Spatial localization in left and right visual fields.

Presented a series of single dots tachistoscopically in either the left or the right visual field, Ss task being to locate the dot on a spatial map depicting all of the lot locations presented. 7 experiments were carried out with 232 right-handed male and female undergraduates. For men, localization of the dot was more accurate in the left than in the right visual field, under all testing conditions. Women showed the left-field superiority under some testing conditions; under others they showed no difference between fields. There was no sex difference in over-all accuracy of performance, and simple detection of a dot was not more accurate in 1 field than another for either sex. Results are discussed in terms of a probable "spatial coordinate" system in the right hemisphere of the brain. (French summary) (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of the left and right cerebral hemispheres to line bisection

Thirty-one right-hemisphere lesioned (RHL) patients, 11 left-hemisphere lesioned patients (LHL) and 10 normal controls (NC) bisected lines in three spatial location and four directional cuing conditions. The error direction and error size were analyzed as separate and combined variables. Seventy-seven percent of RHL patients and 45% of LHL patients made abnormally large errors in line bisection. Right-hemisphere lesioned patients were more sensitive to spatial location and directional cuing than NC subjects. In contrast, LHL patients were less sensitive to either condition than NCs. The error direction and error size emerged as dissociable components of line bisection. Right-hemisphere lesioned patients and NC subjects bisected lines consistently to one side of the true center. Left-hemisphere lesioned patients bisected lines equally often on both sides of the true center. Both RHL and LHL patients made larger absolute bisection errors than NC subjects, but the RHL patient's errors were larger than those of the LHL patients. We propose that the greater sensitivity of RHL patients to spatial location and directional cues and the directional consistency of their bisection errors represent contributions of the intact left cerebral hemisphere to line bisection. In contrast, the LHL patient's unrestrained ability to orient to both ends of the line reflects a contribution of the intact right cerebral hemisphere to line bisection. The failure of both groups to accurately bisect lines reflects a common visuospatial processing deficit that is more pronounced following RHLs than LHLs.     

Electroencephalographic signs of compensatory reactions following stroke with location of the focus in the right and left cerebral hemispheres

The authors studied 41 patients with acute disorders of cerebral circulation, a focus in the right hemisphere and 14 with foci in the left hemisphere. The traits of compensatory reactions were studied according to the background and functional EEG, depending upon the severity, stage, localization and lateralization of focal vascular brain lesions. The authors indicate to a rigidity of clinical and EEG changes in patients with right hemispheric localization of the focus which is explained by the authors by disturbances of the higher cortical functions in these patients.     

Physiological responses to verbally inaccessible pictorial information in the left and right hemispheres.

The effects of brief pictorial information on transfer between the cerebral hemispheres were investigated through recordings of skin conductance responses. The stimuli had been judged previously as neutral, positive, or negative by an independent group of participants. The verbally accessible (VA) stimuli were neutral, whereas the brief, verbally inaccessible (VI) stimuli were positive or negative. The VA and VI stimuli were presented simultaneously, in the same visual half-field (intrahemispheric), or in the opposite visual half-field (interhemispheric). In a 3rd condition, there were only VA stimuli in either visual field. The right hemisphere was especially sensitive to negative VI presentations in both the inter- and intrahemispheric groups. The left hemisphere showed a corresponding sensitivity to positive stimuli, but only in the interhemispheric group. These findings confirm the hemispheric roles in mediating positive versus negative emotions and show that left-to-right transfer can take place without linguistic cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical priming in the cerebral hemispheres: automatic in the left hemisphere, postlexical in the right hemisphere?

