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S J Segalowitz

Publications and source records attributed to S J Segalowitz.

At least 19 recordsLinked to original sources
PubMed2004

Charting the maturation of the frontal lobe: an electrophysiological strategy.

Tracking the functional development of specific regions of the prefrontal cortex in children using event-related potentials (ERPs) is challenging for both technical and conceptual reasons. In this paper we outline our strategy for studying frontal lobe development and present preliminary results from children aged 7-17 years and young adults using ERPs functionally associated with anterior cingulate and prefrontal cortex, especially the orbitofrontal, ventral, and medial portions. Our analysis of contingent negative variation, error-related negativity, and novelty P300 data show that the ERPs associated with these regions are still maturing into late adolescence, and that their amplitude has significant correlations with behavioral capacities.

Adolescent↗
PubMed2001

P300 event-related potential decrements in well-functioning university students with mild head injury.

We compared the performance of 10 well-functioning university students who had experienced a mild head injury (MHI) an average of 6.4 years previously and 12 controls on a series of standard psychometric tests of attention, memory, and thinking and on a series of auditory oddball vigilance tasks to which we also took event-related potentials (ERPs). The MHI and Control groups performed equivalently on all the psychometric tasks and on self-report questionnaires of everyday memory and attention difficulties. The MHI group performed more slowly and with lower accuracy on only the most difficult of the oddball tasks, yet they showed substantially and significantly reduced P300 amplitudes and subsequent attentuation on all the oddball tasks, both easy and difficult. There were no alterations of N1, P2, and N2 components. These data suggest that despite excellent behavioral recovery, subtle information processing deficits involving attention nevertheless may persist long after the original injury and may not be apparent on a variety of standard psychometric measures.

Cognition Disorders↗
PubMed2001

Error-negativity and positivity as they relate to other ERP indices of attentional control and stimulus processing.

We compared individual differences in the ERP associated with incorrect responses in a discrimination task with other ERP components associated with attentional control and stimulus discrimination (N2, P3, CNV). Trials with errors that are detected by the subject normally produce a negativity (N(E)) immediately following the response followed by a positivity (P(E)). The morphology of the N(E) and the P(E) is similar to that of the standard N2-P3 complex on correct discrimination trials. Our findings suggest that the P(E) is a P3 response to the internal detection of errors. The N(E), however, appears to be distinct from the N2. Finally, even though both the contingent negative variation (CNV) and the N(E) are associated with prefrontal cortex and the allocation of attention to response accuracy, the N(E) and CNV did not relate to one another.

Adult↗
PubMed2001

P3 topographical change with task familiarization and task complexity.

The P3 event-related potential (ERP) component is usually reported as having a centro-parietal maximum. However, a more frontal P3 topography is also evident in early-session trials which may be masked by averaging over the entire session, and is also present longer in elderly subjects. This maintenance of hyperfrontal topography is interpreted as a sign of reduced prefrontal adaptive functioning. In the present study, P3 amplitude was examined in young adults to determine: (1) how early in the test session the reduction in hyperfrontality occurs; and (2) the effect of task complexity on the P3 amplitude across electrode sites (Fz, Cz, Pz). ERPs were elicited using a working memory n-back task. Single-trial ERP waveforms were averaged in successive blocks of five trials. There was a greater decrease in P3 amplitude at Fz compared to Cz and Pz sites after the first block, and the decrease reached an asymptote by the third block. The results are interpreted as indicating rapid decrease in initial P3 hyperfrontality for a simple task in young adults, and an increased ratio of P3 amplitude at frontal versus posterior sites in more complex tasks.

Adult↗
PubMed2001

The effect of differing scoring methods for the Tower of London task on developmental patterns of performance.

The Tower of London (TOL) task is frequently used to assess executive functioning in both adults and children, although there remains considerable controversy over what it measures and how to score it. In this study we compare two scoring methods and find that correlations between them were high for 7-year-olds (.86), and dropped to a low of .47 for adults. These results demonstrate that the TOL necessarily has different construct validity in adults and children. Second, results of one method (based on errors only) show a developmental trend in performance from middle childhood to adulthood, while the other (based on errors and time) shows a developmental progression from ages 7 to 13, but not between 13-year-olds and young adults. Thus, scoring method influences the resulting developmental model.

Adolescent↗
PubMed2001

Event-related potential evidence for age-related differences in attentional allocation during a source monitoring task.

