Dissociating the performance of cortical and subcortical patients on phonemic tasks

A neurocomputational view of the effects of Parkinson's disease on speech production

The purpose of this article is to review the scientific literature concerning speech in Parkinson's disease (PD) with reference to the DIVA/GODIVA neurocomputational modeling framework. Within this theoretical view, the basal ganglia (BG) contribute to several different aspects of speech motor learning and execution. First, the BG are posited to play a role in the initiation and scaling of speech movements. Within the DIVA/GODIVA framework, initiation and scaling are carried out by initiation map nodes in the supplementary motor area acting in concert with the BG. Reduced support of the initiation map from the BG in PD would result in reduced movement intensity as well as susceptibility to early termination of movement. A second proposed role concerns the learning of common speech sequences, such as phoneme sequences comprising words; this view receives support from the animal literature as well as studies identifying speech sequence learning deficits in PD. Third, the BG may play a role in the temporary buffering and sequencing of longer speech utterances such as phrases during conversational speech. Although the literature does not support a critical role for the BG in representing sequence order (since incorrectly ordered speech is not characteristic of PD), the BG are posited to contribute to the scaling of individual movements in the sequence, including increasing movement intensity for emphatic stress on key words. Therapeutic interventions for PD have inconsistent effects on speech. In contrast to dopaminergic treatments, which typically either leave speech unchanged or lead to minor improvements, deep brain stimulation (DBS) can degrade speech in some cases and improve it in others. However, cases of degradation may be due to unintended stimulation of efferent motor projections to the speech articulators. Findings of spared speech after bilateral pallidotomy appear to indicate that any role played by the BG in adult speech must be supplementary rather than mandatory, with the sequential order of well-learned sequences apparently represented elsewhere (e.g., in cortico-cortical projections).

VOT y VOT ratio en hispanohablantes con Enfermedad de Parkinson

El Voice Onset Time (VOT) es una medida acústica que hace referencia a la diferencia entre el tiempo de la liberación de la oclusión y el inicio de la vibración de las cuerdas vocales en los sonidos oclusivos; el VOT ratio (VOTr), por su parte, se refiere a la relación entre el VOT y la duración de la sílaba que busca modelar el efecto de la velocidad del habla sobre el VOT. Ambas medidas han sido estudiadas en hablantes con Enfermedad de Parkinson (EP) en tareas de habla experimentales, pero existen pocos trabajos en personas con EP que sean hispanohablantes y en el contexto de habla conectada. En este estudio se investigó el comportamiento del VOT y VOTr en habla conectada en hispanohablantes colombianos con EP. Mediante el software Praat se calculó el VOT y VOTr de los sonidos /p, b, t, d, k, g/ en grabaciones tomadas del corpus PC-GITA que correspondían a 50 personas con EP y 50 sin EP pareadas por edad y sexo. Se encontró que, con algunas variaciones, el VOT y el VOTr en habla conectada se comportan de manera similar entre sí y respecto a otros contextos de análisis previamente estudiados; comparado con el grupo control, se hallaron diferencias en las personas con EP, pero estas solamente fueron significativas en el VOT y VOTr de /p/, que fue más largo para las mujeres con EP(p < .05) así como en el VOT y VOTr de /d/ para ambos sexos con EP, pues fueron menores(p ≤ .05). Las diferencias relacionadas con el sexo solamente estuvieron entre hombres y mujeres con EP en el VOT de /p/, que fue más largo en las mujeres (p < .05). Esta evidencia podría indicar que en español, en habla conectada, el VOT y el VOTr son igual de sensibles a los cambios en el VOT asociados a la EP y al parecer el sexo no tiene un efecto significativo sobre ellas.

Speech Rate Mediated Vowel and Stop Voicing Distinctiveness in Parkinson's Disease

Purpose The purpose of this study was to quantify changes in acoustic distinctiveness in two groups of talkers with Parkinson's disease as they modify across a wide range of speaking rates. Method People with Parkinson's disease with and without deep brain stimulation and older healthy controls read 24 carrier phrases at different speech rates. Target nonsense words in the carrier phrases were designed to elicit stop consonants and corner vowels. Participants spoke at seven self-selected speech rates from very slow to very fast, elicited via magnitude production. Speech rate was measured in absolute words per minute and as a proportion of each talker's habitual rate. Measures of segmental distinctiveness included a temporal consonant measure, namely, voice onset time, and a spectral vowel measure, namely, vowel articulation index. Results All talkers successfully modified their rate of speech from slow to fast. Talkers with Parkinson's disease and deep brain stimulation demonstrated greater baseline speech impairment and produced smaller proportional changes at the fast end of the continuum. Increasingly slower speaking rates were associated with increased temporal contrasts (voice onset time) but not spectral contrasts (vowel articulation). Faster speech was associated with decreased contrasts in both domains. Talkers with deep brain stimulation demonstrated more aberrant productions across all speaking rates. Conclusions Findings suggest that temporal and spectral segmental distinctiveness are asymmetrically affected by speaking rate modifications in Parkinson's disease. Talkers with deep brain stimulation warrant further investigation with regard to speech changes they make as they adjust their speaking rate.

