No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Interhemispheric Rivalry During Simultaneous Bilateral Task Presentation in Commissurotomized Patients
Abstract
Six commissurotomized patients were tested and the performances of their left and right hemisphere on a dot counting task were compared during unilateral and bilateral input to study aspects of interhemispheric interference. From 1 to 5 dots were flashed, either in the left or the right visual field alone, or in each of the two fields simultaneously, and the patients were asked to indicate the number of dots seen in each field by extending the same number of fingers with the ipsilateral hand. Comparison trials were also presented where the number of dots were replaced by a corresponding numeral to eliminate counting. Comparable incidences of responses extinction to the dots and to the numerals were frequently observed during bilateral input. Their occurrence bore no clear relationship to the performance levels during unilateral input. Rather, the predominant side of extinction varied among the patients and seems to be related to the presence of some contralateral brain damage. Despite frequent response extinctions, no concurrent increase in counting errors was observed during bilateral input, indicating that interhemispheric interference in the present case is not equally present in all stages of the input-output chain, but takes the form of an all-or-none rivalry in some gating mechanism. Ancillary findings support different modes of information processing by the two hemispheres, and a possible presence of weak ipsilateral projection of visual information.
... Thus, both tasks have equivalent claims to be cognitive by an anatomical criterion. Second, enumeration typically results in RH advantage (Boles, 1986;Kimura, 1966;McGlone & Davidson , 1973;Teng & Sperry, 1974;Young & Bion, 1979), which converges on the task 's use as a cognitive task in Sergent's usage . As she has claimed (1982b), "hemispheric asymmetries emerge .. . ...
... Again, no evidence was found in support of a hemispheric association to spatial frequency. Instead, a general LVF advantage was found, replicating the reported L VF advantage for the enumeration of nonverbal items (Boles, 1986;Kimura, 1966;McGlone & Davidson, 1973;Teng & Sperry, 1974;Young & Bion, 1979). The effect was quite independentof spatial frequency. ...
This experiment examined possible hemispheric differences in sensitivity to spatial frequencies. The experiment comprised two reaction-time tasks, the same- different matching of gratings and the enumeration of bars within a grating. Although little evidence was found for an interaction between visual field of presentation and spatial frequency, the obtained field differences always favored a left visual field advantage. In addition, such an advantage was found regardless of whether the processing took place at apparent sensory or at cognitive levels. It is concluded that prior studies supporting the theory of hemispheric asymmetry in spatial-frequency processing are methodologically insufficient, and that any further such research efforts should include a focus on higher frequencies and on stimulus degradation effects.
... For instance, patients with epilepsy (especially during focal seizures) can show the selective disruption and preservation of cognitive performances, behavioral responses, and conscious phenomena (Gloor, 1986(Gloor, , 1990Porter, 1991). Studies on splitbrain patients highlighted subtle cognitive reorganizations in which specific contents of consciousness are confined to one hemisphere (Gazzaniga et al., 1963;Sperry, 1966;Teng and Sperry, 1974). In turn, neuropsychological conditions, such as blindsight, anosognosia, prosopagnosia, and neglect, show that certain features of conscious experience can be selectively damaged or abolished (Tranel and Damasio, 1985;Berti and Rizzolatti, 1992;Bisiach, 1992;Weiskrantz, 1997). ...
During the last three decades our understanding of the brain processes underlying consciousness and attention has significantly improved, mainly because of the advances in functional neuroimaging techniques. Still, caution is needed for the correct interpretation of these empirical findings, as both research and theoretical proposals are hampered by a number of conceptual difficulties. We review some of the most significant theoretical issues concerning the concepts of consciousness and attention in the neuroscientific literature, and put forward the implications of these reflections for a coherent model of the neural correlates of these brain functions. Even though consciousness and attention have an overlapping pattern of neural activity, they should be considered as essentially separate brain processes. The contents of phenomenal consciousness are supposed to be associated with the activity of multiple synchronized networks in the temporo-parietal-occipital areas. Only subsequently, attention, supported by fronto-parietal networks, enters the process of consciousness to provide focal awareness of specific features of reality.
... e Results are frequency scores. f Note: Studies with lesion patients [61] [82] [84] also suggest a right hemisphere dominance in dot enumeration. Table 1b VHF differences in the recognition/enumeration of Arabic digits, word numerals, dot clusters and bar graphs (percentage of correct recognition) ...
We investigated bilateral field interactions and hemispheric asymmetry in number comparison. A numerical comparison task with three different stimulus notations (Arabic numerals, word numerals and bar graphs) was used. In all conditions, a target was displayed in one visual field, simultaneously with a distractor of the same format in the other visual field. Participants had to indicate manually whether the magnitude of the target was small or large, ignoring the distractor stimulus. Only in the condition with Arabic numerals did we obtain some evidence for a LVF advantage, which argues against a strong laterality of number magnitude representations. Significant interactions between target and distractor values were observed, indicating rich interhemispheric interactions. The interactions were mainly situated at the response stage, but the presence of a bilateral identity effect also points to interactions at the input level.
... That is, it mattered whether the nonprobed hemisphere had viewed one (mixed) versus three (redundant) targets. Other studies (e.g., Teng and Sperry, 1974) also report indirect task interference between the hemispheres of human split-brain subjects. Interestingly, even for neurologically intact subjects, interhemispheric interference is typically less than intrahemispheric interference. ...
