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H G Vaughan

Publications and source records attributed to H G Vaughan.

At least 73 records · Page 4Linked to original sources
PubMed1986

Topography of visual event-related potentials during geometric and phonetic discriminations.

Event-related potentials (ERPs) were obtained to letters during 3 tasks that involved a SIMPLE RESPONSE (SR) to each letter presentation, a FORM discrimination of the letters that formed a closed loop, and a RHYME discrimination of the letters that rhymed with the letter 'v'. The first task only required detection of the letters, the FORM task required a visual-spatial analysis, and the RHYME task, a grapheme-phoneme conversion of the letters followed by a determination of rhyming characteristics. The SR ERPs were morphologically different from the discriminative ERPs, notably by the absence of N2 and P3. The difference wave forms between the discrimination and SR conditions and between the targets and non-targets indicated differential topographies of components associated with the FORM and RHYME tasks in the 300 msec latency region. In both of these tasks, components exhibited distributions localized primarily in the occipital regions, whereas in the RHYME task they extended more anteriorly and encompassed temporo-parietal regions. Thus, although the stimulus presentation was visual, the requirement of a visual-auditory conversion in the RHYME task resulted in activity that was more proximal to auditory regions than when only a FORM analysis of the letters was required.

Adult↗
PubMed1985

Return to alertness after brain-stem hemorrhage. A case with evoked potential and roentgenographic evidence of bilateral tegmental damage.

After a 65-year-old man had received anticoagulation therapy for brain-stem ischemia, a large, bilateral pontomesencephalic hemorrhage developed in the ischemic region. He survived a period of being "locked in" to attain a limited functional recovery. When he first became alert, brain-stem auditory evoked potentials and short-latency somatosensory evoked potentials (SEPs) demonstrated bilateral brain-stem damage; computed tomography revealed a bilateral tegmental hematoma. Results of repeated studies changed little as clinical improvement occurred. Recovery from brain-stem hemorrhage is rare, and return of consciousness with bilateral tegmental involvement is even more rare. The short-latency SEPs are useful in defining the extent of brain-stem damage, but they evaluate structures distinct from those regulating consciousness and cannot predict a return to alertness.

Aged↗
PubMed1985

Event-related potentials associated with the discrimination of acoustic and semantic aspects of speech.

Analysis of a word's acoustic structure must precede identification of its meaning. Therefore, these aspects of speech processing could be associated with event-related potential (ERP) components that differed in their timing. To identify electrophysiologic indices of the cortical processing of acoustic and semantic features of speech, we recorded ERPs to the random presentation of nonsense or real words in four conditions designed to manipulate the extent to which the speech sounds were processed. In one condition subjects responded to all stimuli; in a second and third, to a designated nonsense or real word; and in the final condition to words within a specified semantic category. To define the cortical activity associated with acoustic processing, ERPs obtained when no discrimination was required were subtracted from those recorded during the identification of a specified speech target. The difference waveforms exhibited a negative potential that began about 50 msec after stimulus onset and lasted about 200 msec. Difference waveforms obtained by subtracting the non-discrimination ERP from those obtained during semantic discrimination exhibited a negative potential with similar onset timing. We concluded that the early negative potential indexed acoustic processes necessary for stimulus identification. To identify potentials associated with determination of a word's meaning, we subtracted the verbal discrimination from the semantic discrimination ERPs. This difference waveform exhibited a later negativity beginning at 150 msec and lasting about 250 msec. This potential may be related to the semantic processing of speech.

Adolescent↗
PubMed1985

Intracortical generators of the flash VEP in monkeys.

