Biomedical subjects

Lisa D Sanders

Publications and source records attributed to Lisa D Sanders.

7 recordsLinked to original sources

PubMed2006

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.

Acoustic Stimulation↗

PubMed2005

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.

Adolescent↗

PubMed2005

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.

Acoustic Stimulation↗

PubMed2003

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.

Adult↗

PubMed2003

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

Speech segmentation, breaking continuous streams of sound into units that can be recognized, is a necessary step in auditory language processing. To date, most studies of speech segmentation have been limited to behavioral measures that may not index online segmentation as it occurs when listening to natural speech. In the present study, we measured event-related potentials (ERPs) evoked by word-initial and word-medial syllables equated for loudness, length, and phonemic content. This comparison provided an online measure of natural speech segmentation. Word-initial sounds elicited a larger early sensory component (N100). In addition, we measured the effects of semantic and syntactic information on speech segmentation by comparing ERPs to word-initial and word-medial syllables in sentences with varying amounts of semantic and syntactic content. The results indicated that neither semantic nor syntactic information is necessary for the word-onset segmentation effect to be observed. We also identified additional ERP components that index more general semantic and syntactic aspects of natural speech processing.

Adult↗

PubMed2002

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.

Acoustic Stimulation↗

PubMed2002

Speech segmentation by native and non-native speakers: the use of lexical, syntactic, and stress-pattern cues.

Varying degrees of plasticity in different subsystems of language have been demonstrated by studies showing that some aspects of language are processed similarly by native speakers and late-learners whereas other aspects are processed differently by the two groups. The study of speech segmentation provides a means by which the ability to process different types of linguistic information can be measured within the same task, because lexical, syntactic, and stress-pattern information can all indicate where one word ends and the next begins in continuous speech. In this study, native Japanese and native Spanish late-learners of English (as well as near-monolingual Japanese and Spanish speakers) were asked to determine whether specific sounds fell at the beginning or in the middle of words in English sentences. Similar to native English speakers, late-learners employed lexical information to perform the segmentation task. However, nonnative speakers did not use syntactic information to the same extent as native English speakers. Although both groups of late-learners of English used stress pattern as a segmentation cue, the extent to which this cue was relied upon depended on the stress-pattern characteristics of their native language. These findings support the hypothesis that learning a second language later in life has differential effects on subsystems within language.

Adult↗