Biomedical subjects

O Koenig

Publications and source records attributed to O Koenig.

7 recordsLinked to original sources

PubMed1992

Categorical versus coordinate spatial relations: computational analyses and computer simulations.

Results of 4 sets of neural network simulations support the distinction between categorical and coordinate spatial relations representations: (a) Networks that were split so that different hidden units contributed to each type of judgment performed better than unsplit networks; the reverse was observed when they made 2 coordinate judgments. (b) Both computations were more difficult when finer discriminations were required; this result mirrored findings with human Ss. (c) Networks with large, overlapping "receptive fields" performed the coordinate task better than did networks with small, less overlapping receptive fields, but vice versa for the categorical task; this suggests a possible basis for observed cerebral lateralization of the 2 kinds of processing. (d) The previously observed effect of stimulus contrast on this hemispheric asymmetry could reflect contributions of more neuronal input in high-contrast conditions.

Computer Simulation↗

PubMed1991

Transposon mutagenesis in Staphylococcus epidermidis using the Enterococcus faecalis transposon Tn917.

We transformed a clinical Staphylococcus epidermidis isolate with the Enterococcus faecalis transposon Tn917-carrying plasmid pTV1. Loss of plasmid replication was observed at 47 degrees C. Tn917 transposes efficiently and apparently randomly. The transposition frequency could be stimulated by erythromycin. Transposon mutagenesis in S. epidermidis provides a means for genetic study of the various virulence factors of this pathogen.

Blotting, Southern↗

PubMed1991

Mental imagery and dyslexia: a deficit in processing multipart visual objects?

Dyslexic and normal control subjects memorized simple line patterns inside a grid and subsequently judged whether an "X" would have fallen on the pattern had it been present in an empty grid. The patterns were letters and novel shapes. The grids were presented to the left visual field, to the right visual field, or in central vision. Dyslexic subjects had difficulty generating images of multipart patterns, but this deficit was limited to letters. The findings suggest that dyslexics may have selective difficulty integrating visual information stored in long-term memory.

Adolescent↗

PubMed1990

The development of spatial relation representations: evidence from studies of cerebral lateralization.

Twenty-four-5-year-olds and 24 7-year-olds completed two divided-visual-field tasks; one task required subjects to categorize a dot as above or below a line, whereas the other required subjects to determine whether the dot was within 3 mm of the line. There was a relative left-hemisphere advantage for the above/below task and a relative right-hemisphere advantage for the distance task. The results indicate that distinct processing subsystems compute different kinds of visuo-spatial relations as early as 5 years of age.

Attention↗

PubMed1989

Evidence for two types of spatial representations: hemispheric specialization for categorical and coordinate relations.

Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments--on/off, left/right, and above/below--faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance--in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)--faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice.

Adult↗

PubMed1988

Tactual extinction without anomia: evidence of attentional factors in a patient with a partial callosal disconnection.

Tactual extinction was examined in a 43-yr-old left-handed male patient (MM) with a hematoma in the trunk of the corpus callosum sparing the genu and the ventral part of the splenium as well as the cerebral hemispheres. Experiments I and II showed no deficit in tactual perception nor in the inter-hemispheric transfer of tactual information. In Experiment III, MM palpated stimuli differing in their association value, and responded vocally or manually. There was no difference in performance between the hands in unimanual control conditions, but in a dichhaptic condition an overall right-hand advantage was observed, depending on the kind of stimulus and on the mode of response: such results were not observed in control subjects. Results showed that MM's left-hand performance reached right-hand levels after specific modifications in the allocation of attention between the hands or the load of information in haptic memory (Experiment IV). Experiment V revealed a major deficit in the matching of left- and right-hand information only for the dichhaptic procedure. The results are discussed with a view of cerebral mechanisms as dynamic rather than structurally determined: it is suggested that extinction phenomena are sensitive to cognitive strategies and attentional factors and that the corpus callosum plays a critical role in the lateral control of attention to tactual as well as to auditory and visual information.

Adult↗

PubMed1987

Dichhaptic recognition of textures in normal adults.

Dichhaptic procedures usually use nonsense shapes or letters as stimuli. The present study was designed to investigate hand asymmetry in a texture recognition task, in male right-handed adults. An overall left hand (right hemisphere) advantage was observed. However, when examining the order-of-report effect, the asymmetry appeared for the first report only. These results are discussed in terms of inter-hemispheric cooperation that can emerge for the second report.

Adult↗