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Biomedical subjects

R C Martin

Publications and source records attributed to R C Martin.

At least 73 records · Page 4Linked to original sources
PubMed1991

Differential effects of unilateral temporal lobectomy on visuospatial memory and attention.

We investigated free recall of visuospatial arrays in a free-field format in epileptic patients following unilateral temporal lobectomy (TL) (left = 15, right = 17). TL patients exhibited leftward deviation in right hemispace, but more variable response in left hemispace, a pattern that has been observed in healthy adults. This finding is postulated to result from combined preferential right cerebral activation and a tendency to err toward peri-personal space. Temporal lobectomy affected overall leftward deviation by initially shifting deviation more toward the side of lesion. The initial directional shift in immediate memory dissipated over time suggesting that these subtle attentional shifts may be compensated by learning. Consistent with differential cerebral hemispheric mechanisms, absolute vertical errors were greater in right than left TL patients, and absolute horizontal errors were worse in right hemispace.

Adult↗
PubMed1990

The effects of lateralized temporal lobe dysfunction on formal and semantic word fluency.

Word fluency performance was studied in 32 patients with unilateral temporal lobe epilepsy (TLE) and 25 healthy dextral controls. Two word fluency tasks were administered conforming to either formal-based criteria or semantic-based criteria. Performance for TLE patients was assessed both pre-operatively and approximately 1 week following anterior temporal lobectomy. Both formal and semantic word fluency decreased regardless of resection laterality. Left TLE patients performed significantly worse at both pre- and post-operative assessments compared to the right TLE patients, while right TLE patients performed significantly poorer than controls on all verbal fluency criteria at pre- and post-operative assessments. In addition, both TLE and control groups produced significantly fewer formal and semantic words during the second 30-sec portion of each task. These findings are discussed in terms of temporal lobe contributions to word fluency production and lexical semantic processing.

Adult↗
PubMed1990

The consequences of reduced memory span for the comprehension of semantic versus syntactic information.

Aphasic patients with restricted memory spans were assessed on their comprehension of syntactically simple sentences varying in numbers of content words and on their comprehension of sentences matched in content words but varying in syntactic complexity. Three different presentation modes were used: unlimited visual presentation, limited visual presentation, and auditory presentation. The difference between performance in the unlimited and limited modes was used as a measure of the extent to which memory decrements caused comprehension failure. These difference scores were related to memory span in order to assess whether the memory involved in sentence processing overlaps that assessed by a memory span task. For the sentences varying in number of content words, performance was worse for the limited presentation modes than the unlimited mode, and the difference between unlimited and limited presentation modes was highly related to memory span. For the sentences varying in syntactic complexity, there was no clear reduction in performance for limited presentation modes, and the difference scores did not relate to memory span. The results support the view that the processing of sentences with many content words draws on the short-term memory capacity assessed by memory span, while the processing of syntactic complexity does not.

Aged↗
PubMed1990

The contribution of an imagery code to verbal memory.

Free recall for auditorially presented spatial information was examined in a patient with a large right cerebral infarction. Despite normal verbal memory at immediate and 30-minute conditions, the patient exhibited a significant loss in verbal recall at 24 hours and a more severe deficit in the recall of the spatial components of prose passages across all delayed recall conditions. These results suggest that although the verbal code is important early in the learning process, spatial imagery exerts an increasing influence over time. Thus, reliance upon a left hemispheric mediated verbal encoding process may only allow for partial integration of linguistic and visuospatial properties.

Adult↗
PubMed1990

A monoclonal antibody specific to zeatin o-glycosyltransferases of phaseolus.

