Systematic review of ultrasound visual biofeedback in intervention for speech sound disorders

As cost and access barriers to ultrasound technology have decreased, interest in using ultrasound visual biofeedback (U-VBF) as a tool for remediating speech sound disorders (SSD) has increased. A growing body of research has investigated U-VBF in intervention for developmental SSD; however, diversity in study design, participant characteristics, clinical methods and outcomes complicate the interpretation of this literature. Thus, there is a need for a synthesis and review of the evidence base for using U-VBF in intervention for SSD.

To synthesise and evaluate the research evidence for U-VBF in intervention for developmental SSD.

A systematic review was conducted. Eight electronic databases were searched for peer-reviewed articles published before 2018. Details about study design, participants, intervention procedures, service delivery, intervention intensity and outcomes were extracted from each study that met the inclusion criteria. The included studies were rated using both a critical appraisal tool and for their reporting of intervention detail.

Twenty-eight papers, comprising 29 studies, met the inclusion criteria. The most common research design was single-case experimental design (44.8% of studies). The studies included between one and 13 participants (mean = 4.1) who had a mean age of approximately 11 years (range = 4;0-27 years). Within the research evidence, U-VBF intervention was typically provided as part of, or as an adjunct to, other articulatory-based therapy approaches. A range of lingual sounds were targeted in intervention, with 80.6% of participants across all reviewed studies receiving intervention targeting rhotics. Outcomes following therapy were generally positive with the majority of studies reporting that U-VBF facilitated acquisition of targets, with effect sizes ranging from no effect to a large effect. Difficulties with generalisation were observed for some participants. Most studies (79.3%) were categorised as efficacy rather than effectiveness studies and represented lower levels of evidence. Overall, the reviewed studies scored more highly on measures of external validity than internal validity.

The evidence base for U-VBF is developing; however, most studies used small sample sizes and lower strength designs. Current evidence indicates that U-VBF may be an effective adjunct to intervention for some individuals whose speech errors persist despite previous intervention. The results of this systematic review underscore the need for more high-quality and large-scale research exploring the use of this intervention in both controlled and community contexts.