Central-tendency estimation and nearest-estimate classification of multi-channel evoked potentials.

By modeling evoked potentials (EPs) as random vectors in which the EP samples are random variables, a generalized strategy is introduced to determine multivariate central-tendency estimates such as the arithmetic mean, geometric mean, harmonic mean, median, tri-mean, and trimmed-mean. Additionally, a generalized strategy is introduced to develop minimum-distance classifiers based on central tendency estimates. Furthermore, procedures are developed to fuse the decisions of the nearest-estimate classifiers for multi-channel EP classification. The central-tendency estimates of real EPs are compared and it is shown that although the mathematical operations to compute the estimates are quite different, the EP estimates are similar with respect to their overall waveform shapes and latencies. It is also shown that by fusing the classifier decisions across multiple channels, the classification accuracy can be improved significantly when compared with the accuracies of individual channel classifiers.

Anterior cingulate cortex and response conflict: effects of frequency, inhibition and errors.

Anterior cingulate cortex (ACC) may play a key role in cognitive control by monitoring for the occurrence of response conflict (i.e. simultaneous activation of incompatible response tendencies). Low-frequency responding might provide a minimal condition for eliciting such conflict, as a result of the need to overcome a prepotent response tendency. We predicted that ACC would be selectively engaged during low-frequency responding, irrespective of the specific task situation. To test this hypothesis, we examined ACC activity during the performance of simple choice-discrimination tasks, using rapid event-related functional magnetic resonance imaging. Subjects were scanned while performing three tasks thought to tap different cognitive processes: 'Go/No-go' (response inhibition), 'oddball' (target detection), and two-alternative forced- choice (response selection). Separate conditions manipulated the frequency of relevant task events. Consistent with our hypothesis, the same ACC region was equally responsive to low-frequency events across all three tasks, but did not show differential responding when events occurred with equal frequency. Subregions of the ACC were also identified that showed heightened activity during the response inhibition condition, and on trials in which errors were committed. Task-sensitive activity was also found in right prefrontal and parietal cortex (response inhibition), left superior temporal and tempoparietal cortex (target detection), and supplementary motor area (response selection). Taken together, the results are consistent with the hypothesis that the ACC serves as a generic detector of processing conflict arising when low-frequency responses must be executed, but also leave open the possibility that further functional specialization may occur within ACC subregions.

Newborn and preschool predictors of second-grade reading scores: an evaluation of categorical and continuous scores.

This study examined how the development of foundation skills in speech perception, language, short-term memory, and family demographics and activities in the home environment influence the development of reading skills. Data from 96 children participating in a longitudinal research project were used. It was hypothesized that measures of specific foundation skills in the preschool period and measures of family demographics and home environment could be used to identify children's reading abilities. As expected, most of the foundation skills were found to be related to and predictive of reading scores. Event-related potential (ERP) measures of speech perception, which have previously been found to be predictive of reading abilities, and measures of family and home activities and language measures were related to reading scores. Verbal short-term memory scores contributed little to the prediction of reading scores. These variables influenced the results whether they were used to discriminate reading groups or to predict a continuum of reading scores, but there were large differences in the amount of variance accounted for. More variance was accounted for in the group analyses than in the continuum analyses.

Cerebral activation during multiplication: a functional MR imaging study of number processing.

BACKGROUND AND PURPOSE: Current models of brain function propose that number processing involves the interaction of different neuronal networks. Our purpose was to use functional MR (fMR) imaging to elucidate the brain regions engaged by multiplication. METHODS: Eighteen adults underwent fMR imaging while performing matching, multiplication, and control tasks. For each task, three or four single-digit or low-value double-digit numbers were presented serially followed by a 12-second delay. A target stimulus then appeared and subjects made a judgement by pressing a button box that recorded responses. During the matching task, subjects judged whether the target stimulus matched one of the previous numbers. During the multiplication task, subjects judged whether the target stimulus was the product of the previous numbers. For the control task, the numbers were always zeros, and the subjects responded to a target stimulus that was always four zeros. Composite statistical parametric maps of the time course of activation comparing the control task with the matching and multiplication tasks, respectively, were generated and the significance of signal changes was estimated by randomization of statistical parametric maps. RESULTS: The matching and multiplication tasks resulted in activation (P < .005) in the medial superior frontal gyrus; the anterior cingulate gyrus; the intraparietal sulci, bilaterally; the right superior frontal sulcus bilaterally; the middle, inferior and precentral frontal gyri (left greater than right); the left basal ganglia; and the right lateral and inferior occipital gyri. There was a larger area of early activation in the right middle frontal gyrus during the matching task compared with the multiplication task, and there was a longer interval of activation in the left middle frontal gyrus during the multiplication task (10 seconds) than in the matching task (6 seconds). CONCLUSION: Multiplication and memory of numbers share an integrated network of brain regions. The left frontal lobe, an area also involved in memory and language processes, appears to play an important role in multiplication.

Predicting dyslexia at 8 years of age using neonatal brain responses.

