Abstract
Attention-Deficit Hyperactivity Disorder (ADHD) is a predominant neurobehavioral disorder of childhood with motor and sensory symptoms often persisting into adulthood. Motor control theories highlight the importance of the bidirectional relationship between sensation and movement for maintaining skilled behaviors like speech. The impact of ADHD on speech in adults has not been well established. The purpose of this study is to assess group differences in quantitative speech and oral somatosensory measures in adults with and without ADHD and to describe the relationship between ADHD symptomology and speech production. A total of 50 adults (18–26 years) were recruited and divided in two groups based on diagnosis: those with (n=28) and those without (n=22) ADHD. All participants provided a speech sample to measure articulatory accuracy and speech rate and completed quantitative point-pressure testing using tactile detection and discrimination on bilateral sites on the lower lip and lateral edge of the tongue tip. Independent t-tests corrected for multiple comparisons identified significant group differences using FDR corrected q values in speech production for correct syllables per second and overall speech rate (q<.05). Additionally, there were significant group differences (q<.05) for detection and discrimination threshold estimates at one testing location. Bivariate correlations identified a relationship between several speech measures and self-reported ADHD symptoms such that as symptom severity increased, speech accuracy for correct syllables per second decreased. Young adults with ADHD have subtle differences in speech production compared to non-ADHD control participants. Speech scientists might consider screening for ADHD when collecting normative data samples.
Keywords: speech production, somatosensation, sensorimotor, motor control, attention-deficit/hyperactivity disorder (ADHD)
Introduction
Speech production is a highly-skilled, goal-directed behavior and the focus of numerous motor control theories that highlight the importance of precise temporal synchrony between motor output and sensory perception [21, 26, 29, 30]. Alterations in skilled behaviors may be associated with changes in sensory perception and processing [3, 12]. Adults with ADHD have been observed to have alterations in somatosensation across the body [13, 37] and sensory perceptual processing [6, 20, 33]. In fact, ADHD is frequently comorbid with speech production and language disorders [31] characterized by an increased number of disfluencies [14], poor auditory comprehension [32], pragmatic difficulties [4, 7, 19], and poor articulation [24]. Although motor control theories suggestion a bidirectional relationship between sensation and production, there is a paucity of work focused on the relationship between orofacial somatosensory perception and its significance for skilled speech production [22, 23, 34] in adults with ADHD. To the best of our knowledge, even though there are known speech production changes in children with ADHD [5, 28, 31], no work has evaluated whether differences in oral somatosensation exist in adults with ADHD and if so, whether these differences are associated with changes in speech motor control.
The current study has two Aims. First, we assess group differences in quantitative speech and oral somatosensory measures in young adults with ADHD and non-ADHD controls. As previous work has shown deficits in motor control in adults with ADHD, we hypothesized that speech production accuracy for individuals with ADHD would be lower than non-ADHD controls. We hypothesized adults with ADHD would demonstrate increased lip and tongue somatosensory threshold estimates, indicating possible hyposensitivity, as compared to non-ADHD controls [25]. Second, we describe the relationship between ADHD symptomology and speech measures. We hypothesized that alterations in speech production will be negatively related, while point-pressure somatosensation measures will be positively related to ADHD symptomology [28].
Material and methods
Participants, ages 18–26 years, were recruited from a database of research participants created and maintained by the Brain and Behavior Lab (PI: Neely). Consistent with our previous work [25, 35, 36], all participants in the current study had previously completed an in-lab session during which they completed the Conners’ Adult ADHD Diagnostic Interview (CAADID) [15]. Diagnosis of ADHD was assigned based on the results of the CAADID. Further, prior to the current study, all participants had completed a self-report of ADHD-related symptoms using the long form of the Conners’ Adult ADHD Rating Scales (CAARS S:L) [9]. The CAARS has 66 items and 8 factor-derived subscales: Inattention/Memory Problems, Hyperactivity/Restlessness, Impulsivity/Emotional Lability, Problems with Self-Concept, DSM-IV Inattentive Symptoms, DSM-IV Hyperactive/Impulsive Symptoms, DSM-IV ADHD Symptoms Total, and an ADHD Index. These measures are included to describe the current sample, as well as to evaluate whether measures of speech production are associated with ADHD-related symptoms.
