Examining the impact of distraction on tic suppression in children and adolescents with Tourette syndrome

Behaviour Research and Therapy 46 (2008) 1193–1200

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Examining the impact of distraction on tic suppression in children and adolescents with Tourette syndrome Christine A. Conelea, Douglas W. Woods* Department of Psychology, Garland Hall, P.O. Box 413, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, United States

a r t i c l e i n f o

a b s t r a c t

Article history: Received 31 May 2008 Received in revised form 22 July 2008 Accepted 23 July 2008

Tourette syndrome (TS) is characterized by motor and/or vocal tics. Tics are thought to be temporarily suppressible, and it is believed that suppression requires significant attentional resources. The aim of the current study was to examine the impact of an attention-demanding distraction task on tic suppression. A secondary aim was to examine whether performance on that task decreased during concomitant periods of suppression. Nine children with TS, ages 9–15, participated in the study. An alternating treatment design was used to compare three conditions, free-to-tic baseline (BL), reinforced tic suppression (SUP) and reinforced tic suppression plus a distraction task (SUP þ DIS). Tic frequencies were significantly higher during BL conditions than both SUP and SUP þ DIS conditions, and tic frequencies during SUP and SUP þ DIS did not differ. Accuracy on the distraction task decreased during SUP þ DIS as compared to BL. Results suggest that contextual distractions may not negatively impact tic frequencies. In addition, accuracy on an attention-demanding task may be impacted if a child is simultaneously suppressing. Ó 2008 Elsevier Ltd. All rights reserved.

Keywords: Tourette Tic Behavior Suppression Attention

Introduction Tourette syndrome (TS) is a childhood onset neuropsychiatric disorder characterized by recurrent, sudden, stereotyped motor movements and vocalizations called motor and vocal ‘‘tics,’’ respectively (American Psychiatric Association [APA], 2000). Tic disorders are estimated to occur in 0.04–3.0% of the population (Hornsey, Banerjee, Zeitlin, & Robertson, 2001; Mason, Banerjee, Eapen, Zeitlin, & Robertson, 1998) and are more common in males than females. Over 50% of those with TS have a co-occurring psychiatric condition, the most common being attention-deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD; Freeman et al., 2000). Although tics are involuntary, research has supported the notion that they can be temporarily suppressed to varying degrees (Jankovic & Fahn, 1986). Unfortunately, little is known about the development of tic suppression abilities or the mechanisms responsible for suppression. Research in this area has suggested that contextual factors and attentional processes may play key roles in tic suppression (Conelea & Woods, in press; Himle & Woods, 2005; Peterson et al., 1998). Numerous studies using survey or otherwise uncontrolled research designs have suggested that tic expression can vary

* Corresponding author. Tel.: þ1 (414) 229 5335. E-mail address: [email protected] (D.W. Woods). 0005-7967/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.brat.2008.07.005

depending on one’s context or emotional state (e.g., Bornstein, Stefl, & Hammond, 1990; Eapen, Fox-Hiley, Banerjee, & Robetrson, 2004; O’Connor, Brisebois, Brault, Robillard, & Loiselle, 2003; Silva, Munoz, Barickman, & Friedhoff, 1995). To better understand how such factors impact tic expression, researchers have begun to examine tic suppression in studies using controlled experimental designs. Meidinger et al. (2005) examined the impact of instructing children and adults with TS (N ¼ 7) to suppress their tics. Using a withdrawal design, two conditions were compared: (1) a nonsuppression baseline and (2) a condition in which the subject was told to suppress his/her tics. Significant reductions in tic frequencies were observed in almost one half of all suppression conditions, indicating that tics are somewhat suppressible in the presence of a verbal instruction to do so, at least for temporary amounts of time. Woods and Himle (2004) suggested that natural suppression rarely involves reacting to simple instructions to suppress. Rather, they noted that children may encounter reinforcing consequences for successfully suppressing tics. For example, suppression may result in avoidance of teasing or increased ability to engage in activities that might be disrupted by tics, such as playing sports or talking with others. To determine if reinforcement for suppression could impact tic occurrence, Woods and Himle used a withdrawal design in which three 5-min conditions were administered repeatedly: (1) baseline, (2) verbal instructions to suppress, and (3) contingent reinforcement for suppression, in which tokens (exchangeable for a prize) were delivered for every 10-s tic-free period. Averaged across the four participants, the verbal

