Deryk Beal | University of Alberta (original) (raw)

Papers by Deryk Beal

Frontiers in human neuroscience, 2014

Deficits in brain white matter have been a main focus of recent neuroimaging studies on stutterin... more Deficits in brain white matter have been a main focus of recent neuroimaging studies on stuttering. However, no prior study has examined brain connectivity on the global level of the cerebral cortex in persons who stutter (PWS). In the current study, we analyzed the results from probabilistic tractography between regions comprising the cortical speech network. An anatomical parcellation scheme was used to define 28 speech production-related ROIs in each hemisphere. We used network-based statistic (NBS) and graph theory to analyze the connectivity patterns obtained from tractography. At the network-level, the probabilistic corticocortical connectivity from the PWS group were significantly weaker than that from persons with fluent speech (PFS). NBS analysis revealed significant components in the bilateral speech networks with negative correlations with stuttering severity. To facilitate comparison with previous studies, we also performed tract-based spatial statistics (TBSS) and regio...

Frontiers in Human Neuroscience, 2015

The acquisition and mastery of speech-motor control requires years of practice spanning the cours... more The acquisition and mastery of speech-motor control requires years of practice spanning the course of development. People who stutter often perform poorly on speech-motor tasks thereby calling into question their ability to establish the stable neural motor programs required for masterful speech-motor control. There is evidence to support the assertion that these neural motor programs are represented in the posterior part of Broca's area, specifically the left pars opercularis. Consequently, various theories of stuttering causation posit that the disorder is related to a breakdown in the formation of the neural motor programs for speech early in development and that this breakdown is maintained throughout life. To date, no study has examined the potential neurodevelopmental signatures of the disorder across pediatric and adult populations. The current study aimed to fill this gap in our knowledge. We hypothesized that the developmental trajectory of cortical thickness in people who stutter would differ across the lifespan in the left pars opercularis relative to a group of control participants. We collected structural magnetic resonance images from 116 males (55 people who stutter) ranging in age from 6 to 48 years old. Differences in cortical thickness across ages and between patients and controls were investigated in 30 brain regions previously implicated in speech-motor control. An interaction between age and group was found for the left pars opercularis only. In people who stutter, the pars opercularis did not demonstrate the typical maturational pattern of gradual gray matter thinning with age across the lifespan that we observed in control participants. In contrast, the developmental trajectory of gray matter thickness in other regions of interest within the neural network for speech-motor control was similar for both groups. Our findings indicate that the developmental trajectory of gray matter in left pars opercularis is abnormal in people who stutter.

PLoS ONE, 2012

Previous empirical observations have led researchers to propose that auditory feedback (the audit... more Previous empirical observations have led researchers to propose that auditory feedback (the auditory perception of selfproduced sounds when speaking) functions abnormally in the speech motor systems of persons who stutter (PWS). Researchers have theorized that an important neural basis of stuttering is the aberrant integration of auditory information into incipient speech motor commands. Because of the circumstantial support for these hypotheses and the differences and contradictions between them, there is a need for carefully designed experiments that directly examine auditory-motor integration during speech production in PWS. In the current study, we used real-time manipulation of auditory feedback to directly investigate whether the speech motor system of PWS utilizes auditory feedback abnormally during articulation and to characterize potential deficits of this auditory-motor integration. Twenty-one PWS and 18 fluent control participants were recruited. Using a short-latency formant-perturbation system, we examined participants' compensatory responses to unanticipated perturbation of auditory feedback of the first formant frequency during the production of the monophthong [e]. The PWS showed compensatory responses that were qualitatively similar to the controls' and had close-to-normal latencies (,150 ms), but the magnitudes of their responses were substantially and significantly smaller than those of the control participants (by 47% on average, p,0.05). Measurements of auditory acuity indicate that the weaker-than-normal compensatory responses in PWS were not attributable to a deficit in low-level auditory processing. These findings are consistent with the hypothesis that stuttering is associated with functional defects in the inverse models responsible for the transformation from the domain of auditory targets and auditory error information into the domain of speech motor commands.

NeuroImage, 2010

We used magnetoencephalography to investigate auditory evoked responses to speech vocalizations a... more We used magnetoencephalography to investigate auditory evoked responses to speech vocalizations and non-speech tones in adults who do and do not stutter. Neuromagnetic field patterns were recorded as participants listened to a 1 kHz tone, playback of their own productions of the vowel /i/ and vowel-initial words, and actively generated the vowel /i/ and vowel-initial words. Activation of the auditory cortex at approximately 50 and 100 ms was observed during all tasks. A reduction in the peak amplitudes of the M50 and M100 components was observed during the active generation versus passive listening tasks dependent on the stimuli. Adults who stutter did not differ in the amount of speech-induced auditory suppression relative to fluent speakers. Adults who stutter had shorter M100 latencies for the actively generated speaking tasks in the right hemisphere relative to the left hemisphere but the fluent speakers showed similar latencies across hemispheres. During passive listening tasks, adults who stutter had longer M50 and M100 latencies than fluent speakers. The results suggest that there are timing, rather than amplitude, differences in auditory processing during speech in adults who stutter and are discussed in relation to hypotheses of auditory-motor integration breakdown in stuttering.

