"support giving" and involvement. This may result into higher levels of mutual
interpersonal satisfaction and, hence, into improvement of the depression. Under this
assumption, our results indicate that in particular those patients who demonstrate high
pre-treatment levels of E or of a capability to attune nonverbal behaviour may benefit
from this energizing effect.
The response of the patients with seasonal affective disorder to the light
treatment in the present study (43%) can be considered small (see for instance Terman
et al., 1989; Wirz-Justice et al., 1993; Meesters et al., 1995). A possible explanation
for this relatively poor treatment success may be that the response was assessed by the
BDI (i.e. self-report), in comparison to the use of the HRSD (i.e. external judgement) in
the other studies.
Conclusions
The present study demonstrates that nonverbal attunement between depressed patients
and an interviewer and extravert personality predict a favourable outcome of light
treatment in SAD. These findings support the suggestion that interpersonal processes
may play a role in the etiology and course of SAD. It would be of interest to further
explore the role of these factors in the etiology in SAD. Information from such studies
may enable optimization of therapeutic interventions.