A serial probe recognition task was used to examine the interhemispheric exchange of visual data in macaques. Each block of trials began with the memorization of one to six visual target images. The monkeys then had to determine, in tests that followed immediately, whether probe images were or were not members of the learned target set. Previous work with both humans and macaques has shown that the time required for the evaluation of probes generally increases, while response accuracy decreases, as a function of the number of targets, the "memory load". By testing animals with bisected optic chiasm, it was possible to direct visual information to only one hemisphere at a time, simply by occluding the opposite eye. In this fashion, the quality of intrahemispheric evaluations (in which a monocular probe was a match for a target previously viewed through the same eye) was compared with that of interhemispheric evaluations (in which a probe was a match for a target previously designated through the opposite eye). A key question was whether division of the target list between the hemispheres modified the relationships between reaction time, response accuracy, and memory load. Provided that either the anterior commissure or the splenium of the corpus callosum was intact, interhemispheric processing was only subtly less efficient than intrahemispheric processing. The ability to perform interhemispheric evaluations was selectively and completely disrupted if all forebrain commissural fibers were transected. In this latter split-brain condition, the time required for probe evaluations was, as expected, determined solely by the number of target items memorized by the probed hemisphere. Accuracy, however, was always a function of the total memory load, regardless of the distribution of targets between the hemispheres. This implies, first, that accuracy and latency do not reflect identical mnemonic factors, as frequently held, and second, that in mnemonic processing, the two hemispheres draw upon a unified, shared resource, probably allocated by the intact brainstem.
Ricevuto: 26 gennaio 2018; accettato: 7 luglio 2018 █ Riassunto - L'esperienza cosciente sembra essere un soggetto di studio elusivo per la ricerca neuroscientifica. Tuttavia, da un punto di vista operazionale e neurocognitivo, l'esperienza cosciente può essere vista come una collezione di eventi inseriti in una cornice bidimensionale. Una dimensione è relativa al livello di vigilanza o grado di veglia, l'altra dimensione è relativa ai contenuti esperienziali, gli oggetti della nostra consapevolezza fenomenica. A dispetto della variabilità di queste due dimensioni, il senso di unità cosciente sembra essere di norma profondo, reale e immediato. Nondimeno, alcune condizioni neurologiche avvalorano l'ipotesi che quest'unità sia il risultato di una costruzione operata da delicati e complessi mec-canismi cerebrali. Si esamineranno pertanto, in una prospettiva neurocognitiva, i dati provenienti da alcune ricerche empiriche su pazienti affetti da epilessia, i risultati degli esperimenti condotti su persone split-brain e di minima coscienza, che dimostrano come l'esperienza cosciente si basi su un'organizzazione modulare del cervello.
PAROLE CHIAVE: Coscienza; Modularità; Livello; Contenuto; Epilessia; Split-brains; Stato di minima co-scienza
█ Abstract
Conscious experience seems to be an elusive matter of study for neuroscientific research. From an operational and neurocogni-tive point of view, however, conscious experience can be considered as a collection of events within a bi-dimensional framework. One dimension relates to wakefulness or the level of arousal, the other dimension relates to experiential contents, the objects of our phenomenal awareness. The variability of these two dimensions notwithstanding, the sense of conscious unity generally appears to be deep, real and immediate. Still, certain neurological conditions provide evidence for the hypothesis that this unity may be the result of a construction achieved by subtle and complex brain mechanisms. Taking the neurocognitive perspective, I will examine data coming from empirical research on patients with epilepsy and present some results from experiments conducted on split-brain patients and individuals in a minimally conscious state, which show how conscious experience may be rooted in the modular organisation of the brain.
L’agénésie du corps calleux (ACC) est une malformation neurologique fréquente découverte en anténatal. Le devenir des enfants porteurs d’une ACC est essentiellement corrélé à l’association ou non d’anomalies intra ou extra-cérébrales avec un pronostic beaucoup plus péjoratif en cas de formes associées. Malgré la réalisation de nombreuses études, le pronostic reste incertain pouvant conduire au recours à l’interruption médicale de grossesse. L’objectif de notre étude était d’étudier le devenir neuro-développemental des enfants pour lesquels avaient été diagnostiquée une ACC isolée en anténatal et de comparer les différentes formes d’atteintes. Il s’agit d’une étude prospective et descriptive réalisée en Haute Normandie incluant une cohorte de 30 enfants nés entre janvier 1991 et février 2013, avec un diagnostic prénatal d’ACC isolée et un suivi d'au-moins deux ans. La moyenne de suivi était de 7+/-5 ans. Le pronostic était favorable : 83% [Intervalle de Confiance (IC) à 95% (69.6-96.4)] des enfants présentaient un développement psycho-moteur normal ou des anomalies neurologiques modérées. Les troubles sévères représentaient 17% [IC 95% (3.4-30)] de notre cohorte. Lors des tests neuro-psychologiques, les QIT étaient dans les limites de la normale mais nous avons observé une compréhension verbale diminuée pour toutes les atteintes avec des difficultés notamment dans le jugement social ainsi que des difficultés dans les épreuves à tâches multiples et complexes pour les enfants porteurs d’une ACCC. 47% des enfants de notre cohorte présentaient des troubles du langage oral avec un retentissement sur les trois composantes du langage en particulier sur le lexique et la morphosyntaxe où 25% des enfants ayant bénéficié d’un bilan orthophonique avaient un profil pathologique. Ainsi, le pronostic était pour la majorité des enfants favorable mais beaucoup présentaient des troubles des apprentissages. Le suivi prolongé après l’âge scolaire de ces enfants est indispensable afin d’apporter une prise en charge précoce et des aides appropriées dès l’apparition de troubles. Le recours à l’IMG dans les ACC isolées reste discutable et discuté.
