The Effectiveness of the Snug Vest on Stereotypic Behaviors in Children Diagnosed With an Autism Spectrum Disorder

Abstract

Various reviews of the effects of sensory integration therapy (SIT) have concluded that such interventions fail to reduce stereotypy. However, a new, and as yet untested, SIT iteration, an inflatable wearable vest known as the Snug Vest purports to decrease such repetitive behavior. In the current study, three children who emitted different forms of stereotypy participated in an alternating treatments design in which each participant wore a fully inflated vest and either a fully deflated vest or no vest. The results of the study show that the Snug Vest failed to reduce any participants’ stereotypy. We highlight our findings in the context of professional practice and discuss several potential limitations.

Keywords

autism stereotypy sensory integration deep pressure Snug Vest QABF

Stereotypy refers to repetitive, invariant, and contextually inappropriate maladaptive operants most often maintained by automatic reinforcement contingencies (Cunningham & Schreibman, 2008; Rapp & Vollmer, 2005). Examples include rocking back and forth, flapping hands, manipulating objects, and uttering noncontextual vocalizations (NCV). The majority of individuals diagnosed with an autism spectrum disorder (ASD) emit stereotypic behaviors (Bodfish, Symons, Parker, & Lewis, 2000; Goldman et al., 2009; MacDonald et al., 2007; Matson, Dempsey, & Fodstad, 2009). Because such behaviors are frequently emitted across different settings, their occurrence often hampers the development of various adaptive social behaviors (Koegel, Firestone, Kramme, & Dunlap, 1974; Lang et al., 2009; Matson & Nebel-Schwalm, 2007; Morrison & Rosales-Ruiz, 1997).

Stereotypy often presents as persistent, intractable, and exceedingly difficult for both researchers and clinicians to remediate. Nevertheless, researchers have noted the effectiveness of various behavioral procedures including antecedent exercise (e.g., Bahrami, Movahedi, Marandi, & Abedi, 2012; Celiberti, Bobo, Kelly, Harris, & Handleman, 1997; Lang et al., 2010; Prupas & Reid, 2001), environmental enrichment (Ahearn, Clark, DeBar, & Florentino, 2005; Britton, Carr, Landaburu, & Romick, 2002; Piazza, Adelinis, Hanley, Goh, & Delia, 2000; Roscoe, Iwata, & Goh, 1998), differential reinforcement (Lanovaz & Argumedes, 2010; Nuernberger, Vargo, & Ringdahl, 2013; Taylor, Hoch, & Weissman, 2005), and punishment (Ahearn, Clark, MacDonald, & Chung, 2007; Ahrens, Lerman, Kodak, Worsdell, & Keegan, 2011; Athens, Vollmer, Sloman, & Pipkin, 2008; Rapp, Patel, Ghezzi, O’Flaherty, & Titterington, 2009; Watkins & Rapp, 2014).

However, other nonbehavioral professionals have advocated different clinical interventions. In particular, Ayres (1972, 1974, 1979) proposed a neurodevelopmental theory known as sensory integration therapy (SIT), a currently en vogue set of interventions in which a practitioner, most often an occupational therapist (OT), endorses individualized exercises, activities, or routines—a “sensory diet” of body brushing, joint compression, deep pressure, hammock swinging, scooter board spinning, or weighted vests (Devlin, Healy, Leader, & Hughes, 2011). It is important to note, however, that the conceptual foundations underpinning SIT have been vigorously opposed (Hoehn & Baumeister, 1994; Smith, Mruzek, & Mozingo, 2005). In particular, the National Standards Report categorized SIT as “unestablished” (National Autism Center, 2009), and the most recent authoritative review of SIT advocated against its clinical use (Lang et al., 2012). Perhaps most cautionary, the ethical appropriateness of SIT has been forcefully challenged (Schreck & Miller, 2010).