Flash visual evoked potentials (VEPs) in unanesthetized monkeys were recorded from the cortical surface and from closely spaced intracortical sites together with associated multiple unit activity (MUA). The VEP depth profiles were subjected to current source density (CSD) analysis to delineate the laminar pattern of transmembrane current flows manifested by extracellular source and sinks. The initial surface recorded components (P15 and P18) were generated subcortically within the thalamocortical radiations. The distribution of current sources and sinks associated with two subsequent surface negative components. N24 and N40. demonstrates their generation within laminae IVA and IVCb respectively, both parvocellular thalamorecipient layers. Oscillatory potentials resembling those seen in human VEPs are observed riding on N40; analysis of MUA in conjunction with sources and sinks coincident with these wavelets provides evidence that they derive from both thalamocortical and cortical activity. MUA in the 20-60 msec range shows phasic increases throughout lamina IV, which are maximum in amplitude within lamina IVA. This increased firing is concurrent with the sinks observed within the parvocellular thalamorecipient sublaminae IVCb and IVA. A subsequent component, P65, coincident with a decrease in MUA to below the spontaneous level co-located with a lamina IVCb current source, probably arises from intracortically generated inhibitory activity within IVCb. The next VEP component, a surface negative potential at 95 msec, is coincident with current sources and sinks in lamina III, and is consistent with stellate cell input to supragranular elements. VEP components after N95 are not associated with either MUA or CSD activity and are probably generated in extrastriate cortex. Human counterparts of the simian VEP are proposed.

Animals↗
PubMed1985

Effects of expectation on negative potentials during visual processing.

ERPs were recorded during several RT tasks: simple RT; oddball choice RT; a LIE condition in which subjects were told stimuli would infrequently change, but did not; differential responding to two equiprobable stimuli that were randomized in one condition and alternated in another condition. Subtracting ERPs elicited during simple RT from those elicited during the other conditions, it was found that a negative component, NA, was enhanced, relative to simple RT, in all the other RT tasks. The data of the LIE condition indicated that NA was enhanced by the expectation that unpredictable stimulus changes would occur, even when they did not. The data of the 50/50 alternating RT condition indicated that stimulus changes by themselves enhance NA, even when they are predictable. There appear to be several deflections that comprise NA. NA was obtained with a variety of subtractions that balanced stimulus probability, the structure of the stimulus sequence and task instructions. Similar results were obtained whether subjects made a finger lift response or counted stimuli.

Adult↗
PubMed1985

Electrophysiologic assessment of auditory and visual function in the newborn.

This chapter describes the utility of event-related potential recordings in the assessment of auditory and visual system integrity in the newborn infant. A battery of electrophysiologic tests is described that permits the evaluation of sequential levels of processing within these sensory system.

Auditory Cortex↗
PubMed1985

Patterns of looking behavior in full-term and low birth weight infants at 40 weeks post-conceptional age.

Given the usefulness of visual behavior as an assessment method in older infants, a simple method of visual behavioral evaluation applicable in clinical settings was utilized to gather descriptive data on 42 infants at term. Using an "infant control" method for determining the duration of stimulus presentation, a series of four patterned targets was presented to 25 healthy full-term (FT) and 17 low birth weight (LBW) infants at 40 weeks postconceptional age. Infants were examined in their nursery cribs, and each stimulus was presented until the infant reached a criterion of a 50% or greater decrement in looking time. LBW infants looked for longer time periods, without pause, than FT infants; LBW mean trial length was twice that of FTs. Although total looking time was longer for the LBW group, LBW infants took twice the length of time as FTs to reach the decrement criterion for the first target and thus viewed fewer targets than FT infants. Despite the longer looking of LBW infants, only 41%, as compared to 56% of the FT group, showed an increase in looking time when a new stimulus was presented. The quality of LBW infants' visual behavior was more often marked by long, continuous looking at the same pattern, in contrast to shorter, more discrete and rapidly decrementing looks by the FT newborn. While there was a large variability within groups, the differential patterns of visual behavior are considered likely to reflect variations in processing of information, possibly associated with differences in integrity or maturation of the visual system.

Child Behavior↗
PubMed1984

Differential maturation of cortical auditory evoked potentials to speech sounds in normal fullterm and very low-birthweight infants.

