A Developmental Perspective on Processing Semantic Context: Preliminary Evidence from Sentential Auditory Word Repetition in School-Aged Children.

The current investigation examined the developmental changes involved in processing semantic context in auditorily presented sentences, as well as underlying attentional and suppression mechanisms. Thirty-nine typically developing school-aged children aged 6;0-14;0 years participated in the current cross-sectional sentential auditory word repetition study. Component processes involved in auditory word recognition were examined and their respective developmental trajectories systematically delineated. Experimental manipulations included semantic congruity (congruous, incongruous), sentence constraint (high, low), cloze probability (high, low), and processing mode. High sentence constraints elicited top-down pre-potency type effects, which resulted in active suppression of anticipated cloze words and longer naming latencies of perceived cloze words when violated with conflicting bottom-up information. In addition, developmental changes in component processes reflected underlying changes in attention, with evidence that suppression mechanisms remained relatively constant with age. Findings are interpreted in line with the Trace (McClelland and Elman in Cogn Psychol 18(1):1-86, 1986) model of auditory word recognition.

Deep brain stimulation for Parkinson disease in Australia: current scientific and clinical status.

There is currently no cure for Parkinson disease (PD). Disease management is directed primarily at motor symptom relief, but the impact of non-motor symptoms associated with PD should not be underestimated. Medical and surgical treatment options aim to increase functional independence and quality of life. Deep brain stimulation (DBS) has proven to be a safe, effective and cost-efficient surgical treatment option. In 2009, the Australian referral guidelines, developed to provide a synopsis of DBS therapy for PD, were introduced, and since then novel findings have been reported regarding the timing of intervention, target selection and symptom management. Our aim is to provide an update of DBS for PD in Australia. Intervention at earlier stages of the disease can potentially improve quality of life over a longer period with greater possibilities for meaningful social and professional contributions. For less responsive motor symptoms (e.g. freezing of gait, postural instability), the pedunculopontine nucleus has emerged as a promising new surgical target. Traditional PD treatment is focused on improvement of motor symptoms, but the disorder is also characterised by non-motor symptoms, often undiagnosed or undisclosed, that have the potential to impact quality of life to a greater extent than motor symptoms. It is essential to identify and routinely monitor for non-motor symptoms as they can emerge at all stages of the disease or can result from treatment. Many of these current advances require long-term monitoring of treatment outcomes to improve future clinical practice, refine patient selection and ensure best patient outcomes.

Effects of subthalamic deep brain stimulation on noun/verb generation and selection from competing alternatives in Parkinson's disease.

BACKGROUND AND AIMS: Impaired generation of verbs relative to nouns has been reported in Parkinson's disease (PD) and has been associated with the frontal pathophysiology of PD. The aim of the present study was to measure noun/verb generation abilities in PD and to determine whether noun/verb generation is affected by stimulation of the subthalamic nucleus (STN). PATIENTS AND METHODS: 8 participants who had been diagnosed with PD and had received surgery for deep brain stimulation (DBS) of the STN as well as 15 control participants completed a noun/verb generation task with four probe-response conditions-namely, noun-noun, verb-noun, noun-verb and verb-verb conditions. Patients with PD were assessed while receiving STN stimulation and without stimulation. RESULTS: During the off stimulation condition, patients with PD presented with a selective deficit in verb generation compared with control participants. However, when receiving STN stimulation, patients with PD produced significantly more errors than controls during the noun-noun and verb-verb conditions, supporting evidence from previous studies that STN stimulation modulates a frontotemporal network associated with word generation. Finally, errors during verb generation were significantly correlated with item selection constraint (ie, the degree to which a response competes with other response alternatives) in the on stimulation condition, but not the off stimulation condition. CONCLUSION: Our results suggest that STN stimulation affects the ability to select from many competing lexical alternatives during verb generation.

Semantic priming in Alzheimer's dementia: evidence for dissociation of automatic and attentional processes.