Central auditory processing in parkinsonian disorders: A systematic review

Altered auditory processing has been increasingly recognized as a non-motor feature in parkinsonian disorders. This systematic review provides an overview of behavioral and electrophysiological literature on central auditory processing in patients with Parkinson's disease (PD), multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). A systematic database search was conducted and yielded 88 studies that met the intelligibility criteria. The collected data revealed distinct impairments in a range of central auditory processes in PD, including altered deviance detection of basic auditory features, auditory brainstem processing, auditory gating and selective auditory attention. In contrast to PD, literature on central auditory processing in atypical parkinsonian disorders was relatively scarce, but provided some evidence for impaired central auditory processing in MSA and PSP. The interpretation of these findings is discussed and suggestions for further research are offered.

Sociophonetic voice onset time variation in Mississippi English

Differences in the way voice onset time (VOT) is used across languages to maintain stop voicing contrasts have been well-documented, but less research has focused on VOT variation within voicing categories. For example, native English speakers are generally reported to produce word-initial voiced stops with short positive VOTs, but within category differences connected to self-reported gender and ethnicity have been reported in one preliminary study, with male speakers prevoicing more than female speakers and with African American speakers prevoicing more than Caucasian American speakers. For the current study, native speakers of English from Mississippi were recorded reading three repetitions of a pseudo-randomized list of words designed to investigate the connections between gender, ethnicity, and prevoicing of word-initial voiced stops. Participants self-identified their gender and ethnicity in an open-ended language background survey completed after recordings. Significant ethnicity, but not gender, differences were found, with African American speakers prevoicing voiced stops far more than their Caucasian American counterparts. Presumably, this difference is linked, not to ethnicity, but to dialect. These findings suggest that dialectal differences play a role in the VOT variation of word-initial voiced stops and that prevoicing may be a heretofore unidentified characteristic of African American English.

Distinct patterns of imprecise consonant articulation among Parkinson's disease, progressive supranuclear palsy and multiple system atrophy

Distinct speech characteristics that may aid in differentiation between Parkinson's disease (PD), progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) remain tremendously under-explored. Here, the patterns and degree of consonant articulation deficits across voiced and voiceless stop plosives in 16 PD, 16 PSP, 16 MSA and 16 healthy control speakers were evaluated using acoustic and perceptual methods. Imprecise consonant articulation was observed across all Parkinsonian groups. Voice onset time of voiceless plosives was more prolonged in both PSP and MSA compared to PD, presumably due to greater severity of dysarthria and slower articulation rate. Voice onset time of voiced plosives was significantly shorter only in MSA, likely as a consequence of damage to cerebellar structures. In agreement with the reduction of pre-voicing, MSA manifested increased number of voiced plosives misclassified as voiceless at perceptual evaluation. Timing of articulatory movements may provide important clues about the pathophysiology of underlying disease.

The effect of increased vocal intensity on interarticulator timing in speakers with Parkinson’s disease: a preliminary analysis

PURPOSE

The purpose of the current study was to investigate the effect of increased vocal intensity on interarticulator timing in individuals with Parkinson's disease (PD).

METHODS

Ten individuals with mild to moderate hypophonia, secondary to PD, were selected for study. Over an 8-week treatment period, multi-talker babble noise was presented monaurally to the individuals with PD during everyday communication contexts to elicit increased vocal intensity (Lombard effect). Outcome measures included sound pressure level (SPL), voice onset time (VOT), VOT ratio, percent voicing, and speech intelligibility.

RESULTS

Group and individual participant responses to the treatment are reported and discussed. Speakers with PD were shown to significantly increase SPL in response to treatment. Six of the 10 speakers showed improved temporal coordination between the laryngeal and supralaryngeal mechanisms (interarticulator timing) in response to treatment. Four of the 10 speakers, however, showed reduced laryngeal–supralaryngeal timing at the end of treatment. Group speech intelligibility scores were significantly higher post-treatment as compared to pre-treatment.

CONCLUSIONS

Voice treatment during everyday communication resulted in improved temporal coordination across the laryngeal and supralaryngeal mechanisms for the majority of speakers with PD and made them easier to understand. Further investigations are planned to explore individual differences in response to treatment. The identification of speaker-specific voicing and devoicing strategies is consistent with the heterogeneous nature of PD.

LEARNING OUTCOMES

Readers will be able to: 1. Describe the speech and voice characteristics of individuals with Parkinson's disease. 2. Define the Lombard effect. 3. Describe acoustic measures of voice onset time and percent voicing. 4. Describe the effect of voice treatment on voice onset time and percent voicing in individuals with Parkinson's disease.