Advocates of SIT assert that problem behaviors may relate to dysfunctions in the various sensory systems including the proprioceptive, tactile, or vestibular sensory systems (Case-Smith & Bryan, 1999). In particular, the proprioceptive system (also known as the position sense) receives sensory input from muscles, joints, ligaments, and tendons (Kranowitz, 2005). According to SIT supporters, individuals with a dysfunctional proprioceptive system may engage in repetitive movements in an attempt to self-regulate (Williamson & Anzalone, 1997). To assist the individual with this regulation, OTs may endorse wearing a weighted vest (e.g., Fertel-Daly, Bedell, & Hinojosa, 2001; Olson & Moulton, 2004a; VandenBerg, 2001). Proponents of weighted vests claim that the deep pressure can rebalance the proprioceptive system and occasion a calming consequence within the body and thereby reduce repetitive behavior (Ayres, 1972; Knickerbocker, as cited in VandenBerg, 2001). However, a preponderance of the well-designed studies has found that weighted vests do not achieve their intended outcomes (Carter, 2005; Cox, Gast, Luscre, & Ayres, 2009; Davis et al., 2013; Hodgetts, Magill-Evans, & Misiaszek, 2011; Kane, Luiselli, Dearborn, & Young, 2004; Leew, Stein, & Gibbard, 2010; Quigley, Peterson, Frieder, & Peterson, 2011; Reichow, Barton, Sewell, Good, & Wolery, 2010; Wallen, 2012).

Despite the lack of research supporting weighted vests in particular and SIT more generally, SIT activities remain among the most commonly used interventions for young children diagnosed with an ASD. For example, a survey conducted by Green et al. (2006) found that more than 70% of parents with a child diagnosed with an ASD reported currently or previously using SIT procedures. Watling, Deitz, Kanny, and McLaughlin (1999) found that 99% of OTs routinely implement SIT with this population of children and, even more noteworthy, Schreck and Mazur (2008) found that among board certified behavior analysts, 16.4% reported using SIT.

One recently developed garment, the Snug Vest, is an inflatable vest fashioned to provide deep pressure. However, unlike weighted vests that achieve deep pressure via added weights often equal to between 5% and 10% of a user’s body weight (cf. Olson & Moulton, 2004b; VandenBerg, 2001), the Snug Vest achieves deep pressure by manually inflating an internal airbag. Although the developers of the Snug Vest claim that deep pressure can reduce “stimming” and “stimi” repetitive behaviors (“Clinical Support,” 2013), we were unable to locate any published, peer-reviewed study on the Snug Vest that would support this claim. Thus, the aim of this study was to assess the clinical effectiveness of wearing an inflated Snug Vest on stereotypic behaviors in children diagnosed with an ASD.

Method

Participants and Settings

Three children living in the Pacific Northwest participated in this study. All the children (a) carried an ASD diagnosis, (b) were receiving behavior analytic services from the second author, and (c) emitted at least one long-standing (for at least 3 years) repetitive behavior. At the start of the study, Carl was 6 years old and Jason was 5 years and 3 months old, both of whom emitted vocal stereotypy defined as any NCV and included all audible words or sounds produced by the vocal apparatus including the repetition of phrases from television, movies, and iPad games for Carl, and the “sss” or “shh” sounds for Jason. Lloyd was 5 years and 4 months old and emitted motor stereotypy defined as any noncontextual repetitive pacing (three or more back-and-forth steps in at least 3 s), arm flapping (two or more up-and-down movements in at least 2 s), or rocking side to side (two or more side-to-side movements in at least 2 s). All sessions were conducted in one of three treatment rooms measuring 4.7 m by 3.5 m, 4.9 m by 2.9 m, and 3.0 m by 3.4 m for Jason, Lloyd, and Carl respectively. Each room was devoid of leisure items.

