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Biomedical subjects

G Geffen

Publications and source records attributed to G Geffen.

At least 19 recordsLinked to original sources
PubMed2002

Lateralization of speech production using verbal/manual dual tasks: meta-analysis of sex differences and practice effects.

The present paper reviews the findings of 30 years of verbal/manual dual task studies, the method most commonly used to assess lateralization of speech production in non-clinical samples. Meta-analysis of 64 results revealed that both the type of manual task used and the nature of practice that is given influence the size of the laterality effect. A meta-analysis of 36 results examining the effect size of sex differences in estimates of lateralization of speech production indicated that males appear to show slightly larger laterality effects than females.

Attention↗
PubMed2001

Genetics of cognition: outline of a collaborative twin study.

A multidisciplinary collaborative study examining cognition in a large sample of twins is outlined. A common experimental protocol and design is used in The Netherlands, Australia and Japan to measure cognitive ability using traditional IQ measures (i.e., psychometric IQ), processing speed (e.g., reaction time [RT] and inspection time [IT]), and working memory (e.g., spatial span, delayed response [DR] performance). The main aim is to investigate the genetic covariation among these cognitive phenotypes in order to use the correlated biological markers in future linkage and association analyses to detect quantitative-trait loci (QTLs). We outline the study and methodology, and report results from our preliminary analyses that examines the heritability of processing speed and working memory indices, and their phenotypic correlation with IQ. Heritability of Full Scale IQ was 87% in the Netherlands, 83% in Australia, and 71% in Japan. Heritability estimates for processing speed and working memory indices ranged from 33-64%. Associations of IQ with RT and IT (-0.28 to -0.36) replicated previous findings with those of higher cognitive ability showing faster speed of processing. Similarly, significant correlations were indicated between IQ and the spatial span working memory task (storage [0.31], executive processing [0.37]) and the DR working memory task (0.25), with those of higher cognitive ability showing better memory performance. These analyses establish the heritability of the processing speed and working memory measures to be used in our collaborative twin study of cognition, and support the findings that individual differences in processing speed and working memory may underlie individual differences in psychometric IQ.

Adolescent↗
PubMed2000

Sex differences in the perception of tactile simultaneity.

A tactile simultaneity task was used to investigate the effects of sex on simultaneity thresholds. Participants were required to judge whether pairs of tactile stimuli delivered unimanually or bimanually were simultaneous. Unimanual stimulation delivered stimuli to the same cerebral hemisphere, while bimanual stimulation resulted in the delivery of one stimulus to each hemisphere, therefore requiring interhemispheric transmission before judging simultaneity. The data of 114 right-handed participants were analysed. Females (N = 56) perceived simultaneity at longer intervals than males (N = 58) when bimanual stimulation was received. Furthermore, males had shorter interhemispheric transmission times (10.9 ms) than those of females (15.0 ms). The results also provided some support for the predictions of the Hemispheric Equivalence Model of temporal processing since bimanual simultaneity thresholds were longer than unimanual; and unimanual stimulation of the left vs right hand did not differ. An advantage for stimulation of right hand first (vs left first) in the bimanual condition was small (2.7 ms), and was the only prediction of the Left Hemisphere Specialisation Model to receive support. A modification of the Equivalence Model which allows for a slight left hemispheric advantage is proposed.

Adolescent↗
PubMed2000

Effects of preferred hand and sex on the perception of tactile simultaneity.

The effects of handedness, sex and the influence of hand placement in extrapersonal space on temporal information processing was investigated by measuring thresholds for perceiving the simultaneity of pairs of tactile stimuli. Simultaneity thresholds of preferred right handed and left handed university students with left hemisphere speech representation were compared using unimanual and bimanual stimulation at three hand placements (midline, lateral and crossed). In unimanual conditions two fingers of one hand were stimulated (single hemisphere), whereas in the bimanual conditions one finger of each hand was stimulated (cross hemispheres). Bimanual minus unimanual thresholds provided an estimate of interhemisphere transmission time (IHTT) regardless of hand placement. The effects of hemispace varied with the type of stimulation. With unimanual stimulation, overall thresholds were longer at the midline placement, however, with bimanual stimulation, thresholds were longer when the hands were spatially separated (crossed and/or uncrossed). Left handers' IHTTs were 8 ms faster than those of right handers. IHTTs in males were faster than females with hands placed in lateral (by 10.8 ms) or crossed (by 9.8 ms) but not midline positions. It was concluded that the cerebral hemispheres are equally capable of discriminating temporal intervals, but that the left hemisphere predominates when there is uncertainty about location of stimulation.

Adolescent↗
PubMed1997

Mild head injury and speed of information processing: a prospective study of professional rugby league players.

The sensitivity of several short tests of speed of information processing to the effects of mild head injury in rugby league football was investigated. The measures used were the Symbol Digit Modalities Test, the Digit Symbol Substitution Test, and the Speed of Comprehension Test. Two studies were conducted, the first to examine the effect of practice, the second to determine sensitivity to cognitive impairment immediately following injury. The first study established alternate form equivalence and demonstrated that performance on the Speed of Comprehension and Digit Symbol Substitution tests improved with practice, whereas the Symbol Digit Modalities test remained stable. A second study of 10 players who subsequently sustained mild head injuries showed that measures of speed of information processing were sensitive to impairment in the postacute phase, whereas an untimed task of word recognition (Spot-the-Word) was not. Speed of Comprehension was more sensitive to postinjury impairment than either the Digit Symbol Substitution or Symbol Digit Modalities tests. A repeated baseline assessment before injury using the higher score to reflect a player's potential, allowed measurement of impaired performance on sensitive tests.

Acute Disease↗
PubMed1996

Temporal integration of events within and between the cerebral hemispheres.

The effect of interhemispheric transmission time (IHTT) on temporal perception was investigated by comparing simultaneity thresholds under unimanual and bimanual stimulation conditions. In the unimanual conditions the tactile stimuli were delivered to the same hand and were received by the same hemisphere, but in bimanual conditions, where stimuli were delivered to different hands, interhemispheric communication was necessary in order to compare the timing of the two stimuli. Randomised order of stimulating the fingers of the hands was compared with consistent stimulation of each hand. Previous studies have used only consistent stimulation. Thirty-two undergraduate university students (16 males and 16 females) were tested. Bimanual simultaneity thresholds were significantly higher than unimanual. Previous research showing an absence of laterality effects for simultaneity judgements was confirmed, supporting a hemispheric equivalence model of temporal processing. Simultaneity thresholds were not affected by randomisation of stimulus location, indicating that expectancy effects were not responsible for the difference between bimanual and unimanual thresholds. The implication of these findings is that temporal perceptions are affected by the process of interhemispheric transmission.

Adolescent↗
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↗