Biomedical subjects

M H Fischer

Publications and source records attributed to M H Fischer.

At least 19 recordsLinked to original sources

PubMed1999

Visuomotor mental rotation of saccade direction.

This investigation studied the latencies of saccadic eye movements that were directed away from a target by a variable angular distance, which was given by instruction. Such a movement presumably requires an intentional, visuomotor mental rotation of the saccade vector, resulting in prolonged reaction times. From a study on the control of directed hand movements, it has been hypothesized that all visuomotor and visual mental rotation tasks share a common processing stage. We tested this hypothesis with a saccade task in which subjects shifted their gaze either towards (0 degrees, pro-saccade), or 30, 60, 90, 120, 150, or 180 degrees(anti-saccade) away from a randomly cued position on an imaginary clock face. With four different cueing conditions, latencies increased monotonically with required gaze shift from 0-150 degrees, thus exhibiting a mental rotation latency pattern. However, we also found anti-saccades faster than 150 degrees gaze shift and slower rotation speeds with peripheral cues than with central cues. Together with the overall shallower latency increase compared with previous findings with mental rotation tasks, these results cast doubt on the notion of a common, central processing mechanism for the different types of tasks.

Cues↗

PubMed1998

Unspaced text interferes with both word identification and eye movement control.

Subjects read either normal text, text in which the space information between words was absent (either spaces were removed filled with x), or text in which spaces were preserved but the words were flanked by x. In two experiments, reading rate decreased by approx. 50% when space information was not available, suggesting that reading unspaced text is relatively difficult. The removal of space information increased the effect of word frequency on the fixation times for selected target words, indicating that word identification was interfered with by the lack of spaces. In addition, removal of space information influenced the initial landing positions on words, indicating that eye movement control was affected by the absence of spaces. Further analyses were conducted that explored the relationship between these two effects.

Eye Movements↗

PubMed1997

Speed and sequential effects in reaching.

To investigate the impact of future task demands on reaching, participants performed repetitive sagittal-plane reaches at low and high speeds. In a control condition, they reached from a start location to a target and back. In the experimental conditions, they reached from the start to the target, then to a second target (the location of which varied between trials), then back to the first target, and finally back to the start. Contributions of the hip, shoulder, and elbow to reaches made to the first target depended on the second target's location, on movement speed, and on repetition. Participants combined sustained and transient postural adjustments to minimize effort. The results support the knowledge model of movement selection (D. A. Rosenbaum, L. D. Loukopoulos, R. G. M. Meulenbroek, J. Vaughan, & S. E. Engelbrecht, 1995) but also call for its elaboration. Variants of the model are explored through simulations of the above study.

Adult↗

PubMed1996

Bisection performance indicates spatial word representation.

From reading errors of a neurological patient, Caramazza and Hillis concluded: (1) that word length is part of the cognitive representation of words; (2) that the spatial reference frame of this representation is centered on the word; and (3) that this representation is orientation-invariant [Nature (London), 346 (1990) 267-269]. To test these three hypotheses about normal cognition, healthy subjects bisected either lines with word flankers or English words. The length of word flankers systematically affected line bisection, supporting the first hypothesis. In conflict with the remaining hypotheses, however, word bisection was biased toward their beginnings for horizontal words but not for vertical words. A similar bias with pronounceable non-words (but not with meaningless letter strings) and an increase of the word bisection bias in non-native readers suggest that overestimation of the spatial extent of word beginnings is related to lexical access. An attentional scaling hypothesis is proposed that also accounts for a similar eye fixation bias in normal reading.

Adolescent↗

PubMed1996

Mindless reading revisited: eye movements during reading and scanning are different.

In an extension of a study by Vitu, O'Regan, Inhoff, and Topolski (1995), we compared global and local characteristics of eye movements during (1) reading, (2) the scanning of transformed text (in which each letter was replaced with a z), and (3) visual search. Additionally, we examined eye behavior with respect to specific target words of high or low frequency. Globally, the reading condition led to shorter fixations, longer saccades, and less frequent skipping of target strings than did scanning transformed text. Locally, the manipulation of word frequency affected fixation durations on the target word during reading, but not during visual search or z-string scanning. There were also more refixations on target words in reading than in scanning. Contrary to Vitu et al.'s (1995) findings, our results show that eye movements are not guided by a global strategy and local tactics, but by immediate processing demands.

Adult↗

PubMed1994

Less attention and more perception in cued line bisection.

Two experiments tested whether bias in cued line bisection resulted from perceptual grouping or attentional factors. Before trying to bisect a line, subjects had to report two lateralized letters. These cues were either equally spaced (Experiment 1) or asymmetrically spaced (Experiment 2) with respect to the line. No effect of order of cue-report on performance was found, arguing against the role of attentional factors. Bisection was systematically biased toward the closer-spaced cue. These findings in normal subjects suggest that cuing effects are due to perceptual rather than attentional factors.

Adult↗

PubMed1989

Apparent nutrient absorption and upper gastrointestinal transit with fiber-containing enteral feedings.

Upper gastrointestinal tract function in humans was investigated by studying the acute effects of supplementing enteral feedings with dietary fiber. Serum concentrations of folate, zinc, and glucose were determined at timed intervals for 4 h after ingestion of nutritionally complete liquid meals containing test doses of folate and Zn of two and six times the RDA, respectively, with or without addition of 10 or 15 g of soy polysaccharide fiber. Mouth-to-cecum transit time was determined by measuring breath hydrogen produced from lactulose added to the meals. Both levels of fiber significantly lengthened transit time. Serum folate concentrations were significantly lower from 45 to 150 min after one or both fiber-containing meals relative to the fiber-free meal. Only the higher-fiber meal significantly lowered serum Zn concentrations. This study demonstrated that dietary fiber can decrease apparent nutrient absorption and increase transit time in the upper gastrointestinal tract without affecting apparent glucose absorption.

