Evidence for causal top-down frontal contributions to predictive processes in speech perception.

Perception relies on the integration of sensory information and prior expectations. Here we show that selective neurodegeneration of human frontal speech regions results in delayed reconciliation of predictions in temporal cortex. These temporal regions were not atrophic, displayed normal evoked magnetic and electrical power, and preserved neural sensitivity to manipulations of sensory detail. Frontal neurodegeneration does not prevent the perceptual effects of contextual information; instead, prior expectations are applied inflexibly. The precision of predictions correlates with beta power, in line with theoretical models of the neural instantiation of predictive coding. Fronto-temporal interactions are enhanced while participants reconcile prior predictions with degraded sensory signals. Excessively precise predictions can explain several challenging phenomena in frontal aphasias, including agrammatism and subjective difficulties with speech perception. This work demonstrates that higher-level frontal mechanisms for cognitive and behavioural flexibility make a causal functional contribution to the hierarchical generative models underlying speech perception.

Artificial grammar learning in vascular and progressive non-fluent aphasias.

Patients with non-fluent aphasias display impairments of expressive and receptive grammar. This has been attributed to deficits in processing configurational and hierarchical sequencing relationships. This hypothesis had not been formally tested. It was also controversial whether impairments are specific to language, or reflect domain general deficits in processing structured auditory sequences. Here we used an artificial grammar learning paradigm to compare the abilities of controls to participants with agrammatic aphasia of two different aetiologies: stroke and frontotemporal dementia. Ten patients with non-fluent variant primary progressive aphasia (nfvPPA), 12 with non-fluent aphasia due to stroke, and 11 controls implicitly learned a novel mixed-complexity artificial grammar designed to assess processing of increasingly complex sequencing relationships. We compared response profiles for otherwise identical sequences of speech tokens (nonsense words) and tone sweeps. In all three groups the ability to detect grammatical violations varied with sequence complexity, with performance improving over time and being better for adjacent than non-adjacent relationships. Patients performed less well than controls overall, and this was related more strongly to aphasia severity than to aetiology. All groups improved with practice and performed well at a control task of detecting oddball nonwords. Crucially, group differences did not interact with sequence complexity, demonstrating that aphasic patients were not disproportionately impaired on complex structures. Hierarchical cluster analysis revealed that response patterns were very similar across all three groups, but very different between the nonsense word and tone tasks, despite identical artificial grammar structures. Overall, we demonstrate that agrammatic aphasics of two different aetiologies are not disproportionately impaired on complex sequencing relationships, and that the learning of phonological and non-linguistic sequences occurs independently. The similarity of profiles of discriminatory abilities and rule learning across groups suggests that insights from previous studies of implicit sequence learning in vascular aphasia are likely to prove applicable in nfvPPA.

Thyrotoxic periodic paralysis: correct hypokalemia with caution.

BACKGROUND: Thyrotoxic periodic paralysis is rare in Caucasian populations, but affects approximately 2% of East Asians with thyrotoxicosis (13% of males, 0.17% of females). The presentation is characterized by abrupt-onset hypokalemia and profound proximal muscular weakness, and commonly occurs after carbohydrate loading or exercise. OBJECTIVES: To raise awareness of this condition through the description of a typical case of thyrotoxic periodic paralysis; to remind readers that, despite intravascular hypokalemia, total body potassium is normal and that correction must be done with caution; to highlight the differences in treatment compared to familial hypokalemic periodic paralysis. CASE REPORT: We describe the presentation of a 36-year-old Filipino man with a background history of Graves disease. Over-administration of intravenous potassium was narrowly averted in this case. CONCLUSION: It may be important to check thyroid function in patients presenting with acute paralysis, especially those of Asian origin. In patients with thyrotoxic periodic paralysis, administration of potassium, with cardiac monitoring and a total dose of <50 mmol, limits the dysrhythmia risk. Patients are likely to benefit from the prescription of non-selective beta-blockers until they become euthyroid. In contrast to familial periodic paralysis, regular oral potassium supplementation is ineffective in thyrotoxic periodic paralysis, and acetazolamide precipitates, rather than prevents, attacks.

Auditory temporal-envelope processing in high-functioning children with Autism Spectrum Disorder.