The most difficult, but crucial, aspect of higher brain function concerns ‘centrencephalic1 regulations, from inside the brain. They can change how cortical cells associate sensory information, how different sectors of cortical tissue, including the two hemispheres, interact and complement each other in psychological function, and how efferent influences from cortex and basal ganglia impinge on final common path motoneurones of stem and cord. We must understand these facilitatory and organizing processes if we are to explain the arousal of consciousness, selective attention, intentional movement, motiviation and a variety of active memory functions. Here the experimental virtues of the split-brain preparation meet advances in knowledge of anatomy, physiology and pharmacology of the interneuronal networks and nuclei of the core of the brain, and their upward projections through the thalamus, basal ganglia and limbic system. Findings in this area, and comparisons to lower vertebrates in which cortical processes are less dominant, will help us dispel obscurity in our conception of the emotional, purposeful and aware states of our minds. They have immense importance for comprehending disorders of human motivation and emotion and of cognitive processes as well. They help balance what may be a rationalist bias to treat concrete or factual, environmentally-driven behaviour, memory, awareness and reasoning as belonging to a separate computational level of processing that might be carried out autonomously in the neocortex.
One of the most dramatic and reliable behavioral consequences of the surgical transection of the corpus callosum in humans is the perceptual disconnection of the visual world. In general, following callosal surgery each hemisphere only perceives stimuli that are presented to the contralateral visual field: the perception of left field stimuli is isolated to the right hemisphere, and the perception of right field stimuli is isolated to the left hemisphere (Gazzaniga, 1970; Gazzaniga and LeDoux, 1978). As a consequence, each hemisphere can identify stimuli that appear within its sensory field, but the patient is unable to perform perceptual tasks that require the integration of visual information from both hemifields. Typically such tasks involve a forced choice decision such as whether two stimuli are the same or whether they are members of the same class. When both items appear in the same hemifield performance is generally quite accurate. When they are presented to different fields performance usually falls to chance levels.
The most difficult, but crucial, aspect of higher brain function concerns ‘centrencephalic’ regulations, from inside the brain. They can change how cortical cells associate sensory information, how different sectors of cortical tissue, including the two hemispheres, interact and complement each other in psychological function, and how efferent influences from cortex and basal ganglia impinge on final common path motoneurones of stem and cord. We must understand these facilitatory and organizing processes if we are to explain the arousal of consciousness, selective attention, intentional movement, motiviation and a variety of active memory functions. Here the experimental virtues of the split-brain preparation meet advances in knowledge of anatomy, physiology and pharmacology of the interneuronal networks and nuclei of the core of the brain, and their upward projections through the thalamus, basal ganglia and limbic system. Findings in this area, and comparisons to lower vertebrates in which cortical processes are less dominant, will help us dispel obscurity in our conception of the emotional, purposeful and aware states of our minds. They have immense importance for comprehending disorders of human motivation and emotion and of cognitive processes as well. They help balance what may be a rationalist bias to treat concrete or factual, environmentally-driven behaviour, memory, awareness and reasoning as belonging to a separate computational level of processing that might be carried out autonomously in the neocortex.
Consciousness seems to be an elusive subject for scientific research, given the vast range of meanings that can be attached to this concept. However, from an operational point of view, consciousness can be identified with its two dimensions of level and contents. The level of consciousness or arousal is related to the state of wakefulness or vigilance, whereas the contents of consciousness are related to the awareness of phenomenal experience.Together these conscious processes generate a global system that is able to elaborate information coming from inside and outside the body. The sense of unity which derives from conscious experience seems to be deep and real, however some neurological syndromes give support to the hypothesis that the unity of consciousness might be apparent. We argue that it is when certain brain structures are selectively impaired that consciousness reveals its composite nature. From this perspective, we shall examine some empirical data from the study of epilepsy and split-brain syndrome, which can demonstrate how consciousness may be based on a modular organization, especially with regards to its phenomenal contents. Our phenomenal awareness could therefore emerge from different neural processes, which are vastly distributed across the brain rather than being the product of a specific cerebral circuitry.
The lateral distribution of the P300 component of the event-related brain potential (ERP) was studied in five epileptic patients whose corpus callosum had been surgically sectioned and in seven neurologically intact controls. The P300 was elicited in an auditory "oddball" task using high- and low-pitched tones and in a visual oddball task in which target words were presented either to the left or right visual fields, or to both fields simultaneously. Commissurotomy altered the normal pattern of bilaterally symmetrical P300 waves over the left and right hemispheres, but in a different manner for auditory and visual stimuli. The auditory P3 to binaural tones was larger in amplitude over the right than the left hemisphere for the patients. In the visual task, the laterality of the P300 varied with the visual field of the target presentation. Left field targets elicited much larger P300 amplitudes over the right than the left hemisphere, as did bilateral targets. In contrast, right field targets triggered P300 waves of about the same amplitude over the two hemispheres. The overall amplitude of the P300 to simultaneous bilateral targets was less than the sum of the individual P300 amplitudes produced in response to the unilateral right and left field targets. These shifts in P300 laterality argue against the view that the P300 is an index of diffuse arousal or activation that is triggered in both hemispheres simultaneously irrespective of which hemisphere processes the target information. The results further demonstrate that the P300 does not depend for its production on interhemispheric comparisons of information mediated by the corpus callosum, as suggested recently by Knight et al. (1989).
