Investigative Interviewing with Minimally Verbal Adults – Best Practices and New Findings

Investigative Interviewing with Minimally Verbal Adults – Best Practices and New Findings

Investigative interviewing with minimally verbal adults requires a unique scaffolding approach for recalling repeated events of victimization. This is the bottom line of a recently published article in Psychology, Public Policy, and Law em>. Below is a summary of the research and findings as well as a translation of this research into practice.


Featured Article | Psychology, Public Policy, and Law | 2019, Vol. 25, No. 4, 239-252

Trial of Three Investigative Interview Techniques With Minimally Verbal
Adults Reporting About Occurrences of a Staged Repeated Event


Madeleine Bearman, Griffith University
Sonja P. Brubacher, Griffith University
Lydia Timms, Curtin University
Martine Powell, Griffith University


The current study explored the effectiveness of three interview protocols on the number and specificity of details provided by minimally verbal adults about a staged repeated event. Eighty adults (with expressive sentence length of around 5 words, matched on measures of expressive language and intellectual functioning) participated in 3 live events and were pseudorandomly assigned to receive 1 of 3 interviews. The narrative-first protocol exhausted recall with open-ended questions before focused questions were asked, the intermixed protocol paired open-ended questions immediately followed by related focused questions, and the visual cues protocol mimicked the narrative-first protocol but with the use of cue cards. Overall, participants reported more correct information about the last occurrence in the intermixed and visual than narrative-first interview. The narrative-first interview elicited fewer internal intrusions (experienced details attributed to the wrong occurrence) compared with the visual, but not the intermixed, interview. Expressive language and intellectual function were positively associated with the reporting of event-related details. Providing information about repeated events was challenging for minimally verbal adults; reporting of generic event details was more frequent than occurrence-specific details, one third of participants answered a question about event frequency incorrectly (by saying they participated once), and the remaining participants provided few details about the other occurrences when directed to do so. Findings were consistent with the broader repeated event literature on children and adult witnesses recalling repeated events. This research provides guidance for investigative interviewers on how best to obtain accurate event-related information from minimally verbal adults about their experiences.


investigative interviewing, minimally verbal adults, repeated events, expressive language difficulty

Summary of the Research

“Adults with disabilities, including those with communication and/or cognitive impairment, are overrepresented as victims of abuse compared with the general population. Further, they may be at increased risk of repeated victimization, as they tend to be dependent on caregivers who are commonly the perpetrators of abuse. Routine tasks such as personal care activities (e.g., bathing, dressing, and feeding) may conceal ongoing abusive caregiving behaviors. When questioned about their victimization, adults with disability encounter a number of problems in providing evidence to an investigative interviewer unfamiliar with their capabilities. For example, interviewers will often resort to asking specific, repeated, and leading questions, resulting in inaccurate responses. Further, investigative interviewers have concerns about the limited detail provided by individuals with communication or cognitive impairment and the reliability of their accounts. These concerns have added to the reduced likelihood of offense allegations proceeding onward from the interview to court or leading to a charge.” (p.239)

“Adults who are minimally verbal are a heterogeneous group and can have a range of complex conditions such as neurodevelopmental disorders (e.g., autism, cerebral palsy), traumatic brain injury, and anatomical/voice difficulties. These conditions may lead to challenges in expressing information through speech, writing, or gesture. Further, such individuals often have difficulty combining words to create comprehensible sentences, and their vocabulary is smaller and more basic than their verbally fluent peers, making it more difficult to provide a narrative account. Although a narrative-based protocol is generally advised for all witnesses, it has yet to be determined whether this approach is suitable for minimally verbal adults. Additionally, as adults with disability could be at greater risk of repeated abuse, determining how best to elicit details of a specific occurrence is relevant.” (p.240)

“Research concerning the investigative interviewing of vulnerable witnesses has largely concentrated on children, or on adults with intellectual disability. This focus has led to broad guidelines that suggest how individuals with communication impairment might be interviewed effectively by investigative interviewers. On the one hand, the research has highlighted the suggestibility of vulnerable witnesses and, therefore, the importance of maintaining open-ended questions to improve the accuracy of responses. On the other hand, limited detail may be provided in response to open-ended questions. For example…adults and adolescents with mild and moderate intellectual disability provided fewer details than their mental age matches across all prompt types, including open-ended, directive, and option-posing.” (p.240)