Individuals with Autism Spectrum Disorder (ASD) perform worse than controls when listening to speech in a temporally modulated noise (Alcántara, Weisblatt, Moore, & Bolton, 2004; Groen et al., 2009). The current study examined whether this is due to poor auditory temporal-envelope processing. Temporal modulation transfer functions were measured in 6 high-functioning children with ASD and 6 control listeners, using sinusoidal amplitude modulation of a broadband noise. Modulation-depth thresholds at low modulation rates were significantly higher for the ASD group than for the Control group, and generally higher at all modulation rates tested. Low-pass filter model estimates of temporal-envelope resolution and temporal-processing efficiency showed significant differences between the groups for modulation-depth threshold values at low modulation rates. Intensity increment-detection thresholds, measured on a subset of individuals in the ASD and Control groups, were not significantly different. The results are consistent with ASD individuals having reduced processing efficiency of temporal modulations. Possible neural mechanisms that might underlie these findings are discussed.

Tinnitus loudness in quiet and noise after resection of vestibular schwannoma.

OBJECTIVES: (1) To use a loudness model to assess the influence of loudness recruitment on estimates of the loudness of tinnitus obtained by loudness matching; (2) To compare the effect of background noise on the loudness of tinnitus for individuals who are unilaterally deaf after resection of vestibular schwannoma (VS) and those with idiopathic tinnitus. BACKGROUND: After translabyrinthine resection of VS, patients experience unilateral deafness and tinnitus in the operated ear. Most complain that their tinnitus is more bothersome in noisy environments, unlike those with idiopathic tinnitus. PARTICIPANTS: Unilaterally deaf individuals experiencing tinnitus as a consequence of VS surgery and a comparison group with idiopathic tinnitus. METHODS: Participants adjusted the level of a probe tone at the frequency where their hearing was best to match the loudness of their tinnitus in quiet; for VS participants, matches were made using a probe in the unaffected ear. Matches were then obtained in the presence of threshold-equalizing noise. RESULTS: For those with idiopathic tinnitus, the probe loudness level, calculated using a loudness model, was almost invariant with hearing loss at the probe frequency and was usually between 20 and 50 phons. For the VS group, the probe loudness level ranged from 6 to 51 phons. With increasing threshold-equalizing-noise level, the loudness match decreased slightly for the comparison group but increased significantly for the VS group. CONCLUSION: The tinnitus in quiet had a moderate loudness for both groups. Background noise slightly decreased tinnitus loudness for most participants with idiopathic tinnitus but increased tinnitus loudness for VS participants. We propose 2 possible mechanisms for the effect of noise in the VS group.

Clinical hypnosis for the alleviation of tinnitus.

The neurophysiology of tinnitus is poorly understood, and it can have an origin at a number of neural levels, making a psychological approach to treatment attractive. Clinical hypnosis has been demonstrated to be effective in a number of clinical situations, such as irritable bowel syndrome but, in other areas for which it is commonly employed, such as smoking cessation, the evidence is poor. Its use for the management of troublesome tinnitus has been discussed in the literature for more than 30 years, but little formal research has been conducted into efficacy of this treatment or the relative suitability of techniques. Despite this, a success rate of 70% is commonly quoted by hypnosis practitioners in promotional material. This review summarizes the few peer-reviewed studies on this subject and concludes that, though evidence suggests that hypnosis provides a benefit in some subjects, how this benefit compares to more mainstream approaches is not yet clear. This area is currently under-researched, and engagement is encouraged between researchers in audiology and hypnotherapists to undertake large, well-structured controlled trials with standardized measures of outcome.

Effects of level and frequency on the audibility of partials in inharmonic complex tones.

The effect of level and frequency on the audibility of partials was measured for complex tones with partials uniformly spaced on an equivalent rectangular bandwidth (ERB(N)) number scale. On each trial, subjects heard a sinusoidal "probe" followed by a complex tone. The probe was mistuned downwards or upwards (at random) by 4.5% from the frequency of one randomly selected partial in the complex. The subject indicated whether the probe was higher or lower in frequency than the nearest partial in the complex. The frequencies were roved from trial to trial, keeping frequency ratios fixed. In experiment 1, the level per partial, L, was 40 or 70 dB SPL and the mean frequency of the central partial, f(c), was 1201 Hz. Scores for the highest and lowest partials in the complexes were generally high for all spacings. Scores for the inner partials were close to chance at 0.75-ERB(N) spacing, and improved as the spacing was increased up to 2 ERB(N). For intermediate spacings, performance was better for the lower level used. In experiment 2, L was 70 dB SPL and f(c) was 3544 Hz. Performance worsened markedly for partial frequencies above 3544 Hz, consistent with a role of phase locking.