Participants with ADHD had more than 5 symptoms of inattention or hyperactivity, which were impaired in at least two settings (e.g., family and work). Those taking a psychostimulant completed the assessments after a 24-hour washout period and none reported taking medications known to affect motor control at the time of testing, including antipsychotics, stimulants, or anticonvulsants [38]. To be classified as a non-ADHD control, participants reported less than 3 total symptoms and less than 2 symptoms per ADHD dimension and confirmed they had never been diagnosed with ADHD.
A total of fifty adults, 28 with ADHD (17 females) and 22 non-ADHD controls (12 females), were recruited for the current study. Written informed consent was obtained from all participants prior to starting the study. All procedures were approved by the Institutional Review Board at The Pennsylvania State University and were consistent with the Declaration of Helsinki. All participants received monetary compensation for their participation in the study.
Speech Sample Procedures
Participants provided a speech sample using four commonly used speech assessment measures. First, participants completed alternating motion rates (AMRs) and sequential motion rates (SMRs). AMRs test the ability to rapidly and accurately repeat a single consonant-vowel syllable. Participants are instructed to take a deep breath and repeat the syllable /pa/ as accurately and as many times as possible on one breath. Participants use the same procedures for the syllables /ta/ and /ka/. SMRs test the ability to rapidly and accurately repeat a combination of consonant-vowel syllables. Participants are instructed to take a deep breath and repeat the combined syllables /pa-ta-ka/ as accurately and as many times as possible on one breath. Participants repeated both tasks three times. The AMR and SMR values for each consonant-vowel series was the total number of accurately produced syllables divided by the total time (in seconds) speaking. Next, participants were asked to read the Grandfather passage [11], a short, standardized paragraph containing a variety of sounds in the English language. The amount of time it took to read the passage was recorded for each participant. Last, participants provided a one-minute spontaneous speech sample in response to the prompt, “tell me about your last vacation.” Words per minute (i.e., speech rate) was calculated using duration of speaking and total number of words spoken. All speech data was recorded using a portable digital audio recorder (Zoom H1 Audiorecorder).
Labiolingual Point-Pressure Somatosensory Assessment Procedures
To assess labiolingual tactile somatosensation, participants completed three somatosensory assessments, including, (a) two-point discrimination threshold estimates, (b) tactile detection threshold estimates, and (c) tactile discrimination threshold estimates. Consistent with our previously published protocol [16], each somatosensory assessment was completed at four locations: right and left lower lip between midline and the oral angle, and right and left lateral edge of the tongue tip.
Two-point discrimination threshold estimates were achieved with discrimination disks (BASELINE 2-point Discrim-A-Gon 12–1492 (D2)) using a method of limits approach [17]. Initially, participants were presented with 2-points from the disk such that they could easily, verbally identify two distinct points of pressure applied perpendicularly to the skin. As the investigator slowly rotated the disc, gradually making the interval between the two points smaller and smaller, participants indicated when they felt only one point of pressure – the distance between the two points was recorded in millimeters. Then, the investigator switched the starting point of the trial such that the participant felt only one point of pressure. The disk was rotated, gradually making the interval between the two points larger, until participants reported feeling two points of pressure. This procedure continued for a total of six series of trials – three ascending and three descending. The final two-point discrimination threshold estimate in millimeters(mm) was the average of the end points of those six trials.
Tactile detection threshold estimates were obtained using Von Frey hair monofilaments that can range from 0.008 g to 15 g of force (DanMic Global, San Jose, CA). A two-alternative forced-choice paradigm was used, such that participants verbally indicated in which of two presented trials they felt a point of pressure [18]. When a participant made a correct response in three sequential trials at the same force level, the monofilament of next smaller force was applied. If a participant made an incorrect response, the monofilament of the next higher force was applied in the next trial. The assessment ended when a given force level was applied a total of five times – this force was recorded as the detection threshold estimate in grams (g).
