Sample recruitment and description
Altogether, 38 right-handed adolescent refugees participated. Thirteen of them were diagnosed with PTSD at the time of evaluation. Twenty-five did not suffer from PTSD according to DSM-IV (APA, 2000) and were thus assigned to a refugee control group. Sufficient attention and completion of the full experimental procedure were defined as inclusion criteria, which led to the exclusion of 2 subjects in the PTSD and 11 subjects in the control group. Finally, 10 subjects with PTSD and 15 subjects without such a diagnosis were included in the analyses.
To guarantee adequate reading ability for the reaction time experiment, reading ability of each subject was tested in advance by a subtest of the Salzburger Lesetest (Landerl, Wimmer, & Moser, 1995). This test assesses the speed of reading words used in every day life. A percentile of 25 was defined as additional inclusion criterion.
Recruitment of the complete sample occurred within an epidemiologic study addressing the prevalence of psychiatric disorders among adolescent refugees (Ruf, in preparation). All participants suffering from PTSD according to DSM-IV (APA, 2000) were offered psychological treatment. Additionally, all adolescents were rewarded with a small present.
A survey of demographic variables is depicted in Table 8.1 (next page). Both groups did not differ statistically in terms of age (t(23) = -.52, p = .61) and German reading ability (t(23) = .56, p = .58). In addition, groups did not differ in general intelligence (t(21) = 1.68, p = .11) and concentration performance (t(21) = -.46, p = .65 for overall performance, t(21) = .36, p = .72 for error rate).
Table 8.1 Demographic specifications of subjects
One traumatic experience is requested at least for the diagnosis of PTSD in DSM-IV (APA, 2000). Hence, all adolescents of the PTSD group experienced a minimum of one such experience (range: 2 – 10 different event categories6). In the control group, too, all participants experienced or witnessed at least one life-threatening event (up to 4 different event categories). In the latter group, the most often reported experiences consisted of war-related experiences as witnessing a physical attack on somebody else, seeing dead people (funerals excluded) or direct combat experiences, such as bombing, shelling, burning houses, and attacks by soldiers. Many adolescents reported having been involved in an accident. By contrast, the number and variety of reported different event categories is much broader in the PTSD group: These participants reported witnessing physical attacks against a stranger or experiencing attacks on themselves
6 Note that the number of different reported event categories is listed, not the total number of traumatic experiences.
(most often by soldiers) and witnessed assaults against family members (most by soldiers) most frequently.
Diagnostic and experimental procedure
Diagnostic and experimental procedure were both performed individually. Prior to the experimental procedure, subjects were asked for demographic variables as well as diagnosed with respect to PTSD using the UCLA Posttraumatic Stress Disorder (PTSD) Reaction Index (Rodriguez et al., 1999). The Mini-international neuropsychiatric interview (M.I.N.I., Sheehan et al., 1998) was further applied to assess other possible psychiatric disorders. Additionally, general intelligence was measured by Coloured/Standard Progressive Matrices (Raven, 1962, 1976) as well as concentration performance using Test d2 (Brickenkamp, 2002).
Participants were instructed in written form that they would see a sequence of word pairs presented consecutively and asked to answer the following question about the second word as fast as possible: “Is this a good word or a bad word?” (evaluative decision task). The answer was recorded with two colored buttons on the keyboard. The position of the colors was counter-balanced across (all right-handed) subjects.
The understanding of the whole instruction was confirmed within a 5-word-pair test trial (items not included in the final trial). Stimuli that were not understood by the individual subject were noted and excluded from the analysis.
Stimulus selection and presentation
The stimulus set consisted of 120 prime target word pairs, all German nouns. All stimuli were previously rated with respect to valence and arousal by a similar population, see section 6. Nouns were categorized as pleasant, if mean valence ratings on the nine-point SAM-scale were above 6.5, between 6.5 and 4.5 for neutral, and below 4.5 for unpleasant affective valence. Unequal scale width for the different valences resulted from a central tendency. Participants tended to favor answers in the middle of the scale in the prestudy. Additionally, understandability of the words was affirmed within the prestudy (see section 6). Stimuli were matched for word length and frequency (F(2,57) = 2.01, p = .14 for word length; F(2,52) = 1.17, p = .32 for word frequency) across the different affective categories. The word frequency was determined by CELEX data base (Baayan et al., 1993).
Affective valence was varied for both primes (pleasant, unpleasant, and neutral) and targets (pleasant and unpleasant). The consistency of affective valence between prime and target was varied as well. The complete set of stimuli contained the following categories (see Table 8.2), each represented by 20 word pairs:
Table 8.2: Variations of affective valence in the prime – target pairs
prime target
pleasant pleasant
pleasant unpleasant
neutral pleasant
neutral unpleasant
unpleasant pleasant
unpleasant unpleasant
Primes and targets were presented on a laptop (15“ screen diameter, font “Times new roman”, 54pt, black on white screen) using Presentation. Stimulus onset asynchrony (SOA) was set at 400 ms. The inter-stimulus interval (ISI) was randomized between 2 to 3.5 s. The target was shown until the answer occurred or for a maximum of 3 seconds. Within the a priori affective category, primes, and targets were presented in random order. The full set of stimuli is depicted in Table 12.4 in the appendix.
Statistical analysis
Data inclusion criteria were defined as follows: performance of 80 prime target pairs (= 2/3 of the whole experiment), individual word understanding, and sufficient stimulus attention (reaction times < two standard deviations from the group mean). The remaining data were averaged per participant and condition. Thus, the dependent variable consists of averaged reaction times in ms for each condition.
Kolmogorov-Smirnov tests indicated normal distribution in all design cells. A 2 (group; control, PTSD) x 3 (prime valence; pleasant, unpleasant, neutral) x 2 (target valence; pleasant, unpleasant) analysis of variance was run in SPSS with group as between- and prime and target valence as within-subjects factor. In case of no sphericity (Mauchly), Greenhouse-Geisser corrected degrees of freedom will be reported. Post hoc tests were performed as Fisher LSD and pair wise t-tests in Statistica.
Task involvement was tested for each target: Chi2-tests formally tested for each target whether evaluations across all subjects differed from chance level (.50). The
evaluation was compared to the prestudy rating: Words evaluated as “good” should be rated as “pleasant” in the prestudy. The same was true for “bad” words and
“unpleasant” ratings. Task involvement should be indicated by evaluations above chance level that are consistent with the prestudy ratings.