Automatic and postlexical semantic processing in the cerebral hemispheres was studied by presenting categorically related but nonassociated word pairs (e.g., TABLE-BED) to the left visual field (LVF) or to the right visual field (RVF) in semantic priming experiments. Experiment 1 examined automatic priming across stimulus onset asynchronies (SOAs) of 165 and 750 ms with a low proportion of related pairs and a low nonword ratio, employing a GO-NOGO lexical decision task. In contrast to an earlier view that a larger range of meanings is automatically activated in the right than in the left hemisphere, priming was observed in the RVF/left hemisphere only. SOA did not exert any effects. In Experiment 2, postlexical semantic matching of the prime and the target was encouraged by requiring subjects to respond to both of them at the same time. Now there was priming in the LVF, suggesting that a postlexical matching process works in the right hemisphere. The earlier studies showing a right hemisphere advantage in categorical priming are reinterpreted according to the postlexical right hemisphere hypothesis.     

Form-specific visual priming in the right cerebral hemisphere.

Results of 4 experiments indicate that both within-modality and case-specific visual priming for words are greater when test stimuli are presented initially to the right cerebral hemisphere (RH). In contrast, neither within-modality nor case-specific explicit memory for words is greater when stimuli are presented initially to the RH. Priming is measured using word-stem completion, and explicit memory is measured using word-stem cued recall. In both cases, Ss first rate how much they like words, and then word stems are presented briefly to the RH (in the left visual field) or to the left hemisphere (in the right visual field). Results suggest that at least 2 separate systems encode the visual representations that produce priming. The system that is more effective in the RH is better at representing form-specific information, whereas another system that is not more effective in the RH does not distinguish among distinct instances of word forms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Encoding of geometric and landmark information in the left and right hemispheres of the avian brain.

Chicks were trained binocularly to find food buried under sawdust in the center of a square enclosure. When tested in an enclosure made larger or smaller in size, binocular and left-eyed chicks searched mainly on the basis of relative distance of the food from the enclosure walls, whereas right-eyed chicks searched on the basis of absolute distance. Moreover, binocular and left-eyed chicks relied mainly on global spatial information (i.e., distances from the walls), whereas right-eyed chicks also used information provided by visual landmarks. These results suggest that the right hemisphere of the avian brain (fed mostly by the left eye) is primarily concerned with encoding of relational spatial information, whereas the left hemisphere (fed mainly by the right eye) is concerned with absolute metric information, possibly as part of an encoding strategy based primarily on local (both spatial and nonspatial) cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields—a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Specification of movement amplitudes for the left and right hands: Evidence for transient parametric coupling from overlapping-task performance.

Bimanual coordination tasks suggest transient cross-talk between concurrent specification processes for movements of the left and right hand that vanishes as the time for specification increases. In 2 experiments with overlapping and successive unimanual tasks, the hypothesis of transient coupling was examined for a psychological-refractory-period paradigm. Time for specification was manipulated by varying the delay between first and second signal (Experiment 1) and by precuing the first response (Experiment 2). Participants performed rapid reversal movements of same or different amplitudes with the left and right hands. With different amplitudes, reaction times (RTs) of the second responses were longer than with same amplitudes at short delays, and this disappeared at longer delays in Experiment 1. In Experiment 2, precuing also reduced the difference between RTs of second responses in same-amplitude and different-amplitude trials. These findings are consistent with the hypothesis of transient coupling during amplitude specification obtained with bimanual tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seeing and imagining in the cerebral hemispheres: A computational approach.

Visual recognition, navigation, tracking, and imagery are posited to share certain high-level processing subsystems. A theory of some of these subsystems is formulated, developed in light of an analysis of problems that must be solved by the visual system and the constraints on the solutions to these problems. Inferences about perceptual subsystems are used to develop a theory of how mental images are generated. Support for this theory is adduced from studies of split-brain patients and a review of relevant neuropsychological findings. A computational mechanism is developed to account for how visual function becomes lateralized in the brain; this mechanism is used to predict how the hypothesized processing subsystems become lateralized. Some critical tests of the theory of lateralization of perceptual processing subsystems are reported, and the theory is extended to account for the lateralization of image-transformation subsystems and is used to account for the almost ubiquitous variability evident in the neuropsychological literature on lateralization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorization of disoriented faces in the cerebral hemispheres of normal and commissurotomized subjects.