Previous studies of visuospatial attention indicated that the isolated cerebral hemispheres of split-brain patients maintain an integrated, unitary focus of attention, presumably due to subcortical attentional mechanisms. The present study examined whether a unitary attentional focus would also be observed during a visual search task in which subjects scanned stimulus arrays for a target item. In a group of four commis-surotomy patients, the search rate for bilateral stimulus arrays was found to be approximately twice as fast as the search rate for unilateral arrays, indicating that the separated hemispheres were able to scan their respective hemifields independently. In contrast, the search rates for unilateral and bilateral arrays were approximately equal in a group of six normal control subjects, suggesting that the intact corpus callosum in these subjects is responsible for maintaining a unitary attentional focus during visual search.
A right-handed woman suffered destruction of the anterior two thirds of the corpus callosum and the adjacent medial frontal lobes as a sequel of bleeding from an anterior cerebral artery aneurysm. When drawing and writing with her right hand, the patient displayed neglect of the left hemispace. In line bisection each hand deviated towards the side ipsilateral to the lesion, but the size of error decreased when the lines were placed to the ipsilateral side of the body. When tested for her verbal report of tachistoscopically presented, horizontal pairs of simple geometrical figures, she showed a systematic rightward shift of attention when stimuli were presented to the left hemispace or to the centre, but not with presentation to the right hemispace. These results cannot be attributed to a mere deficit in motor control of the hand, nor can they be entirely referred to perceptual rivalry between simultaneous bilateral stimuli. It seems that a directional bias in favour of the right side is introduced when the left hemisphere processes sensory information to prepare a motor or verbal response.
One of the features of consciousness that has been largely overlooked in recent treatments of the topic is its unity. What is the unity of consciousness? To what degree might consciousness be unified? And what implications might the unity of consciousness have for our conception of consciousness and the self? Drawing on philosophy, psychology and neuroscience, this book presents answers to these questions. The first part of the book develops a conception of the unity of consciousness according to which a subject has a unified conscious if and only if it has a single conscious state that subsumes each and every one of its conscious states. This conception of the unity of consciousness gives rise to the unity thesis-the claim that consciousness in human beings is necessarily unified. The second part of the volume examines the plausibility of the unity thesis. The book develops a model for evaluating the unity thesis and then goes on to apply this model to a wide range of syndromes-such as anosognosia, the hidden observer in hypnosis, and the split-brain syndrome-in which the unity of consciousness is often said to breakdown. In each case the evidence in favour of disunity models is found wanting. The final third of the volume examines points of contact between the unity of consciousness on the one hand and theories of theories of consciousness, the sense of embodiment, and accounts of the self on the other.
Although interhemispheric interaction via the callosum is most often conceived as a mechanism for transferring sensory information and coordinating processing between the hemispheres, it will be argued here that the callosum also plays an important role in attentional processing. Experiments will be presented that support this viewpoint, both when attention is conceptualized as a resource and when it is conceptualized as a selective mechanism for gating sensory information. Interhemispheric interaction is posited to aid attentional processing because it allows for a division of labor across the hemispheres, and allows for parallel processing so that operations performed in one hemisphere can be insulated from those executed in the other. Given this additional role for interhemispheric processing, it is suggested that the corpus callosum should be considered a component in the network of neural structures that underlie attentional control.
Major depressive disorder is one of the most common psychiatric disorders, with a worldwide lifetime prevalence rate of 10%-20% in women and a slightly lower rate in men. While many patients are successfully treated using established therapeutic strategies, a significant percentage of patients fail to respond. This report describes the successful recovery of a previously treatment-resistant patient following right unilateral deep brain stimulation of Brodmann's area 25. Current therapeutic approaches to treatment-resistant patients are reviewed in the context of this case with an emphasis on the role of the right and left hemispheres in mediating disease pathogenesis and clinical recovery.
A range of tasks which are known to be lateralized in commissurotomy patients have been used in an experimental design in which each subject performed two tasks concurrently. Results indicate that the two disconnected hemispheres are capable of effective processing of entirely unrelated information concurrently, while the same double task processing within a hemisphere causes severe interference.RésuméOn a utilisé une série d'épreuves connues pour être latéralisées chez les malades ayant subi une commissurotomie dans des expériences où chaque sujet accomplissait concurrement deux tâches. Les résultats indiquent que les 2 hémisphères disconnectés sont capables de traiter concurremment et efficacement des informations totalement sans relation tandis que cette même double épreuve lorsqu'elle doit être traitée par un seul hémisphère entraine des interférences graves.ZusammenfassungEine Reihe von Aufgaben, von denen bekannt ist, daβ sie bei kommissurotomierten Patienten einhemisphärisch wirksam sind, wurden in einem experimentellen Plan verwandt, in dem jede Versuchsperson zwei Aufgaben gleichzeitig ausführte. Die Ergebnisse zeigen an, daβ die zwei getrennten Hemisphären fähig sind, gleichzeitig gänzlich unzusammengehörige Information wirksam zu verarbeiten, während die gleiche Doppelaufgabe der Verarbeitung innerhalb einer Hemisphäre schwere wechselseitige Störungen hervorruft.