Tactile discrimination threshold estimates were also obtained using Von Frey hair monofilaments (DanMic Global, San Jose, CA) and a two-alternative forced-choice paradigm. In this assessment, participants were presented with a point of pressure in two subsequent trials and then asked to identify which trial contained the “harder” or “stronger” pressure. Trials began with the monofilament that was three levels above the detection threshold estimate and followed the same testing and stopping rules as described above. The final tactile discrimination threshold estimate recorded in grams (g). All somatosensory assessments were conducted in the same order (2-point discrimination, tactile detection, and finally tactile discrimination). Testing location was randomized within each asessment.
Data Analysis
Speech samples were evaluated for interrater reliability prior to the onset of analyses. Specifically, five speech samples from each of the two groups were analyzed by a second evaluator (20% of the dataset). Intraclass correlations identified good interrater reliability for AMRs (ICC = .848) and excellent interrater reliability for SMRs (ICC = .999). Therefore, data analysis proceeded with the first rater.
Statistical tests were conducted using IBM SPSS Statistics for Macintosh, Version 24.0 (IBM Corp). A Chi-square was run to assess group differences between sex and CAARS scores. For our first aim, independent samples t-tests were used to assess for differences between groups for the quantitative speech and somatosensory measures. Using the Levene’s test the assumption of equal variances across groups was violated for several somatosensory variables including: detection threshold estimates for the right tongue and discrimination threshold estimates for the right and left lip and right tongue. Therefore, a corrected p-value was interpreted for these variables. The data was not transformed. Correction for multiple comparisons for 7 assessments (3 somatosensation and 4 speech measures) was applied using false discovery rate (FDR). FDR adjusted q-value < 0.05 [8, 27]. Cohen’s d effect sizes were also calculated for each variable. To address the second aim of the study, bivariate Pearson product-moment r correlation coefficients were calculated. As this is the first study to examine the relationship between ADHD, quantitative orofacial somatosensation variables, and speech output, raw p-values are provided for correlation interpretations.
Results
Participant characteristics
As expected, adults with ADHD demonstrated more severe ADHD-related symptoms as measured by the CAARS and CAADID when compared to non-ADHD controls, all p-values < .001. No significant differences between sex and CAARS scores for ADHD symptomology were identified using a Chi-squared (p=.377). No group differences were observed for age or pure tone hearing thresholds (p-values > .401). See Table 1 for participant demographics.
Table 1.
Participant Characteristics
| Age | Sex | Speech Usage | Pure Tone Hearing Threshold (dB) | CAARS | |||||
|---|---|---|---|---|---|---|---|---|---|
| Right | Left | Inattention/Memory | Hyperactivity/Restlessness | Impulsivity/Emotional | ADHD Index Score | ||||
|
ADHD
(n=28) |
21.57 (2.142) |
m=11 f=17 |
3.11 (0.916) |
6.53 (3.22) |
6.39 (3.60) |
63.79 (13.36) |
57.25 (11.19) |
53.11 (12.88) |
59.64 (9.98) |
|
Non-ADHD Control
(n=22) |
21.27 (2.080) |
m=10 f=12 |
2.77 (0.752) |
7.33 (4.36) |
7.33 (4.17) |
38.32 (5.69) |
40.23 (6.26) |
38.05 (7.11) |
38.82 (6.28) |
| p-value | .621 | n/a | .815 | .467 | .401 | < .001* | < .001* | < .001* | < .001* |
Note: Values are means and standard deviations (in parentheses). Group differences are identified with an asterisk
() using p-values. Sex is noted with m (male) and f (female).
Speech Sample
Table 2 provides means and standard deviations, t-statistics, q-values, and Cohen’s d effect sizes for each speech measure by group. Individuals with ADHD demonstrated faster speaking rates for all tasks. Group differences reached the level of significance for AMRs for (/pa/ q=.029, /ta/ q=.036, and /ka/ q=.043) with small to medium effect sizes, SMRs (q=0.21) with a medium effect size and storytelling rate words per minute (q=.007) with a medium effect size. There was no significant difference between groups for reading time (q=.129).