Materials

Based on the manufacturer’s sizing rubrics, we purchased a Snug Vest for each participant. The garment is made of various fabrics (including polyester, spandex, bamboo, and cotton) whereas the inflatable airbag is composed of urethane-coated ripstop nylon and includes several valves. The small-sized Snug Vests used in this study each weighed 374 g, and the weight remained essentially constant regardless of its inflation or deflation state. Each vest costs $395.00 (CAD). Importantly, the vest’s airbag is safely distributed so that the inflated pressure targets the shoulders, back, and sides without constricting either the chest or the stomach (“Instructional Manual,” n.d.).

Experimental Design

The effects of the Snug Vest on each participant’s stereotypy were evaluated using an alternating treatments design (Barlow, Nock, & Hersen, 2009). The alternating conditions included wearing (a) the Snug Vest fully inflated (all participants), (b) the Snug Vest fully deflated (Jason), and (c) no Snug Vest (Carl and Lloyd). For each participant, the extent to which the Snug Vest decreased stereotypy was determined by visual inspection of the data paths. During all sessions, we assessed each participant in a treatment room under conditions similar to that of a no-interaction condition of a functional analysis (FA; e.g., Iwata & Dozier, 2008). Agency policy precluded the use of an alone series. The duration of the experiment was 22 days, 32 days, and 50 days for Carl, Jason, and Lloyd, respectively. Lloyd was ill for several weeks necessitating a longer time in which to complete the experiment.

Data Collection

We video recorded all observation sessions, after which, we collected post hoc continuous duration data using computer software. We added 2 s onto each instance of stereotypy and before we marked offset, any occurrence of stereotypy that stopped but resumed within the added 2-s window was judged part of the same duration count (Lanovaz & Sladeczek, 2011; Watkins & Rapp, 2014). Raw data were then converted into a percentage of time metric by summing the total time engaged in stereotypy divided by the total time of the observation session and multiplied by 100%. The authors were the primary data collectors, and trained research assistants functioned as secondary (reliability) observers. Reliability observers independently collected data by watching the same video recordings for at least 33% of all sessions (Kennedy, 2005). Prior to each secondary observer collecting data, he or she participated in competency-based data collection training that included (a) reading specific behavioral definitions and data recording procedures, (b) asking questions, and (c) scoring 100% accuracy on a written test. Each secondary observer collected data from videotaped vignettes and received feedback. Training continued until each observer achieved at least 85% agreement with the primary observer over three consecutive sessions (Kennedy, 2005).

Using the block-by-block method (Mudford, Martin, Hui, & Taylor, 2009; also known as mean count-per-interval agreement), we divided each session into 10-s bins. An interobserver agreement (IOA) score for each 10-s bin was calculated by first dividing the shorter duration into the larger of the two durations and multiplying the quotient by 100% after which the mean agreement across all bins was calculated using the following formula: (bin 1 IOA + bin 2 IOA + bin N IOA)/n bins × 100%. Across all conditions, the mean IOA score for Carl’s behavior was 85.0% (range = 73.5%-92.1%). For Jason’s behavior, the mean IOA score was 92.8% (range = 88.5%-96.8%). For Lloyd’s behavior, the mean IOA score was 87.0% (range = 80.6%-91.8%).

Procedures

To evaluate the function of each participant’s repetitive behavior, we used both indirect and experimental assessments (see below). We invited the children whose repetitive behaviors were maintained by automatic reinforcement to participate in the subsequent alternating treatment design to assess the effects of the Snug Vest on their stereotypy.

Indirect assessment

Following signed informed consent, each participant’s parent or behavior interventionist was interviewed using the Questions About Behavioral Function Rating Scale (QABF; Matson & Vollmer, 1995) in which a therapist read aloud each of the 25 QABF questions and immediately scored each respondent’s answers using the scale’s four-point Likert-type options where 0 = never, 1 = rarely, 2 = some, and 3 = often. Each administration of the QABF took less than 15 min and assessed for five putative functions: attention, escape, nonsocial, physical, and tangible. A recent review of the QABF showed that it is currently the most research-supported indirect behavioral assessment (Matson, Tureck, & Rieske, 2012). In particular, several very recent studies have demonstrated high convergence between QABF scores and experimental analysis data, especially when the behaviors are maintained by automatic reinforcement (e.g., Lanovaz, Argumedes, Roy, Duquette, & Watkins, 2013; Watkins & Rapp, 2013).

