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Biomedical subjects

G Geffen

Publications and source records attributed to G Geffen.

At least 19 recordsLinked to original sources
PubMed1989

Focused and divided attention in each half of space with disconnected hemispheres.

The effects of spatial location and strategy of attention on the processing of speech messages were investigated in ten right-handed subjects and four persons with complete forebrain commissurotomy and one case of right hemispherectomy. Lists of simultaneous but different words, with one of each pair spoken by a male and the other by a female, were monitored for target words. The lists were presented to the left ear, the right ear and to both ears (central) in separate conditions. Unimanual responses were made to targets in either voice (divided attention) or to only one of the voices (focused attention). The performance of the clinical subjects was generally less efficient than that of the controls. In contrast to intact subjects, they responded to more distractor and unattended items. They also showed a nonsignificant tendency for better processing of right rather than centrally-presented words. With right-sided presentation two clinical subjects, with extracallosal damage to the right cortex, were unable to divide attention and responded to only one of the voices. These results implicate an intact corpus callosum for efficient use of attention strategies as well as hemispheric differences in the control of attention.

Adolescent↗
PubMed1988

The effects of orientation and maintenance of attention on hemispheric asymmetry for speech perception.

The contributions of orientation and maintenance of attention to the measurement of ear asymmetry was investigated in 20 right handed subjects. The subject listened to dichotic lists and had to respond to a target word in either the male or the female voice only (focused attention), or both voices (divided attention). At random positions throughout the lists the voices changed ears. A switch in voices from one side of space to the other interfered with speech processing during focused attention, but facilitated the detection of targets during divided attention. The interference was greater for the left than the right ear during focused attention. Likewise, facilitation during divided attention was asymmetrical, with right targets receiving faster processing. The qualitative differences of attention strategy on ear asymmetry during dichotic listening may be due to hemispheric differences in preferred attentional modes.

Adult↗
PubMed1987

Perception of similarity and laterality effects in tactile shape recognition.

Similarity judgements were made about pairs of shapes explored haptically with the hands moving in the same (congruent), or opposite direction. Scanning shapes using an opposite manual direction was slower and less accurate. These results enabled stimulus selection for a further experiment that examined laterality effects in the haptic modality. Pairs of shapes were explored and the presence/absence of a target shape indicated using a pedal switch. Males showed a right hand disadvantage, whereas females were equally accurate at recognising target shapes with either hand, and were equivalent to males' left hand recognition accuracy. Direction of hand movements (congruent vs opposite) and target type also interacted with sex. These interactions and the 1-2 sec longer decision time by females suggest sex differences in the use of cognitive strategies rather than in hemispheric specialization of function.

Adult↗
PubMed1986

The development of tactile transfer of information.

A finger localization task was used to investigate interhemispheric transfer of tactile information in children aged 5, 7, 9 and 11 yr. Other-hand responses (cross-localization) were less accurate than same-hand responses for all ages tested. However, the size of the cross-localization deficit was strongly age-dependent, and provided evidence for a developmental improvement in interhemispheric transfer which is consistent with the sequence of myelination of the corpus callosum during the first decade of life. Transfer with mirror-imaged finger positions on the opposite hands was more accurate for younger children, whereas older children were more accurate when finger positions were spatially aligned.

Brain Mapping↗
PubMed1986

Hemispheric specialization and attention: effects of complete and partial callosal section and hemispherectomy on dichotic monitoring.

Dichotic word monitoring tasks were given to four cases with complete forebrain comissurotomy, three cases of partial section of the corpus callosum, one case of right hemispherectomy, and control subjects. The task involved a unimanual response to target words in either ear (divided attention, Experiment 1) or to target words in one voice that changed ears unpredictably (focused attention, Experiment 2). Left-ear extinction, defined as chance level (25%) detection of left-ear targets and 75% right-ear target detection, varied both between and within subjects during divided attention. No examples of extinction were obtained with focused attention. These results highlight attentional aspects of dichotic listening. Neither the structural, hemispheric asymmetry model (Cortex 3, 163-178, 1967), nor the cognitive, attention priming model (Attention and Performance V, pp. 87-97, Academic Press, New York) could account for the obtained results. We propose an alternative account in terms of the different processing modes and attentional capabilities of the two cerebral hemispheres.

Adolescent↗
PubMed1985

The effect of lesions of the corpus callosum on finger localization.

Finger localization was studied in 10 cases of cerebral commissurotomy (four complete, six partial) and 24 normal subjects. Stimulation of one finger with the same hand responding produced ceiling performance in all subjects. Responses with the other hand (cross-localization) were 82% worse with full commissurotomy, 28% worse with the trunk of the corpus callosum sectioned, and 7% worse in the controls. The trunk of the corpus callosum normally transfers tactile information, but the splenium can subsume 50% of this function and tactile transfer with complete commissurotomy exceeded chance levels. The partially sectioned and normal male subjects showed a right-hand stimulation advantage for sequences. In both normals and partially sectioned subjects, cross-localization was poorest when mirror-image transfer of finger sequences was required, while spatial alignment of the fingers facilitated transfer. With complete commissurotomy, response hand orientation did not affect cross-localization. Thus the corpus callosum transmits the position of each hand between the hemispheres.

Adolescent↗
PubMed1985

Auditory attentional abilities in hyperactive children.

Using dichotic monitoring procedures, various aspects of auditory attention were examined in hyperactive children and matched normal controls. Hyperactive children did not show deficits in the ability to sustain attention, although signal detection analysis showed some lowered capacity in both focused and selective attention to targets. Subsamples of learning-disabled and neurologically impaired hyperactive children showed minimal impairment of auditory attentional capacities. It was argued that more evidence concerning task and situational effects is needed before it can be claimed that hyperactive children show attention deficits.

Attention↗
PubMed1982

Speech lateralization assessed by concurrent task performance.

A sequential button pressing task using either the left or the right hand while concurrently performing a speech task was investigated. Subjects with left-hemisphere speech representation, determined by a dichotic monitoring task showed a lateralized practice effect: left-hand performance improved with practice during the speech task, but right-handed performance did not. Subjects with right-hemisphere speech representation showed disruption of either hand with concurrent speech, and no lateralized practice effect. The results from this study suggest the mechanisms mediating speech perception and speech production may not always be concordantly lateralized. A discriminant analysis of the data showed that 93% of subjects could be correctly classified according to side of representation of speech perception given the performance measures on the concurrent tasks.

Adolescent↗
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↗