Biomedical subjects

M H Fischer

Publications and source records attributed to M H Fischer.

At least 19 recordsLinked to original sources

PubMed2001

Number processing induces spatial performance biases.

BACKGROUND: Response speed in parity judgments is faster with the left hand for small numbers (e.g., 1 or 2) and faster with the right hand for larger numbers (e.g., 8 or 9). This effect suggests that number processing can induce systematic spatial biases in bisection tasks. METHOD: Neurologically healthy participants bisected visually presented stimuli with a pencil. Stimuli were long strings of uniform digits (experiment 1) or lines with single digit flankers (experiment 2). RESULTS: Bisection performance was biased to the left of center for strings made of digits 1 or 2 and to the right of center for strings made of digits 8 or 9. Line bisection was biased toward the flanker representing the larger magnitude, regardless of its position. CONCLUSIONS: These results extend previous findings and support the notion of an automatic association of number magnitudes with spatial response codes. The effect may be useful for an assessment of semantic number processing in special populations.

Adult↗

PubMed2001

Probing spatial working memory with the Corsi Blocks task.

The Corsi Blocks task (CBT) measures spatial memory span, but methodological differences across previous studies prevent a clear appreciation of perceptual, memory, and motor contributions to spatial span. CBT performance in a standard condition was compared to performance with longer encoding intervals (3 vs 1 s), longer memory intervals (9 vs 1 s), or fewer response alternatives (all nine vs only the relevant positions). All experiments also contrasted ascending vs descending order of item difficulty and recorded response-initiation times. Performance improved with longer encoding and maintenance intervals and with fewer response alternatives. Item order had no reliable effects. Response-initiation times were a useful additional measure of spatial span. Implications of these findings for research using the CBT are discussed.

Humans↗

PubMed2001

How sensitive is hand transport to illusory context effects?

A recent report that hand transport was sensitive to a size-contrast illusion (SCI) implied that the distinction between visual processing for perception versus action might only affect visual information obtained late during reaching. In this study, the presence of a perceptual SCI did not affect reaction time, movement time, or movement amplitude. However, both perception and action became sensitive to the SCI with memory-based responses. It is concluded that the distinction between visual processing for perception versus action does extend to hand transport. Immediate action is entirely based on veridical visuo-motor representations, whereas even slightly delayed actions begin to reflect distorted perceptual representations.

Adult↗

PubMed2001

Distractor effects on pointing: the role of spatial layout.

There is a debate about how task-irrelevant visual distractors influence motor responses. Inconsistent findings in previous studies may reflect the use of different spatial layouts. In this study, participants pointed to randomly lateralized targets under full viewing conditions, either with or without a single distractor present. Distractor location, size, and spacing from the target were systematically manipulated while target size and movement amplitude remained constant. Larger distractors facilitated reaction times and slowed movement times. Distant distractors facilitated only reaction times. Movement endpoints were biased away from distractors. The single distractor also modulated perceived target size. These results are discussed in the context of current theories of the role of visual perception for action control.

Adult↗

PubMed2001

An investigation of the time course of flanker effects in the landmark task.

To assess attentional, perceptual and motor contributions to pseudoneglect, the landmark task requires pointing to the subjectively shorter end of accurately pre-transected horizontal lines. We presented irrelevant flankers 317, 567 or 967 ms prior to the line transector on a touch screen and recorded reaction times, movement times, landing points and uncertainty of pointing decisions. Flankers were visible for 167 ms to exclude perceptual biases and lines disappeared upon response initiation to prevent subsequent corrections. Healthy participants showed pseudoneglect and a response bias toward the flanker. This finding is interpreted as evidence for inhibition of return and casts doubt on an attentional interpretation of previously reported flanker effects.

Adolescent↗

PubMed2001

The influence of nutrition on IGF-1 in tube-fed profoundly retarded adults.