The nature of the semantic memory deficit in dementia of the Alzheimer's type (DAT) was investigated in a semantic priming task which was designed to assess both automatic and attention-induced priming effects. Ten DAT patients and 10 age-matched control subjects completed a word naming semantic priming task in which both relatedness proportion (RP) and stimulus-onset asynchrony (SOA) were varied. A clear dissociation between automatic and attentional priming effects in both groups was demonstrated; however, the DAT subjects' pattern of priming deviated significantly from that of the normal controls. The DAT patients failed to produce any priming under conditions which encouraged automatic semantic processing and produced facilitation only when the RP was high. In addition, the DAT group produced hyperpriming, with significantly larger facilitation effects than the control group. These results suggest an impairment of automatic spreading activation in DAT and have implications for theories of semantic memory impairment in DAT as well as models of normal priming.

Semantic priming in Parkinson's disease: evidence for delayed spreading activation.

Nineteen persons with Parkinson's disease (PD) and 19 matched control participants completed a battery of online lexical decision tasks designed to isolate the automatic and attentional aspects of semantic activation within the semantic priming paradigm. Results highlighted key processing abnormalities in PD. Specifically, persons with PD exhibited a delayed time course of semantic activation. In addition, results suggest that experimental participants were unable to implicitly process prime information and, therefore, failed to engage strategic processing mechanisms in response to manipulations of the relatedness proportion. Results are discussed in terms of the 'Gain/Decay' hypothesis (Milberg, McGlinchey-Berroth, Duncan, & Higgins, 1999) and the dopaminergic modulation of signal to noise ratios in semantic networks.

Discourse priming of homophones in individuals with dominant nonthalamic subcortical lesions, cortical lesions and Parkinson's disease.

An on-line priming experiment was used to investigate discourse-level processing in four matched groups of subjects: individuals with nonthalamic subcortical lesions (NSL) (n = 10), normal control subjects (n = 10), subjects with Parkinson's disease (PD) (n = 10), and subjects with cortical lesions (n = 10). Subjects listened to paragraphs that ended in lexical ambiguities, and then made speeded lexical decisions on visual letter strings that were: nonwords, matched control words, contextually appropriate associates of the lexical ambiguity, contextually inappropriate associates of the ambiguity, and inferences (representing information which could be drawn from the paragraphs but was not explicitly stated). Targets were presented at an interstimulus interval (ISI) of 0 or 1000 ms. NSL and PD subjects demonstrated priming for appropriate and inappropriate associates at the short ISI, similar to control subjects and cortical lesion subjects, but were unable to demonstrate selective priming of the appropriate associate and inference words at the long ISI. These results imply intact automatic lexical processing and a breakdown in discourse-based meaning selection and inference development via attentional/strategic mechanisms.

Processing lexical ambiguities in word triplets: evidence of lexical-semantic deficits following dominant nonthalamic subcortical lesions.

Lexical-semantic function was investigated in 10 participants with lesions of the dominant nonthalamic subcortical (NS) region and a matched normal control group. Participants performed speeded lexical decisions on the 3rd member of auditorily presented word triplets. The 4 critical triplet conditions were concordant (coin-bank-money), discordant (river-bank-money), neutral (day-bank-money), and unrelated (river-day-money). When the interstimulus interval (ISI) between the words in the triplets was 100 ms, patients with NS lesions obtained priming that indicated nonselective lexical access; at 1,250-ms ISI, however, there was no significant priming effect. This pattern of results is consistent with the view that patients with NS lesions can automatically access lexical-semantic information but may be unable to sustain lexical activation through controlled or attentional forms of processing.

Understanding ambiguous words in biased sentences: evidence of transient contextual effects in individuals with nonthalamic subcortical lesions and Parkinson's disease.