Zeatin O-xylosyltransferase and zeatin O-glucosyltransferase occur in immature embryos of Phaseolus vulgaris and P. lunatus, respectively. Purified preparations of the xylosyltransferase were used as antigen to elicit the formation of antibodies in mice. Hybridoma clones were produced by fusion of mouse spleen cells with myeloma cell line Fox-NY. A clone secreting monoclonal antibody (MAb), XZT-1, capable of immunoprecipitating both enzymes was obtained. The MAb detected a unique protein band from crude embryo extracts of each species with the correct molecular mass (50 kilodaltons) and relative charge (R(F) = 0.5 and 0.3) of the respective enzymes. Competition experiments with substrates indicated that the glycosyl dinucleotide binding sites of the enzymes are probably not involved in MAb-enzyme recognition. Western blotting of samples from vegetative tissues of P. vulgaris detected a low level of O-glucosyltransferase but not O-xylosyltransferase, in leaves. These findings suggest the occurrence of two genes in P. vulgaris coding for O-glycosylation enzymes with tissue-specific expression. The MAb will be used to screen expression libraries and to obtain pure enzymes for amino acid sequencing and for the production of additional MAbs.

Journal Article↗
PubMed1990

The intracarotid amobarbital procedure as a predictor of memory failure following unilateral temporal lobectomy.

We investigated the efficacy of the intracarotid amobarbital procedure to accurately predict post-temporal lobectomy anterograde amnesia. We presented items at 2 separate times during amobarbital assessment; both early and late item recall were decreased during the injection contralateral to seizure onset indicating sensitivity to bilateral temporal lobe dysfunction. Ten patients for whom follow-up neuropsychological assessment was available failed either the early or late item recognition portions of their amobarbital evaluation ipsilateral to seizure onset, but had hippocampus included in the temporal lobectomy by virtue of satisfactory performance on other tests of hippocampal function. None of these 10 patients displayed postoperative anterograde amnesia, although there was a reduction in material-specific memory in some patients. These results indicate that relying solely on amobarbital memory testing to assess the functional ability of the contralateral temporal lobe to sustain global memory prior to temporal lobectomy may needlessly exclude patients from a viable therapeutic option.

Amnesia↗
PubMed1990

Anterograde memory for visuospatial arrays.

A new test was developed to assess direction of errors and hemispatial differences in anterograde memory for visuospatial arrays of abstract figures. After a series of learning trials, delayed recall of figure placement was obtained in 12 healthy dextral adults. Horizontal and vertical errors were measured for each figure. Mean directional error and mean absolute error were calculated for each subject in left and right hemispace for horizontal and vertical dimensions. Although no hemispatial effect was found for mean absolute error, hemispatial differences were present for mean directional error in both horizontal and vertical dimensions. Overall, horizontal deviations were medial, and vertical deviations were downward. However, these effects reached statistical significance only in right hemispace. The directional errors are believed to be due to an attentional shift toward proximal peripersonal space, in combination with attentional shifts from differential left/right cerebral activation.

Adult↗
PubMed1990

Psychometric construction of the Rey-Osterrieth Complex Figure: methodological considerations and interrater reliability.

Formal scoring criteria for the standard 18 elements of the Rey-Osterrieth Complex Figure were developed and applied to reproductions of 87 healthy young adults. In addition, the effects of immediate recall on delayed performance was investigated. Results indicate (a) the formal scoring criteria can be reliably applied by independent raters; (b) 30-minute recall is significantly higher if immediate reproduction is included compared to 30-minute delay performance without immediate recall; (c) significantly fewer qualitative scoring errors are present at the 30-minute delay if immediate memory is previously assessed; and (d) in addition to an absence of decay over a 30-minute delay, performance significantly improves over this interval. These findings underscore the caution that must be exercised when making specific inferences from test scores alone based upon measures that were obtained in a variety of contexts employing unspecified scoring criteria.

Journal Article↗
PubMed1990

Evaluation of adult aphasics with the Pediatric Speech Intelligibility test.

