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Biomedical subjects

G Geffen

Publications and source records attributed to G Geffen.

At least 37 records · Page 2Linked to original sources
PubMed1981

Dichotic monitoring as a test of hemispheric dominance in cases of epilepsy.

The predictive validity and reliability of a dichotic monitoring test of speech lateralization was assessed in four cases of epilepsy. Speech dominance was subsequently determined by both the intracarotid amylobarbitone test and the results of neurosurgery. On the patients tested, faster reaction times (RT) to target words in one ear was an accurate and consistent indication of contralateral hemispheric dominance. The variability in performance associated with epileptic disorders was reflected in the inconsistent ear differences obtained using target detection rates, however the RT measures yielded stable ear differences.

Adolescent↗
PubMed1981

Phonological fusion in dichotic monitoring.

Phonological fusion (e.g., BACK + LACK perceived as BLACK) was examined in a dichotic monitoring task that required subjects to press a button whenever they thought a predesignated target (e.g., BLACK) occurred. Fusion rate was determined from incidental response to fusible pairs in this task. It was found that a voluntary strategy of selective attention to one ear reduced fusion rate. However, fusions could not be entirely eliminated using this strategy. A signal detection analysis indicated that strategy did not involve a response bias shift, although individual differences in fusion rates unimodally distributed) could be partly accounted for by differences in response bias and discriminatory ability. Phenomenological data suggested that a fusible stimulus pair may yield more than one percept on a single presentation, but not necessarily that same percept on repeated presentations. Reaction time data supported the view that phonological fusion involves parallel processing of fusible items in the language-dominant hemisphere.

Adolescent↗
PubMed1980

The effects of duration of stimulation, preferred hand and familial sinistrality in dichotic monitoring.

Ear asymmetries in dichotic monitoring performance were assessed in 105 subjects (77 M, 28 F). A right ear advantage (REA) was found more often in right than mixed or left handed subjects. Similarly, more left than right handers exhibited left (LEA) or no ear advantages. Handedness did not affect the magnitude of asymmetry. Familial sinistrality could only be examined in male left handers, and was found to increase the incidence of REA's. Non familial sinistrals were equally distributed in terms of left, right and no ear advantage. Overall target detection rates decreased and RT increased as dichotic stimulation progressed, but the ear advantage remained constant throughout the duration of stimulation. Responding hand did not interact with ear stimulated. Dichotic monitoring appears to be a useful non-invasive tool for determining hemispheric dominance for speech perception.

Adult↗
PubMed1980

Comparison of the effects of transcortical and transcallosal removal of intraventricular tumours.

Intelligence and memory functions were tested in 2 patients in whom the corpus callosum had been partially sectioned to remove intraventricular cysts or tumours and in 2 patients in whom similarly-located cysts or tumours had been removed transcortically. A patient with congenital absence of the corpus callosum was also tested. Callosal lesions per se did not appear to be responsible for memory deficits.

Adult↗
PubMed1979

Functional consequences of the transcallosal removal of intraventricular tumours.

Colloid cysts and other benign tumours of the third and lateral ventricles may be exposed through a small incision in the body of the corpus callosum. This approach is practicable even when ventricular dilatation is slight, and is theoretically less likely to cause epilepsy than the more usual transcortical approach. Disturbances of memory have been noted soon after such operations, but do not cause serious long-term disability. Three patients who underwent transcallosal removal of cysts or tumours some years earlier have been tested by procedures designed to demonstrate interhemispheric transfer of information: they were all found to have defects in transfer of tactile data, but not of information obtained visually. They were not aware of this inability, and do not appear to be inconvenienced by it. The transcallosal route is convenient. The operation sacrifices a functionally significant part of the corpus callosum, but the neurological sequelae have seemed acceptable. However, especially in the elderly, stereoventriculoscopic aspiration may be considered as the initial method of treatment.

Adolescent↗
PubMed1978

The development of the right ear advantage in dichotic listening with focused attention.

The influence of selective attention on cerebral asymmetry in 6, 8 and 10 year old children was studied using pre-cued dichotic recall of 1 to 4 pairs of digits. A constant right ear advantage for correct recall from the attended ear and intrusions from the unattended ear was found in all three age groups. The ear difference increased with set size and across serial position with a set size of 4 digit pairs. Thus the number of items in acoustic memory determined the degree of lateral asymmetry. The ability to focus attention on the left ear improved between 6 and 8 years. It was concluded that control of directed attention, which improves with development, and left hemisphere specialization for speech processing, which remains constant, both determine performance in dichotic verbal listening.

Age Factors↗
PubMed1978

Language laterality assessed by unilateral ECT and dichotic monitoring.

A dichotic monitoring test for the lateralisation of speech dominance was compared with testing for dysphasia after unilateral electroconvulsive therapy to each side of the head in 31 patients, and the intracarotid amylobarbitone test in four epileptic patients. Twenty-eight patients shown to be left speech dominant also showed right ear advantages in the dichotic test. Four of the five right speech dominant patients showed left ear advantages. Two patients with bilateral speech representation showed nonsignificant ear asymmetries. The noninvasive dichotic monitoring task is quick and simple and produces large mean ear advantages (14 to 25%) in normal subjects as well as patients.

Adolescent↗
PubMed1976

Development of hemispheric specialization for speech perception.

When lists of word pairs were presented simultaneously in a dichotic monitoring task to three groups of right-handed subjects aged 5, 7 and 11 years, more target words were responded to, and reaction times was shorter, when these occurred in the right rather than the left ear. The magnitude of the effect did not change with age. A signal detection analysis showed that the right ear advantage was due to greater sensitivity of the right ear, rather than a response bias. Hand effects were assessed separately by using binaural stimulation in which each ear received two inputs, one in a male voice and the other in a female voice. The right hand responded to target words in one voice, and the left hand to target words in the other voice. The contribution of a right hand superiority to the ear effect was found to be minimal. The effects of language acquisition and attention strategies on the right ear advantage are discussed. It was concluded that at 5 years of age the left hemisphere is specialized for the analysis of speech signals. This produces a right ear advantage in competitive verbal listening.

Age Factors↗