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instructions condition produced a 10.3% reduction in tic rates from baseline levels, whereas the reinforcement condition produced a 76.3% reduction. These results suggested that tic suppressability may be enhanced by operant contingencies. Other studies have used the Woods and Himle (2004) preparation to further examine the relationship between contextual factors and tic suppression (Himle & Woods, 2005; Himle, Woods, & Bunaciu, 2008; Himle, Woods, Conelea, Bauer, & Rice, 2007; Woods et al., 2008). These studies have shown that tic suppression (a) does not necessarily produce a rebound in tic frequency (Himle & Woods; Woods et al.), (b) is capable of being maintained for up to 40 min (Woods et al.), (c) requires the contingent delivery of a reinforcer to produce maximum suppression (Himle et al., 2007), and (d) is functionally related to urges to tic (Himle et al., 2008). Combined, these studies have examined a number of factors that could give rise to tic suppression. However, contextual factors may also disrupt successful suppression. Identification of such factors may help to answer the question of how tic suppression is accomplished. In addition, it may help to inform behavioral interventions designed to enhance tic suppression ability (e.g., Azrin & Nunn, 1973; Deckersbach, Rauch, Buhlmann, & Wilhelm, 2006). Many factors may be related to one’s ability to suppress tics, but research to date has suggested that attentional processes may be particularly important. Himle and Woods (2005) found a significant negative correlation between the Attention Problems subscale of the CBCL and tic suppressability (r(7) ¼ .89, p < .01), suggesting that poorer suppressability is related to increasing attention problems. Likewise, Woods et al. (2008) found a significant correlation between the ability to suppress and omission errors on a continuous performance task (r(11) ¼ 0.63, p < 0.05), leading the authors to conclude that poor task orientation was related to poor tic suppression ability. Brain imaging research also supports the notion that tic suppression involves attentional processes. Using fMRI, Peterson et al. (1998) observed significant changes in cortical regions thought to subserve attention-demanding tasks during periods of voluntary suppression. The authors concluded that tic suppression is an attention-demanding task that involves a constant monitoring of somatosensory information. Finally, it has been suggested that performance deficits on attention-demanding tasks may occur when attentional efforts are directed to tic suppression (Shimberg, 1995). Although attentional processes have been implicated in tic suppression, the relationship has not been experimentally tested at the behavioral level. In the current study, we sought to explore the link between attentional processes and tic suppression by examining tic suppression in the presence and absence of a competing attention-demanding task. We proposed two hypotheses based upon research suggesting that tic suppression is an attentiondemanding task. First, we hypothesized that tic frequencies would be higher during periods of suppression plus distraction as compared to periods of suppression alone. Second, we hypothesized that children would demonstrate decreased accuracy on an attention-demanding task during periods in which suppression was coupled with distraction as compared to performance on the task before and after the experimental portion of the study. Methods Participants Children were recruited via referrals and print advertising at an outpatient tic disorders specialty clinic located at the University of Wisconsin – Milwaukee. Following informed consent/assent, an initial assessment with the parent and child was conducted to determine study eligibility. Children were deemed eligible for the study if they (1) met criteria for Tourette Disorder (i.e., Tourette