No-interaction series

Following the QABF interviews, each child participated in an extended no-interaction series based on procedures outlined by Iwata and Dozier (2008). We used the no-interaction series to confirm the function suggested by the QABF scores. Each no-interaction session lasted 5 min. We selected the duration of 5 min based on procedures summarized by Querim et al. (2013). Specifically, each participant was brought to an assessment room without leisure activities and a therapist gave the direction, “You can play by yourself,” after which, the therapist remained in the room ignoring all behaviors emitted by the participant for the duration of the session.

Following the no-interaction series, we purchased the appropriately sized Snug Vest for each child. The procedures and rationale for each condition within the alternating treatments design are outlined below. Several days prior to the start of the experiment, a therapist introduced the Snug Vest to help desensitize each child to it, assisted each child to wear the vest (deflated at first), and then inflated over subsequent sessions. As per the Snug Vest’s instructions, the therapist was able to insert his or her hand between the child’s back and the Snug Vest when it was maximally inflated.

Vest-inflated condition

A therapist brought each child to the treatment room, assisted the participant to don his Snug Vest and following procedures outlined in the Instructional Manual (n.d.), manually hand pumped the vest to maximum inflation. Although the Snug Vest is designed with a hood, it was never placed over a participant’s head in any of the sessions. Sessions began immediately following the therapist’s directive, “You can play by yourself,” and lasted 20 min. This timing was specifically chosen to align with the recommendation that a user not wear his Snug Vest inflated beyond 20 min at a time (“Instructional Manual,” n.d.). This 20-min duration also falls within the standard practice among OTs who use weighted vests (Olson & Moulton, 2004a). The therapist began videotaping each session beginning at the 15-min mark. We elected to collect data during the last 5 min of each session to capture what we hypothesized as the maximum clinical effects. As Williamson and Anzalone (1997) observed, “Sensory input is cumulative . . . you may not see the influence of sensory input immediately” (p. 33). To avoid potential carryover effects, especially any subsequent effects from deep pressure, only one condition was implemented on any given day.

Vest-deflated condition

This control condition (for Jason only) was identical to the vest-inflated condition except that after the therapist assisted Jason to put on his vest, it was not inflated. As with the vest-inflated condition, data were collected during the final 5 min of each 20-min session.

No-vest condition

This control condition (for Carl and Lloyd) was identical to the vest-deflated condition except that neither child put on his vest. As with the above two conditions, data were collected during the final 5 min of each 20-min session.

Results

Figure 1 illustrates the putative function scores from the QABF (left panels) with data from the no-interaction sessions (right panels) for Carl (upper panel), Jason (middle panel), and Lloyd (lower panel). Bar height illustrates severity scores (range = 1-15) whereas the integer positioned above each bar denotes the endorsement score (i.e., the number of questions scored nonzero by each respondent; range = 0-5). During every no-interaction session, all participants emitted stereotypy. Carl engaged in NCV (M = 46.8%, range = 33.0%-67.8%), Jason engaged in NCV (M = 38.2%, range = 20.0%-63.3%), and Lloyd engaged in motor stereotypy (M = 36.7%, range = 22.7%-49.7%). Both the QABF scores and the FA data strongly suggest that each child’s stereotypy was maintained by nonsocial reinforcement.

Figure 1.

Comparison of putative function scores from the QABF (left panels) with the percentage of time engaged in stereotypy during no-interaction sessions for Carl (upper panel), Jason (middle panel), and Lloyd (lower panel).

