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Perceptual Unity of the Ambient Visual Field in Human Commissurotomy Patients
Abstract
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.
... The lines were positioned in such a way that extending them across the gap would either cause the lines to coincide or to run in parallel. When split-brain patients indicate whether the lines are parallel or coincident, they are highly accurate, even when both line segments are located in different halffields (Corballis, 1995;Pinto, de Haan, Lamme, & Fabri, n.d.;Sergent, 1987;Trevarthen & Sperry, 1973). Another example of visual integration across the midline involves apparent motion. ...
... Another observation that suggests some form of unity across the two visual half fields concerns detection and localization of stimulation, for instance, a brief flash (see, for example, an early study on the response times to light flashes with the ipsi-or contralateral hand: Clarke & Zaidel, 1989). Several investigations (Corballis, Corballis, Fabri, Paggi, & Manzoni, 2005;Trevarthen & Sperry, 1973) have demonstrated convincingly that split-brain patients can accurately report the presence and location of stimuli for any position in the whole visual field, with either hand, and even verbally. Accurate detection and localization appears to be possible for all patients and all stimuli (different shapes, figures, equiluminant stimuli) tested so far. ...
... The first proposal (Corballis Corballis, Berlucchi, & Marzi, 2018;de Haan et al., 2019;Pinto, Lamme, & de Haan, 2017b;Savazzi et al., 2007;Mancuso, Uddin, Nani, Costa, & Cauda, 2019) suggests that the multitude of subcortical connections that are spared during surgery are responsible for the transfer of information. As was initially pointed out by Trevarthen (1968) and Trevarthen and Sperry (1973) and recently stressed by and Corballis et al. (2018), there are many commissures (white matter tracts that connect homologous structures on both sides of the central nervous system) and decussations (bundles that connect different structures on both sides) that link nuclei that are known to be involved in perceptual processing. The importance of these commisural connections for transferring visual information in split-brain patients has been highlighted by Trevarthen and Sperry (1973). ...
Recently, the discussion regarding the consequences of cutting the corpus callosum (“split-brain”) has regained momentum (Corballis, Corballis, Berlucchi, & Marzi, Brain, 141(6), e46, 2018; Pinto et al., Brain, 140(5), 1231–1237, 2017a; Pinto, Lamme, & de Haan, Brain, 140(11), e68, 2017; Volz & Gazzaniga, Brain, 140(7), 2051–2060, 2017; Volz, Hillyard, Miller, & Gazzaniga, Brain, 141(3), e15, 2018). This collective review paper aims to summarize the empirical common ground, to delineate the different interpretations, and to identify the remaining questions. In short, callosotomy leads to a broad breakdown of functional integration ranging from perception to attention. However, the breakdown is not absolute as several processes, such as action control, seem to remain unified. Disagreement exists about the responsible mechanisms for this remaining unity. The main issue concerns the first-person perspective of a split-brain patient. Does a split-brain harbor a split consciousness or is consciousness unified? The current consensus is that the body of evidence is insufficient to answer this question, and different suggestions are made with respect to how future studies might address this paucity. In addition, it is suggested that the answers might not be a simple yes or no but that intermediate conceptualizations need to be considered.
... An intention to move one hand determines which cortical visual system will perceive and learn (Trevarthen, 1962(Trevarthen, , 1965(Trevarthen, , 1974a(Trevarthen, , 1987. Perception around the body in the periphery of the visual field, including 'ambient' preattentive awareness of space and motion properties of objects, is not divided in the split brain, indicating that subhemispheric (brain stem) systems, which remain unified, can integrate core perceptuo-motor functions directed to the 'behavior space' surrounding the body (Trevarthen and Sperry, 1973;Trevarthen, 1987). ...
