Lisa D. Sanders

Neural mechanisms of selective auditory attention are enhanced by computerized training : Electrophysiological evidence from language-impaired and typically developing children

Recent proposals suggest that some interventions designed to improve language skills might also target or train selective attention. The present study examined whether six weeks of high-intensity (100 min/day) training with a computerized intervention program designed to improve language skills would also influence neural mechanisms of selective auditory attention previously shown to be deficient in children with specific language impairment (SLI). Twenty children received computerized training, including 8 children diagnosed with SLI and 12 children with typically developing language. An additional 13 children with typically developing language received no specialized training (NoTx control group) but were tested and retested after a comparable time period to control for maturational and test-retest effects. Before and after training (or a comparable delay period for the NoTx control group), children completed standardized language assessments and an event-related brain potential (ERP) measure of selective auditory attention. Relative to the NoTx control group, children receiving training showed increases in standardized measures of receptive language. In addition, children receiving training showed larger increases in the effects of attention on neural processing following training relative to the NoTx control group. The enhanced effect of attention on neural processing represented a large effect size (Cohens d=0.8), and was specific to changes in signal enhancement of attended stimuli. These findings indicate that the neural mechanisms of selective auditory attention, previously shown to be deficient in children with SLI, can be remediated through training and can accompany improvements on standardized measures of language.

Segmenting Nonsense: An Event-Related Potential Index of Perceived Onsets in Continuous Speech

Speech segmentation, determining where one word ends and the next begins in continuous speech, is necessary for auditory language processing. However, because there are few direct indices of this fast, automatic process, it has been difficult to study. We recorded event-related brain potentials (ERPs) while adult humans listened to six pronounceable nonwords presented as continuous speech and compared the responses to nonword onsets before and after participants learned the nonsense words. In subjects showing the greatest behavioral evidence of word learning, word onsets elicited a larger N100 after than before training. Thus N100 amplitude indexes speech segmentation even for recently learned words without any acoustic segmentation cues. The timing and distribution of these results suggest specific processes that may be central to speech segmentation.

An ERP study of continuous speech processing. II. Segmentation, semantics, and syntax in non-native speakers.

Behavioral and electrophysiological studies indicate that altered language experience has different effects on distinct subsystems within language. In this study, we recorded event-related potentials (ERPs) in native Japanese late-learners of English listening to English sentences. ERP indices of semantic processing, syntactic processing, and speech segmentation were compared and contrasted for native Japanese and previously tested native English speakers. Native and non-native speakers showed similar semantic processing effects including an N400 for words as opposed to nonwords. In contrast, native Japanese speakers showed none of the effects associated with syntactic processing in native English speakers including an anterior negativity to nonwords presented in a syntactic context. Furthermore, the ERP word-onset effect evident in native English speakers was not found for the native Japanese speakers in this study. These data contribute additional and specific evidence to the proposal that subsystems within language display varying degrees of plasticity.

An Event-related Potential Study of Selective Auditory Attention in Children and Adults

In a dichotic listening paradigm, event-related potentials (ERPs) were recorded to linguistic and nonlinguistic probe stimuli embedded in 2 different narrative contexts as they were either attended or unattended. In adults, the typical N1 attention effect was observed for both types of probes: Probes superimposed on the attended narrative elicited an enhanced negativity compared to the same probes when unattended. Overall, this sustained attention effect was greater over medial and left lateral sites, but was more posteriorly distributed and of longer duration for linguistic as compared to nonlinguistic probes. In contrast, in 6-to 8-year-old children the ERPs were morphologically dissimilar to those elicited in adults and children displayed a greater positivity to both types of probe stimuli when embedded in the attended as compared to the unattended narrative. Although both adults and children showed attention effects beginning at about 100 msec, only adults displayed left-lateralized attention effects and a distinct, posterior distribution for linguistic probes. These results suggest that the attentional networks indexed by this task continue to develop beyond the age of 8 years.

Neurophysiological evidence for selective auditory attention deficits in children with specific language impairment

Recent behavioral studies suggest that children with poor language abilities have difficulty with attentional filtering, or noise exclusion. However, as behavioral performance represents the summed activity of multiple stages of processing, the temporal locus of the filtering deficit remains unclear. Here, we used an event-related potential (ERP) paradigm to compare the earliest mechanisms of selective auditory attention in 12 children with specific language impairment (SLI) and 12 matched control children. Participants were cued to attend selectively to one of two simultaneously presented narrative stories. The stories differed in location (left/right speaker), narration voice (male/female), and content. ERPs were recorded to linguistic and nonlinguistic probe stimuli embedded in the attended and unattended story. By 100 ms, typically developing children showed an amplification of the sensorineural response to attended as compared to unattended stimuli. In contrast, children with SLI showed no evidence of sensorineural modulation with attention, despite behavioral performance indicating that they were performing the task as directed. These data are the first to show that SLI children have marked and specific deficits in the neural mechanisms of attention and, further, localize the timing of the attentional deficit to the earliest stages of sensory processing. Deficits in the effects of selective attention on early sensorineural processing may give rise to the diverse set of sensory and linguistic impairments in SLI children.