Syndrome) or Chronic Tic Disorder according to the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition-Text Revision (DSM-IV-TR; APA, 2000), (2) had a minimum level of total tic severity as indicated by a severity score of 14 for TS and 10 for CTD on the Yale Global Tic Severity Scale (YGTSS; Leckman et al., 1989), (3) had at least one discernable tic per minute, as observed in an initial videotaped observation, and (4) performed in the low average range or above in intellectual functioning as indicated by a score of 80 or greater on the Wechsler Abbreviated Scale of Intelligence (WASI; The Psychological Corporation, 1999). Children were excluded if they (1) had comorbid ADHD, Conduct Disorder, or Oppositional Defiant Disorder with a rating of >6 on the Anxiety Disorders Interview Schedule-Fourth Edition (ADIS-IV; Silverman & Albano, 1996) or (2) had a history of 3 sessions of behavioral treatment primarily comprised of tic suppression strategies. Psychiatric diagnoses were determined by combining information from the ADIS-IV, the YGTSS, and direct observation. Eleven children were recruited and nine met the inclusion criteria. One child was excluded because she did not have 1 tic/min during an initial direct observation, and one child was excluded because he did not meet DSM-IV-TR criteria for TS or CTD. The nine participants had a mean age of 11.5 (range ¼ 9–15) and consisted of seven boys and two girls. Comorbid diagnoses and their ADIS clinician rated severity scores, tic severity scores, and current tics for each participant are provided in Table 1. Six of the children had past or current medication treatment for TS, and three had no previous treatment for TS. None of the children had previously received behavior therapy for tics. Written informed consent/assent was obtained prior to study participation. During the initial assent, children were not told about live observation and videotape recording procedures. Children were informed of these procedures at the end of the study, and written assent was obtained from the child following the debriefing. Parents were fully informed of study procedures prior to study participation. The study was approved by the University of Wisconsin – Milwaukee Institutional Review Board. Setup and materials During all experimental conditions, the child was seated by him/ herself in a 100  150 observation room equipped with a one-way observation mirror that allowed for covert observation and video recording from an adjacent room. A 1200  1200  2400 token dispenser, with a clear plastic receptacle attached to the front, was placed in front of the child. Using a protocol established by Woods and Himle (2004) and Himle and Woods (2005), the child was informed that the dispenser was a ‘‘tic detector’’ that had the ability to monitor and count his/her tics (note: the device was actually a token dispenser manually operated by the investigator in the observation room). In order to enhance the likelihood that the dispenser appeared to be a ‘‘tic detector’’ capable of monitoring tics, a non-functioning Internet camera and power supply box were attached to the dispenser. In addition, a laptop computer was placed next to the dispenser and was used to run the auditory continuous performance test described below. The child was told that he/she would have the opportunity to earn tokens from the ‘‘tic detector’’ during various tasks. The child was told that tokens were exchangeable for a reward upon study completion, such that more preferred rewards required earning more tokens (note: the child always received his/her preferred reward at the end of the study regardless of the number of tokens earned). The child and investigator then identified preferred rewards and created a reward hierarchy prior to the start of the experimental conditions. To increase the salience of the reward for each child, preferred reward hierarchies were created individually for each child. Rewards were delivered by the experimenter following study completion.

C.A. Conelea, D.W. Woods / Behaviour Research and Therapy 46 (2008) 1193–1200 Table 1 Participant comorbid diagnoses, tic severity, and current tics Participant number

Sex

Age

DSM-IV-TR YGTSS comorbid severity diagnoses, score ADIS severity

Tics

1

Male

11

None

Eye blink plus roll Nose scrunching Head jerk Arm tensing ‘‘Kissing’’ sound Throat clear

20

2

Female 11

None

23

Facial grimace Abdominal tensing Slow, low grunting Quick grunting Coughing Slurping Sniffing

3

Male

ADHD, 6 GAD, 6 Social Phobia, 5

26

Eye blinking Eye darting Head jerk

15

Wrist cracking Leg kick Sniffing ‘‘Oh’’ syllable 4

Male

9

GAD, 4

16

Lip licking Jaw movements Toe scrunching Writing tic Sniffing Throat clearing Tongue clicking Coughing

5

Male

12

OCD, 6

27

Smile Lip pucker Teeth clicking Rapid lip flutter Lip licking Head jerk Hand gestures Copropraxia Evening out tics Tongue click Animal sounds Coprolalia Palalalia

6

Male

10

7

Female 11

ADHD, 4 GAD, 6 Social Phobia, 6

22

ADHD, 4 GAD, 3 OCD, 7

22

Eye blinking Rapid lip flutter Arm and shoulder movement Abdominal tensing Toe movements Touching tics Facial grimace Throat clearing Sniffing Fast breath out Several syllables Arm jerking Abdominal tensing Facial grimace Shoulder shrugs Pointing Leg kick Growl sound Buzzing Repeating words