Figure 2 illustrates the percentage of time that Carl (upper panel), Jason (middle panel), and Lloyd (lower panel) engaged in stereotypy across vest-inflated and either no-vest (Carl and Lloyd) or vest-deflated (Jason) control conditions. Results for Carl show that he engaged in undifferentiated levels of NCV during the vest-inflated (M = 50.0%, range = 35.5%-62.7%) and the no-vest control (M = 32.5%, range = 14.7%-52.2%) conditions. Similarly for Lloyd, the data paths for both vest-inflated (M = 32.1%, range = 20.3%-42.0%) and no-vest control (M = 21.5%, range = 7.3%-45.0%) conditions appear undifferentiated. Finally, during the vest-inflated and deflated conditions, Jason’s NCV also appears undifferentiated (inflated: M = 21.3%, range = 1.0%-47.4%; deflated: M = 22.1% range = 4.3%-48.0%).

Figure 2.

Percentage of time Carl (upper panel), Jason (middle panel), and Lloyd (lower panel) engaged in stereotypy during no-vest (Carl and Lloyd), deflated vest (Jason only), and inflated vest conditions.

Discussion

Results of this study suggest that the Snug Vest failed to reduce any participant’s stereotypy. In short, results do not support the manufacturer’s claim that the Snug Vest reduces repetitive behavior. Instead, the data align with previous research showing that deep pressure fails to ameliorate stereotypy (e.g., Hodgetts et al., 2011; Kane et al., 2004).

A number of limitations are noteworthy. First, it may be the case that the inflated vests failed to reduce any participant’s stereotypy because none wore the vest for a sufficient duration. However, we conformed our study with the directives written in the Snug Vest Instructional Manual. Specifically, the manual stated that a person should not wear his or her vest inflated for longer than 20 min at a time. Moreover, peer-reviewed research has yet to definitively determine the ideal length of time that a user should wear a deep-pressure garment, and when compared with surveys completed by OTs, our 20-min duration falls within the reported range of SIT practitioners (Olson & Moulton, 2004a).

Second, the no-interaction series does not rule out other functions. It is possible that the stereotypies assessed in this study were also maintained by social consequences (i.e., multiple control; Hanley, Iwata, & McCord, 2003). However, this limitation is improbable for at least three reasons. First, in the vast majority of instances, stereotypy appears to be maintained by automatic reinforcement (Rapp & Vollmer, 2005). Second, Beavers and Iwata (2011) found that in only a minority of cases are problem behaviors sustained by more than one function, and third, Querim and colleagues (2013) found that FA using alone or no-interaction conditions accurately identified repetitive behaviors maintained by automatic reinforcement.

Finally, this study only assessed the effects of the Snug Vest on stereotypy. We did not attempt to measure the effects of the Snug Vest on other behaviors. It is therefore possible that the Snug Vest produced a clinical effect beyond our restricted focus. Although we did not anecdotally observe other behavior changes, such changes remain possible.

Although we are doubtful of the clinical utility of the Snug Vest as an effective treatment for stereotypy, given that the developer also claims that their product may increase attention, future researchers could conduct parametric research to identify any differential effects from wearing the Snug Vest for varying durations on other behaviors (e.g., “on-task behaviors”). Moreover, we believe there is a robust role for using single-subject experimental designs to the evaluation of any non-empirically supported intervention (Bulkeley, Bundy, Roberts, & Einfeld, 2013). For example, single-subject designs can be implemented in the same environments in which children with autism live and learn and such designs lend themselves to assessing novel interventions for which the time and resources to implement a randomized clinical trial would be unjustified. In the meantime, however, and based on a visual analysis of our data, practitioners who are required by ethical duty or are mandated by law to use interventions that are evidence-based should avoid the use of the Snug Vest outside a clearly defined research context.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Author Biographies

Nicholas Watkins is a board certified behavior analyst and faculty in the Department of Disability and Community Studies at Douglas College. His primary areas of research interests are the assessment and treatment of stereotypy.

Elizabeth Sparling is a board certified behavior analyst and the clinical director of Pivot Point Family Growth Centre Inc. Her area of expertise is the early intervention for children diagnosed with an autism spectrum disorder.

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