... Only when the subject shifted visual fixation or passed an object from one hand to the other did the one hemisphere know what the other perceived. As with the monkeys, human commissurotomy subjects experienced unified ambient visual functions but split focal vision (Trevarthen and Sperry, 1973;Trevarthen, 1990Trevarthen, , 2004. This difference in functional level of control, defined by the motor activities of the subject in selective engagement with objects in the world, is of fundamental significance for interpretations of the meaning and value of knowledge gained by research on commissurotomy patients (see Figure 2). ...
... Commissurotomy patients have a color anomia, an inability to name colors, because the disconnected right hemisphere has a superior but inarticulate ability to perceive and evaluate color (Levy and Trevarthen, 1981). There is evidence that an undivided brain-stem color vision defines a dichromatic distinction between blue space and the reddish-brown solids, part of the natural layering of the conscious mind to serve different forms of action in the world (Trevarthen and Sperry, 1973). ...
Research on the consequences of complete section of the forebrain commissures in cats and monkeys, and in human patients operated to control epilepsy, has clarified how the brain mediates perception, learning, memory, and the control of movements, and has raised many questions. No single process of consciousness and no simple localization of ‘modules’ of perception or reasoning have been found. However, consistent differences between the awareness of the left and right hemispheres in human beings, and regarding their capacity to integrate experience of objects with skilled action, to employ language in speech or writing, to imagine contexts for discrimination and decision making, to attribute qualia to objects, and to sympathize with the motives and feelings of other persons, cast light on how the human brain is uniquely adapted for cooperative cultural life. The findings of split brain research have importance for the whole range of scholarship that attempts to explain the human condition.
... 5). Where their visuospatial processing seems integrated, it may well be sustained by a subcortical system, sometimes called the 'second visual system' or the 'ambient system' (Trevarthen and Sperry, 1973), which courses through the superior colliculi, the pulvinar nuclei, and thence to the parietal lobes, bypassing the 'focal' geniculo-striate system, and is connected interhemispherically via the collicular commissure or other possible subcortical routes. The superior colliculi themselves play a role in implementing both saccadic and pursuit eye movements, and are also involved in the normal control of spatial attention during perceptual judgements (Krauzlis et al., 2013). ...
... Several lines of evidence suggest that the intact ambient system may be key to the sense of visuospatial unity in the split brain. For instance, Trevarthen and Sperry (1973) presented stimuli to split-brained patients in peripheral vision while they held fixation on a point. Two patients could easily tell whether two circles in opposite hemifields moved in the same direction (up or down) or in opposite directions. ...
... mmissurotomy) cross-matches shadows moving on the screen, reporting when the black shadows are "in line'. Right: The biplanar screen with two point-source lamps. An object rotating in the subject's left field (innervating the right hemisphere) is perceived, and an accurate verbal report is made of its motions (by the left hemisphere) (adapted from Trevarthen & Sperry. 1973). ...
... imination of the fine structure of specific objects and substances Introduced by TREVARTMEN (Trevarthen, 1968b; Fig. 2 and 4). Later, with Roger Sperry, I experimentally isolated the ambient vision capacities of commissurotomy patients for vision in the peripheral field, and we proved that ambient vision was undivided after the forebrain bisection (Trevarthen & Sperry. 1973;Fig. 5) ...
... Previous evidence suggests that the transfer of color information is largely abolished following forebrain commissurotomy (Corballis, 1996;Johnson, 1984;Reuter-Lorenz, Nozawa, Gazzaniga, & Hughes, 1995;Sergent, 1986), although it has been suggested that subcortical transfer may enable a crude distinction between short and long wavelengths of light (Trevarthen & Sperry, 1973). Evidence as to whether those with agenesis of the corpus callosum can transfer color information interhemispherically is somewhat mixed. ...
