Neurobiologic responses to speech in noise in children with learning problems: deficits and strategies for improvement

OBJECTIVES

Some children with learning problems (LP) experience speech-sound perception deficits that worsen in background noise. The first goal was to determine whether these impairments are associated with abnormal neurophysiologic representation of speech features in noise reflected at brain-stem and cortical levels. The second goal was to examine the perceptual and neurophysiological benefits provided to an impaired system by acoustic cue enhancements.

METHODS

Behavioral speech perception measures (just noticeable difference scores), auditory brain-stem responses, frequency-following responses and cortical-evoked potentials (P1, N1, P1', N1') were studied in a group of LP children and compared to responses in normal children.

RESULTS

We report abnormalities in the fundamental sensory representation of sound at brain-stem and cortical levels in the LP children when speech sounds were presented in noise, but not in quiet. Specifically, the neurophysiologic responses from these LP children displayed a different spectral pattern and lacked precision in the neural representation of key stimulus features. Cue enhancement benefited both behavioral and neurophysiological responses.

CONCLUSIONS

Overall, these findings contribute to our understanding of the preconscious biological processes underlying perception deficits and may assist in the design of effective intervention strategies.

Stimulant therapy and seizure risk in children with ADHD

Stimulants are an effective treatment frequently prescribed for attention-deficit-hyperactivity disorder (ADHD), but they commonly are believed to lower the threshold for seizures. Although several studies have revealed that stimulants do not exacerbate well-controlled epilepsy, there is a paucity of data about seizure risk in nonepileptic children treated with stimulants. Two hundred thirty-four children (179 males, 9.1 +/- 3.6 years of age; 55 females, 9.6 +/- 3.9 years of age) with uncomplicated ADHD received electroencephalograms (EEGs) performed in our institution. Thirty-six patients (15.4%) demonstrated epileptiform abnormalities, and 198 (84.6%) demonstrated normal or nonepileptiform EEGs. Rolandic spikes accounted for 40% of the abnormal EEGs and 60% of those with focal abnormalities. Stimulant therapy was elected by 205 of 234 patients (87.6%). Seizures occurred only in the treated group, in one of 175 patients with a normal EEG (incidence 0.6%, 95% confidence intervals 0%-1.7%) and three of 30 treated patients with epileptiform EEGs (incidence 10%, 95% confidence interval 0%-20.7%). Seizures occurred in two of 12 children (16.7%) with rolandic spikes. These data suggest that a normal EEG can be used to assign children with ADHD to a category of minimal risk for seizure. In contrast, an epileptiform EEG in neurologically normal children with ADHD predicts considerable risk for the eventual occurrence of seizure. The risk, however, is not necessarily attributable to stimulant use.

Nonlinguistic perceptual deficits associated with reading and language disorders

Recent behavioral evidence supports the idea that some individuals with reading and language disorders are impaired in their perception of nonlinguistic auditory and visual information. More sophisticated measurement paradigms and analysis techniques are leading to a clearer understanding of these deficits and to possibilities for their remediation.

Effects of lengthened formant transition duration on discrimination and neural representation of synthetic CV syllables by normal and learning-disabled children

In order to investigate the precise acoustic features of stop consonants that pose perceptual difficulties for some children with learning problems, discrimination thresholds along two separate synthetic /da-ga/ continua were compared in a group of children with learning problems (LP) and a group of normal children. The continua differed only in the duration of the formant transitions. Results showed that simply lengthening the formant transition duration from 40 to 80 ms did not result in improved discrimination thresholds for the LP group relative to the normal group. Consistent with previous findings, an electrophysiologic response that is known to reflect the brain's representation of a change from one auditory stimulus to another--the mismatch negativity (MMN)--indicated diminished responses in the LP group relative to the normal group to /da/ versus /ga/ when the transition duration was 40 ms. In the lengthened transition duration condition the MMN responses from the LP group were more similar to those from the normal group, and were enhanced relative to the short transition duration condition. These data suggest that extending the duration of the critical portion of the acoustic stimulus can result in enhanced encoding at a preattentive neural level; however, this stimulus manipulation on its own is not a sufficient acoustic enhancement to facilitate increased perceptual discrimination of this place-of-articulation contrast.

