Date Published: June 13, 2019
Publisher: Public Library of Science
Author(s): Silvia Gubi-Kelm, Alexander F. Schmidt, Hedwig Eisenbarth.
Based on recent findings that interrogator intonation can enhance interrogative suggestibility during recall phases, the present study tested influences of interrogator intonation on memory performance even as early as at the encoding stage. We experimentally manipulated interrogator intonation during encoding of a story to be recalled in immediate and delayed subsequent memory tests (Experiment 1, N = 50). As expected, a symmetrically structuring vs. an isolating-emphasizing speaking style generally increased the amount of freely recalled details. In a more fine-grained experiment (N = 50), we additionally manipulated emphasized story details and tested recall rates for peripheral, neutral, and central items. We found that emphasized peripheral details of the story were easier reproduced than central details realized in a neutral fashion, whereas the opposite pattern emerged for emphasized central details. Results are discussed in terms of their implications for forensic (interrogation) contexts and their legal psychological relevance.
Testimonies in forensic contexts are the result of the interaction between the reproduction efforts of the person answering questions, on the one hand, and the interrogative conduct of the person asking questions, on the other hand. The psychologist William Stern  expressed this as early as 1904, when he described a statement as a mental achievement and product of interrogation. As in all conversational situations, the communicative exchange between the interrogator and the interrogee in forensic settings cannot be reduced to verbal content exclusively. It also comprises communicative signals such as, for example, facial expressions, and gestures that accompany speech as well as communicative signals transported via the prosodic features of spoken language and, specifically, its intonation. Jones  defines intonation as “the variations which take place in the pitch of the voice in connected speech” (p. 275). Accordingly, from a legal psychological perspective, it has been only recently demonstrated that phrase-falling intonations (indicating claims/facts rather than questions) on the interrogator’s side contributed to increased interrogative suggestibility (i.e. “the extent to which, within a closed social interaction, people come to accept messages communicated during formal questioning, as the result of which their subsequent behavioral response is affected”, p. 84) in interviewed participants during the recall phase of more complex verbal information . However, it remains an open empirical question whether the influence of intonation comes into effect as early as in the encoding phase of verbally presented episodes. Such possible early memory alteration effects due to interrogator intonation artifacts should not only be important particularly to research on interrogative suggestibility but forensic practice as well (e.g. during interviews of suspects or witnesses).
In order to test our hypotheses, participants in both experiments heard a story that they had to recall immediately and after a delay of 50 minutes. The presented story differed in the tonal patterns of the representation. The experimental procedure was in accordance with the ethical standards on human experimentation of the institutional ethics committee. As the study involved no intervention/treatment/drug application nor any distressing or personally sensitive content and participants were not sampled from a vulnerable or clinical population no official ethics votum was required at the research institution. The whole procedure was in accordance with the Helsinki declaration and all of its amendments. Informed consent was signed before participation in the study. Participants were free to withdraw consent and terminate their participation at any time during the experiments.
Table 4 gives a descriptive overview of the focal dependent variables for both experiments.
A number of limitations of the present study need to be acknowledged. First, participant gender (due to only a few male participants) was not well-balanced across both studies. However, although there has been a general main effect of decreased recall in the male subgroup in Experiment 1, Gender did not impact the focal intonation effects on memory encoding as revealed by further control analyses. More importantly, the influence of the tonal pattern was investigated solely within reading speech. It is open whether the effects can be transferred onto spontaneous speech. Furthermore, whether the functions for the described German prototypical intonation patterns similarly work in English must be analyzed in language related research taking into consideration the differential syntactic and pragmatic conditions of both languages. Moreover, both manipulated speaking styles should be understood as endpoints of a bipolar dimension either avoiding any emphasis or marking all novel and contrasting information with noticeable accent contours. Hence, intonation effects here are likely to be artificially inflated. Thus, to which extent the determined effects can be validated with other melodic realization remains an open empirical question. However, all these restrictions of the external validity dovetail with a strengthened internal validity as it was our primary aim to maximize chances to demonstrate intonation effects for more complex verbal material in the encoding phase for the first time at all. Finally, unlike in the standard GSS procedure, participants solely were asked to reproduce the GGSS-1 story without follow-up interviews that purposely introduce suggestive elements. We expect exacerbated interrogative suggestibility effects when intonation effects during the interrogation phase  are added on top of the intonation effects shown here for the encoding phase.
From an applied legal psychological perspective, this study underscores that intonation influences memory recollection to a significant degree. As our focal dependent variable (i.e. correct recall rate) was based on self-report assessments that did not involve any further interrogative interaction with an interviewer we can safely conclude that the experimental manipulations indeed impacted memory performance as early as in the encoding phase. Hence, our findings differentiate results from Frankish  by corroborating that the effects of intonation on memory performance can be allocated to several prosodic devices that differentially interact with information encoding as well as information processing. Although a symmetrically structuring speaking style generally promotes memory performance, it is highly unlikely that an interrogator treats all content elements of a text/statement that he reads out equally important. It is much more likely that some details are regarded as more important than others, for example due to (involuntary) confirmation bias , and hence are presented in an isolating-emphasizing fashion. This might lead to interrogation situations (or test instructions) where the listener’s memory is influenced in favor of the a priori interpretation of the assessor–a worst-case scenario in applied forensic contexts.