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Biomedical subjects

T Landis

Publications and source records attributed to T Landis.

At least 163 records · Page 9Linked to original sources
PubMed1985

Hemispheric control of speech expression in aphasia. A mouth asymmetry study.

Clinical observation of aphasic patients often shows a dissociation between impaired propositional speech and preserved automatic speech. The question of differing hemispheric control between these speech tasks was examined by measuring asymmetry in facial muscle activity. In spite of right-sided facial palsy, greater opening of the right side of the mouth was seen for spontaneous speech, repetition, and word list generation, suggesting that the damaged left hemisphere still controlled motor output in these propositional tasks. However, greater opening of the left side of the mouth for serial speech and singing indicated at least a relatively greater role of the right hemisphere in these "automatic" tasks.

Adult↗
PubMed1985

Functional inhibition and release: unilateral tachistoscopic performance and stereoelectroencephalographic activity in a case with left limbic status epilepticus.

During prolonged nonconvulsive unilateral left limbic status epilepticus, a natural model of functional hemispheric inhibition, we performed two tachistoscopic experiments, a lexical decision task associated with a RVF (left hemisphere) superiority and a facial matching task associated with a LVF (right hemisphere) superiority. We found that epileptic activity in the left hemisphere, especially rhythmic high-frequency "tonic" discharges, inhibited performance on the lexical task but not on the facial matching task. This suggests that only cognitive activity in the discharging hemisphere is inhibited. Strikingly, the best performance of the right hemisphere was obtained while the left hemisphere was most inhibited, suggesting a functional balance of inhibition and release.

Adult↗
PubMed1985

Dissociated hemispheric superiorities for reading stenography vs print.

In two lateralized tachistoscopic lexical decision experiments at different exposure durations, we found for high-frequency function words written in stenography a shift from a RVF advantage at long exposures to a LVF advantage at short exposures, while for the same words written in print a strong RVF effect persisted. We suggest that a reduction of exposure duration, together with the strong visuo-spatial features in stenography, activate right-hemispheric word recognition. Stenography, a non-orthographic and syllabic-ideographic writing system, could be a model to investigate different hemispheric reading processes in Western subjects.

Adult↗
PubMed1985

On the interpretation of mouth asymmetry.

Greater right-side mouth opening during propositional speech has now been observed in at least eight studies. All current data are consistent with the interpretation that left-hemisphere control of articulation of propositional speech results in greater activity of the right-side lip opening muscles. In addition, expression of automatic speech such as singing, emotion, and possibly prosody can also influence mouth asymmetry, but in the opposite direction, suggesting a relatively greater right-hemisphere role for these types of expression. Further work is needed to confirm these interpretations and to elaborate on the exact neuro-muscular mechanisms and task dependencies responsible for mouth asymmetry.

Facial Expression↗
PubMed1985

Left hemispheric functional compensation in prosopagnosia? A tachistoscopic study with unilaterally lesioned patients.

Clinical observations suggest left hemispheric compensation for prosopagnosia in patients with isolated right posterior lesions. To test this hypothesis we investigated six patients with right posterior lesions, three with and three without prosopagnosia, with a series of tachistoscopic matching experiments. Faces with and without paraphernalia, shapes, objects and words were presented at different exposure durations (unlimited, 1000, 200, 50 and 20 ms). Prosopagnosia patients performed better than non-prosopagnosia patients if pure faces (eyes, nose and mouth only) were presented for an unlimited time, but performed worse than non-prosopagnosia patients if exposure duration was reduced. Patients with prosopagnosia were especially handicapped when required to match emotional expressions. Both patient groups had no difficulty in matching objects and words, even at short exposure durations. The results are discussed with respect to a possible left hemispheric compensation in prosopagnosia patients.

Adult↗
PubMed1984

Evoked potential correlates of figure and ground.

Brain potentials averaged during the viewing of an alternating, positive and negative "hidden man" puzzle picture were averaged from 8 subjects before and after they learned to recognize the figure. After figure recognition in comparison to before recognition, there was significantly more evoked positivity at 64/96 ms latency, and more negativity at 224/256 ms and at 352-480 ms latency over parietal areas during the viewing of the positive picture (recognizable as face) referred to the values obtained during viewing of the negative picture (not recognizable as face). It is hypothesized that separate physiological changes might reflect learned meaningfulness of the figure (which entails increased attention) and figure extraction from ground.

Attention↗
PubMed1984

Experimentally induced semantic paralexias in normals: a property of the right hemisphere.

The recently proposed association between semantic paralexias and right hemispheric reading processes was investigated in normals with a tachistoscopic half-field reading experiment. With extremely brief lateralized exposure of nouns, permitting only 25% of correct reading, semantic paralexias were induced. These semantic substitutions occurred three times more often to LVF (right hemisphere) than to RVF (left hemisphere) presentations, whereas other errors were observed with similar frequency to both visual fields. We concluded that semantic paralexias, as they are observed in patients, occur in normals induced by reduced reading time and are the product of right hemispheric reading processes.

Adult↗
PubMed1984

Transient global amnesia: neuropsychological dysfunction during attack and recovery in two "pure" cases.

Two patients with transient global amnesia are reported. Comprehensive neuropsychological evaluation, during the amnesic episode, as well as follow-up examinations on memory were performed. The course of the amnesia was exemplified by two comparable memory tests in different modalities. Partial retrograde amnesia and complete anterograde amnesia were demonstrated during the transient episode. Objective recovery was found to be slower than subjectively experienced, but test performance was completely normal one month after onset.

Adult↗
PubMed1982

Mouth asymmetry during spontaneous speech.

A high proportion of normal subjects have speech expression controlled predominantly by the left hemisphere. Since the left hemisphere also has stronger control of the right side of the lower face, it might be expected that normal subjects would show a right-sided asymmetry in mouth opening during speech. This hypothesis was tested by measuring lip opening in 196 subjects. Of these, 150 (76%) showed greater right-side opening. This tendency was found for males, females, left- and right-handers in four experiments using two different techniques. Mouth asymmetry during speech may provide an indication of which hemisphere is dominant for expressive speech.

Adolescent↗
PubMed1982

Dissociation of ear preference in monaural word and voice recognition.

The ambiguity in the literature concerning cerebral dominance for voice recognition, has been investigated with a monaural go-no go task, using male and female voices. A left ear advantage for the male, and a right ear advantage for the female voice was found, suggesting that both hemispheres can perform voice recognition. A monaural word recognition test showed the expected left hemisphere dominance.

Adult↗
PubMed1982

Aphasic reading and writing: possible evidence for right hemisphere participation.

Aphasic patients performed two tasks, reading aloud and writing to dictation. In both tasks, success was positively correlated to the emotionality, the imageability and the frequency of the target words. In addition, the patients made more semantic Also, the relative difficulty of words was similar for aphasic patients to read and for normal male subjects to recognize in the left visual field. These results suggest that the performance of the aphasic patients on these language tasks were mediated in part by the right hemisphere.

Agraphia↗
PubMed1982

Visual recognition through kinaesthetic mediation.

A case is reported in which mercury intoxication produced visual symptoms with an unusual compensation. The similarity of this patient to Schn., a much reported neuropsychiatric case, was striking and prompted correlation of the two cases. Experimental psychological studies performed on the present case provide a basis for an understanding of both cases.

Adult↗