Cortical auditory evoked potentials (AEP) to the consonant-vowel syllables/da/and/ta/and 800Hz tone were recorded at 40 weeks post-conceptional age and at one, two and three months after term in normal fullterm and very low-birthweight infants. As a group, the very low-birthweight infants exhibited significantly less mature AEPs to consonant-vowel syllables than the normal-birthweight infants at 40 weeks post-conceptional age. Consistent but statistically non-significant differences also were found for tones at 40 weeks post-conceptional age, and for all stimuli at one and two months after term. By three months, all the infants exhibited mature AEP morphology and topography.

Age Factors↗
PubMed1984

Preterm infants' manipulative exploration of objects.

Because manipulative exploration of objects may be important to the infant's perception and conceptualization of objects, this study compared full-term infants with preterm infants who are considered to be at risk for cognitive deficits. 30 preterms at 9 months, with age corrected for prematurity, and 20 9-month-old full-terms were videotaped while they explored novel objects; the videotapes were scored for behaviors such as looking, handling, mouthing, turning the object around, fingering, transferring from hand to hand, and banging. There were no differences between the preterms and the full-terms. A "low-risk" subgroup and a "high-risk" subgroup of preterms were then compared with each other as well as to the full-terms. The low-risk subgroup was essentially the same as the full-terms. The high-risk preterms, however, fingered, rotated, and transferred the objects less than either the full-terms or the low-risk preterms. There was a relationship between manipulative exploration at 9 months and later cognitive functioning, suggesting that lower levels of manipulation may be one way in which cognitive deficits originate or are maintained.

Child, Preschool↗
PubMed1983

Periventricular low density as a predictor of neurobehavioral outcome in very low-birthweight infants.

Sixty-four low-birthweight infants (less than 1500 g) were studied prospectively by cranial computerized tomography (CT) and by periodic neurobehavioral assessments. CT scans were obtained at 40 weeks postconceptional age. Neurobehavioral development was assessed by the Bayley Scales of Infant Development at seven, 12 and 18 months corrected age. 47 infants (73 per cent) had areas of diffuse periventricular low densities (PVLD). As a group, infants with PVLD had deviant Bayley scores for both mental and motor development at all follow-up ages. Scores for these infants were significantly lower than scores for infants with normal CT scans or scans with only focal low densities. It is concluded that very-low birthweight infants have an unexpectedly high prevalence of diffuse PVLD, and that this CT finding at 40 weeks postconceptional age is associated with abnormal neurobehavioral development throughout the first 18 months of life.

Brain Diseases↗
PubMed1982

Speech evoked activity in the auditory radiations and cortex of the awake monkey.

To determine whether phonetic features of human speech are reflected in activity patterns of the auditory cortex and its thalamic afferents, concurrent recordings of multiple unit activity (MUA) and averaged evoked potentials (AEP) to 3 synthetic syllables: /da/,/ba/ and /ta/, were performed in awake monkeys. Using clicks, responses from thalamocortical axons and cortical cells were differentiated on the basis of their response latency, spatial distribution, and relationships to AEP components. Voice onset time was reflected in MUA time-locked to consonant release and voicing onset, and phase-locked to the syllables' fundamental frequency. Place of articulation was reflected in discriminative 'on' and phase-locked responses occurring to the formant transitions of the syllables. Duration of the voiced formant transitions was represented by an accentuation of the phase-locked responses occurring to this period. Activity of thalamocortical fibers and cortical cells differed. Thalamocortical fibers were more responsive to speech sounds, as well as responding more frequently with a phase-locked response pattern. Cortical cells responded with sustained activity to a greater degree. Responses to identical portions of the vowels were biased by the preceding consonant. The spatial extent and timing of the responses demonstrate that speech sounds are processed along parallel, but not synchronous, channels. Relevance to human psychoacoustical phenomena is discussed.

Acoustic Stimulation↗