4.1. Changes in Severity of Negative Symptoms
In the randomized controlled trial at hand we aimed to examine the effects of a manualized movement therapy intervention (based on DMT; [35
]) on negative symptoms in participants with autism spectrum disorder. Relying on the embodiment approach and related research we hypothesized that participants receiving the DMT intervention should display a stronger decrease in negative symptoms over the period of the intervention compared to participants receiving no treatment.
As expected, symptom reduction on the overall negative symptoms was greater in the treatment group, yet this effect was only significant at the 0.10 level and can thus be regarded as marginally significant (by convention). The observed symptom reduction of 15.27% is classified as a small effect and corresponds with a CGI-I (Clinical Global Impression-Improvement) score of “minimally improved”, which is regarded as clinically substantial [45
]. In the light of the strong association of negative symptoms with poor quality of life and their extensive resistance to conventional treatment methods [5
], a small improvement can be highly meaningful to the individual.
Participation in the treatment did not lead to a significantly different symptom reduction for any of the specific symptom subtypes. However, the symptom development pattern was consistent with the hypotheses for the NS subtypes anhedonia, blunted affect, abulia/avolition (ordered by decreasing effect size), and diminished attention (with a truly negligible effect size). Thus, symptom severity of these subtypes tended to decrease more in the treatment group and hence contributes to the effect observed for overall negative symptoms. Only with regard to alogia did symptom severity worsen in both conditions, however not significantly and with a truly negligible effect size (see Table 4
). This pattern of response conforms to the predictions of embodiment theory, because the subtypes most affected by the intervention (anhedonia and blunted affect) are more closely related to diminished self-perception as the connection of bodily states to emotions, postulated to underlie the social deficits in autism spectrum disorder.
As the intervention is mainly targeting the increase of empathy and perspective taking, and only to a minor degree of emotion expression, we would argue that the results are particularly encouraging. In future studies gearing the intervention more specifically to emotion expression, we would expect greater effects of DMT. DMT research at present is increasing its efforts to detect working mechanisms and active factors of specific interventions (e.g., [47
]), which helps future studies in this research field.
The study at hand provides encouraging results and coincides with the benefits of dance movement therapy described in some case studies, for example, the increase of empathy and self-awareness in children with ASD [30
]. Regarding quantitative approaches there are no studies with similar outcome variables, thus this study adds new insight to the limited quantitative evidence and research on DMT for young adults with ASD and demonstrates the far-ranging effects of DMT.
4.2. Limitations and Further Directions
Unfortunately, this study, as in many other studies working with longitudinal designs with clinical samples, there was a comparably high drop-out rate that led to two critical problems. First, a large amount of missing data needed to be accounted for. Although we carefully considered all possible methodic approaches and abided by statistical rules to avoid biased results, a great portion of valuable information was unavailable. This lead to the second problem: Due to the missing data, we could not comply with the required sample size of 90 participants to detect a medium to large effect with a power of 0.8 computed prior to the study. Taking the effect size found in this trial (generalized η2 = 0.009) as a basis, the required sample size to detect it would be even higher.
Furthermore, several limitations regarding the treatment and the data acquisition are likely due to financial constraints. Firstly, and most importantly, the dyadic mirroring part of the intervention was predominantly performed in dyads of two participants rather than in dyads of a participant and a co-therapist. We learned from the comparison of the feasibility study and the main trial that, as the intervention aims to strengthen perception of others’ emotions (and thereby also perception of the self) by mirroring their movements, it seems to be crucial that the partner displays emotions in a non-autistic manner. If emotion expression is limited to the extent in which we find it in other participants with ASD, the effect seems to be strongly reduced. In the feasibility study for the present research project, dyadic mirroring was, barring rare exceptions, always performed with a co-therapist and treatment effects on all variables are stronger despite a smaller sample size [35
Moreover, SANS ratings were conducted by trained student apprentices. In order to obtain reliable ratings, participation in more detailed workshops and a certain level of experience of the raters would be desirable. It can thus not be ruled out that raters in this study differed in their judgments, leading to unreliable ratings. Unfortunately, it was not possible to compute an inter-rater-reliability measure due to documentation. Hence, it was especially problematic that ratings on pre- and posttest of a participant were always conducted by different raters, while at the same time this was a good set-up for avoiding familiarity with tester as a confounding variable.
The use of a waiting control group is certainly a valid method to evaluate the effect of dance/movement therapy compared to the daily routine. Still, regarding the evaluation of embodiment approaches, it would be particularly interesting to examine whether advantages in symptom reduction are only due to general properties of physical and/or group activities or to specific properties postulated as effective by the embodiment notion. Future research should therefore focus on control interventions that differ from the movement therapy only in such aspects as for example, (1) the focus on mirroring; (2) the link of movement and self-perception; and (3) the link of movement and emotion. Another option would be to measure after each part of the intervention; e.g., after dyadic mirroring, after group mirroring with low exposure, and after group mirroring with high exposure; to be able to differentiate more effective from less effective interventions.
Lastly, the overall symptom severity in the autistic sample was merely at the threshold of non-normal values, which might be due to the fact that not all symptom subgroups of negative symptoms assessed with the SANS are typical for participants with ASD, and not all social symptoms relevant in ASD are measured by the SANS. This may have resulted in a floor effect on the SANS scores, which might partially explain why the observed effects were so small. Assessing the schizophrenia-typical symptom cluster of negative symptoms in autism was illustrative in order to compare effects of the intervention on participants with different disorders (see Appendix C
). The comparison of the two populations showed that participants with ASD scored pronouncedly higher in negative affect values than participants from the schizophrenia spectrum (in a Chi2
-test of the aggregated SANS Total Score Values over experimental group (EG) and control group (CG) for each diagnostic group the differences were significant at the p
= 0.05-level; see Appendix C
). Nonetheless, the use of ASD specific assessment instruments for the social symptom cluster would provide better and more comprehensive information about the relevant domains and thus be more serviceable in the search for truly effective treatment methods.