Measuring Linguistic Synchrony in Psychotherapy (2022)

Abstract: We study the phenomenon of linguistic synchrony between clients and therapists in a psychotherapy process. Linguistic Synchrony (LS) can be viewed as any observed interdependence or association between more than one person?s linguistic behavior. Accordingly, we establish LS as a methodological task. We suggest a LS function that applies a linguistic similarity measure based on the Jensen-Shannon distance across the observed part-of-speech tag distributions (JSDuPos) of the speakers in different time frames. We perform a study over a unique corpus of 872 transcribed sessions, covering 68 clients and 59 therapists. After establishing the presence of client-therapist LS, we verify its association with therapeutic alliance and treatment outcome (measured using WAI and ORS), and additionally analyse the behavior of JSDuPos throughout treatment. Results indicate that (1) higher linguistic similarity at the session level associates with higher therapeutic alliance as reported by the client and therapist at the end of the session, (2) higher linguistic similarity at the session level associates with higher level of treatment outcome as reported by the client at the beginnings of the next sessions, (3) there is a significant linear increase in linguistic similarity throughout treatment, (4) surprisingly, higher LS associates with lower treatment outcome. Finally, we demonstrate how the LS function can be used to interpret and explore the mechanism for synchrony.

## introduction when people interact, they tend to naturally coordinate their behavior over time. interpersonal synchrony is defined as the degree to which the behaviors in an interaction are nonrandom and patterned in both timing and form @xcite . when this pattern occurs, it is 1 for code availability please contact authors. the growing acknowledgment of the importance of synchrony in interpersonal relationships has recently led psychotherapy researchers to address the impact of synchrony in the psychotherapeutic process as a way to predict better therapeutic outcomes @xcite . recent studies have demonstrated synchrony between clients and therapists through different modalities @xcite . for example, higher levels of body-movement synchrony have been tied to more positive therapeutic relationships and treatment outcomes @xcite @xcite , vocal synchrony was associated with higher empathy ratings @xcite , and physiological arousal coordination has been tied to client-perceived therapist empathy @xcite . however, linguistic synchrony (ls) between client and therapist has received relatively little attention. the words and language clients and therapists use in psychotherapy sessions reflect their internal thoughts and emotions and reveal important information about their interaction. thus, many of the active ingredients of psychotherapy are found in the words and how they are uttered within psychotherapy sessions. client and therapist ls may reflect their ability to work together in concert and their adjustment to each other's language over time, which may in turn lead to better therapeutic outcome. with the increased amount of conversational texts accessible, applying natural language processing is an appealing step for mental health research (e.g. @xcite . indeed, transcripts of psychotherapy sessions have recently become more readily available thanks to advanced asr transcription technology. these transcripts allow the analysis of ls in psychotherapy (see section 2). the few studies that have considered clienttherapist ls have tended to focus on one session, and assessed it's association with therapy processes (e.g., @xcite . the extent to which ls develops from session to session and its association with treatment outcome were yet to be explored in a statistically sound manner. furthermore, a major criticism on studies on interpersonal synchrony concerns the lack of control for coincidental random synchrony @xcite . based on studies that distinguish genuine synchrony from pseudosynchrony in physiological data, the current study proposes a method to assess ls, that is adapted for sequences of texts (section 4). section 5 presents a ls function, inspired by previous work addressing ls. 2 we examine client-therapist ls throughout treatment (@xmath0, average number of @xmath1.56, a total of 872 transcripts), session by session, and the association between ls and treatment process and outcome. in section 6 we demonstrate the implications of the ability to measure ls. synchrony is viewed as an important mechanism of change between the client and the therapist, which leads in turn to a better bond and to a better outcome (for review see @xcite . when applying the proposed ls function on our dataset, the method displays an association to quality of client-therapist relationship and treatment outcome (section 6.1), as well as a significant linear change across treatment (section 6.2). additionally, we show how the ls function can be used to interpret and explore the mechanism for synchrony (section 6.3). finally, we discuss limitations and potential future work in section 7. ## related work we focus on previous work researching ls in psychotherapy. @xcite dealt with motivational interview training treatment (@xmath2, where each treat-ment has a single 20-min transcribed session. they measured synchrony between client and therapist with function word coordination on the ordered utterances in a session @xcite . they show that high empathy sessions display greater coordination of function words compared to low empathy sessions. overall, average coordination of function words is notably higher in high empathy vs. low empathy sessions. @xcite explored counseling interaction dynamics (@xmath3; each session with 5 annotation points) and their relation to counselor empathy during motivational interviewing. the two latter studies were based on synchrony within a single session. thus, they could not examine patterns of change across treatment. in addition, while these studies demonstrated the presence of ls in sessions characterized by high empathy between clients and therapists, they do not explore the association between ls and other treatment processes and outcome. @xcite measured how various linguistic aspects of written conversations (15,555), as opposed to spoken, correlate with outcomes. this dataset is much larger than in our study, however they analyze the counselor's point of view (@xmath4. @xcite examine how language style matching (lsm; niederhoffer and pennebaker, 2002), clients' relational histories, and symptoms were associated within treatment. on a pilot test using a small sample (@xmath5, @xmath6, and that greater client interpersonal