We examined the capacity of the cerebral hemispheres to process faces that deviate from canonical perspective. In Experiment 1, normal Ss performed a gender categorization of faces presented at varying angular orientations in the left visual field (LVF) or right visual field (RVF). Orientation affected processing speed, more so in the RVF than in the LVF. The function relating reaction times to disorientation of the faces was approximately monotonic and reflected the increased difficulty in extracting relevant configurational information as the faces were rotated from canonical perspective. In Experiment 2, 3 commissurotomized Ss performed the same task. They responded above chance in the 2 visual fields, and the pattern of their results was similar to that obtained with the normal Ss, but the effect of disorientation was considerably more pronounced. It is suggested that the right hemisphere contribution becomes more critical the further the visual pattern departs from conventional view. Issues regarding the specification of processes correcting for disorientation and comparison of normal and commissurotomized Ss are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex dimorphism in the functional organization of the cerebral hemispheres during the memorization of verbal information]

Sexual differences in the hemispheric organization of verbal functions were shown in experiments with dichotic presentation of word lists, in Sternbeg's memory scanning task, in studies of EEG power and coherence while memorizing the lists of dichotically presented words. The efficiency of word retrieval and speed of memory scanning for stimuli presented to the right hemisphere were higher in women. EEG activation while memorizing words was more pronounced in men. There were negative correlations between left ear word retrieval and EEG activation in women. The author's findings showed sexual dimorphism in functional connections within the cortical regions of the brain while memorizing verbal information. The changes in coherence were in positive correlation with the efficiency of word retrieval in women and in inverse correlation in men, and this was evidence for the different physiological significance of changes in coherence in men and women. This suggests that the physiological significance of changes in coherence differs in men and women.     

Prognostic factors in low grade (WHO grade II) gliomas of the cerebral hemispheres: the role of surgery

OBJECTIVE: To assess the role of surgery on survival of patients with grade II gliomas of the cerebral hemispheres. METHODS: One hundred and thirty one low grade hemispheric gliomas surgically treated (biopsied patients excluded) between 1978 and 1989 were retrospectively reviewed. Thalamic, basal ganglia, callosal, or ventricular location were not considered. All tumours were World Health Organisation (WHO) grade II gliomas: 42 fibrillary and 11 gemistocytic astrocytomas, 49 oligodendrogliomas, and 29 oligoastrocytomas. Patients' ages ranged from 14 to 63 (mean 32.9, median 34) years, Karnofsky performance from 0.50 to 0.90 (mean 80.7, median 80), and postsurgical follow up of the living patients from 24 to 190 (mean 97.02, median 93) months. Postoperative external radiotherapy was performed in 49 cases. RESULTS: The overall survival probability at five years was 97.1%, at eight years 76.1%, and at 10 years 62.7% (median survival time 144 months). The impact on survival of the following variables was analysed: age (< 20, 21-40, and > 40 years), Karnofsky score (80-100, 70 < or = 70), histology, tumour extension (T1 < 3 cm, T2 3-5 cm, T3 > 5 cm maximum diameter), extent of surgical resection (S1 radical, S2 subtotal < 10% residual tumour, S3 partial-10%-50% residual tumour), and radiotherapy (either performed or not). A significant positive association with survival at univariate analysis was found for the age group < 20 years (P = 0.003), for total and subtotal surgical resections (S1 and S2; P < 0.001) and for the non-irradiated patients (P = 0.0049), whereas a shorter survival probability was noticed for gemistocytic astrocytomas (P < 0.001) and for tumour extension > 5 cm (T3; P = 0.0193). Karnofsky performance did not show any significant association with survival. The most relevant factor affecting survival at the multivariate analysis was the extent of surgical resection, which resulted as the only variable retaining a significant value (P = 0.001, risk factor = 2.20). CONCLUSIONS: The data strongly support the role of a surgical removal as extensive as possible in the treatment of these tumours.     