Table 2.
Descriptive and inferential statistics for speech & somatosensation assessments
| SPEECH MEASURES | ADHD | Non-ADHD Control | Group Differences using q-values | |
|---|---|---|---|---|
|
| ||||
| Alternating Motion Rates, (/pa/) | 3.95 (1.13) | 3.33 (1.14) | t(−1.890) = 48.0, q=.029* | effect size =0.5463 |
| Alternating Motion Rates, (/ta/) | 3.92 (1.27) | 3.29 (1.28) | t(−1.741) = 48.0, q=.036* | effect size =0.4941 |
| Alternating Motion Rates, (/ka/) | 3.67 (1.23) | 3.12 (1.19) | t(−1.612) = 48.0, q=.043* | effect size =0.4545 |
| Alternating Motion Rates, (/pataka/) | 5.58 (0.99) | 5.04 (0.98) | t(−1.920) = 48.0, q=.021* | effect size =0.5482 |
| Reading Time (seconds) | 40.48 (6.32) | 40.15 (4.67) | t(0.204) = 46.0, q=.129 | effect size =0.0594 |
| Storytelling Rate (words/minute) | 178.27 (21.17) | 160.72 (28.68) | t(−2.435) = 46.0, q=007* | effect size =0.6963 |
|
| ||||
|
|
||||
| SOMATOSENSATION | 2-Point Discrimination (mm) |
|||
| MEASURES BY LOCATION | ADHD | Non-ADHD Control | Group Differences | |
|
| ||||
| Lip-Right | 2.93 (0.51) | 3.11 (0.64) | t(1.060) = 48.0, q.=079 | effect size =0.3111 |
| Lip-Left | 2.81 (0.67) | 2.97 (0.73) | (0.853) = 48.0, q.=093 | effect size =0.2283 |
| Tongue-Right | 2.82 (0.81) | 2.95 (0.96) | t(0.551) = 48.0, q.=121 | effect size =0.1464 |
| Tongue-Left | 3.78 (0.74) | 2.99 (1.08) | t(0.805) = 48.0, q.=100 | effect size =0.8534 |
|
| ||||
| Detection (g) |
||||
| ADHD | Non-ADHD Control | Group Differences | ||
|
| ||||
| Lip-Right | 0.019 (0.025) | 0.014 (0.021) | t(−0.773) = 48.0, q=.107 | effect size =0.2166 |
| Lip-Left | 0.011 (0.004) | 1.013 (0.011) | t(0.883) = 48.0, q=.086 | effect size =0.2416 |
| Tongue-Right | 0.015 (0.014) | 0.011 (0.005) | t(−1.518) = 36.4, q=.050* | effect size =0.3805 |
| Tongue-Left | 0.017 (0.016) | 0.012 (0.008) | t(−1.259) = 48.0, q=.064 | effect size =0.3953 |
|
| ||||
| Discrimination (g) |
||||
| ADHD | Non-ADHD Control | Group Differences | ||
|
|
||||
| Lip-Right | 0.212 (0.457) | 0.094 (0.083) | t(−1.198) = 48.0, q=071 | effect size =0.3593 |
| Lip-Left | 0.608 (2.125) | 0.093 (0.054) | t(−1.281) = 27.0, q=057 | effect size =0.3426 |
| Tongue-Right | 0.878 (1.842) | 0.151 (0.208) | t(−2.074) = 27.9, q=.014* | effect size =0.5546 |
| Tongue-Left | 0.768 (2.015) | 0.480 (0.886) | t(−0.623) = 48.0, q=.114 | effect size =0.1850 |
Note. Mean and standard deviation (in parentheses) for each group. Statistics evaluating group differences are presented in the right most column. Corrected df are reported when Levene’s test was violated. FDR-adjusted q-value <.05. Significant q-values are noted with an
. Small effect size d=0.2, medium effect size d=0.5, large effect size d=0.8
Labiolingual Somatosensory Assessments
The threshold estimate means and standard deviations, t-statistics, q-values, and Cohen’s d effect sizes for each assessment are also reported in Table 2. There were no significant group differences for the two-point discrimination task at any test location. On average, the ADHD group demonstrated increased point-pressure detection and discrimination threshold estimates; however, significant group differences were only identified for the right tongue testing location for detection (q=.050) and discrimination (q=.014) with a small and medium effect sizes, respectively.