Selective auditory attention in 3- to 5-year-old children: An event-related potential study

Behavioral and electrophysiological evidence suggests that the development of selective attention extends over the first two decades of life. However, much of this research may underestimate the attention abilities of young children. By providing strong, redundant attention cues, we show that sustained endogenous selective attention has similar effects on ERP indices of auditory processing in adults and children as young as 3 years old. All participants were cued to selectively attend to one of two simultaneously presented stories that differed in location (left/right), voice (male/female), and content. The morphology of the ERP waveforms elicited by probes embedded in the stories was very different for adults, who showed a typical positive-negative-positive pattern in the 300 ms after probe onset, and children, who showed a single broad positivity during this epoch. However, for 3- to 5-year-olds, 6- to 8-year-olds, and adults, probes in the attended story elicited larger amplitude ERPs beginning around 100 ms after probe onset. This attentional modulation of exogenously driven components was longer in duration for the youngest children. In addition, attended linguistic probes elicited a larger negativity 300-500 ms for all groups, indicative of additional attentional processing. These data show that with adequate cues, even children as young as 3 years old can selectively attend to one auditory stream while ignoring another and that doing so alters auditory sensory processing at an early stage. Furthermore, they suggest that the neural mechanisms by which selective attention affects auditory processing are remarkably adult-like by this age.

Temporally selective attention modulates early perceptual processing: Event-related potential evidence

Some of the most important information we encounter changes so rapidly that our perceptual systems cannot process all of it in detail. Spatially selective attention is critical for perception when more information than can be processed in detail is presented simultaneously at distinct locations. When presented with complex, rapidly changing information, listeners may need to selectively attend to specific times rather than to locations. We present evidence that listeners can direct selective attention to time points that differ by as little as 500 msec, and that doing so improves target detection, affects baseline neural activity preceding stimulus presentation, and modulates auditory evoked potentials at a perceptually early stage. These data demonstrate that attentional modulation of early perceptual processing is temporally precise and that listeners can flexibly allocate temporally selective attention over short intervals, making it a viable mechanism for preferentially processing the most relevant segments in rapidly changing streams.

Listeners modulate temporally selective attention during natural speech processing.

Spatially selective attention allows for the preferential processing of relevant stimuli when more information than can be processed in detail is presented simultaneously at distinct locations. Temporally selective attention may serve a similar function during speech perception by allowing listeners to allocate attentional resources to time windows that contain highly relevant acoustic information. To test this hypothesis, event-related potentials were compared in response to attention probes presented in six conditions during a narrative: concurrently with word onsets, beginning 50 and 100 ms before and after word onsets, and at random control intervals. Times for probe presentation were selected such that the acoustic environments of the narrative were matched for all conditions. Linguistic attention probes presented at and immediately following word onsets elicited larger amplitude N1s than control probes over medial and anterior regions. These results indicate that native speakers selectively process sounds presented at specific times during normal speech perception.

Skilled Readers Begin Processing Sub-phonemic Features by 80 ms during Visual Word Recognition: Evidence from ERPs

Two masked priming experiments investigated the time-course of the activation of sub-phonemic information during visual word recognition. EEG was recorded as participants read targets with voiced and unvoiced final consonants (e.g., fad and fat), preceded by nonword primes that were incongruent or congruent in voicing and vowel duration (e.g., fap or faz). Experiment 1 used a long duration mask (100 ms) between prime and target, whereas Experiment 2 used a short mask (22 ms). Phonological feature congruency began modulating the amplitude of brain potentials by 80 ms; the feature incongruent condition evoked greater negativity than the feature congruent condition in both experiments. The early onset of the congruency effect indicates that skilled readers initially activate sub-phonemic feature information during word identification. Congruency effects also appeared in the middle and late periods of word recognition, suggesting that readers use phonological representations in multiple aspects of visual word recognition.

Local and global auditory processing: behavioral and ERP evidence.

Differential processing of local and global visual features is well established. Global precedence effects, differences in event-related potentials (ERPs) elicited when attention is focused on local versus global levels, and hemispheric specialization for local and global features all indicate that relative scale of detail is an important distinction in visual processing. Observing analogous differential processing of local and global auditory information would suggest that scale of detail is a general organizational principle of the brain. However, to date the research on auditory local and global processing has primarily focused on music perception or on the perceptual analysis of relatively higher and lower frequencies. The study described here suggests that temporal aspects of auditory stimuli better capture the local-global distinction. By combining short (40 ms) frequency modulated tones in series to create global auditory patterns (500 ms), we independently varied whether pitch increased or decreased over short time spans (local) and longer time spans (global). Accuracy and reaction time measures revealed better performance for global judgments and asymmetric interference that were modulated by amount of pitch change. ERPs recorded while participants listened to identical sounds and indicated the direction of pitch change at the local or global levels provided evidence for differential processing similar to that found in ERP studies employing hierarchical visual stimuli. ERP measures failed to provide evidence for lateralization of local and global auditory perception, but differences in distributions suggest preferential processing in more ventral and dorsal areas respectively.