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Table 1 (continued) Participant number

Sex

Age

DSM-IV-TR YGTSS comorbid severity diagnoses, score ADIS severity

Tics

8

Male

11

ADHD, 4

17

Abdominal tensing Gyrating movement Coughing Sniffing

9

Male

12

CD, 5 OCD, 6 Social phobia, 5

21

Eye blinking Nose scrunch and stretch Arm movements Shoulder plus head jerk Seated hopping movement Sniffing

A modified auditory Continuous Performance Test of Attention (CPT) based on the CPT described by Cicerone (1997) and Shucard et al. (1997) was administered once prior to the start of any experimental conditions, once during each of three suppression þ distraction (SUP þ DIS) conditions, and once after administration of all experimental conditions was complete. During the CPT, the child listened to a 6 min long mp3 audio file presenting a series of letters read at the rate of one per second (for a total of 200 single-letter trials). The letters A and L were used for target trials, and 10 letters were randomly selected to be non-target letters. The target sequence was any A immediately preceding an L. Children were asked to say ‘‘there’’ each time this target sequence was presented. The A–L sequence was presented 21 times per block of 100 single-letter presentations for a total of 42 presentations. During each 6 min segment, non-target Ls were presented 15 times and non-target As were presented 51 times. Correct identifications of the target sequence (‘‘hits’’) and errors of commission were measured when the videotape of the task was coded. To reduce the likelihood of practice effects, five different versions of the CPT were recorded and presented in a random order. In these different versions, the number of target and non-target presentations and the rate of presentation remained the same, but the order of targets and non-targets was varied. Experimental design and procedures Children were exposed to a series of three 6 min conditions replicated three times each in a random order (for a total of nine observations). Due to the small sample size, the condition order across subjects was not fully counterbalanced. These three conditions are described in detail below. All conditions were conducted during one visit. Before each condition began, the child was given standardized instructions explaining the condition and was asked to repeat the instructions to ensure that he/she understood the task. The investigator then left the room and monitored the child from the adjacent observation room. Following each condition, the investigator returned to the room and conducted a manipulation check. Baseline (BL) The instructions given for the BL conditions were as follows: ‘‘For the next 6 min we are going to have you just sit in this chair. The tic detector will be on, but try to ignore it and feel free to tic as much or as little as you need to.’’ No instructions to suppress were given and no tokens were delivered during the BL condition. Suppression (SUP) During the SUP conditions, the child was reinforced for suppressing his/her tics. The child was told, ‘‘For the next 6 minutes,

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the tic detector will count your tics, and it will also give you a token for every 10 seconds you go without having a tic. At the end of the day, we will count your tokens and you will be able to exchange them for prizes. Depending upon how many tokens you get, you can earn the prizes we talked about earlier. Again, you will get a token for every 10 seconds you go without having a tic, but if you do have a tic the timer will start over and you will not get a token.’’ The ‘‘tic detector’’ was controlled by the investigator in the observation room by using a manually operated plunger. The investigator delivered a token for each consecutive 10-s interval in which the child did not have a tic. If tics occurred during the 10-s interval, the interval was reset. Suppression and distraction (SUP þ DIS) The SUP þ DIS conditions followed the same procedures as the SUP conditions. In addition, the child was asked to simultaneously complete the modified auditory version of the CPT as described above. Instructions were as the same as those for the SUP conditions but included the additional statement, ‘‘At the same time, you will hear a voice on a tape say some letters. Every time you hear the voice say an ‘‘A’’ followed by an ‘‘L,’’ say ‘‘there’’ out loud. The tic detector will record your voice.’’

coder in order to establish inter-rater reliability. Separate reliability indices for hits and commission errors were calculated by dividing the lowest observed hits and commission errors over the highest observed hits and commission errors. Agreement for each participant for both scores was high (100%). Post-experimental CPT data were not obtained for participants 1, 5, and 9, who elected to end their participation after the experimental conditions due to fatigue. The pre-experimental CPT was administered for participant 7, but it was not taped due to a malfunction of our recording equipment. Manipulation check data were collected to determine if the independent variable (condition instructions) occurred as instructed. Children were asked if they had followed instructions for the previously administered condition using yes/no questions. With two exceptions, all children reported accurately the tasks they had been asked to do. For the two exceptions, participants 3 and 6 indicated that they were trying to suppress some of their tics during their first BL conditions. Participant 9 demonstrated fatigue during the experiment and the experimental portion of the study was terminated after each condition was replicated twice. We decided to take a conservative approach and include all data points (first two BL data points from participants 3 and 6) in all analyses.

