Posted by Callier Library on February 25, 2008
from JARO — Journal of the Association for Research in Otolaryngology
Abstract Most contemporary cochlear implants (CIs) stimulate the auditory nerve with trains of amplitude-modulated, symmetric biphasic pulses. Although both polarities of a pulse can depolarize the nerve fibers and generate action potentials, it remains unknown which of the two (positive or negative) phases has the stronger effect. Understanding the effects of pulse polarity will help to optimize the stimulation protocols and to deliver the most relevant information to the implant listeners. Animal experiments have shown that cathodic (negative) current flows are more effective than anodic (positive) ones in eliciting neural responses, and this finding has motivated the development of novel speech-processing algorithms. In this study, we show electrophysiologically and psychophysically that the human auditory system exhibits the opposite pattern, being more sensitive to anodic stimulation. We measured electrically evoked compound action potentials in CI listeners for phase-separated pulses, allowing us to tease out the responses to each of the two opposite-polarity phases. At an equal stimulus level, the anodic phase yielded the larger response. Furthermore, a measure of psychophysical masking patterns revealed that this polarity difference was still present at higher levels of the auditory system and was therefore not solely due to antidromic propagation of the neural response. This finding may relate to a particular orientation of the nerve fibers relative to the electrode or to a substantial degeneration and demyelination of the peripheral processes. Potential applications to improve CI speech-processing strategies are discussed.
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Posted by Callier Library on February 25, 2008
from Clinical Otolaryngology
Objective of review: To determine evidence for a relationship between vascular loops in contact with the vestibulocochlear nerve (CN VIII) and otological symptoms.
Type of review: Systematic review and meta-analysis of observational studies.
Search strategy: Comprehensive search of MEDLINE, EMBASE, CINAHL, Cochrane Library, Clinical Evidence and Cochrane Central Register of Trials. Reference lists cross-referenced and authors contacted for missing data. No language restrictions.
Evaluation methods: Included studies: (1) compared symptoms in subjects with a vascular loop contacting CN VIII to subjects without (inter-subject control); (2) compared the prevalence of vascular loop in contact with CN VIII in symptomatic ears to contra-lateral asymptomatic ears (intra-subject control). Study quality systematically appraised.
Results: Five case–control studies included. A statistically significant association was demonstrated for the prevalence of vascular loops in contact with CN VIII, with unilateral sensorineural hearing loss: pooled odds ratio (OR) 2.0 [95% confidence interval (CI): 1.5–2.6]. No association was demonstrated for non-pulsatile tinnitus. A highly significant association with vascular loops was shown in subjects having pulsatile tinnitus, with pooled OR: 78.8 (95% CI: 10.9–821.8).
Conclusions: Vascular loops in contact with CN VIII are a normal variant. Subjects with unilateral hearing loss were twice as likely to have these vascular loops in the symptomatic ear, than in the asymptomatic ear. Subjects with pulsatile tinnitus were 80 times more likely to have a contacting vascular loop than patients with non-pulsatile tinnitus, suggesting in some cases a causal relationship exists for pulsatile tinnitus, where surgical intervention may be occasionally indicated.
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Posted by Callier Library on February 25, 2008
from Brain Injury
Primary objective: This study used an object definitions test to examine semantic memory and the organization of semantic knowledge during the early stage of recovery from traumatic brain injury (TBI).
Research design: Twenty-four participants with moderate-to-severe TBI and 24 controls described three living and three non-living objects as if they were describing them to someone who had never heard of or seen such things before.
Methods and procedures: The verbal definitions were examined at a feature level and for whether they communicated the core concept (i.e. could a blind rater identify the object).
Main outcomes and results: Compared to the control group, the TBI group less often provided object definitions that communicated the core concept and included superordinate category information. The TBI group also produced a smaller proportion of physical specific features and the production of fewer physical specific features was associated with lower production of the core concept. Despite these group differences, both groups produced more specific feature information about the objects than general feature information; and more physical specific features for living objects and associative specific features for non-living objects.
Conclusions: The findings were interpreted as suggesting a decreased efficiency in ability to access semantic information following moderate-to-severe TBI, which influenced core concept production, despite intact organization of semantic knowledge.