A cross-modal priming experiment was used to investigate lexical ambiguity resolution during sentence processing in individuals with nonthalamic subcortical lesions (NSL) (n = 10), compared to matched normal controls (n = 10), and individuals with cortical lesions (CL) (n = 10) and Parkinson's disease (PD) (n = 10). Critical sentences biased towards the dominant or subordinate meaning of a sentence-final lexical ambiguity were presented auditorily, followed after a short interstimulus-interval (ISI) (0 msec) or a long ISI (1000 msec), by the presentation of a visual target which was related to the dominant or subordinate meaning, or was an unrelated control word. Subjects made speeded lexical decisions on the targets. At the short ISI, lexical activation for the neurological patient groups appeared influenced by contextual information to a greater extent than in normal controls, which may indicate delayed lexical decision making or disturbed automatic lexical activation. At the long ISI, only the PD and NSL individuals failed to selectively activate the contextually appropriate meaning, suggesting a breakdown in the attention-based control of semantic activation through contextual integration. This finding may implicate disruptions to proposed frontal-striatal mechanisms which mediate attentional allocation and strategy formation.

Lexical decision in Parkinson's disease: A comment on Spicer, Brown, and Gorell (1994), and McDonald, Brown, and Gorell (1996)

Recent semantic priming investigations conducted by Spicer, Brown and Gorell (1994) and McDonald, Brown and Gorell (1996) reported hyperpriming in persons with Parkinson's disease (PD) and provided evidence supporting impaired set-shifting as the underlying cause. This paper discusses notable priming behaviours exhibited by the normal control groups employed by Spicer and McDonald and colleagues. The argument is developed that these studies only measured attention-dependent semantic processing and, therefore, their results do not speak to issues of automatic semantic activation in PD as originally proposed by Spicer et al. nor to putative deficits in set-shifting as proposed by McDonald et al. The implications for future priming research in PD are also discussed.

Cognitive-linguistic subgroups in closed-head injury.

This study examined variability in the interrelationship between language skill and neuropsychological function within a group of 25 severe closed head injury (CHI) subjects and 23 matched controls. All subjects underwent a battery of standardized language and neuropsychological tests. Cluster analyses were conducted to determine whether the CHI sample was universally or differentially impaired. Further subgroup analysis using a Q-type factor analysis outlined the differences in performance profiles within the group of CHI subjects. Results support the hypothesis that while some deficits were common to all CHI subjects, impairments delineated by whole group analysis do not necessarily represent universal impairments. In particular, ability to perform tasks involving auditory comprehension, naming, verbal memory, visual memory and visuospatial skills appeared to be important components in group differentiation. The cognitive-linguistic impairments which were common to all CHI subjects and considered to be the 'cardinal' cognitive-linguistic deficits following severe CHI were deficits in lexical-semantic and sentential semantic skills, verbal fluency, complex auditory comprehension, and attentional operations. Profile analysis revealed the existence of a double dissociation between performances on naming and verbal memory tasks and performances on visually related cognitive tasks. Results are discussed with reference to findings on previous studies of subgroups in the CHI population.

Towards a conceptualization of language and cognitive impairment in closed-head injury: use of clinical measures.

Language deficits following closed-head injury (CHI) are widely considered as impairments secondary to the cognitive disruptions common to closed-head injury. In addition, the use of standardized measures to assess the functioning of the language system in closed-head injury has mostly been limited to aphasia test batteries which examine primary language functions only. This has resulted in generalizations as to the integrity of the language system following closed-head injury, and as a consequence, consideration of the contribution of the language system to the achievement of communicative competence in this population has been minimized. This paper presents a framework in which the functional language system is identified as a hierarchical system containing primary and higher-order language processes involved in reciprocal relationships with cognitive functions at each level. A group of 25 closed-head injury subjects and 23 demographically matched control subjects were examined for linguistic proficiency using a battery of standardized tests which investigated the language system across a hierarchy of complexity, structure and predictability. In addition, 23 of the closed-head subjects were administered a comprehensive neuropsychological test battery in order to determine the nature and extent of concomitant impairments in cognitive processes and their relationship with impairments in the language system. The language battery was found to consistently discriminate between the control and clinical groups indicating that the linguistic system is significantly impaired following CHI, with the lexical-semantic system being the most vulnerable to disruption. A strong influential relationship between language and cognitive processes was statistically confirmed and the nature of the relationship between aspects of language and cognition further delineated.