Relationship between Speech Production and ADHD Symptoms
To determine whether speech production is related to ADHD symptomatology, we conducted Pearson-Product Moment Correlations for the four speech variables (Storytelling, Paragraph Reading, SMRs, and AMRs for three phonemes) and three of the subscales of the CAARS (reported in Table 3). Sample sizes vary due to errors in recording for two participants in the spontaneous storytelling task. The results demonstrate that increases in symptom severity on the ADHD Index subscale were associated with decreases in AMRs for /pa/, /ta/, and /ka/, ps < .012. Furthermore, higher symptom ratings on the subscale Inattention/Memory Problems were related to decreased accuracy in AMR syllables per second for /ka/. In summary, more severe ADHD-related symptoms were associated with decreased numbers of correct syllables per second in the alternating motion rates task.
Table 3.
Pearson product-moment correlation coefficients for speech variables and ADHD symptom index for all participants.
| CAARS - ADHD Subscale T-Scores | |||||
|---|---|---|---|---|---|
| Inattention/Memory Problems | Hyperactivity/Restlessness Index | ADHD Index | |||
| Speech Measures | Sequential Motion Rates (Syllables per second) | Pearson Correlation | −0.078 | 0.028 | −0.077 |
| Sig. (2-tailed) | 0.595 | 0.849 | 0.6 | ||
| N | 49 | 49 | 49 | ||
| Alternating Motion Rates /pa/ (Syllables per second) | Pearson Correlation | −0.268 | −0.208 | −.363** | |
| Sig. (2-tailed) | 0.063 | 0.152 | 0.01 | ||
| N | 49 | 49 | 49 | ||
| Alternating Motion Rates /ta/ (Syllables per second) | Pearson Correlation | −0.273 | −0.227 | −.373** | |
| Sig. (2-tailed) | 0.058 | 0.116 | 0.008 | ||
| N | 49 | 49 | 49 | ||
| Alternating Motion Rates /ka/ (Syllables per second) | Pearson Correlation | −.293* | −0.216 | −.357* | |
| Sig. (2-tailed) | 0.041 | 0.136 | 0.012 | ||
| N | 49 | 49 | 49 | ||
| Paragraph Reading (Time in seconds) | Pearson Correlation | 0.081 | −0.033 | 0.081 | |
| Sig. (2-tailed) | 0.579 | 0.823 | 0.582 | ||
| N | 49 | 49 | 49 | ||
| Storytelling (Words per minute) | Pearson Correlation | −0.257 | −0.135 | −0.247 | |
| Sig. (2-tailed) | 0.081 | 0.367 | 0.094 | ||
| N | 47 | 47 | 47 | ||
Note. Asterisks and shading indicate p-values. Light shading and one asterisk
() indicate p-values < .05. Dark shading and two asterisks
() indicate p-values < .01.
Discussion
The current work provides a novel examination of speech motor control and somatosensation in adults with ADHD. Importantly, this work provides a foundation for characterizing the relationship between speech output, point-pressure sensation, and self-reported ADHD symptoms in young adults with ADHD. Significant group differences were identified for multiple speech production tasks, indicating increased speech rate for spontaneous storytelling and alternating and sequential motion rates. Additionally, findings indicate a relationship between ADHD symptomology and alternating motion rates correct syllables per second.
The primary aim of this study was to assess differences in speech and point-pressure somatosensation in adults with and without ADHD. Previous research reports increased disfluencies [14] and poor articulation [24] in people with ADHD. Therefore, we anticipated speech accuracy differences. In the current study, individuals with ADHD completed syllable repetition and reading tasks faster than non-ADHD controls. Group differences are consistent with previously reported speech and language delays comorbid with ADHD in childhood [4, 14, 24, 32]. Because speech disruptions in adults with ADHD have been reported [2] and approximately 2.5% of the U.S. adult population has ADHD [1], researchers developing normative datasets should consider asking participants if they have a previous or current diagnosis of ADHD when collecting normative speech samples for comparison with clinical populations.