Auditory event-related potentials recorded at birth to speech and nonspeech syllables from six scalp electrodes discriminated between newborn infants who 8 years later would be characterized as dyslexic, poor, or normal readers. These findings indicate that reading problems can be identified and possible interventions undertaken up to 9 years earlier than is currently possible.

Event-related potentials in a two-choice task involving within-form comparisons of pictures and words.

Behavioral as well as electrophysiological evidence suggests that words are processed differently than pictures in a variety of tasks. In this study fifteen adult subjects were tested on a speeded "same-different" judgment task between printed names and drawings of common objects. In one condition, subjects decided on the identity between their internal image of the object that was named by S1 (word) and a subsequently presented drawing of an object (Word-Picture condition). In a second condition, comparisons were made on the basis of the name of the depicted object (Picture-Word trials). Event-related potentials (ERPs) were recorded from 12 scalp locations in response to the second item in each pair. No-match waveforms were characterized by larger N350 and P500 deflections compared to Match ERPs. The two responses could be distinguished on the basis of their lateral and anterior-posterior scalp distribution. Within-form comparisons involving pictures produced increased positivity between 150 and 600 ms poststimulus onset at posterior recording sites, whereas the opposite effect was noted at anterior sites during the early portion of the ERP. Decisions on word stimuli were associated with prolonged reaction time and longer N350 peak latency compared to decisions on pictures. These results demonstrate the existence of independent sources of ERP variability, each possibly reflecting a different aspect of cognitive comparisons. Latency and reaction time data provided valuable information regarding differences in the course of the comparison process when linguistic, as opposed to pictorial, stimuli/representations were involved.

Behavioral and electrophysiological indices of voicing-cue discrimination: laterality patterns and development.

Voicing is an important phonetic dimension that distinguishes voiced (i.e., /b/) from voiceless-aspirated stop consonants (i.e.,/ph/) in English. Perception of discrete voicing categories is affected by a number of acoustic cues. The present paper reviews evidence from brain-damaged populations indicating that the perception of certain voicing cues is less dependent upon left hemisphere mechanisms than the ability to perceive place of articulation contrasts (e.g., /b/ vs./d/). In addition, electrophysiological and dichotic listening studies with neurologically normal individuals support the view that the right hemisphere may play a special role in the categorical processing of voicing. These findings are discussed in relation to current models of hemispheric specialization and laterality for language.

Electrophysiological responses from a temporal order continuum in the newborn infant.

Auditory Evoked Responses (AERs) were used to investigate discrimination of temporal order differences in eight male and eight female newborn infants. The temporal lags in two-tone non-speech stimuli-known as tone-onset time (TOT)-modeled the temporal delay of voicing-onset time (VOT), an important cue for voicing contrasts. Analyses on peak amplitude measures and principal component scores indicated that the amplitude of the second negative AER deflection (N530) recorded from the left and right parietal leads changed abruptly as TOT values increased from +20 to +40 msec. However, no differences were noted between tokens that belonged in the same adult perceptual categories. A similar pattern of variability was observed for the amplitude of the first major negative peak (N200). Our findings indicate that the neurophysiological mechanisms underlying categorical-like distinctions of a temporal voicing cue used in speech perception may have an innate basis. Since both hemispheres produced similar responses at birth, the present data suggest that brain mechanisms involved in temporal order processing undergo significant reorganization during the first years of life.

Electrophysiological correlates of noun-verb processing in adults.

Auditory event related potentials (ERPs) were recorded to a series of nouns and verbs while 16 adults watched videotaped scenes. The scenes depicted an individual using objects or performing actions that were either labeled or not named by the auditorily presented nouns or verbs. Electrodes were placed over the left and right hemisphere frontal, temporal, and parietal regions of the scalp. Analyses compared ERPs elicited by words that matched or failed to match the scenes. Marked changes were noted in the ERPs recorded from electrode placements across the two hemispheres in response to words that served two different syntactic functions. This procedure is viewed as a useful technique for use with younger subject populations.

Nonlinear alignment and averaging for estimating the evoked potential.

This paper addresses the problems associated with averaging brain responses evoked through a repetitive application of an external stimulus. In order to improve the estimate of the evoked potential (EP) through signal averaging, a method which incorporates nonlinear alignment of the EP's into the averaging operation is developed. The method makes no prior assumptions about the properties of the EP or which response in the set best characterizes the EP to be estimated. The nonlinear alignment procedure is designed to pairwise generate optimally aligned EP's by backtracking along the optimal alignment path. The nonlinear alignment and averaging operations are systematically combined to develop methods to estimate the EP. Results from a series of experiments conducted on simulated and real sets of responses show that, through nonlinear alignment and averaging, the events in the EP's are preserved and the estimates of the EP are quite robust.

An artificial neural network approach to ERP classification.