Video taping and debriefing procedures

Results

During all phases, the participant was video recorded from behind the one-way observation mirror. Parents were informed of the recording and study procedures. Although the children believed they were being observed by the ‘‘tic detector,’’ they were uninformed of the live observation until they were debriefed at the end of the study. This subtle deception was used because previous research has shown that many children’s tics are reactive to observation, and that the degree of reactivity is difficult to predict (Piacentini et al., 2006). Following completion of the experimental conditions, the investigator debriefed the child by explaining the purpose of the study as well as the nature of the deception. The child was also told that he/she would earn his/her most preferred reward regardless of the number of tokens earned. After debriefing, children were asked for their assent to use their data, and all children provided their assent.

Analytic plan

Data coding Videotapes were scored for tic frequencies using standard observation and scoring procedures (see Himle et al., 2006; Himle & Woods, 2005; Woods & Himle, 2004). All videotaped segments were independently scored by a secondary coder using the same scoring methods to establish inter-rater reliability. A reliability index was calculated using the frequency-within-interval method of agreement (Himle et al., 2006). The overall agreement across all participants was acceptable (M ¼ 91%; range ¼ 83–98%). Independent variable integrity was also assessed. Tape coders recorded whether or not the investigator correctly delivered the instructions for each condition by comparing the instructions given to those on the experimental script. Condition instructions were delivered correctly for all conditions. Accuracy of token delivery was recorded by calculating the time between token delivery and the previous tic. As in previous studies (Woods & Himle, 2004; Himle & Woods, 2005) an accurate token delivery was defined as any token delivered 10  2 s after the previous tic. Data were to be excluded if less than 70% of the tokens were delivered inaccurately for a given subject. Tokens were delivered accurately 88% of the time across all subjects. CPT performance was scored by trained coders who marked hits and errors of commission on a printed transcript of the audiotape. All CPT administrations were independently scored by a secondary

Although the study was designed as a single-subject experimental design, our use of an alternating treatment approach allows us to summarize the results using inferential group statistics. After the summary of these analyses, we discuss the individual data patterns. Suppression findings Mean tic frequency scores for each condition were calculated by summing the mean scores for each child in each of the three conditions (BL, SUP, SUP þ DIS). A one-way repeated measures analysis of variance was significant, F(1, 2) ¼ 7.4, p ¼ .005, d ¼ 1.34. Subsequent analyses indicated that tic frequencies were significantly higher during the BL conditions (M ¼ 46.6, SD ¼ 42.8) than the SUP (M ¼ 5.5, SD ¼ 6.1, p ¼ .02, d ¼ 1.34) and the SUP þ DIS conditions (M ¼ 7.1, SD ¼ 5.7, p ¼ .03, d ¼ 1.29). Tic frequencies during SUP and SUP þ DIS did not significantly differ (p ¼ .51, d ¼ .27). CPT accuracy findings CPT data were examined to determine if CPT performance during the SUP þ DIS conditions differed from performance before and after the experimental procedure was conducted. First, baseline (pre- and post-experimental) CPT administrations were compared using a paired samples t-test to ensure that they did not differ. Hits on the pre (M ¼ 40.2, SD ¼ 2.5) and post (M ¼ 40.8, SD ¼ 1.3) CPT administrations did not differ (t ¼ .5, p ¼ .6), nor did errors of commission (pre: M ¼ .6, SD ¼ .4; post: M ¼ 0, SD ¼ 0; t ¼ 1.5, p ¼ .2). Therefore, we combined these scores to create one baseline mean of hits and one baseline mean of commission error scores. These means were compared to mean scores obtained during the SUP þ DIS conditions using paired samples t-tests. Hits significantly differed between pre/post (M ¼ 39.6, SD ¼ 2.7) and SUP þ DIS (M ¼ 35.9, SD ¼ 6.2) administrations (t ¼ 2.5, p ¼ .04, d ¼ .77). Commission errors did not differ between pre/post (M ¼ .5, SD ¼ .7) and SUP þ DIS (M ¼ .8, SD ¼ .9) administrations (t ¼ .8, p ¼ .42, d ¼ .37). Individual CPT data are presented in Table 2.