The resolution of lexical ambiguity with reference to context in dementia of the Alzheimer's type.

The present study investigated how a dementing illness such as Alzheimer's disease, might affect an individual's recourse to higher order contextual information in the access and integration of lexical material in on-line discourse comprehension. More specifically, the experiment investigated the priming of homophones in a discourse context, by use of a cross-modal lexical decision task, and compared the performances of a group of six subjects with mild to moderate dementia of the Alzheimer's type (DAT) with those of a matched control group. The subjects listened to 2-sentence paragraphs and performed a lexical decision on visually presented targets that followed ambiguous prime words (or homophones) at two inter-stimulus intervals (ISIs): 330 and 1000 msec. When the target was a word, it was either an associate of the prime word, a probable inference suggested by the discourse, or an unrelated word. The control subjects primed both the discourse-appropriate and discourse-inappropriate associate of the homophone at short (330 msec) ISIs (but not an appropriate inference word), a finding which supports the exhaustive access model of ambiguity resolution. As the ISI was lengthened to 1000 msec, however, the discourse-appropriate inference word was primed, and reflects the operation of attention-dependent integrative strategies. The subjects with DAT primed both appropriate associates and inference words at the short ISI. At ISI of 1000 msec, the DAT subjects primed the appropriate associate and showed substantial inhibition priming of the inappropriate associate. These results point to disturbances in the selective automatic activation of lexical material, and in the conscious integration and elaboration of lexical material in ongoing discourse comprehension in persons with DAT.

The effect of repeated prime-target presentation in manipulating attention-induced priming in persons with dementia of the Alzheimer's type.

The present experiment manipulated attention-induced semantic priming in seven persons with dementia of the Alzheimer's type (DAT) and 16 healthy aged controls in a word-nonword lexical decision task by means of repeated prime-target presentations. The experimental paradigm allowed for the simultaneous comparison of automatic processing and attention-induced strategic processing. The results showed that both the healthy aged subjects and the subjects with DAT demonstrated semantic facilitation in the automatic processing of information. The two groups differed, however, on the attention-induced component of the task. The control subjects consciously generated a strategic response bias favoring the real word targets and thus used their processing of the prime to induce an expectancy about the following target. The DAT subjects showed no such attention-dependent expectancy, a deficit which is most probably related to the general cognitive impairments which are a hallmark of the disease.

Perceptual speech characteristics of dysarthric speakers following severe closed head injury.

The perceptual speech characteristics of a group of 20 severely closed head-injured (CHI) subjects were compared with those of a normal non-neurologically impaired control group matched for age and sex. The CHI subjects were found to be significantly less intelligible than the controls, and exhibited deficits in the prosodic, resonatory, articulatory, respiratory and phonatory aspects of speech production. The most frequently occurring deviant speech dimensions related to disturbances of prosody, resonance, articulation and respiration, with those deviant speech dimensions pertaining to phonation being less apparent in the speech of the CHI subjects. The findings are discussed in relation to the heterogeneity of the CHI population and the effects of CHI on neuromuscular function. The study highlights the need for accurate, instrumental physiological evaluation of the motor subsystems involved in speech production.

Abnormal patterns of speech breathing in dysarthric speakers following severe closed head injury.

The respiratory abilities of a group of 20 subjects with a speech disorder resulting from severe closed head injury (CHI) were assessed using both spirometric and kinematic techniques and compared with those of a group of 20 non-neurologically impaired controls matched for age and gender. Results of the spirometric assessment showed that the CHI subjects as a group had lower vital capacities and lower forced expiratory volumes 1 second than the controls. Kinematic assessment also showed that the CHI subjects had problems co-ordinating the action of the rib-cage and abdomen when carrying out speech tasks such as vowel prolongations, syllable repetitions and reading. Results are discussed in terms of the effects of CHI on neuromuscular function.