“The primary aim of the current study was to determine the interview method that would elicit the most accurate and complete information from minimally verbal adults. Secondary goals involved characterizing the reports of this population with regard to repeated events—in particular, the specificity of details they report and their ability to respond to recommended questions about event frequency. To meet these aims, 80 adults with minimal verbal ability took part in three occurrences of a staged repeated event and then were interviewed using one of three protocols: a narrative-first interview (participants’ narratives were exhausted through open-ended questions before directive questions were asked), an intermixed interview (participants were interviewed using paired nonleading open-ended and cued recall questions in an intermixed fashion), or a visual interview (the same as the narrative-first interview but paired with visual cue cards).” (p.240)

“…participants reported more correct information in the intermixed and visual cues compared with the narrative-first interview. Regarding errors, hypotheses were partially confirmed. The narrative-first interview did elicit fewer internal intrusions compared with the visual cues but not compared with the intermixed interview, and there were no differences for external intrusions. Contrary to prediction, participants provided fewer “don’t know” responses in the intermixed and visual interview than the narrative-first interview. In sum, key findings regarding interview type were that some type of nonsuggestive scaffolding provided added benefit to the participants’ accounts compared with an interview without (i.e., narrative-first interview).” (p.246)

Translating Research into Practice

“Open-ended questions are recommended for eliciting narrative detail and encouraging an elaborate response that does not dictate what specific details are required. Examples of openended questions include “Tell me everything that happened and start from the beginning,” “What happened after?” and “Tell me more about the part where [pre-disclosed detail].” Although openended prompts are generally thought to be superior to other question types, some research involving preschoolers suggests that cued recall prompts (“Wh” format, e.g., “What color was his hair?”) may be necessary to structure the narratives of this population.” (p.240)

“Because open-ended prompts tend to elicit more accurate information than other types, experts have suggested pairing open-ended prompts with more focused ones when the latter are needed. It is possible that adults with limited verbal ability might benefit from an interview protocol that alternates open-ended with cued recall prompts, thus providing opportunity for elaboration within a structured, scaffolded approach.” (p.240)

“Visual aids are another way that the narrative capacity of some individuals who are minimally verbal might be improved without needing to resort to specific questions early in the interview. Visual scaffolds in the form of mind maps depicting the narrative elements (e.g., who, where, when) have provided successful narrative intervention for adults with aphasia and other cognitive communication difficulties.” (p.240)

“The present study has demonstrated that, like children and verbally fluent adults, those with limited expressive language report more generic than specific details following repeated experience, and they are prone to internal intrusion errors. These findings are indicative of similar memory organization across the populations and indicate that interviewers should be sensitive to the ways in which they question minimally verbal adults about experiences that may be repeated.” (p. 247)

“From a policy standpoint, these findings serve as a reminder that there cannot be a “one size fits all” approach to interviewing. Interviewers and their trainers must be aware of the broader empirical literature that supports various interviewing approaches so that they can tailor best practice protocols according to their needs.” (p.248)

“We make the following recommendations for interviewing policy: (a) Charges of continuous abuse should be considered for multiple subcategories of vulnerable witnesses; (b) when continuous abuse charges are allowed, scaffolding (i.e., the visual or intermixed protocol) may help to increase the amount of detail reported; and (c) if particularization is critical, the narrative-first protocol will be the most advantageous because of the lower risk of internal intrusion errors compared with the visual cues interview and greater ease of training compared with the intermixed protocol.” (p.248)

Other Interesting Tidbits for Researchers and Clinicians

“Lab studies are critical for understanding memory reports under controlled conditions and provide ground truth. They can be criticized, however, for a lack of generalizability. Although the modified Deakin zctivities used in the current study bear no resemblance to a criminal offense about which victims might need to be interviewed, the event purposefully includes several details which would have forensic relevance if reported during an interview, such as donning and removal of clothes (leader’s top), body parts to be reported (i.e., during the relaxation), and photographs being shown. Multiple sensory elements (e.g., auditory—music for relaxing; gustatory—snack) are also incorporated.” (p.248)

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