C.A. Conelea, D.W. Woods / Behaviour Research and Therapy 46 (2008) 1193–1200

Single-subject analyses We examined the data at the individual level by plotting tic frequency data and analyzing them for changes in magnitude using both visual inspection procedures and randomization tests (Levin, Marascuilo, & Hubert, 1978) with accompanying effect size estimates (Olive & Smith, 2005). Individual tic frequency data are presented in Fig. 1, and individual statistical data are presented in Table 3. Five children (participants 1, 2, 4, 6, and 8) demonstrated a similar data pattern. There were no BL data points that overlapped with SUP or SUP þ DIS data points, while in all cases the SUP and SUP þ DIS data points did overlap. This pattern suggests a clear difference in tic frequencies between BL and both suppression conditions. Individual statistical data (see Table 3) indicated that the mean difference between tic frequencies during BL and SUP was significantly different for eight children (participants 1–4 and 6–9), and the mean difference between BL and SUP þ DIS was significantly different for six children (participants 1,2, 4–6, 8). These findings suggest that tic suppression reliably occurred in both suppression conditions for the majority of participants (1, 2, 4, 6, 8). Only a few children deviated from this pattern (3, 5, 7, 9) and it is worth noting that if the first BL condition for participants 3 and 5 were removed (as they failed the manipulation check for these conditions), their response pattern would have been similar to participants 1, 2, 4, 6, and 8. Only tic frequency data from participants 7 and 9 showed patterns that were inconsistent with the remaining participants. Both participants 7 and 9 demonstrated successful suppression in the SUP condition, but not when distraction was added. Although reasons for this are unclear, it is interesting to note that both children had co-occurring OCD and disruptive behavior disorder (e.g., conduct disorder or ADHD) diagnoses.

Discussion The purpose of the current study was to examine the role of attention in tic suppression by measuring the impact of a competing distraction task on tic frequencies during periods of suppression. Performance on the distraction task was also examined to determine if suppression efforts were associated with diminished task accuracy. Based on previous research (Himle & Woods, 2005; Peterson et al., 1998; Shimberg, 1995; Shucard et al., 1997), it was hypothesized that tic frequencies during SUP þ DIS conditions would be higher than during SUP conditions. In addition, it was hypothesized that accuracy on the auditory CPT would decrease when administered during the SUP þ DIS conditions. Group analyses indicated that there was a reliable suppression effect, as shown by the significant difference between BL and SUP. Results failed to support the hypothesis that tic frequencies during SUP þ DIS conditions would be higher than those in the SUP

Table 2 Hits and commission errors (Com.) on the auditory CPT for each participant Participant

1 2 3 4 5 6 7 8 9

SUP þ DIS 1

SUP þ DIS 2

SUP þ DIS 3

Post

Hits

Pre Com.

Hits

Com.

Hits

Com.

Hits

Com.

Hits

Com.