We investigated group differences in orofacial point-pressure somatosensation in people with and without ADHD. Previous work demonstrates adults with ADHD have alterations in somatosensation across the body [13, 37], including differences in discrimination assessments of temperature and pain to the right forearm [39]. Further, our recent work demonstrates that adults with ADHD have sensory hypo- and hyper-sensitivities across sensory modalities, in comparison to non-ADHD controls [25]. Although the current findings indicate subtle group differences across all orofacial locations, differences only reached significance for point-pressure detection and discrimination threshold estimates at one body location (right tongue for both measures). Future studies may assess other forms of somatosensory inputs, such as texture appreciation, or pain and temperature to assess group differences.
The second aim of this study was to characterize the relationship between speech output and self-reported ADHD symptoms. Our previous work demonstrates a link between self-reported ADHD-related symptoms and motor output [35, 36]. Thus, we anticipated that ADHD-related symptoms would be similarly associated with speech output. Since ADHD-related symptoms occur on a continuum in all individuals, all participants in our study were included in the analysis. The results demonstrated an association between speech production and ADHD symptomology such that greater symptom severity was associated with decreased numbers of correct syllables per second in AMR tasks. Specifically, the ADHD Index score is a measure of the overall level of symptoms an individual is experiencing, such that high-scorers have clinically significant levels of symptoms relative to low-scorers [10]. In our sample, high ADHD Index scores were associated with more mistakes in the AMR task for /pa/, /ta/, and /ka/. A similar finding was identified for the CAARS subscale Inattention/Memory Problems. High-scorers on this subscale learn more slowly, have difficulty organizing and completing tasks, and difficulty concentrating [10]. We found that high scores for Inattention/Memory Problems were associated with more mistakes in the AMR task for the syllable /ka/. These findings are supported by pediatric studies in which researchers noted that children with moderate-severe speech sound disorders scored higher on scales of inattention and hyperactivity than children with no speech sound disorders [28]. Interestingly, the CAARS subscale Hyperactivity/Restlessness was not associated with any of the speech output variables.
Limitations
The current study focused on young adults because this is a period when speech motor control should be at a peak level of proficiency. Participants with ADHD in our sample were all students attending a four-year university. It is likely they present with less impairment than the general population with ADHD. Thus, the identification of subtle differences in our college-attending ADHD group suggests that larger differences may exist in the larger clinical population.
Conclusions
Our findings indicate that young adults with ADHD have speech production differences compared to non-ADHD controls and that differences in speech production are associated with self-reported ADHD-related symptoms. Researchers collecting speech samples may want to consider screening for ADHD in their normative samples.
Highlights.
Attention-Deficit Hyperactivity Disorder is comorbid with speech disorders.
ADHD-related symptoms are correlated with differences in speech production.
Speech scientists may want to screen for ADHD when collecting normative data samples.
Funding:
This work was supported, in part, by the Social Science Research Institute (SSRI) at The Pennsylvania State University to NME and KAN, a Grant UL1 TR002014 and KL2 TR002015 from the National Center for Advancing Translational Sciences (NCATS) to KAN, and a NARSAD Young Investigator Award to KAN. The content is solely the responsibility of the authors and does not necessarily represent the official views of the SSRI, the NIH, or the Brain and Behavior Research Foundation.
Footnotes
Credit Author Statement
The individuals meeting the requirements for authorship are:
Nicole M. Etter, Ph.D., CCC-SLP
Conceptualization and Methodology, Funding acquisition, Supervision, Writing-Original Draft
Farlah A. Cadely, MS, SLP-CF
Data curation and Investigation
Madison G. Peters
Data curation and Investigation
Crystal R. Dahm
Data curation and Investigation
Kristina A. Neely, PhD
Conceptualization and Methodology, Funding acquisition, Supervision, Writing-Review and Editing
Conflict of interest: The authors have no conflicts of interest to report.
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