Biomedical subjects

Burkhart Fischer

Publications and source records attributed to Burkhart Fischer.

8 recordsLinked to original sources

PubMed2005

Lifespan development of pro- and anti-saccades: multiple regression models for point estimates.

The comparative study of anti- and pro-saccade task performance contributes to our functional understanding of the frontal lobes, their alterations in psychiatric or neurological populations, and their changes during the life span. In the present study, we apply regression analysis to model life span developmental effects on various pro- and anti-saccade task parameters, using data of a non-representative sample of 327 participants aged 9 to 88 years. Development up to the age of about 27 years was dominated by curvilinear rather than linear effects of age. Furthermore, the largest developmental differences were found for intra-subject variability measures and the anti-saccade task parameters. Ageing, by contrast, had the shape of a global linear decline of the investigated saccade functions, lacking the differential effects of age observed during development. While these results do support the assumption that frontal lobe functions can be distinguished from other functions by their strong and protracted development, they do not confirm the assumption of disproportionate deterioration of frontal lobe functions with ageing. We finally show that the regression models applied here to quantify life span developmental effects can also be used for individual predictions in applied research contexts or clinical practice.

Adolescent↗

PubMed2005

Developmental fractionation and differential discrimination of the anti-saccadic direction error.

This partial re-analysis of the data of a total of 433 experimental sessions transfers the distinction of "express" and "regular" latency ranges from the pro-saccade task to the latencies of the anti-saccadic direction errors. Express errors and express saccades (ES) loaded on one and the same PCA factor, and both variables were subject to only minor developmental changes from childhood to young adulthood. Regular direction errors loaded, with opposite signs, on the same factor as pro-saccadic reaction times and were unrelated to express errors; these direction errors showed substantial developmental changes. Our data contribute with new evidence from the anti-saccade task to the long standing debate on whether ES should be considered as a separate type of saccade. Anti-saccadic direction errors with express latencies can be distinguished from those with regular latencies. Future anti-saccade task research should therefore analyse these error types separately in order to look for further evidence in favour of their conceptual and statistical distinction.

Adolescent↗

PubMed2005

Instrumental and test-retest reliability of saccadic measures.

Little is known about the reliabilities of the various measures of saccade control that can be derived from pro- and anti-saccade tasks. This paper presents correlational results of 2 different studies comprising altogether 446 psychiatrically and neurologically healthy participants in the range of 6-88 years. Saccades were elicited under different stimulation conditions and during task blocks of 100 or 200 trials. Odd-even and split-half correlations determined for study 1 (N = 327, age 9-88 years) were found to be good to excellent (.60 < or = r < or = .97) for most measures and generalisable over the entire life-span. The 19-month test-retest correlations obtained in study 2 (N = 117, age 6-18 years) ranged between .43 and .66 after controlling for age, and suggest moderate stability of individual differences over time during childhood and adolescence. Hence, these parameters are very useful for concurrent validity studies at every age, but less so for predictive validity studies with children and adolescents.

Adolescent↗

PubMed2004

The effect of practice on low-level auditory discrimination, phonological skills, and spelling in dyslexia.

Phonological awareness is believed to play a major role in the auditory contribution to spelling skills. The previous paper reports low-level auditory deficits in five different subdomains in 33-70% of the dyslexics. The first study of this paper reports the results of an attempt to improve low-level auditory skills by systematic daily practice of those tasks that had not been passed in previous diagnostic sessions. The data of 140 dyslexics indicate that the average number of unsolved tasks can be reduced from 3 of 5 to 1 of 5. The success rates have values of 70-80% for intensity and frequency discrimination and for gap detection, but reach only 36% for time-order judgement and 6% for side-order judgement. The second study reports that successful low-level auditory training transfers completely to language-related phonological skills and also to spelling with the largest profit in spelling errors due to poor auditory analysis. Control groups (waiting and placebo) did not exhibit significant improvements. It is concluded that low-level auditory deficits should be considered and improved by practice in order to give the dyslexics more phonological help when trying to transfer what they hear to spelling.

Adolescent↗

PubMed2004

On the development of low-level auditory discrimination and deficits in dyslexia.

Absolute auditory thresholds, frequency resolution and temporal resolution develop with age. It is still discussed whether low-level auditory performance is of clinical significance--specifically, for delayed maturation of central auditory processing. Recently, five new auditory tasks were used to study the development of low-level auditory discrimination. It was found that the development lasts up to the age of 16-18 years (on an average). Very similar tasks were now used with 432 controls and 250 dyslexic subjects in the age range of 7-22 years. For both groups the performance in one of the tasks was not related to the performance in another task indicating that the five tasks challenge independent subfunctions of auditory processing. Surprisingly high numbers of subjects were classified as low performers (LP), because they could not perform one or the other task at its easiest level and no threshold value could be assigned. For the dyslexics the incidence of LP was considerably increased in all tasks and age groups as compared with the age matched controls. The development of dynamic visual and optomotor functions and the corresponding deficits in dyslexia are discussed in relation to the auditory data presented here.

Adolescent↗

PubMed2003

Illusory illusions: the significance of fixation on the perception of geometrical illusions.

Some well-known geometrical illusions disappear when the eyes are fixating and saccades are suppressed for a period of time. This disappearance is not accompanied by fading due to stabilisation of the retinal image. Any saccade made on purpose restores the illusion immediately. The fixation time after which some illusions disappeared was measured for four illusions and four subjects each. Effects of practice have been observed after measurements were repeated on successive days. Present theories of vision cannot readily explain the effect.

Fixation, Ocular↗

PubMed2002

Age effects in dynamic vision based on orientation identification.

Dynamic vision considers the time domain of visual processing, presumably a function of the magnocellular system. The temporal visual component is not completely developed at the beginning of school age. The effects of age on a certain aspect of dynamic visual perception are reported in this study of 286 subjects in the age range of 7-68 years. Three simple orientation identification tasks were used: a fixation, a saccade, and an anti task. In each case the subjects had to identify the last of a series of fast changing orientations of a T-symbol before it disappeared after a random time period. The percentage of correct identifications in 50-100 trials was measured for each of the three tasks. In the age range of about 14 to about 28 years the subjects could perform the tasks at 90% correct or better. At younger and at older ages the mean values of the scores are considerably lower due to a higher percentage of subjects with difficulties in the performance of the tasks. It is discussed whether it is the magnocellular system which mediates the dynamic orientation identification in these tasks and which begins to decline relatively early in life in parallel with a relative loss of saccade control.

Adolescent↗

PubMed2002

A turn-key transportable eye-tracking instrument for clinical assessment.

This paper describes a combined instrument (eye tracker and target generator, both head mounted, with integrated data analysis) that tests parameters of saccadic eye movement and fixation control to give insight into the status of functional brain systems. Using three minilasers, the target generato rprojects three visual stimuli, a fixation point and two lateral stimuli, with programmable timing. The controller allows the selection of overlap, 200-msec gap, or remembered saccade trials. Size, maximal velocity, and reaction time are determined for each primary saccade. The number of prosaccades and antisaccades are counted. More saccades--for example, the occurrence and latency of corrective saccades--may be evaluated off line by an interactive PC analysis program. The eye position data can be transferred to a PC. Off-line analysis compares each observed variable relative to an age-matched control group (300 healthy control subjects 7-70 years of age, tested in the overlap condition with prosaccade instructions and in the gap condition with antisaccades). The diagnostic results can be used to elaborate an individual optomotor training program.

Fixation, Ocular↗