Oral sensory discrimination of fluid viscosity

This study was designed to investigate the ability of normal young adult volunteers to sensorially identify Newtonian fluids of specified viscosities. Twenty subjects, 10 men and 10 women between the ages of 18 and 29 years participated. Seven stimuli, consisting of combinations of corn syrup and water, with viscosities ranging from 2 to 2,240 centipoise (cP) were prepared and characterized using a coaxial rotational viscometer. Subjects were presented with two anchor stimuli representing the extremes of the range of viscosities as a basis from which the experimental stimuli were judged. The seven experimental stimuli were randomly presented to each subject 10 times. The accuracy with which the subjects identified the viscosity of the fluid was significant at p < 0.01. The pattern of response was not significantly different across subjects nor gender. There were no differences in performance throughout the duration of the study. The repeat presentation of the anchor points did not significantly affect performance. Further research on oral perception of viscosity, and the processes that mediate changes in swallow physiology resulting from changes in viscosity is required.

Auditory neurophysiologic responses and discrimination deficits in children with learning problems

Children with learning problems often cannot discriminate rapid acoustic changes that occur in speech. In this study of normal children and children with learning problems, impaired behavioral discrimination of a rapid speech change (/dalpha/versus/galpha/) was correlated with diminished magnitude of an electrophysiologic measure that is not dependent on attention or a voluntary response. The ability of children with learning problems to discriminate another rapid speech change (/balpha/versus/walpha/) also was reflected in the neurophysiology. These results indicate that some children's discrimination deficits originate in the auditory pathway before conscious perception and have implications for differential diagnosis and targeted therapeutic strategies for children with learning disabilities and attention disorders.

The go-no go test in attention deficit disorder is sensitive to methylphenidate

The go-no go test requires a subject to emit a simple motor response to one cue while inhibiting the response in the presence of another cue. This test has been effective in demonstrating impulsivity (elevated commission error rate) in children with attention deficit disorder (ADD). In this study, we examined the effects on go-no go test performance of two doses of methylphenidate (0.15 mg/kg and 0.3 mg/kg) administered in double-blind placebo-controlled fashion to children with ADD. Our results indicate that even modest doses of methylphenidate improve the go-no go performance of these children by decreasing their tendency to make impulsive commission errors. Thus the test is sensitive to the effects of methylphenidate and can be used to monitor a response to therapy.

The orthographic code: Developmental trends in reading-disabled and normally-achieving children

An auditory rhyme detection task was employed to examine orthographic code development in 27 reading-disabled (RD) and 27 normally-achieving (NA) children ranging in age from 7-0 to 11-5. The amount of orthographic facilitation (that is, the reduction in response latencies for orthographically similar as opposed to orthographically dissimilar rhyme pairs) was recorded for each subject. Results indicated that RD children exhibit significantly less facilitation overall than NA children and that RD children do not demonstrate comparable orthographic facilitation effects to NA children until they are about two years older than their NA peers. It is concluded that children with a reading disability have a lessened ability to access automatically and make available stored lexical information relating to orthography.

Visual similarity effects in detecting letter rhymes

Previous demonstrations of "visual" effects in auditory tasks have been largely restricted to orthographic effects with word stimuli. As a result, explanations of such effects have centered around a shared orthography--the similarity of the spelling patterns at the ends of the words. In the present study, these effects were extended to single-letter stimuli. Subjects made rhyming decisions about pairs of letters presented auditorily. Visually similar letter pairs facilitated responses to rhyming pairs and inhibited responses to nonrhyming pairs. The results indicate that visual effects are not restricted to word stimuli and suggest that additive effects of visual similarity and shared orthography may be responsible for these findings.

Subvocal motor activity and contextual processing

Twenty male and female subjects listened for mispronounced words while minimizing either subvocal or frontalis electromyographic activity. Stimuli were varied on size of the distortion, lexical constraint, and contextual constraint, all known to influence detections. Analysis of both the reaction time and detection data indicated that the minimization of subvocal EMG activity reduced or eliminated the effect of contextual constraint, effect. Results indicate that subvocal activity is related to contextual processing. Additionally, reaction time data are reported that indicate that although low contextual constraint greatly slows the decision process, detectability is actually superior. A possible underlying mechanism for this reversal of the speed-accuracy trade-off is discussed.