problems prospectively predict lower early lsm in clienttherapist dyads, which in turn predicts greater post treatment psychiatric distress. aafjes-van doorn et al. (2020) demonstrate the clinical usefulness of the lsm and rlsm @xcite approach in psychotherapy outcome measures with a small sample (@xmath7, ses-@xmath8. they also described a case study comparing lsm values to observer-rated measure of working alliance, and conclude that a larger-scale study is required for examining the relationship between synchrony and alliance and outcome. ## linguistic synchrony definition inspired by behavioral and physiological synchrony @xcite , 2017), linguistic synchrony (ls) can be viewed as any observed association or interdependence between people's language dynamics, as indexed by their continuous spoken words, that are nonrandom or patterned in both timing and form. association is a relationship between variables that makes them statistically dependent (e.g., as measured by correlation coefficient see figure 1 .a,b). interdependence is the state in which two or more variables rely on or react with one another such that one cannot change without affecting the other (vandenbos, 2007) (e.g., see figure 1 .c,d). language dynamics of a conversation are the changes in language use, for each participant individually, that can be captured over time by assessing utterances at a number of time points. non-random or patterned associations or interdependences are quantified by adopting an approach by @xcite , "surrogate test", that distinguishes genuine synchrony from pseudosynchrony, which may arise due to random coincidence. this definition outlines the statistical tests required to show that a function can indeed measure ls, by pairing texts with non-original replacements and showing a significant difference in the synchrony measure. ## formalizing a task with respect to the ls definition, we formalize a task, for finding a function that measures ls, as follows: given a sample [[(c i j , t i j )] m i @xmath9.g., clients and their therapists) with m i repeated measures (e.g., sessions in treatment) of lingual texts (i.e., c i j , t i j are each a written or transcribed text sequence) from a population p, function f : @xmath10, where l is a list of text pairs, if for a set of random texts r i j , the sample of values [f ([(c i j , t i j )] m i @xmath11, r i j )] m i @xmath12, t i j )] m i @xmath13. foot_1 intuitively, we would like to find a function that is able to recognize that a given list of text pairs has a non-random dependence. to capture more than just "any observed interdependence or association", defined are two additional pseudosynchrony tests that use surrogates in place of the random texts. within challenge: a text c i j is paired with a different text contained within t i 's list of repeated measures. formally, [f ([(c i j , t i j )] m i @xmath14, t i l j )] m i @xmath15, . . . , m i } and l j ̸ = j. between challenge: a text c i j is paired with any text not contained within t i 's list of repeated measures. formally, [f ([(c i j , t i j )] m i @xmath16, t k j l j )] m i @xmath17.t. k @xmath18, . . . , n}, k j ̸ = i and l @xmath19, . . . , m k j }. ## exemplifying solution adhering to the formalized conception of mls, we next lay out a use case brought from psychotherapy research. first, the data we use is described, then a candidate mls function is presented, and finally the function is tested for mls. ## implications of the candidate function psychology research puts forth much effort in trying to understand the synchrony phenomenon and mechanism (section 1). in addition, studies show a link between client-therapist synchrony and treatment processes and outcomes (sections 2). thus, we examine the relationship between ls and treatment measures through the candidate function (section 6.1), analyze the change of jsdupos over the course of treatments (section 6.2), and demonstrate what can be extracted from the function to further understand ls (section 6.3). ## discussion and future work in section 5.2 we propose a function that is able to measure ls, based on a similarity approach. future work may assess ls functions that apply different similarity methods. additionally, new ls functions should examine other forms of synchrony such as coordination and accommodation. the field of authorship attribution @xcite @xcite , for example, may inspire development of new ls functions. this field relies on features of complexity measures (e.g., average word length, average number of words in a sentence), syntax, taxonomies, morphological analysis, orthographic/syntactic errors, idiosyncrasies and others. these may be adapted for measuring ls as well. we note that in this work we describe synchrony as it is commonly referred to in psychology. this definition does not discriminate between intrinsic synchrony and extrinsic synchrony. two bodies synchronize intrinsically when they directly influence each other. for example, the moon's motion synchronizes with sea levels due to the gravitational force exerted by the moon on the sea. in other cases, an external constituent impacts the two bodies in such a way that they synchronize independently. for example, two clocks are in synchrony with each other as a result of the time specified by an independent source. in the case of ls, the use of linguistic features by two "synchronized" speakers may be due to an outside cause, like a seasonal use of words. when discovering synchrony with a measuring function, the underlying root cause remains unknown. more research should be conducted in order to reveal the confounding variables of synchrony. ## conclusion researching synchrony enhances our understanding of the mechanisms of change in psychotherapy treatment. language, in particular, reveals important information about the interaction between a client and a therapist. following previous work on synchrony research, we formally define a task for measuring linguistic synchrony, and describe two tests for quantifying the quality of a function that measures ls. we suggest a function, consisting of a similarity component inspired by methods used in psychology research, that satisfies the definition and tests. the function and its component are shown to correlate with measures of psychotherapy process and outcome and show a significant linear increase across treatment. furthermore, we demonstrate how this function can be interpreted for understanding the interaction between the client and therapist throughout treatment. while this nonstandard task of linguistic synchrony can strongly contribute to analysis in psychology, we also generally see it as an intriguing challenge to undertake in comparative textual analysis.