Artificial neural network-based approaches were developed to classify event-related potential (ERP) waveforms. The networks utilized scalp-recorded ERP returns from six electrode sites. These ERPs were evoked as one individual responded to a series of auditorily presented object names while viewing various objects on a computer screen. The ERPs at the electrode sites were classified as a match decision or a no-match decision. A three-layer backpropagation neural network model was selected to formulate a global and a local classification approach. The backpropagation network in the global approach was designed to operate on a single ERP response which was the average of the ERP responses generated at the six electrode sites. The local ERP classification system consisted of six three-layer backpropagation networks. Each network was designed to operate on the ERPs generated at a single electrode site. A small data base consisting of eight match and eight no-match ERP responses was used to train and test the networks in a variety of ways. The results obtained clearly show that the neural network-based classifiers are able to discriminate with a high degree of accuracy between match and no-match conditions in ERP waveforms.

The processing of presuppositional information contained in sentences: electrophysiological correlates.

In an attempt to observe how the brain processes presuppositional information, event-related potentials (ERPs) were recorded from 12 scalp electrodes placed over the left and right hemispheres of 10 adult subjects as they listened to sentences that contained either factive or nonfactive verbs. The stimulus sentences had been time-compressed to a duration of less than 1.25 sec, allowing ERPs to be recorded over their entire length. A Principal Components Analysis/Analysis of Variance procedure provided evidence that the brain responses could discriminate between factive and nonfactive conditions. It was concluded that the processing of presupposition represents a multidimensional phenomenon that changes across cortical space and time.

Auditory evoked responses recorded from 16-month-old human infants to words they did and did not know.

Auditory evoked responses (AERs) were recorded from the frontal, temporal, and parietal scalp regions of nine male and nine female 16-month-old infants while they listened to a series of words. The brain responses reliably discriminated between words the infants were thought to understand versus those that they did not appear to know as judged by their parents and two independent raters. Findings from this study indicated that the brain wave patterns could discriminate known from unknown words. Sex differences in the patterns of lateralized hemispheric responses to the known and unknown words were also noted. These data indicate that auditory evoked responses may be used to detect differences in word meanings in young infants.

Semantic discrimination in nonspeaking youngsters with moderate or severe retardation: electrophysiological correlates.

Recent studies have used auditory evoked response (AER) procedures to study word meaning in young infants. The present study represents an initial application of these procedures to nonspeaking subjects with moderate or severe mental retardation. AERs were recorded from electrodes placed on the scalp over frontal, temporal, and parietal regions of the left and right hemispheres. As six symbol-experienced subjects viewed visual-graphic symbols (lexigrams), a series of probe tones were presented to elicit the AERs. Half of the symbols were meaningful to the subjects. AER activity recorded from the left hemisphere frontal and temporal electrode sites discriminated between the meaningful and meaningless symbols. Discriminant function analyses indicated that the wave-forms could be correctly classified in terms of the evoking stimulus with greater than 80% accuracy. These findings support the usefulness of AERs for studying the neurolinguistic processes underlying behavioral measures of language performance of difficult-to-assess populations.

Right-hemisphere responses from preschool children to temporal cues to speech and nonspeech materials: electrophysiological correlates.

Auditory-evoked responses (AERs) were recorded from scalp electrodes placed over the left and right temporal hemisphere regions of 12 preschool children while they listened to a series of velar stop consonants which varied in voice onset time (VOT) and to two-formant tone stimuli with temporal lags comparable to the speech materials. A late occurring negative peak (N400) in the right hemisphere AERs discriminated between both the speech and nonspeech materials in a categorical-like manner. Sex-related hemisphere differences were also noted in response to the two different stimulus types. These results replicate earlier work with speech materials and suggest that temporal delays for both speech and nonspeech auditory materials are processed in the right hemisphere.

Neuroelectrical correlates of categorical perception for place of articulation in normal and lead-treated rhesus monkeys.

Categorical perception of place of articulation contrasts was evaluated in rhesus monkeys. The monkeys had been chronically exposed to subclinical levels of lead, either from conception to birth, or for approximately 6 months beginning at birth, or were never exposed to lead. Auditory evoked responses were recorded from scalp electrodes placed over left and right hemispheres during stimulus presentation. The brain responses recorded from the right hemisphere of the normal control group of monkeys discriminated between the categories of [dae] and [gae]. Categorical discriminations were also noted for monkeys exposed to lead either prenatally or postnatally. These discriminations, in contrast, were found over only the left hemisphere. In additions, postnatal exposure resulted in categorical discrimination associated with slower latency components, suggesting a less mature pattern than that obtained for prenatally exposed monkeys. Finally, the brain responses of the animals in the normal control and postnatal exposure conditions evidenced reliable within-category, as well as between-category, discriminations. These results suggest that the neurocortical mechanisms associated with categorical perception of place information may differ between human and nonhuman primates and that early exposure to lead alters these processes.

The right hemisphere and temporal processing of consonant transition durations: electrophysiological correlates.

Auditory evoked responses (AER) were recorded from frontal, temporal, and parietal scalp regions to a series of consonant-vowel syllables which varied in the duration of the consonant transition. Multivariate analyses of the AER waveforms identified one component of the AERs occurring only over right hemisphere regions which discriminated between differences in transition durations. A second component detected over only left hemisphere areas discriminated differences in place of articulation. These data are consistent with previous behavioral and electrophysiological reports that the right hemisphere is sensitive to temporal discriminations.