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Posted by Callier Library on February 25, 2008
from the Journal of Neuroscience
The relationship between a sound and its neural representation in the auditory cortex remains elusive. Simple measures such as the frequency response area or frequency tuning curve provide little insight into the function of the auditory cortex in complex sound environments. Spectrotemporal receptive field (STRF) models, despite their descriptive potential, perform poorly when used to predict auditory cortical responses, showing that nonlinear features of cortical response functions, which are not captured by STRFs, are functionally important. We introduce a new approach to the description of auditory cortical responses, using multilinear modeling methods. These descriptions simultaneously account for several nonlinearities in the stimulus–response functions of auditory cortical neurons, including adaptation, spectral interactions, and nonlinear sensitivity to sound level. The models reveal multiple inseparabilities in cortical processing of time lag, frequency, and sound level, and suggest functional mechanisms by which auditory cortical neurons are sensitive to stimulus context. By explicitly modeling these contextual influences, the models are able to predict auditory cortical responses more accurately than are STRF models. In addition, they can explain some forms of stimulus dependence in STRFs that were previously poorly understood.
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Posted by Callier Library on February 25, 2008
from Medical News Today.com
Antibiotics are not linked to a significant decrease in fluid buildup in the ear when administered to children with middle ear infections. This is the conclusion of a meta-analysis of previous studies released on February 18, 2008 in the Archives of Otolaryngology – Head & Neck Surgery, one of the JAMA/Archives journals.
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Posted by Callier Library on February 25, 2008
from Research in Developmental Disabilities
The purpose of this review was to identify effective methods for teaching writing to students with intellectual disabilities. After criteria were established, database searches and hand searches of selected peer-reviewed journals were conducted. Findings revealed a relatively small number of studies that met the criteria for inclusion. Participants, settings, research designs, independent variables, dependent variables, and results are synthesized across studies. Writing instruction effects on various written expression outcomes were aggregated by averaging percentage of non-overlapping data (PND) across studies. Findings revealed that strategy instruction was investigated more frequently than other types of approaches. Strategy instruction was consistently found to be very effective for teaching writing skills to students with intellectual disabilities. Limitations, directions for future research, and implications for practice are discussed.
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Posted by Callier Library on February 25, 2008
from Vision Research
Traditionally, explanations of spatial cueing effects posit the operation of orienting mechanisms that act to reposition the spatial locus of attention. This process is often viewed to be analogous to the movement of an attentional ‘spotlight’ across the visual field to the cued region and is thought to occur either in an exogenous or endogenous manner, depending on the nature of the cue. In line with this view, anomalous findings in dyslexic groups using paradigms involving brief peripheral cues have been interpreted as evidence for a particular deficiency with stimulus-driven, exogenous orienting. Here, we demonstrate that an exogenous orienting deficit is an unfeasible explanation of recent findings in which dyslexic individuals fail to derive benefit from peripheral cues indicating the location of a target in a single fixation visual search task. In a series of experiments examining cueing effects in normal readers, we find no evidence to support the operation of an attentional orienting mechanism that is (i) fast but transient; (ii) automatic and involuntary; and (iii) preferentially driven by abrupt luminance transients. Rather, we find that the magnitude of obtained benefits is primarily determined by the informational value of the cue (irrespective of how information is conveyed) and the accessibility of the target representation once the cue had been delivered. In addition, we show that dyslexic individuals’ difficulties with cued search do not reflect problems with detecting and localising the cue, and generalise to different cue types. These results are consistent with a general weakness of attentional selection in dyslexia.
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Posted by Callier Library on February 25, 2008
from the American Journal of Audiology
Purpose: This investigation reports on quantitative and qualitative follow-up information obtained from a preschool audiologic screening program covering a 10-year period (1995 to 2004).
Method: The audiologic screening consisted of a hearing (pure tone) and tympanometry screening. A total of 34,979 children, 3 to 5 years of age, were screened.