42 42 42 37 40 38 n/a 42 33

2 0 0 1 0 2 n/a 0 1

38 39 36 40 40 38 35 42 24

2 0 0 0 0 1 0 0 1

36 37 29 41 37 42 33 42 20

0 0 0 0 1 0 1 0 3

40 42 31 37 29 42 37 40 n/a

1 0 0 1 5 1 0 0 n/a

n/a 42 41 40 n/a 42 39 39 n/a

n/a 0 0 0 n/a 0 0 0 n/a

1197

conditions. CPT data supported the second hypothesis, that performance on the CPT would notably decline when also attempting to suppress tics. There were more hits on the CPT before and after the experimental conditions as compared to the SUP þ DIS conditions, although statistically, errors of commission did not change. As a whole, results of this study suggest that (a) environmental distractions do not necessarily negatively impact tic suppression efforts and (b) performance on attentional measures may be somewhat impacted by tic suppression efforts. This is the first study to directly examine tic frequencies in the presence of environmental distractions in a controlled experimental setting. Although the study has several limitations, as discussed below, it provides initial evidence that tic suppression may not require sustained, focused (i.e., only on suppression) attentional resources, as has been previously suggested (Himle & Woods, 2005; Peterson et al., 1998). Furthermore, some have speculated that successful tic suppression comes at the expense of accuracy on attention-demanding tasks (Shimberg, 1995; Shucard et al., 1997). Although there does appear to be a negative impact, the clinical implications of the impact are still unclear. The current study had some procedural limitations. First, although the auditory CPT used as the distraction task was modeled after standardized CPTs, the task itself was not a standardized or normed instrument, and thereby limits the claims that can be made about the degree to which tic suppression impacted CPT performance. Future research could address this limitation by extending the length of conditions to accommodate standardized CPT measures. CPT performance was also assessed by examining raw scores on the CPT. Although it appears that suppression impacted raw CPT scores, it is possible that the difference observed between suppression and non-suppression administrations is not representative of a meaningful change in performance. To address this, it would be helpful to administer the auditory CPT to a larger sample so that percentile ranks or standardized scores could be used to assess performance. Alternatively, it may also be possible to overcome this limitation by comparing the current sample’s scores to a normal control group yoked on variables such as age and gender. The auditory CPT was also chosen based on concerns that the motor movements needed to complete a computerized CPT would provide a competing response for some tics. However, for children with primarily vocal tics (such as participant 2), it is possible that the spoken response complemented vocal tic suppression efforts. This limitation could be addressed in the future by choosing a response format (either spoken or motor) based upon a particular child’s tic. Other limitations concern the generalizability of findings. It is unclear how well the findings generalize to other situations in which attention-demanding stimuli may be present. For example, it is unclear how the changes observed in CPT performance in the current study translate into possible impairments on school performance or academic tasks during periods of tic suppression. Future research could address this limitation by changing the distraction task to more closely mimic ‘‘real world’’ environmental demands, such as attending to a teacher in a classroom. It would also be beneficial to replicate the study with more children to determine how well the findings generalize to children who differ by age, tic severity, and comorbid conditions. For example, the two children with inconsistent data patterns (participants 7 and 9) both had comorbid OCD and CD or ADHD, suggesting that it may be informative for future research to more closely examine how various comorbidity profiles impact suppression, both alone and with simultaneous attentional demands. As another limitation, the current study did not examine whether the tic suppression observed for most children during the SUP and SUP þ DIS conditions is attributable to the same

Tic Frequency

50 40

BL SUP SUP+DIS

30 20 10 0

1

2

3

4

5

6

7

8

Tic Frequency

Participant 1

60

9

100 90 80 70 60 50 40 30 20 10 0

Participant 2

BL SUP SUP+DIS

1

2

3

Participant 3

Tic Frequency

35

BL SUP SUP+DIS

30 25 20 15 10 5 0

1

2

3

4

5

6

7

8

100 80 60 40

Tic Frequency

Tic Frequency

BL SUP SUP+DIS

120

20 2

3

4

5

6

7

8

9

BL SUP SUP+DIS

10 5 1

2

3

Participant 7

200 180 160 140 120 100 80 60 40 20 0

BL SUP SUP+DIS

10 5 3

4

5

6

7

8

6

7

8

9

BL SUP SUP+DIS 1

2

3

4

5

6

7

8

9

Participant 8

25 20

BL SUP SUP+DIS

15 10 5 0

9

1

2

3

4

5

6

7

8

9

Session

Sessions Participant 9

30

Tic Frequency

Tic Frequency

Tic Frequency

15

2

5

Participant 6

30

20

1

4

Session

25

0

9

15

Session 30

8

Session

Participant 5

1

7

20

0

9

140

0

6

25

Session 160

5

Participant 4

30

Tic Frequency

40

4

Session

Session

25

BL SUP SUP+DIS

20 15 10 5 0

1

2

3

4

5

6

Session Fig. 1. Tic frequencies during baseline (BL), suppression (SUP), and suppression plus distraction (SUP þ DIS) conditions for each participant.