NeuroImage, 2011

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses ... more Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated a reduced amplitude of the auditory M50 and M100 responses to speech during active production relative to passive listening. It is unknown if auditory responses to self-initiated speech-motor acts are suppressed in children or if the phenomenon differs between children who do and do not stutter. As stuttering is a developmental speech disorder, examining speech-induced suppression in children may identify possible neural differences underlying stuttering close to its time of onset. We used magnetoencephalography to determine the presence of speech-induced suppression in children and to characterize the properties of speech-induced suppression in children who stutter. We examined the auditory M50 as this was the earliest robust response reproducible across our child participants and the most likely to reflect a motor-to-auditory relation. Both children who do and do not stutter demonstrated speech-induced suppression of the auditory M50. However, children who stutter had a delayed auditory M50 peak latency to vowel sounds compared to children who do not stutter indicating a possible deficiency in their ability to efficiently integrate auditory speech information for the purpose of establishing neural representations of speech sounds.

Cortex, 2013

It is well documented that neuroanatomical differences exist between adults who stutter and their... more It is well documented that neuroanatomical differences exist between adults who stutter and their fluently speaking peers. Specifically, adults who stutter have been found to have more grey matter volume (GMV) in speech relevant regions including inferior frontal gyrus, insula and superior temporal gyrus (Beal et al., 2007; Song et al., 2007). Despite stuttering having its onset in childhood only one study has investigated the neuroanatomical differences between children who do and do not stutter. Chang et al. (2008) reported children who stutter had less GMV in the bilateral inferior frontal gyri and middle temporal gyrus relative to fluently speaking children. Thus it appears that children who stutter present with unique neuroanatomical abnormalities as compared to those of adults who stutter. In order to better understand the neuroanatomical correlates of stuttering earlier in its development, near the time of onset, we used voxel-based morphometry to examine volumetric differences between 11 children who stutter and 11 fluent children. Children who stutter had less GMV in the bilateral inferior frontal gyri and left putamen but more GMV in right Rolandic operculum and superior temporal gyrus relative to fluent children. Children who stutter also had less white matter volume bilaterally in the forceps minor of the corpus callosum. We discuss our findings of widespread anatomic abnormalities throughout the cortical network for speech motor control within the context of the speech motor skill limitations identified in people who stutter (Namasivayam and van Lieshout, 2008; Smits-Bandstra et al., 2006).

Brain and Language, 2008

Functional magnetic resonance imaging was used to investigate the neural correlates of passive li... more Functional magnetic resonance imaging was used to investigate the neural correlates of passive listening, habitual speech and two modified speech patterns (simulated stuttering and prolonged speech) in stuttering and nonstuttering adults. Within-group comparisons revealed increased right hemisphere biased activation of speech-related regions during the simulated stuttered and prolonged speech tasks, relative to the habitual speech task, in the stuttering group. No significant activation differences were observed within the nonstuttering participants during these speech conditions. Between-group comparisons revealed less left superior temporal gyrus activation in stutterers during habitual speech and increased right inferior frontal gyrus activation during simulated stuttering relative to nonstutterers. Stutterers were also found to have increased activation in the left middle and superior temporal gyri and right insula, primary motor cortex and supplementary motor cortex during the passive listening condition relative to nonstutterers. The results provide further evidence for the presence of functional deficiencies underlying auditory processing, motor planning and execution in people who stutter, with these differences being affected by speech manner.

Disability & Rehabilitation, 2006

The purpose of this position statement is to propose an interactionist framework to bring togethe... more The purpose of this position statement is to propose an interactionist framework to bring together the existing literature and provide a unifying direction for rehabilitation research. The framework comprises three components: the conceptual model, the research question, and the research design. The interactionist conceptual model has been adapted from the World Health Organization International Classification of Functioning, Disability, and Health. The model forms the starting point that guides the specification of the research question, which, in turn, guides the selection of research design. This approach demands that the question takes precedence and that there be an extensive repertoire of research designs, each of which is valued for its 'goodness-of-fit' with the question, rather than an a priori, single hierarchical ordering of designs. Research designs must be appropriate for questions that examine the disability experience, development over the lifespan, multifaceted interventions, low incidence conditions, and development of new interventions. Analytical challenges include dealing with confounding, mediating, and moderating variables. Rehabilitation researchers -and those who fund their work -should consider and value the use of diverse research methods to best answer the questions posed from the interactionist perspective.