Three cases of callosal agenesis (a 39-year-old woman and her 11- and 12-year-old daughters) were tested on their ability to integrate visual information between the visual hemifields. They were all able to name colors and digits in either hemifield with high accuracy and were able to decide whether letters or digits in opposite hemifields were the same or different. They had greater difficulty deciding whether colors in opposite hemifields were the same or different. When shown 6-letter words made up of pairs of 3-letter words that straddled the midline (e.g., MANAGE, ROTATE),they responded to them as whole words and never as 3-letter words,suggesting perceptual continuity across the midline, at least for verbal material. The most likely interpretation is that the integration of form, but not color, is achieved through the intact anterior commissure in these participants.
... These are discussed next. Trevarthen and Sperry (1973) showed that information about movement of objects in the LVF could be reported by splitbrain patients. Patients could also integrate information about large, moving stimuli across the vertical midline. ...
Research on the anatomical bases of interhemispheric interaction, including individual differences in corpus callosum (CC) anatomy, is reviewed. These anatomical findings form the basis for the discussion of two major themes. The first considers interhemispheric transfer time (IHTT) and related issues. These include varieties of IHTT and possible directional asymmetries of IHTT. Evidence suggests that pathological variations in IHTT may have cognitive consequences. The second involves conditions under which interhemispheric interaction is necessary and beneficial. The data suggest that when both hemispheres have some competence at a difficult task, there is a benefit to interhemispheric interaction. The role of the CC in the dynamic distribution of attention may be particularly relevant to this advantage. Throughout the article reference is made to individual differences and developmental changes associated with interhemispheric interaction.
... Attempts to inhibit such interfering responses via distracting tasks generally led to such a reduced level of consciousness in the right half of the brain, that it was almost impossible to elicit any responses whatsoever from it (Levy, 1970). In tests with bilateral presentation of stimuli, fluctuations in the balance of perceptual processes in the two hemispheres of central origin are commonly observed (Kinsbourne, 1974;Trevarthen, 1974;Trevarthen & Sperry, 1973). In the intact brain, it would be expected that asymmetric activation would be, in part, maintained via callosally mediated inhibition or shunting. ...
Tested 4 commissurotomy patients (described in a previous study by J. Levy et al; for ability to match tachistoscopically presented stimuli with pictures in free vision, according to either structural appearance or functional-conceptual category. Patients were given ambiguous, structural, or functional instructions on any given run of trials with simultaneous double stimulus input to the 2 cerebral hemispheres. With ambiguous instructions, appearance and function matches were performed by the right and left hemispheres, respectively. When instructions were specific, appearance instructions tended to elicit appearance matches and right-hemisphere control. When function instructions were given, left-hemisphere control and function matches tended to be elicited. In 3 of the 4 patients, however, there was a significant number of dissociations between controlling hemisphere and strategy of matching. (24 ref)
... These studies suggested that independent perceptual processing and independently generated responses within each hemisphere. However, where the former claim of independent perceptual processing has stood up to the test, the latter claim of independently generated responses has been discredited across a range of patients and tasks (Clarke & Zaidel, 1989;Corballis, Corballis, Fabri, Paggi, & Manzoni, 2005;de Haan, Fabri, et al., 2020;Pinto, Neville, et al., 2017;Trevarthen and Sperry, 1973). This has rekindled the debate of whether the self is split in split-brain patients (Corballis, Corballis, Berlucchi, & Marzi, 2018;de Haan, Fabri, et al., 2020;Pinto, Neville, et al., 2017;Volz & Gazzaniga, 2017;Volz et al., 2018). ...