.— Because lateral corrective eye movements have been shown to influence the results of the dichotic listening test, it was supposed that differences in the scoring on this test by right and left eye movers could be found. Only in the entire group of 22 right handed subjects and in the subgroup of 8 right eye movers a significant right ear superiority was found. In the left mover group (14 subjects) right ear superiority in dichotic listening was not significant. These results are interpreted in terms of possible interhemispheric differences in the level of “activity”, facilitating or hampering perception of verbal material in the contralateral ear.
268 journal articles on hemispheric factors and scanning dynamics involved in the encoding of briefly exposed stimuli by human Ss are grouped into the categories of experiments with normal Ss, experiments with various types of patients, and review and theoretical articles.
Experiments comparing binocular with monocular abilities of monkeys working on visual mnemonic tasks were performed. First, it was shown that even in split-brain monkeys performance was more accurate when both hemispheres were utilized than when the task was performed with only the single (better) hemisphere. Some form of noncommissural integration is thus possible. However, when the forebrain commissures are present, as in four other animals (with only optic chiasm transected) it was shown that integration occurs via callosal mechanisms as well. This was demonstrated by the fact that here, too, binocular performance was normally more accurate than monocular performance, but when different images to be remembered were presented concurrently to the two eyes, the binocular advantage was lost. Finally, in three monkeys with only the anterior commissure allowing interhemispheric communication the superiority of binocular assessment remained even when the two hemispheres simultaneously received such differing images.
Left- and right-hand responses were studied in a patient who had undergone complete corpus callosotomy to examine selective hemispheric processing employing free-field stimuli. Tests of verbal and visual spatial processing were presented, and multiple choice performances were obtained using both left and right hands. A double dissociation emerged, with superior left-handed performance on visual spatial tasks, and better right-handed performance on verbal tasks. In addition, the patient displayed hemispatial dyscalculia in which he solved written arithmetic problems disregarding free-field numerical information presented toward his left. Evidence of multimodality left-sided extinction was also present. Further, despite unilateral callosal apraxia, the left hand displayed superiority during a continuous performance task. These results demonstrate that specialized functions of the cerebral hemispheres may be observed for response output in the absence of restricted hemispheric input, and that components of the neglect syndrome may be seen following corpus callosotomy.
Tactual extinction was examined in a 43-yr-old left-handed male patient (MM) with a hematoma in the trunk of the corpus callosum sparing the genu and the ventral part of the splenium as well as the cerebral hemispheres. Experiments I and II showed no deficit in tactual perception nor in the inter-hemispheric transfer of tactual information. In Experiment III, MM palpated stimuli differing in their association value, and responded vocally or manually. There was no difference in performance between the hands in unimanual control conditions, but in a dichhaptic condition an overall right-hand advantage was observed, depending on the kind of stimulus and on the mode of response: such results were not observed in control subjects. Results showed that MM's left-hand performance reached right-hand levels after specific modifications in the allocation of attention between the hands or the load of information in haptic memory (Experiment IV). Experiment V revealed a major deficit in the matching of left- and right-hand information only for the dichhaptic procedure. The results are discussed with a view of cerebral mechanisms as dynamic rather than structurally determined: it is suggested that extinction phenomena are sensitive to cognitive strategies and attentional factors and that the corpus callosum plays a critical role in the lateral control of attention to tactual as well as to auditory and visual information.
Studies are reviewed that examine how perceptual and attentional systems operate in the cortically disconnected human. The data indicate that even though both simple and complex perceptual information associated with the cognitive activities of each disconnected half brain show virtually no interactions, the attentional system remains largely integrated in the split-brain patient. It also appears that the human brain is subject to a set of finite resources it can allocate to cognitive activities. These resources are not changed following cortical disconnection. Taken together, studies to date support the view that the attentional system is an independently functioning and integrated entity, following brain bisection, that participates in both perceptual and cognitive activities of each hemisphere.
Two manual reaction-time experiments examined visual field differences for the judgment of number. All told, three tasks (recognition/enumeration, magnitude judgment and oddity judgment) were performed on three nonverbal indicators of number (dot clusters, bargraphs and dials) and two verbal indicators (word names of numbers and digits). The results indicated that field differences depended largely on display format, not on the task. Thus, dot clusters, bargraphs and dials all showed a left visual field superiority, while words showed a right visual field superiority. There was no evidence of lateralization for digits.
A commissurotomy patient and two neurologically intact control observers were required to encode spatial patterns presented concurrently to the two hemifields. Under conditions of maximal perceptual load, in which different patterns appeared in the two fields, the commissurotomy patient encoded more information than the control observers. Based on these findings, it is concluded that competition for common internal processing mechanisms interferes with overall processing efficiency.
