Biomedical subjects

D Lovrich

Publications and source records attributed to D Lovrich.

8 recordsLinked to original sources

PubMed1997

Auditory ERPs during rhyme and semantic processing: effects of reading ability in college students.

Event-related potential (ERP), reaction time (RT), and response accuracy measures were obtained during the phonological and semantic categorization of spoken words in 14 undergraduates: 7 were average readers and 7 were reading-impaired. For the impaired readers, motor responses were significantly slower and less accurate than were those of the average readers in both classification tasks. ERPs obtained during rhyme processing displayed a relatively larger amplitude negativity at about 480 ms for the impaired readers as compared to the average readers, whereas semantic processing resulted in no major group differences in the ERPs at this latency. Also, N480 amplitude was larger during semantic relative to phonological classification for the average readers but not for the impaired readers. Results are compared to a previous study of reading-impaired children on the same tasks.

Adolescent↗

PubMed1996

Late cognitive brain potentials, phonological and semantic classification of spoken words, and reading ability in children.

Event-related potential (ERP), reaction time, and response accuracy measures were obtained during rhyming and semantic classification of spoken words in 10 average (mean age 11.64 years) and 9 impaired reading (mean age 12.10 years) children. The behavioral measures of classification did not distinguish the groups. In the ERPs, rhyme processing produced more pronounced group differences than did semantic processing at about 480 ms, with a relatively more negative distribution for the impaired readers at centroparietal sites. At about 800 ms in both classification tasks, the impaired readers displayed a late positivity that was delayed in latency and of larger amplitude at frontal sites than that for the average readers. The ERP findings suggest that the categorization of spoken words for meaning and sound result in increasingly more aberrant correlates of these processing demands in reading-impaired children.

Adolescent↗

PubMed1994

A developmental study of visual ERP distributions during spatial and phonetic processing.

Ten adults (mean age 19.5 years; S.D. = 1.65) and 10 children (12.2 years; S.D. = 1.28) participated in a choice reaction time study of event-related potential (ERP) correlates of pattern and phonological discriminations of letters. In the form condition, the subjects responded discriminately to letters that did (e.g., b, p) and did not (e.g., f, h) have an enclosed area. Likewise, the subjects responded to letters that did and did not rhyme with "e" in the rhyme task. For both groups, the two late positivities (P600 and P3) were significantly later in the rhyme ERPs than the form as were the RTs associated with the tasks. Distribution and group differences were most notable for the positivity at 380 msec. The P380 distribution did not vary between the conditions for the adults, but there was a more negative distribution in the rhyme condition compared to the form at fronto-central sites for the children. The topographic differences between the form and rhyme tasks at 380 msec were consistent with the involvement of auditory areas in the rhyme task. Generally, however, the children's and adults' wave forms were similar in terms of morphology, peak latency and distribution.

Adolescent↗

PubMed1993

Event-related potential asymmetries in children during pattern and phonemic processing of letters.

Event-related potentials (ERPs) were recorded at left and right anterior temporal, temporal, and parietal sites from ten children (mean age 10.45 years) during three tasks. In the detection task every letter required a response; in the form and rhyme discrimination tasks, a response was required to letters without an enclosed area or to those that did not rhyme with 'e', respectively. For all tasks, N170 peak latency was later at right temporal sites and was more negative in amplitude at right anterior temporal locations than homologous left locations. Also, left-right difference waveforms indicated that right hemisphere ERPs were more negative than the left at 200, 300 and 470 ms for most sites. These lateral differences may reflect a differential activation of the hemispheres during letter processing. Differences among the conditions were most evident for the latest positive peak at 475 ms in which detection resulted in shorter latencies and smaller amplitudes than the discrimination tasks.

Age Factors↗

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

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↗

PubMed1983

Event-related potential and behavioral correlates of attention in reading retardation.

Auditory selective and sustained attention was examined in 12-year-old reading-disabled and normal boys. The reading-retarded group obtained generally low scores on verbal and achievement measures. For selective attention, two tone pip series of differing frequencies were presented, one to each ear. Infrequent signal tone pips of varying pitch were interspersed in each series. As the subjects counted the signals in one ear, event-related potentials (ERPs) were recorded. To evaluate the waveforms, the average amplitude within latency ranges that encompassed the ERP peaks was computed. For the ERPs to the signals, the retarded readers showed significantly less positivity than did the controls in the P3 latency range. The ERPs to the tone pip series displayed a 400 msec period of greater negativity to the attended than to nonattended stimuli, which was similar for the groups. Also, no major group differences were found for the behavioral measures of button-press responses to the selectively attended signals, vigilance, motor coordination, lateral preference, and dichotic listening. Attentive abilities appear intact in children with reading retardation, contrary to those with hyperactivity, and may distinguish these learning disorders.

Achievement↗

PubMedDate not supplied

Topographic analysis of auditory event-related potentials associated with acoustic and semantic processing.

The topography of auditory event-related potentials (ERPs) was examined during 3 kinds of tasks: selection of a specified real word or nonsense syllable from a list; simple detection of each of the same stimuli without discrimination; and classification of a set of words according to a specified semantic category. The potentials that were associated with the additional processing required by the discriminative tasks were disclosed by subtracting the wave forms obtained in the detection condition from those obtained during discriminative performance. Difference wave forms were also derived between the semantic classification and verbal discriminative ERP to delineate the changes associated with the extraction of word meaning. The topography of the ERP associated with stimulus detection was comparable to that found in previous studies of evoked potentials to non-speech stimuli. This distribution was consistent with 2 cortical generators, one within the supratemporal plane and the other on the lateral surface of the superior temporal gyrus. When discriminative performance was required on the basis of acoustic stimulus properties, the topography of the difference wave form that reflected this discriminative processing extended more posteriorly over temporal cortex. Semantic processing elicited a further posterior extension of ERP components by 330 msec after stimulus onset, as well as longer latency potentials that were not present in the verbal selection task. These differences imply that a more extensive portion of language cortex is engaged in semantic classification than in verbal identification.

Adolescent↗