Event-related potentials (ERPs) were recorded while older and younger adults were engaged in a source monitoring task. After studying a list of words, participants were presented with a recognition test during which some of the new words were repeated, rendering them as familiar as the study words. Instructions at test indicated whether the goal was to select the previously studied words or the repeated test items. Behaviorally, the younger adults were less likely to make source monitoring errors. ERPs, averaged only for correct trials, indicated that younger adults produced late positivities of greatest amplitude in response to whichever word type was designated as target irrespective of its familiarity. The ERPs of the older adults were generally less differentiated and their late positivities greater for recently repeated words irrespective of target designation. These results suggest that source monitoring in young adults is facilitated by their ability to allocate and withdraw attention from stimuli on the basis of task relevance rather than familiarity alone, and that this attentional flexibility declines with age.

Adult↗
PubMed2000

Predicting child language impairment from too many variables: overinterpreting stepwise discriminant function analysis.

Tallal (1999) defends an earlier presentation of 160 variables predicting classification of 59 children for specific language impairment (SLI) from the statistical criticisms of Zhang and Tomblin (1998). I present here 3 additional reasons why it is wrong to conclude from Tallal's original 1985 analysis and presentation that it is specifically temporal processing variables that underlie SLI. On the contrary, these data lend no support to this position.

Child↗
PubMed2000

Lexical access of function versus content words.

There has been a simmering debate as to whether evidence exists for differential processes of lexical access for function and content words. This has centered around the frequency effect (higher word frequency reducing access times for content words but not function words). Previous work has used the lexical decision paradigm, which has been shown to reflect more than lexical access times. We measured naming times for words in sentences read for meaning. Our findings confirm that lexical access for function words is indeed faster than for content words as predicted by neurolinguistic theory and electrophysiological evidence, but that this difference can be attributed to word predictability (Cloze value) and word familiarity (log frequency). We also show that differences in frequency effect for the two word types holds only for the lower frequency words and not at all for the higher frequency words. We discuss the implications of the results for neurolinguistic theory.

Electrophysiology↗
PubMed1998

Source monitoring: ERP evidence for greater reactivity to nontarget information in older adults.

Event-Related Potentials (ERPs) were collected concurrently with stimulus presentation during a source monitoring task. Younger adults were less likely than older adults to make source monitoring errors and their ERP records showed far greater discrimination between target stimuli and familiar but nontarget foils. Older adults not only made more source errors but produced high amplitude late positivities to the nontarget foils even when these foils were correctly rejected. Under divided attention conditions, younger adults performance was similar to that of the older adults both behaviorally and electrophysiologically. These data illustrate the role that attentional resources play in the ability to inhibit response tendencies and suggest that age differences in source monitoring may be more related to attentional control than inefficiencies in the encoding of contextual information. As well, they suggest that the ERP late positivity may represent a more general response to item salience rather than serve as an index of recollection as is the current view.

Aged↗
PubMed1997

The ERP late positivity: a graduated response to stimulus repetition.

The late positive component of the event-related potential (ERP) is sensitive to stimulus repetition but evidence to date is ambiguous regarding whether it is differentially sensitivity to multiple repetitions, ERPs were monitored in a running recognition paradigm while participants indicated whether a series of test words had been presented earlier. In study 1, some words were repeated up to three times, at lags of 15, 30 and 45. In study 2, words were repeated only once but interstimulus intervals were varied. As expected, the late positivity was sensitive to previous occurrence and although it did not vary reliably in response to the size of interstimulus interval, it did provide a reliable graded reflection of the number of stimulus repetitions.

Adult↗
PubMed1997

Attentional factors in response time variability after traumatic brain injury: an ERP study.

Reaction time (RT) is often used in the assessment of patients with traumatic brain injury (TBI), presumably because it reflects either information processing speed or attentional capacity. To clarify this distinction, we examined behavioral RT and the within-subject variability of RT as they relate to electrophysiological measures of attention and information processing. These include the P300 latency, which reflects stimulus evaluation time, P300 amplitude, which reflects attentional allocation, and the preresponse component of the contingent negative variation (CNV), which reflects sustained attention. We found that the latency and variability in behavioral RT were not correlated with the latency or variability of the P300, suggesting that stimulus evaluation time is not a major contributor to RT and its variability in this paradigm. However, among normal controls, RT was related to P300 amplitude, and therefore to attentional allocation. For the TBI subjects, it was the variability, not the speed, of RT that was related to P300 amplitude and to the preresponse component of the CNV. These data suggest that, while in normal controls RT reflects attentional allocation, among TBI subjects it is the variability in RT that is sensitive to the ability to allocate and sustain attention.