To investigate whether callosal lesions affect the distribution of event-related potentials (ERP) between the two hemispheres and whether hemispheric ERP distribution differs among sensory modalities, a patient with interhemispheric disconnection syndrome and 47 controls were subjected to an oddball paradigm. High (target) and low tone bursts for auditory, red (target) and green lights for visual and electrical stimuli delivered to the index (target) or fifth finger for somatosensory ERPs were presented to the unilateral ear, visual field and hand, respectively. The subjects were instructed to press a button with the hand on the stimulated side. The results showed that the hemispheric asymmetry of the patient's auditory ERPs was not significantly different from that of the controls, regardless of which ear was stimulated. In contrast, the visual and somatosensory ERPs showed a delay of the P3 latency and an attenuation of the N1-P2 and N2-P3 amplitude over the hemisphere ipsilateral to the stimulus, regardless of the stimulated side. These findings suggest that the source of P3 generation is relatively lateralized to the hemisphere contralateral to the stimulus, and that the callosal transfer of visual and somatosensory information is involved in the P3 generation in the hemisphere ipsilateral to the stimulus.
Six normal subjects and a callosotomized man with a prefrontal lesion, mostly on the right side, were tested in a reaction time (RT) task involving a key-pressing response to an extrafoveal light target preceded by an extrafoveal light cue. Cues and targets were presented along the horizontal meridian at 4°and 12°on the right and left of fixation. Fixation was maintained throughout each trial. The cue signalled the occurrence of the target within a time window extending from 200 to 4000 msec from the cue, but did not predict target location. Normal controls responded faster to medial than to lateral targets in both fields, but showed no between-field difference, and their RT was not affected by cue location. Furthermore, they showed the so-called 'ipsilateral inhibition' or 'inhibition of return' effect, their RT being longer when cues and targets occurred in the same held than when they occurred in opposite fields. The RT of the callosotomized subject showed a left-right gradient for both cue location and target location, being longest for the leftmost location and shortest for the right locations. In addition, he showed a significant advantage for the right hand regardless of cue and target location, as well as a consistent ipsilateral inhibition in the left field, whereas in the right field there was ipsilateral inhibition only at the two longest stimulus onset asynchronies. These results suggest that, at least under these experimental conditions, there was a rightward orientational bias which reflected the taking over of the control of performance by the left hemisphere. This attentional bias was reminiscent of that seen in patients with hemi-inattention from right hemisphere damage, although the callosotomized patient showed no sign of such hemi-inattention in routine clinical tests. On the basis of several considerations the rightward bias could be attributed to the callosal interhemispheric disconnection rather than to the right prefrontal lesion.
Normal subjects aged 7-25 years were asked to tap the index fingers of both hands: a) in four different patterns of interlimb coordination; b) at two different response frequencies; and c) both before and after the entraining metronome was turned off. The outcome variables of primary interest were the within-subject variability of interresponse intervals (IRI) as an index of timing precision; and deviations from prescribed response frequency, as an index of temporal tracking accuracy. Stability of timing precision and accuracy of temporal tracking increased significantly from 7 to 9 and from 9 to 11 years, with only minor advances thereafter. There were significant right-left performance asymmetries in all bimanual tasks; variability of IRI and deviations from prescribed rate were greater at the faster of the two response frequencies tested; and stability of IRI and accuracy of temporal tracking were greater with than without the metronome. Stability of IRI and accuracy of temporal tracking were strongly correlated in some bimanual tasks. The findings are discussed in terms of the two major theoretical perspectives on human brain-behavior relationships that have specifically addressed the issue of bimanual coordination.
These experiments explored the interactions remaining between the cerebral hemispheres in two split-brain macaques. The 'split' was earlier confirmed by showing that one hemisphere was incapable of identifying visual images seen by the other. The critical tests for residual interactions were intermingled with control trials in a continuous recognition task. These tests were of two kinds: 'parallel processing', to determine how simultaneous viewing by both hemispheres affected subsequent recognition by one of them alone; and 'conflict', where opposite responses were demanded from the two hemispheres, thus assessing the issue of metacontrol. Two types of stimuli were also employed: ART, in which each hemisphere saw essentially the same image; and BIPARTITE, in which images were entirely different for each hemisphere. Since, with either type of stimulus, performance was best when viewed by both hemispheres at both encoding and retrieval, 'parallel processing' was highly efficient. However, when both hemispheres viewed initially and only one was subsequently queried, performance was significantly worse than when each hemisphere acted alone on each occasion. It is thus reasoned that when both hemisphere view together, the resultant memory trace somehow reflects the bilaterality, a conclusion concordant with observations of Marcel on blindsight. Processing different images (BIPARTITE) was somewhat more disruptive in this regard than if the same image was viewed by each hemisphere. This was particularly true in the conflict situation, where for one hemisphere the item seen was NEW and for the other it was OLD. A response of 'OLD' was, at first, consistently rewarded. When this well-established protocol was changed, the hemispheres in each animal were gradually able to revise their joint behavior. This, together with the effect of disparate images, and the deficiency evoked when the animals were forced to recognize unilaterally an image first viewed under bilateral conditions, all manifest considerable, and complex, interaction between the hemispheres despite absence of the forebrain commissures. The superior colliculus seems a likely focal point for such interhemispheric effects.