OBJECTIVE: This study was conducted to determine whether IGF-I concentrations are low in nonambulant profoundly retarded adults and to identify associated nutritional factors. METHODS: Serum IGF-I, albumin, pre-albumin, creatinine, zinc (Zn) and plasma amino acids were measured before and after a four-week 25% increase in formula in 25 individuals, divided into those fed by day (Group A) or by night (Group B). RESULTS: Circulating IGF-I was low in nine of the 22 subjects (40.9%) included in the analysis. Mean IGF-I increased 10.4% (p=0.004). Despite high intakes of essential amino acids and Zn, initial mean plasma tryptophan and phenylalanine were low, and serum Zn was low in 40.9% of subjects. Plasma tryptophan was low at both samplings and correlated with circulating IGF-I concentrations (p=0.02) at the beginning of the study. Serum IGF-I and Zn also correlated (p=0.02) initially. CONCLUSIONS: IGF-I is commonly low in this population and is associated with low plasma amino acid and Zn concentrations, despite high intakes of these nutrients. The causes and clinical implications of these abnormalities need further study.

Adult↗

PubMed2000

Word centre is misperceived.

Normal readers were asked to mark the middle of visually presented words. They made systematic errors toward the left, indicating an overestimation of the length of the beginning of a word. The number of characters determines the size of this error. The bias extended to pseudowords, letter strings, and symbols, but not to blocks, dashes, and lines. Finally, the bias was sensitive to typographical errors but not to colour cuing. These findings suggest that special cognitive operations determine the perceived spatial extent of words. Implications for our understanding of perceptual and cognitive processes in reading are discussed.

Adult↗

PubMed2000

An unfermented gel component of psyllium seed husk promotes laxation as a lubricant in humans.

BACKGROUND: In addition to increasing stool weight, supplements of psyllium seed husk produce stools that are slick and gelatinous. OBJECTIVE: Our purpose was to test the hypothesis that a gel-forming fraction of psyllium escapes microbial fermentation and is responsible for the characteristics that enhance laxation. DESIGN: Fifteen healthy adults consumed controlled diets for two 7-d periods, one of which included 8.8 g dietary fiber provided by 15 g/d of a psyllium seed husk preparation. All stools were collected and evaluated and diet was monitored throughout. RESULTS: Psyllium significantly increased the apparent viscosity of an aqueous stool extract, stool moisture, and wet and dry stool weights. A very viscous fraction, not present in low-fiber stool and containing predominantly 2 sugars that are also found in abundance in psyllium husk, was isolated from psyllium stool. CONCLUSIONS: In contrast with other viscous fibers that are fermented completely in the colon, a component of psyllium is not fermented. This gel provided lubrication that facilitated propulsion of colon contents and produced a stool that was bulkier and more moist than were stools resulting with use of comparable amounts of other bowel-regulating fiber sources.

Adolescent↗

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↗

PubMed1999

An investigation of attention allocation during sequential eye movement tasks.

Allocation of visuo-spatial attention during dynamic viewing was investigated with a dual task. Primary tasks (reading, scanning, searching) all required sequential left-to-right eye movements. An additional speeded manual response was made to a visual probe that appeared early or late after the onset of a randomly determined fixation (25 or 170 msec probe delay). The probe appeared to the left, directly above, or to the right of the currently fixated character (-10, -5, 0, +5, or +10 characters probe eccentricity). Faster probe detection near the location of the forthcoming eye fixation was found in the search task, but not during reading or scanning. Fixation times increased and saccade lengths decreased as a consequence of probing in all three tasks. Fixations were, however, less prolonged when the probe appeared in the right than when it appeared in the left hemifield, and saccades were greatest when the probe appeared at +10 characters. The results extend the notion of goal-directed attention shifts to free viewing and highlight the impact of task-specific processing requirements.

Adolescent↗

PubMed1999

Memory for word locations in reading.

Sentences were presented in various spatial formats, and readers localised one word of each sentence using a mouse cursor directly after reading. There was a localisation advantage for cumulative over single-word displays, for left-to-right presentation over presentation in a 3 x 3 grid, and for complete over incomplete sentences. Comparing performance for predictable and unpredictable word locations suggests that word location memory in reading decays within three seconds to a span of only 2-3 entries, and that readers can then reconstruct word locations from item memory. Implications for the role of spatial cognition in reading are discussed.

Adolescent↗

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↗