Hypernasality in dysarthric speakers following severe closed head injury: a perceptual and instrumental analysis.

Hypernasality in the dysarthric speech of 20 severely closed-head-injured (CHI) subjects was investigated using both perceptual and instrumental techniques. A perceptual analysis of the speech of the CHI subjects was performed using a four-point rating scale for hypernasality. Instrumental assessment was carried out using a computerized accelerometric technique yielding a nasal coupling index. Results revealed a high incidence of perceived hypernasality (95%) in the speech of subjects in the CHI group. More than half of these subjects exhibited hypernasality of speech to a moderate to severe degree. When compared with a control group matched for age and sex the severely CHI subjects were perceived as being significantly more hypernasal. Instrumental assessment revealed that the functioning of the velopharyngeal valve in the group of CHI subjects was significantly impaired compared to the control group. The study highlighted the need to evaluate the perceptual and instrumental assessment results for the severely CHI subjects on an individual basis. The clinical implications of these findings are discussed.

Respiratory kinematics in speakers with cerebellar disease.

The respiratory abilities of a group of 12 speech disordered subjects with cerebellar disease were assessed using both spirometric and kinematic techniques and compared to those of a group of 12 non-neurologically impaired controls matched for age and gender. Results of the spirometric assessment showed that although all of the cerebellar-diseased subjects had normal total lung capacities, almost half had vital capacities below normal limits. All except 1 of the cerebellar-diseased subjects exhibited irregularities in their chest wall movements while performing sustained vowel and syllable repetition tasks. Over half of the cerebellar-diseased subjects also displayed similar irregularities when reading and conversing. The same irregularities were not present in the chest wall movements exhibited by the control subjects suggesting that their presence was caused by the cerebellar disease. Results are discussed in terms of the effects of cerebellar disease on neuromuscular function.

Automatic and volitional semantic processing in aphasia.

The present study investigated the status of semantic information in aphasia by comparing the performances of aphasic and nonaphasic subjects on two tasks: an automatic semantic facilitation task and a volitional task of relatedness judgment. Both the aphasic and nonaphasic groups evidenced a semantic facilitation effect, in an on-line task of semantic processing. However, those aphasics with severe comprehension and naming disturbances (termed low comprehension aphasics) demonstrated considerable difficulty in judging the relatedness between a pictured object and members of that object's semantic field, the severity of the impairment being greater for those pictures that the low comprehension aphasics were unable to name. The pattern of results can best be explained by supposing the structural integrity of the store of semantic information in aphasia, and in particular in low comprehension aphasia: information that is retrieved and manipulated in judgment-mediated tasks with considerable difficulty.

Respiratory function in Parkinson's subjects exhibiting a perceptible speech deficit: a kinematic and spirometric analysis.

The respiratory abilities of a group of 19 speech-disordered subjects with idiopathic Parkinson's disease were assessed using both spirometric and kinematic techniques and compared to those of a group of 19 nonneurologically impaired controls matched for age and sex. Results of the spirometric assessment showed that only a minority of the Parkinson's subjects had lung volumes and capacities outside normal limits. Consequently in the majority of cases, the speech disorder could not be related to any abnormality in lung function determined spirometrically. Chest wall dynamics during both conversation and reading were essentially normal in all cases. Approximately half of the Parkinson's subjects, however, exhibited irregularities in their chest wall movements while performing vowel prolongation and syllable repetition tasks. The same irregularities were not present in the chest wall movements exhibited by the control subjects, suggesting that their presence was in some way related to the Parkinson's disease. Results are discussed in terms of the effects of Parkinson's disease on neuromuscular function.