Results of conventional adult speech audiometry may be compromised by the presence of speech/language disorders, such as aphasia. The purpose of this project was to determine the efficacy of the speech intelligibility materials and techniques developed for young children in evaluating central auditory function in aphasic adults. Eight adult aphasics were evaluated with the Pediatric Speech Intelligibility (PSI) test, a picture-pointing approach that was carefully developed to be relatively insensitive to linguistic-cognitive skills and relatively sensitive to auditory-perceptual function. Results on message-to-competition ratio (MCR) functions or performance-intensity (PI) functions were abnormal in all subjects. Most subjects served as their own controls, showing normal performance on one ear coupled with abnormal performance on the other ear. The patterns of abnormalities were consistent with the patterns seen (1) on conventional speech audiometry in brain-lesioned adults without aphasia and (2) on the PSI test in brain-lesioned children without aphasia. An exception to this general observation was an atypical pattern of abnormality on PI-function testing in the subgroup of nonfluent aphasics. The nonfluent subjects showed substantially poorer word-max scores than sentence-max scores, a pattern seen previously in only one other patient group, namely young children with recurrent otitis media. The unusually depressed word-max abnormality was not meaningfully related to clinical diagnostic data regarding the degree of hearing loss and the location and severity of the lesions or to experimental data regarding the integrity of phonologic processing abilities. The observations of ear-specific and condition-specific abnormalities suggest that the linguistically- and cognitively-simplified PSI test may be useful in the evaluation of auditory-specific deficits in the aphasic adult.

Adult↗
PubMed1989

Syntactic loss versus processing deficit: an assessment of two theories of agrammatism and syntactic comprehension deficits.

This research evaluated Grodzinsky's (1984, 1986a) syntactic loss and Kolk and van Grunsven's (1985) working memory impairment explanations of syntactic comprehension deficits in agrammatic aphasics. Four aphasic patients were evaluated who showed different patterns of impairment on morphological and structural aspects of production. The comprehension tasks compared performance on full and truncated passive sentences. The syntactic loss hypothesis predicted worse performance on truncated than full passives, while the working memory deficit hypothesis predicted the reverse. Neither hypothesis was supported, as the patients performed at a similar level on both types of passives. In addition, there was little relation between the patients' production indices and their comprehension level. The results argue against any global theory of agrammatism that attempts to attribute all agrammatic speech and co-occurring syntactic comprehension deficits to the same source.

Aged↗
PubMed1989

Distinguishing auditory and speech-specific perceptual deficits.

The ability to discriminate speech and nonspeech auditory stimuli was tested in a learning disabled child. The perception of speech stimuli was normal when the stimuli were presented in quiet but below normal when the stimuli were presented in noise. Although the perception of pure tone stimuli and environmental sounds was normal both in quiet and noise, the perception of nonspeech stimuli with rapid changes in acoustic information was impaired in noise. These findings illustrate the importance of relating performance for speech and complex nonspeech stimuli in investigating the basis of speech perceptual deficits. Whereas abnormal performance for speech stimuli coupled with normal performance for complex nonspeech stimuli argues for the existence of specialized speech processing mechanisms, abnormal performance for both types of stimuli, as was found in the present subject, argues for the existence of more generalized auditory processing mechanisms.

Adolescent↗
PubMed1989

Zeatin Glycosylation Enzymes in Phaseolus: Isolation of O-Glucosyltransferase from P. lunatus and Comparison to O-Xylosyltransferase from P. vulgaris.

An enzyme catalyzing the formation of O-glucosylzeatin in immature embryos of Phaseolus lunatus was purified 2500-fold using ammonium sulfate precipitation followed by affinity and anion exchange chromatography. The enzyme uses trans-zeatin as substrate (K(m) 28 micromolar) but not cis-zeatin, ribosylzeatin, or dihydrozeatin. Both UDP-glucose and UDP-xylose can serve as glycosyl donors, with K(m)s of 0.2 and 2.7 millimolar, respectively, for the formation of O-glucosylzeatin and O-xylosylzeatin. In comparison, the UDPxylose-zeatin:O-xylosyltransferase (JE Turner, DWS Mok, MC Mok, G Shaw [1987] Proc Natl Acad Sci USA 84: 3714-3717) isolated by the same procedures from P. vulgaris embryos uses only UDP-xylose as donor substrate and the K(m)s for both zeatin and UDP-xylose are much lower (2 and 3 micromolar, respectively). The chromatographic behavior on affinity columns and molecular weights (approximate M(r) 44,000 daltons) of the two enzymes are similar. Results from substrate competition experiments and enzyme separation by anion exchange HPLC indicate a single, distinct, zeatin O-glycosylation enzyme occurs in embryos of each of these Phaseolus species.