Clinical study of disorders of eye movements (voluntary and following) after acute vascular accidents involving the cerebral hemispheres (author's transl)

Voluntary eye movements and following movements have been assessed on a 3 point scale in 33 cerebrovascular patients, examined immediately after the stroke and in 52 patients examined 6-9 days after the stroke. The two types of movements were found to be impaired to the same extent in the majority of patients, especially those with severe neurological deficits. The "agreement index" between them, though high, was significantly inferior to 1. This suggests that voluntary and following movements are subserved by adjacent, but not identical neuronal structures. The available neuro-radiological evidence points to the parieto-temporal cortex as the area critically involved in eye movement disorders.     

Cardiac and visual responses to moving stimuli presented either successively or simultaneously to the central and peripheral visual fields in 4-month-old infants.

Measured cardiac and visual orienting responses as indices of attention in 41 4-mo-old infants. Two stimulus situations were used. In the 1st situation, the presentation of a peripheral stimulus followed the offset of a central fixation stimulus. In the 2nd situation, the peripheral stimulus came on while the central fixation stimulus was on. Each stimulus comprised a horizontal black and white bar pattern. Corneal reflection was used to monitor infant gaze. The visual-response measure confirmed that with simultaneous presentation the probability of orienting to the peripheral stimulus decreased. The extent of this reduction was determined by the speed difference between the central and peripheral stimuli. The cardiac data indicate that on the trials in which the peripheral stimulus did not elicit lateral eye/head movements the stimulus was still being detected. Thus, cardiac change can reflect attentional processes without evidence of somatic orienting. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in use of left–right visual cues: A reexamination of mirror-image confusions in preschoolers.

Developed and tested a model that views left–right mirror-image confusions in preschoolers as part of a general difficulty in distinguishing left–right visual cues. It is proposed that left–right development occurs in 3 distinct levels: Level 1 preschoolers have difficulty responding consistently to left–right cues in their visual field; Level 2 children are capable of noticing but need instructions directing their attention to the relevant information; and Level 3 preschoolers spontaneously attend to these cues. In this study, 38 3- and 4-yr-olds' responses to left–right visual cues were evaluated on ability to distinguish left–right mirror-images of objects on a memory task and also on ability to name rows of objects on a page in a consistent lateral direction. Both abilities were assessed, first, without specific instructions on the relevance of left–right information and then with instructions. Ss were divided into 3 subgroups: spontaneous responders (Level 3), instructed learners, (Level 2), and nonlearners (Level 1). As predicted Ss generally performed at the same level for both left–right problems. Thus, levels of mirror-image ability reflect a broader developmental sequence. Confounding effects of general ability are unlikely to account for this, because correlation between left–right problems remained high (.62) when IQ effects were removed. Sharp age differences occurred, and a longitudinal follow-up showed Level 1 3-yr-olds performing at Level 2 for both tasks when retrained after 6–20 mo. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Costs and benefits of integrating information between the cerebral hemispheres: A computational perspective.

Because interaction of the cerebral hemispheres has been found to aid task performance under demanding conditions, the present study examined how this effect is moderated by computational complexity, the degree of lateralization for a task, and individual differences in asymmetric hemispheric activation (AHA). Computational complexity was manipulated across tasks either by increasing the number of inputs to be processed or by increasing the number of steps to a decision. Comparison of within- and across-hemisphere trials indicated that the size of the between-hemisphere advantage increased as a function of task complexity, except for a highly lateralized rhyme decision task that can only be performed by the left hemisphere. Measures of individual differences in AHA revealed that when task demands and an individual's AHA both load on the same hemisphere, the ability to divide the processing between the hemispheres is limited. Thus, interhemispheric division of processing improves performance at higher levels of computational complexity only when the required operations can be divided between the hemispheres. (PsycINFO Database Record (c) 2010 APA, all rights reserved)