In common sense experience based on introspection, consciousness is singular. There is only one ‘me’ and that is the one that is conscious. This means that ‘singularity’ is a defining aspect of ‘consciousness’. However, the three main theories of consciousness, Integrated Information, Global Workspace and Recurrent Processing theory, are generally not very clear on this issue. These theories have traditionally relied heavily on neuropsychological observations and have interpreted various disorders, such as anosognosia, neglect and split‐brain as impairments in conscious awareness without any reference to ‘the singularity’. In this review, we will re‐examine the theoretical implications of these impairments in conscious awareness and propose a new way how to conceptualize consciousness of singularity. We will argue that the subjective feeling of singularity can coexist with several disunified conscious experiences. Singularity awareness may only come into existence due to environmental response constraints. That is, perceptual, language, memory, attentional and motor processes may largely proceed unintegrated in parallel, whereas a sense of unity only arises when organisms need to respond coherently constrained by the affordances of the environment. Next, we examine from this perspective psychiatric disorders and psycho‐active drugs. Finally, we present a first attempt to test this hypothesis with a resting state imaging experiment in a split‐brain patient. The results suggest that there is substantial coherence of activation across the two hemispheres. These data show that a complete lesioning of the corpus callosum does not, in general, alter the resting state networks of the brain. Thus, we propose that we have separate systems in the brain that generate distributed conscious. The sense of singularity, the experience of a ‘Me‐ness’, emerges in the interaction between the world and response‐planning systems, and this leads to coherent activation in the different functional networks across the cortex.
... It has been argued over the past two decades, and somewhat controversially (on the basis of develop-ments in neuroscience and psychology) that cognitive orientations and preferences and identifications can be connected with brain function, and that differences exist between individuals in which 'left brain' or 'right brain' are favored or dominant (Ornstein, 1997;Gazzaniga, 1998;Strauss, 1998). Building on work by Trevarthen and Sperry (1973), theorists within this paradigm maintain that a 'left brain orientation' suggests a more linear, rational, analytical, and linguistic approach, and that a 'right brain orientation' is associated with more artistic, musical, spatial and intuitive skills. It has been asserted (again, controversially) that both camps, i.e., business and design, may readily associate themselves with one or other of these stereotypes, but neither is entirely specific to one group (Nielsen et. ...
This paper focuses on the contribution of the independent product design industry to business and strategy development processes of contemporary organizations. It embarks from the observation that whilst some policy-makers and enlightened businesses recognize the role and value of design beyond the traditional and narrow confines of technical or ‘commodity’ input, many fail to understand its potential as a transformative tool. Applying evidence from three empirical studies, and taking the perspective of design creative, the paper addresses three questions: why is it that product designers have encountered resistance in their efforts to promote themselves as well-placed and knowledgeable providers of strategic development intelligence and advice; what proven contributions can product designers offer with respect to their client’s business development planning?
... Split-brained patients can achieve some integration of low-level visual features between hemispheres, including apparent motion (Naikar and Corballis, 1996;Ramachandran et al., 1986), orientation alignment Sergent, 1987), and spatial attention (Gazzaniga, 1987). An early study suggested unity of ambient vision across the visual field, a general awareness of visual space somewhat separate from focal vision centered on the fovea (Trevarthen and Sperry, 1973). These various findings suggesting a degree of interhemispheric integration might be due to subcortical connections, which remained intact . ...
The human brain is often characterized in terms of a duality, with the left and right brains serving complementary functions, and even individuals are sometimes classified as either “left-brained” or “right-brained.” Recent evidence from brain imaging shows that hemispheric asymmetry is multidimensional, comprised of independent lateralized circuits. Cerebral asymmetries, which include handedness, probably arise in phylogenesis through the fissioning of ancestral systems that divided and lateralized with increasing demand for specialization. They also vary between individuals, with some showing absent or reversed asymmetries. It is unlikely that this variation is controlled by a single gene, as sometimes assumed, but depends rather on complex interplay among several, perhaps many, genes. Hemispheric asymmetry has often been regarded as a unique mark of being human, but it has also become evident that behavioral and cerebral asymmetries are not confined to humans, and are widespread among animal species. They nevertheless exist against a fundamental background of bilateral symmetry, suggesting a tradeoff between the two. Individual differences in asymmetry, moreover, are themselves adaptive, contributing to the cognitive and behavioral specializations necessary for societies to operate efficiently.