Adult↗
PubMed1997

Improvement of hemispatial neglect with cold-water calorics: an electrophysiological test of the arousal hypothesis of neglect.

Introducing ice-water into the left ear of right-brain-damaged patients attenuates unilateral neglect symptoms. By examining EEG changes over each hemisphere during this procedure, we were able to test a hypothesis concerning the mechanism of cold-water calorics and the attention-arousal hypothesis of hemispatial neglect. We present a case study of an 83-year-old woman with a massive right-hemisphere CVA exhibiting severe hemispatial neglect. Caloric stimulation produced a leftward eye deviation to central position, and a temporary partial remission of neglect symptoms. Significant changes in EEG activation indicated a central mechanism associated with the regularization of eye gaze. Caloric stimulation also produced a significant interaction between EEG frequency band and hemisphere, indicating that while both hemispheres increased in cortical activation, the right hemisphere increase was significantly greater. This supports the activation-arousal hypothesis of neglect over the mutual inhibition model.

Aged↗
PubMed1995

Sources of P300 attenuation after head injury: single-trial amplitude, latency jitter, and EEG power.

Single trial amplitude, latency jitter, and electroencephalographic (EEG) power were examined as sources of the group difference in averaged P300 amplitude among 15 traumatically brain injured and 20 control individuals in an auditory oddball paradigm. Mean amplitude of the individual trials was highly correlated with the amplitude of the averaged P300, with little additional unique variance attributable to latency jitter or EEG power. The group difference in P300 amplitude was also explained by the mean amplitude of the single trials. These results support the robustness of the evtent-related potential averaging technique within the paradigm used.

Adolescent↗
PubMed1995

Subtle symptoms associated with self-reported mild head injury.

We conducted a survey on the relationship between mild head injury incidence and a variety of psychological and educational symptoms in a sample of 1,345 high school and 2,321 university students. Once figures were adjusted to represent a 50:50 gender ratio, 30% to 37% of subjects reported having experienced a head injury incident, with 12% to 15% of the total group of subjects reporting such an incident with loss of consciousness. We found significant relationships between the incidence of such mild head injury and gender, sleep difficulties, social difficulties, handedness pattern, and diagnoses of attention deficit, depression, and speech, language, and reading disorders.

Adolescent↗
PubMed1994

If you can replicate the handedness-immune disorder effect, the more power to you.

Bryden, McManus, and Bulman-Fleming's (1994) meta-analysis of studies examining the Geschwind-Behan-Galaburda hypothesis indicates that the original data set supports the hypothesis significantly more than the body of replication attempts. We present data on 2256 subjects that clearly fail to support the hypothesis and describe practical and statistical reasons suggesting why the original data cannot be easily replicated. A power analysis suggests that to find the effect in a general sample, one should plan to have 17,000 to 40,000 subjects.

Child↗
PubMed1994

Source monitoring during name recognition in older adults: psychometric and electrophysiological correlates.

The hypothesis that source monitoring in older adults is specifically related to frontal lobe function was tested. In a fame-judgment task, older adults' ability to monitor the source of name familiarity was independent of their short-term recognition ability. Source errors were not related to performance on the Wisconsin Card Sorting Test, a psychometric index of frontal function, or to the initial orienting response of the contingent negative variation (CNV), a frontally based electrophysiological measure, even though these "frontal" measures were reliably related to each other. Source error was predicted by the latter portion of the CNV, the expectancy response, and by the Benton Facial Recognition Test, a visuoperceptual task not typically linked to frontal function. These data suggest that the accuracy of source attribution in older adults depends on various attentional control processes, not all of which may be frontally based.

Aged↗
PubMed1993

Memory for source after traumatic brain injury.

A fame judgment task was used to distinguish subjects' ability to recognize previously presented information from their ability to recognize the source of that information. Traumatic brain injured (TBI) subjects were impaired relative to controls with respect to verbal recall and recognition as well as memory for source. However, memory for source was demonstrated to be independent of explicit indices of recall and recognition ability. It was also found to be an extremely sensitive index of coma duration in the TBI subjects. The anticipated relationship between source memory and a putative index of frontal function (Wisconsin Card Sorting Test) was modest relative to the relationship between source memory and subjects' performance on a complex visual pattern matching task (Benton Facial Recognition), raising questions about hypothesized cognitive and neurophysiological mechanisms underlying memory for source.

Accidents, Traffic↗