C.A. Conelea, D.W. Woods / Behaviour Research and Therapy 46 (2008) 1193–1200

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Table 3 Tic frequency means, standard deviations, mean differences and non-regression effect sizes for each participant Participant

1 2 3 4 5 6 7 8 9

BL

SUP

SUP þ DIS

BL vs. SUP

BL vs. SUP þ DIS

DRO vs. SUP þ DIS

M

SD

M

SD

M

SD

MBL  MSUP

d

MBL  MDIS

d

MSUP  MDIS

d

45.0 73.7 25.7 16.7 63.3 145.0 17.3 15.0 18.5

10.4 14.3 14.6 10.5 68.5 36.2 3.5 11.1 9.2

12.0 1.7 3.3 1.0 17.0 0 5.0 0 10.0

16.5 0.6 1.2 0 19.9 0 5 0 1.4

16.0 12.0 8.3 3.3 2.7 0.3 9.7 0 11.5

5.3 19.9 10.4 3.1 2.1 0.6 12.7 0 3.5

33.0* 72.0* 22.3* 15.7* 46.3 145.0* 12.3* 15.0* 8.5*

3.1 5.0 1.5 1.5 0.7 4.0 3.5 1.3 0.9

29.0* 61.7* 17.3 13.3* 60.7* 144.7* 7.7 15.0* 7.0

2.8 4.3 1.2 1.3 0.9 4.0 2.2 1.3 0.8

4.0 10.3 5.0 2.3 14.3 0.3 4.7 0 1.5

0.2 18.1 4.4 2.3 0.7 0 0.9 0 1.1

*Mean difference is significant at p ¼ .05.

mechanism. Himle et al. (2008) demonstrated that the mechanism underlying successful suppression in SUP is the reinforcement contingency. However, in the SUP þ DIS condition, it is possible that another mechanism contributed to suppression. For example, the CPT may have distracted children from their tics by directing their attention away from the monitoring of internal sensations. This may have decreased the likelihood that the urge to tic would be detected, resulting in a lowered tic frequency. Given the importance of the reinforcement contingency in producing suppression, we felt that it was necessary to include reinforcement during the SUP þ DIS conditions. However, since CPT performance was not linked to any reinforcement contingency, it is possible that some children primarily allocated their attentional resources toward suppression (the rewarded behavior). The differing contingencies may in part explain why CPT performance, rather than tic suppression, worsened during SUP þ DRO. It would be interesting for future research to examine if CPT performance could be improved in SUP þ DRO by establishing of a reinforcement contingency for accurate CPT performance. Finally, this study did not address whether the SUP þ DIS condition impacted the premonitory urge. It has been suggested that the urge contributes to attention problems and can be more distracting than tics themselves (Leckman, Bloch, Scahill, & King, 2006). In addition, recent research has shown that subjective urge ratings are higher during suppression than during baseline (Himle et al., 2008). To gain a more comprehensive understanding of the processes underlying tic suppression, future research should examine whether the pattern observed by Himle et al. (2008) remains the same when suppression occurs in the presence of environmental distractions. It is possible that providing children with a task to perform simultaneously with suppression actually helps to alleviate the urge by directing the child’s attention away from urge sensations. The results of the current research have clinical implications, particularly for Habit Reversal (HR; Azrin & Nunn, 1973), a behavioral treatment designed to enhance voluntary tic suppression ability. Results suggest that it is likely that the tic suppression strategies taught during HR can be successfully used in environments that include attention-demanding or ‘‘distracting’’ stimuli, such as a classroom or social situation. Results also indicate that successful suppression may come at the expense of accuracy on a task performed simultaneously. However, it is important to point out that the participants in this study had no previous formal behavioral treatment based on tic suppression strategies. It is likely that practice would increase the automaticity of suppression behaviors and make it easier to suppress in distracting situations and engage in simultaneous tasks. Therefore, it may be beneficial for children to first implement suppression during situations in which no additional task performance is required. Once suppression is more automatic in these situations, children may be more able to successfully implement suppression and complete

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