Results: Eighteen percent (6,337) of the children were referred for further hearing and/or medical ear evaluation. Of 1,421 follow-up responses received, 93% complied with the follow-up recommendations while 7% did not. Of 1,316 children in the follow-up group, outer and/or middle ear disorder in one or both ears was medically confirmed for 37%. Unilateral or bilateral hearing loss was diagnosed in 18% as conductive (12%), sensorineural (1%), mixed (0.4%), or unspecified (5%). Overall, hearing loss and/or otologic disorder was confirmed in 49% of the follow-up group, suggesting a prevalence of 1.8% in a preschool-age population. A small (n = 32) sample of unsolicited comments indicated that physicians most influenced noncompliance with hearing evaluation follow-up.
Conclusions: The quantitative hearing and otologic follow-up outcome data affirm the importance of audiologic screening in the preschool population. Qualitative data suggest that some physicians may not be advocating appropriate screening follow-up services.
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Posted by Callier Library on February 25, 2008
from the International Journal of Pediatric Otorhinolaryngology
The objective of this retrospective study is to evaluate the efficiency of hyperosmolar therapy for cerebrum spinal fluid (CSF) leakage in cochlear implant (CI) surgery in children with inner ear malformations. Between 1991 and 2006, 490 cochlear implantations were performed in Armand Trousseau Children’s Hospital. Thirty-seven patients (7.5%) had inner ear malformation. They were classified as isolated enlargement of the vestibular aqueduct (EVA) (18 cases), incomplete partition (IP) (11 cases), common cavity (CC) (1 case) and variable canal and vestibular malformations (VSCC) (7 cases). A hyperosmolar protocol was applied during surgery to 13 patients after 2003 (Gp) to be compared to the 24 patients without treatment previously to this date (G0). Mean age at implant CI was 8.1 years (1–20 years), mean follow up was 3.9 years (1 month–15 years). Per operative observations were collected for all patients with an empiric method of evaluation of the leakage. A grading using five steps ranged from Grade 0 (no leak) to Grade 4 (gusher). Grading, complications and perceptive results in closed and open set word (Lafon lists) at respectively preoperatively, at 3 and 24 months were gathered and compared between the two groups. Important per operative leak was observed (Grade 4) in 24.3% cases (9/37) of Grade 4, 88.8% of them in G0 (8/9). In 66.6% cases there was a severe dysplasia (CC or IP) (6/9), to be compared to the 21.4% of cases of severe dysplasia with Grade 0.05). Grade 4 was seen in 16.6% cases of EVA (3/18); there were no Grade 4 observed in Gp (0/10), and 37.5% cases of EVA in G0 (3/8) (p = 0.04). Grade 4 was observed in 100% case in CC in the G0 (1/1). Severe complications were misplacement of the electrode in one case (G0), persistent leakage in one case (G0) and meningitis in one case (Gp). Vertigo was observed in 29.7% of cases (11/37) in this population, 72.7% of them in G0 (8/11). Vertigo was associated to severe dysplasia in 75% cases in G0 (6/8), and to EVA in all cases in Gp. In G0, mean perceptive scores showed for G0, preoperatively and at 3 months, respectively, 1.3% and 50.6% in closed set word (CSW), and 65.9% in open set words at 2 years. In Gp mean perceptive scores showed preoperatively and at 3 months, respectively 6.1% and 69.8% in CSW, and 81% in open set words at 2 years. The differences between the two groups are not significant (p > 0.05). Osmotherapy is known to be effective for cerebral oedema and regularly used in neurological surgery. In inner ear malformation, gusher at surgery is directly related to the intra-cerebral pressure (ICP). Corresponding to neurosurgical practice, the mainstay of our protocol rests on hyperosmolar treatment, to reduce the ICP the time of the surgery. Our results suggest that this treatment is effective for a better control of leakage at cochleostomy on EVA, and could be effective on more severe malformations. No severe complication related to surgery was seen in Gp. Its good tolerance could allow its use in most patients with inner ear malformation. Vertigo was a frequent complication. The possibility of vertigo depends on the initial vestibular status and on the course of the surgery. The protocol could protect the vestibular function, lowering the pressure and quantity of the liquid issue. The treatment does not seem to influence the perceptive results.
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