Adult↗

PubMed1989

Long-term nutritional status of an enterally nourished institutionalized population.

Growth and nitrogen nutriture were evaluated during a yearlong study of 11 profoundly retarded nonambulatory institutionalized youth who were fed by gastrostomy and received anticonvulsants. The effects of dietary fiber and vitamin D were assessed by determining plasma levels and balances of zinc, magnesium, calcium, and phosphorus in a subset of six patients. Increase in body weight was 3.4 +/- 2.4 kg (means + SD), in height, 5.9 +/- 3.9 cm during the year. N balance remained positive throughout the study. Zn and Ca balances suggested that needs for this population may be greater than or equal to 150% of the Recommended Dietary Allowance. Vitamin D supplementation had no effect. Soy polysaccharide fiber intakes of 18-24 g/d compared with 0 or 12-20 g fiber/d significantly improved N and P retentions. Although the determination of nutrient needs of a severely disabled population is complex, our results suggest N and energy but not Zn and Ca allowances for a healthy population may be satisfactory guidelines.

Adolescent↗

PubMed1988

Bone status in nonambulant, epileptic, institutionalized youth. Improvement with vitamin D therapy.

This study was conducted to determine if the adverse effects of anticonvulsant drug therapy and nonambulancy on bone status could be overcome with vitamin D therapy in severely handicapped individuals. Six male and five female gastrostomy fed, nonambulant, epileptic, profoundly mentally retarded individuals ranging in age from 7 to 17 years were given vitamin D therapy at a dosage of 4,000 IU/m2 body surface area/day for 6 months. Photon absorptiometry and biochemical indices of bone status were measured to follow the effects of therapy. Bone mineral content expressed as a percentage of normal improved by 11 percent (p less than 0.01), from 59.6 to 66.1 percent. Tartrate-resistant acid phosphatase, total alkaline phosphatase, and the bone isoenzyme activities declined 11 percent, 18 percent, and 11 percent respectively. These reductions were not statistically significant but they were consistent with the improvements observed by photon absorptiometry. The results of our study suggest that a conservative supplement of vitamin D will improve the bone status of severely disabled youths.

Adolescent↗

PubMed1981

Urinary levels of blood group A trisaccharide: observations in two siblings with neuronal ceroid lipofuscinosis.

A readily detectable carbohydrate in the urine of two siblings with neuronal ceroid lipofuscinosis was found to be the blood group A trisaccharide. One child expired before blood typing was done while the other sibling was AB. This latter child excreted greater amounts of the trisaccharide than a group of blood type A subjects with different diagnoses when all the subjects were receiving whole or skim milk by nasogastric feedings. While the relevance of this observation to neuronal ceroid lipofuscinosis is unknown, it has been shown that the trisaccharide may be a major urinary carbohydrate depending on diet and blood type.

ABO Blood-Group System↗

PubMed1981

The composition of tuberous sclerosis grey matter.

The chemical analysis of grey matter from a tuberous sclerosis subject indicated the presence of two different types of grey matter based on two distinctly different ganglioside concentrations. Both samples had gangliosides of reduced concentration with an abnormal composition compared to normal grey matter as evidenced from their thin-layer chromatography profiles. Analyses of the glycoprotein fraction from both samples revealed increased glycoprotein content, particularly in total carbohydrate. This observation was consistent with previous studies of angiofibromas and angiomyolipomas.

Brain↗

PubMed1980

Tryptophan and lysine metabolism in alpha-aminoadipic aciduria.

Two brothers previously diagnosed as having alpha-aminoadipic aciduria (alpha-AA) were subjected to a tryptophan loading test to determine if their condition resulted from a defect in the alpha-aminoadipate aminotransferase (kynurenine aminotransferase) system. Normal increases in kynurenic and xanthurenic acids eliminated this possibility. Further analyses of their urines revealed that both boys had measurable amounts of previously undetected alpha-ketoadipic acid (alpha-KA) before and after the loading test. A reexamination of speciments from a prelysine and postlysine loading test reconfirmed the existence of alpha-KA in their urines at the time the original observation of alpha-AA was made. The response to the lysine load was a predictable increase in both alpha-AA and alpha-KA. The boy who had been referred to this institution with a learning defect responded to the tryptophan load with a slight decrease in alpha-AA and an unpredicted decrease in alpha-KA and 3-hydroxykynurenine. His mentally normal brother showed a significant decrease in alpha-AA and major increases in all other measured metabolites including alpha-KA. The latter results were compatible with a defect in the oxidative decarobxylation of alpha-KA. A comparison of the urinary alpha-AA and alpha-KA concentrations in our subjects with comparable data in mentally normal and mentally retarded patients with this condition suggested that the retardation may result from other causes.

2-Aminoadipic Acid↗

PubMed1977

Chemical analysis of an angiofibroma from a patient with tuberous sclerosis.

Amino-acid analyses on the acid hydrolysates of an angiofibroma and skin established that the former tissue contained less collagen than skin based on the reduced content of hydroxyproline, glycine, proline and alanine in the tumour. From lysosomal enzyme measurements it became evident that the specific activities of the hexosaminidases, beta-glucuronidase and beta-galactosidase were elevated. Analyses of the alcohol insoluble fraction following pronase digestion revealed that the tumour contained more acidic glycosaminoglycan (AG) than skin as assessed by uronic acid and hexosamine measurements. More outstanding, however, was the seven-fold increase in the total carbohydrate in the AG fraction of the tumour. The overall composition of this fraction was very similar to comparable material from foetal skin except that the tumour fraction contained increased sulphate concentration.

Adult↗

PubMed1974