Journal Article↗
PubMed1989

An enzyme mediating the conversion of zeatin to dihydrozeatin in phaseolus embryos.

A reductase catalyzing the conversion of zeatin to dihydrozeatin was detected in soluble fractions of immature Phaseolus vulgaris embryos. The enzyme was partially purified by ammonium sulfate fractionation and affinity, gel filtration, and anion exchange chromatography. NADPH was the only cofactor required for enzyme activity, and the pH optimum was 7.5 to 8.0. The enzyme did not recognize compounds closely related to zeatin, such as ribosylzeatin, cls-zeatin, O-xylosylzeatin, N(6)-(Delta(2)-isopentenyl)adenine, or N(6)-(Delta(2)-isopentenyl)adenosine. No conversion of dihydrozeatin to zeatin by the enzyme was observed. Two forms of the reductase could be separated by either gel filtration or anion exchange high performance liquid chromatography. The high molecular weight isozyme (M(r) 55,000 +/- 5,000) eluted as the second peak from the anion exchange column, while the low molecular weight isozyme (M(r) 25,000+/- 5000) was less negatively charged. The results suggest that side chain reduction occurs at the free base level. In addition, Phaseolus embryos are useful for the detection of zeatin-specific metabolic enzymes.

Journal Article↗
PubMed1988

A developmental study of the auditory Stroop effect.

A pediatric auditory version of the Stroop procedure was developed and administered to 48 normal children from 3 to 6 years of age. Our purpose was to define the developmental course characterizing interaction between auditory and semantic speech dimensions in young children. The procedure was a reaction time (RT) task that required children to respond as quickly and as accurately as possible to words spoken by a male or a female voice. Children were instructed to ignore what was said and to push the "Mommy" button if Mommy was talking or the "Daddy" button if Daddy was talking. Performance was obtained for words with neutral, congruent, and conflicting semantic content. Preschool children manifested processing dependencies that were similar to those observed in adults on the visual Stroop procedure. Conflict between semantic and auditory dimensions significantly increased RT and congruence between the two dimensions significantly decreased RT relative to the neutral condition. The pattern of results indicated that the meaning of words was processed automatically in the normal children. The magnitude of the Stroop effect reflected developmental change with increasing age.

Attention↗
PubMed1988

Differential forgetting in patients with temporal lobe dysfunction.

Delayed recall performance was investigated in 13 patients with temporal lobe epilepsy (TLE) and 13 healthy age-matched controls who were matched on a pairwise basis for initial learning on the Selective Reminding test. TLE patients performed significantly worse on the 30-minute delayed recall condition despite equivalent initial continuous long-term retrieval scores. These data suggest that TLE patients forget at disproportionately rapid rates as compared to healthy controls despite equivalent initial learning. Consequently, delayed recall may increase group discrimination when initial learning levels are similar.

Journal Article↗
PubMed1987

Articulatory and phonological deficits in short-term memory and their relation to syntactic processing.

The relationships between sentence comprehension deficits and deficits in the articulatory or phonological components of short-term memory were investigated. Nonfluent agrammatic patients showed very poor comprehension of syntax while a group of nonfluent patients who were not agrammatic showed good comprehension, despite both groups showing similar degrees of deficits in an articulatory component of memory. The results imply that a disruption of inner rehearsal has little consequence for auditory sentence comprehension, and that the syntactic comprehension deficits of the agrammatic patients could not be attributed to their memory deficit. A patient with a disruption in phonological storage showed good comprehension for many sentences, but was impaired when a difficult syntactic structure was encountered early in a sentence. It was proposed that phonological storage serves to hold words in a phonological form when sentence processing cannot keep pace with sentence input. Although a role for phonological storage was postulated, the impressive degree of syntactic processing that could be carried out by patients with very restricted memory spans implies that there is little overlap between the memory systems disrupted in these patients and the working memory system presumed to be involved in sentence comprehension.

Adult↗