Three experiments were carried out to study hemispheric specialization for subitizing (the rapid enumeration of small patterns) and counting (the serial quantification process based on some formal principles). The experiments consist of numerosity identification of dot patterns presented in one visual field, with a tachistoscopic technique, or eye movements monitored through glasses, and comparison between centrally presented dot patterns and lateralized tachistoscopically presented digits. Our experiments show left visual field advantage in the identification and comparison tasks in the subitizing range, whereas right visual field advantage has been found in the comparison task for the counting range.
Conducted 3 experiments, with 6 right-handed undergraduates in each, which examined hemispheric differences in reaction time (RT) to judge a set of items same or different (1 item differing from the rest), as a function of number of items in the set. When the items were letters, the left hemisphere yielded RTs increasing with the number of letters in the set, as in serial processing; the right hemisphere showed no increase of RT for larger numbers of letters, as in parallel or holistic processing. When the items were unnameable shapes, both hemispheres appeared to process in parallel. Thus, a serial vs. parallel processing difference between left and right hemispheres appears to be limited to linguistic material which can be analyzed either verbally or visuospatially. If verbal analysis forces a serial procedure, while visuospatial analysis permits parallel processing, then the results can be explained in terms of the lateralization of these modes of analysis. (24 ref.) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
[Introduction] Until a few years ago, prevailing views regarding the syndrome of the corpus callosum in man were based very largely on the studies of Akelaitis and his co-workers (Akelaitis et al. 1942; Akelaitis 1944). Using a wide variety of tests Akelaitis examined a series of more than two dozen patients with partial and complete surgical sections of the corpus callosum and anterior commissure and was unable to find any consistent neurological or psychological dysfunctions that could be reliably attributed to the commissural sections. Symptoms such as unilateral astereognosis, alexia, agraphia, ideo-motor apraxia (Sweet 1941), as well as apathy, amnesia, personality changes and related effects, that earlier had been ascribed to callosal lesions (Alpers and Grant 1931) seemed accordingly to be more properly explained in terms of the extracallosal cerebral damage that commonly accompanies lesions in the commissures. These Akelaitis reports in combination with confirmatory observations on absence of symptoms after callosum section in animals established the general doctrine of the 1940's and 1950's in which it was believed that behavioral deficits seen in connection with callosal lesions are best ascribed to associated brain damage (Bremer et al. 1956). Meanwhile, the discrepancy between the enormous size and strategic position of the corpus callosum on the one hand and the observed lack of any important functional disturbance following its complete surgical section on the other remained during this period one of the more puzzling enigmas of neurology.
Hemisphere disconnection in man yields two systems, each of which can perform most human activities independently and separately and without help from the other. The present study examines whether both hemispheres working in parallel can process more information than can one working alone. The results affirm this view and suggest that the informational cross-talk ongoing via the callosum in the normal brain limits the short-term memory capacity of each hemisphere and, therefore, of the brain as a whole.
Milner has reported that lesions of the right temporal lobe impair performance on certain visual tests, whereas lesions of the left temporal lobe do not. In a comprehensive comparison of patients with damage to the temporal, frontal, and parietal areas the right temporal group was found to be impaired on a Triangular Blocks test8 and on a complex pictorial task, the McGill Picture Anomalies.9 The deficit on the McGill Picture Anomalies was specific to the right temporal group. Milner suggested that these deficits are related to the nonverbal functions of the right hemisphere and concluded that "the right temporal lobe aids in rapid visual identification."9 The nature of this facilitation has remained a problem, since lesions of the right temporal lobe do not impair performance on all visual tests nor exclusively on visual tests. The present study was designed to investigate this visual deficit further.
Subjects
The
Verbal and nonverbal stimuli were presented to normal subjects by means of a tachistoscope. The method employed was that of successive random presentation to either the left or the right visual half-field. Letters were more accurately identified in the right visual field, as previously established, but the enumeration of certain nonalphabetical stimuli was more accurate when they appeared in the left field. It was concluded that the left posterior part of the brain plays an important role in the identification of verbal-conceptual forms, while the corresponding area on the right has other functions in the registration of nonverbal stimuli.
The performance of 2 choice reactions, 1 with each hand, in response to 2 visual discrimination tasks presented simultaneously, 1 in each ½ of the visual field, normally takes much longer than the performance of either 1 alone. In commissurotomized human patients, however, the double task was performed as rapidly as the single task. The results conform with the view that the neocortical commissures serve to unify adjustment to the visual world and their presence tends to prevent the 2 half brains from making discordant volitional decisions. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
After hemispheric deconnection, patients, whose tapping movements with one index finger at a time are nearly normal, can synchronize or alternate right and left finger tapping only at markedly decreased rates as compared to controls. One callosectomized subject tapped with her index fingers while performing verbal tasks. Moderately difficult tasks disrupted right index tapping only; concentration on more difficult tasks and confusion arrested both index fingers. The deconnected hemispheres have partial but not total independence. Concurrent activities maximally compete when programmed in the same hemisphere; but both hemispheres draw upon the limited and still unified attentional resources of the brain as a whole.
Two experiments are described in which, by a divided visual field technique, simple non-verbal stimulus material is directed to either the right hemisphere, left hemisphere, or divided between the hemispheres. It is found that when material to be matched is shared between the hemispheres, response latencies are reduced, suggesting increased capacity for the processing of such information and supporting the hypothesis that each hemisphere contains its own processing and analysing system. When the material is directed to only one hemisphere, and a bimanual motor response required, a relative superiority of the right hemisphere is found. If the response required is a vocal response, then further relative blocking of the processing undertaken by the left hemisphere is observed.