Speech perception under adverse conditions: insights from behavioral, computational, and neuroscience research

Adult speech perception reflects the long-term regularities of the native language, but it is also flexible such that it accommodates and adapts to adverse listening conditions and short-term deviations from native-language norms. The purpose of this article is to examine how the broader neuroscience literature can inform and advance research efforts in understanding the neural basis of flexibility and adaptive plasticity in speech perception. Specifically, we highlight the potential role of learning algorithms that rely on prediction error signals and discuss specific neural structures that are likely to contribute to such learning. To this end, we review behavioral studies, computational accounts, and neuroimaging findings related to adaptive plasticity in speech perception. Already, a few studies have alluded to a potential role of these mechanisms in adaptive plasticity in speech perception. Furthermore, we consider research topics in neuroscience that offer insight into how perception can be adaptively tuned to short-term deviations while balancing the need to maintain stability in the perception of learned long-term regularities. Consideration of the application and limitations of these algorithms in characterizing flexible speech perception under adverse conditions promises to inform theoretical models of speech.

Localization of sublexical speech perception components

Models of speech perception are in general agreement with respect to the major cortical regions involved, but lack precision with regard to localization and lateralization of processing units. To refine these models we conducted two Activation Likelihood Estimation (ALE) meta-analyses of the neuroimaging literature on sublexical speech perception. Based on foci reported in 23 fMRI experiments, we identified significant activation likelihoods in left and right superior temporal cortex and the left posterior middle frontal gyrus. Sub-analyses examining phonetic and phonological processes revealed only left mid-posterior superior temporal sulcus activation likelihood. A lateralization analysis demonstrated temporal lobe left lateralization in terms of magnitude, extent, and consistency of activity. Experiments requiring explicit attention to phonology drove this lateralization. An ALE analysis of eight fMRI studies on categorical phoneme perception revealed significant activation likelihood in the left supramarginal gyrus and angular gyrus. These results are consistent with a speech processing network in which the bilateral superior temporal cortices perform acoustic analysis of speech and non-speech auditory stimuli, the left mid-posterior superior temporal sulcus performs phonetic and phonological analysis, and the left inferior parietal lobule is involved in detection of differences between phoneme categories. These results modify current speech perception models in three ways: (1) specifying the most likely locations of dorsal stream processing units, (2) clarifying that phonetic and phonological superior temporal sulcus processing is left lateralized and localized to the mid-posterior portion, and (3) suggesting that both the supramarginal gyrus and angular gyrus may be involved in phoneme discrimination.

Voice onset time in Parkinson disease

Research has found that speaking rate has an effect on voice onset time (VOT). Given that Parkinson disease (PD) affects speaking rate, the purpose of this study was to examine VOT with the effect of rate removed (VOT ratio), along with the traditional VOT measure, in individuals with PD. VOT and VOT ratio were examined in 9 individuals with PD (before and after taking medication), along with 9 matched controls. Place of articulation and vowel height had significant effects on VOT and VOT ratio for all groups, and there were no PD versus control differences. PD medication had a greater effect on VOT than VOT ratio, reflecting a rate-related VOT change rather than a pure VOT change. These data support the usefulness of examining both VOT and VOT ratio with individuals with PD, as this allows for dissociation between rate-related VOT changes and true VOT changes.

LEARNING OUTCOMES

The reader will be able to understand and describe: (1) voice onset time (VOT) and VOT ratio; (2) how VOT and VOT ratio are affected in individuals with Parkinson disease; and (3) the effect of medication on VOT and VOT ratio.

Cerebellar damage produces selective deficits in verbal working memory

The cerebellum is often active in imaging studies of verbal working memory, consistent with a putative role in articulatory rehearsal. While patients with cerebellar damage occasionally exhibit a mild impairment on standard neuropsychological tests of working memory, these tests are not diagnostic for exploring these processes in detail. The current study was designed to determine whether damage to the cerebellum is associated with impairments on a range of verbal working memory tasks, and if so, under what circumstances. Moreover, we assessed the hypothesis that these impairments are related to impaired rehearsal mechanisms. Patients with damage to the cerebellum (n = 15) exhibited a selective deficit in verbal working memory: spatial forward and backward spans were normal, but forward and backward verbal spans were lower than controls. While the differences were significant, digit spans were relatively preserved, especially in comparison to the dramatic reductions typically observed in classic 'short-term memory' patients with perisylvian brain damage. The patients tended to be more impaired on a verbal version compared to a spatial version of a working memory task with a long delay and this impairment was correlated with overall symptom and dysarthria severity. These results are consistent with a contribution of the cerebellum to rehearsal and suggest that inclusion of a delay before recall is especially detrimental in individuals with cerebellar damage. However, when we examined markers of rehearsal (i.e. word-length and articulatory suppression effects) in an immediate serial recall task, we found that qualitative aspects of the patients' rehearsal strategies were unaffected. We propose that the cerebellum may contribute to verbal working memory during the initial phonological encoding and/or by strengthening memory traces rather than by fundamentally subserving covert articulatory rehearsal.