Using a refined psychophysical method and appropriate conditions of stimulation, this study determined whether it would be possible to demonstrate “obscuration” of perception of suprathreshold tactile stimulation in healthy subjects who do not show extinction of perceptual response to the weaker of two bilaterally applied tactile stimuli. The procedure was to train subjects to estimate the subjective magnitude of weights dropped on the skin surface and, after this training, to secure their magnitude estimates of the same weights under conditions of both single and double stimulation. Comparison of these magnitude estimates under the two stimulation conditions provided unequivocal evidence of an obscuration effect, the estimates under the condition of double stimulation being significantly lower than those made under the single stimulation condition. There were also indications of individual differences in susceptibility to this effect of double stimulation. The results are interpreted as providing further support for the concept that the clinical phenomena of extinction and obscuration are exaggerated expressions of a normal physiologic mechanism. A modification of the procedure used in this investigation might be fruitfully applied in the study of patients with suspected cerebral disease who do not show extinction or obscuration of perception under the conventional condition of double sensory stimulation of equal intensity.
Interhemispheric interaction after forebrain commissurotomy was studied in six patients. Letters or digits were flashed for 0·1 sec either in the left or in the right visual field alone, or in both fields simultaneously. Patients were asked to identify the stimuli either verbally or by hand. Results showed generally better performance for each hemisphere during unilateral than during bilateral stimulus presentation. For both verbal and manual responses, identification of right-field stimuli was better than that of left-field stimuli, the latter often being completely ignored during bilateral presentations. Some evidence was obtained for right-hemisphere verbalization during unilateral presentation of left-field stimuli.
Long lasting and changing visual stimuli were used to test peripheral field perception of form, motion and colour in four commissurotomy patients. The stimuli were produced by point source shadow casting or by focused projections on large screens surrounding the subjects, and oculomotor fixation was monitored continuously. It was found that appropriately large and 'active' stimuli in left and right fields were combined by the subjects into unified percepts which they saw as cross integrated over the vertical meridian. In addition, they spoke correctly about attributes of similar stimuli that were confined to the left field. These results were obtained while subjects maintained steady central fixation, and in absence of any acts capable of giving non visual sensory feedback and cross cueing between the hemispheres. It is concluded that ambient vision remains undivided after hemisphere deconnexion, in spite of the complete separation of focal visual perceptions at the vertical meridian caused in these same subjects by the operation. A left handed commissurotomy patient in whom speech was better controlled from the right hemisphere was also examined with the methods described. Implications of these findings for the anatomy of the central visual system of the brain are discussed with the aid of additional observations on a patient with right cerebral cortex removed surgically.
Seven patients with presumed complete midline section of the inter-hemispheric commissures were tested for delayed matching of tactile patterns. In six of these patients, left-hand performance was unequivocally superior to right, thus demonstrating right-hemisphere specialization for the perception and recall of spatial patterns. The fact that the non-speaking right hemisphere could bridge intratrial intervals of at least 2 minutes, whereas the left hemisphere could not, shows that verbal coding is neither necessary nor sufficient for the retention of complex perceptual material. The further finding that subjects with cortical lesions but intact commissures were more proficient than the commissurotomized patients (even with the left hand) suggests that both cerebral hemispheres normally participate in such tasks, but with the right playing a preponderant role.
In search for possible functions mediated by anterior portions of the forebrain commissures in man, bilateral motor coordination was studied in two patients in whom the anterior commissure and the anterior two thirds of the corpus callosum had been sectioned to control for intractable epilepsy. Compared with normal controls and persons with a similarly severe history of epilepsy, patients with partial commissurotomy showed less improvement after nearly 500 trials of training, and performed at a consistently inferior level in terms of both quality and speed. It is suggested that the anterior commissurotomy eliminated a control mechanism involving direct interhemispheric interaction of motor corollary outflow, forcing these subjects to rely on slower visual and proprioceptive feedback systems. Direct hemispheric interaction appears to be important for the fine regulation of the lower motor system from within each hemisphere. Certain consistent performance characteristics of the patients and control subjects are discussed with respect to lateral dominance and ipsilateral control in motor functions.
Disorders in Perception, with particular reference to the phenomena of extinction and displacement, Charles C. Thomas, Springfield, Ill. . -(1972) Perceptual interaction and acupuncture anesthesia
- M B Bender
BENDER, M. B. (1952) Disorders in Perception, with particular reference to the phenomena of extinction and displacement, Charles C. Thomas, Springfield, Ill.. -(1972) Perceptual interaction and acupuncture anesthesia, "Trans. Arner. Neurol. Assoc.," 97 1-11.
Box 1909, 1200 N. State Street
- Evelyn Lee Teng
- D Ph
Evelyn Lee Teng, Ph. D., Department of Neurology, University of Southern California School of Medicine, Box 1909, 1200 N. State Street, Los Angeles, California 90033, U.S.A.. R. W. Sperry, Ph. D.@BULLET Division of Biology. California Institute of Technology Pasadena, California 91109. U. S.A
Perceptual interaction and acupuncture anesthesia
- Bender