... The authors provide anatomical evidence citing a 'second visual system' pathway involving midbrain structures. This pathway is believed to go through the superior colliculi, the pulvinar nuclei, and subsequently to the parietal lobes with a subcortical interhemispheric connection at the collicular commissure (Trevarthen and Sperry, 1973;Corballis et al., 2018). In addition to the anatomical evidence, Corballis et al (2018) summarize results from previous behavioral experiments involving split-brain patients that support this possibility. ...
For several decades, split-brain research has provided valuable insight into the fields of psychology and neuroscience. These studies have progressed our knowledge of hemispheric specialization, language processing, the role of the corpus callosum, cognition, and even human consciousness. Following a recent empirical paper by Pinto et al. (2017a) and review by Volz and Gazzaniga (2017), a debate has ensued about the nature of conscious perception of visual stimuli in split-brain patients. This exchange is an ideal platform for generating discussion about both the implications of recent findings and the interpretation of results from split-brain studies in general.
... Several seminal studies in split-brain patients have reported that crude information concerning the spatial location of stimuli can be cross-integrated (for further details see Gazzaniga, 2000). As early as 1968, Trevarthen concluded from research in split-brain monkeys that visual projections to the midbrain that subserve orientation in ambient space might be involved in the transfer of information on the location of objects in the split-brain via intact interhemispheric midbrain connections (Trevarthen, 1968;Trevarthen and Sperry, 1973). Such a subcortical transfer of crude information about stimulus location may well have contributed to the accurate localization responses in the 'incongruent conditions' of Pinto et al.'s Experiment 1. ...
... [16] When seeing objects it also involve in two separate visual processing systems, focal process and ambient process. [17] The ambient visual process helps to work with sensory-motor information. 3D viewing by 3D display images may alter the ambient visual process. ...
Purpose: Three-dimensional (3D) displays are very useful in many fields, but induce physical discomforts in some people. This study is to assess symptom type and severity of asthenopia with their habitual distance corrective spectacle (HDCS) and their binocular vision corrective spectacle lenses (BVCSL) in people who feel physical discomforts. Methods: 35 adult subjects (ages 32.2?4.4 yrs) were pre-screened out of 98 individuals to have the highest symptom/asthenopia scores following 65 minutes of 3D television viewing with HDCS. These 35 individuals were then retested symptom/asthenopia scores during they watched 3D television for 65 minutes at a distance of 2.7 m with wearing BVCSL of horizontal, vertical or base down yoked prisms. A 4-point symptom-rating scale questionnaire (0=no symptom and 3=severe) was used to assess 11 symptoms (e.g., blur, diplopia, etc.) related to visual fatigue/visual discomfort. Distance and near lateral phoria were measured using Howell phoria card and vertical phoria were measured using Maddox rod. Symptoms induced by watching 3D TV were compared between wearing HDCS and BVCSL. Results: Asthenopia in watching 3D TV with wearing BVCS was significantly lower than wearing HDCS at 5, 25, 45, and 65 minutes (all p , paired t-tests). In prism correction groups for binocular imbalance, symptoms of asthenopia, however, was significantly lower for when wearing BVCSL than when wearing HDCS (all p
... wendeten Gazzaniga und Hillyard (1973) (Snyder, 1980;Desmedt, 1977) oder eine leichte Tendenz zeigten, etwas größere Amplituden auf der ipsilateral zur visuellen Halbfeldstimulation gelegenen Hemisphäre aufzuweisen (Heinze, 1990;Hillyard, 1984;Mangun, 1990 Eine Reihe von Autoren nehmen an, daß Alarm-und Aufmerksamkeits-Funktionen eher asymmetrisch in den beiden Hemisphären repräsentiert sind (Trevarthen, 1973;Heilman, 1980;Heilman, 1987;Horn, 1982). ...
... Attempts to inhibit such interfering responses via distracting tasks generally led to such a reduced level of consciousness in the right half of the brain, that it was almost impossible to elicit any responses whatsoever from it (Levy, 1970). In tests with bilateral presentation of stimuli, fluctuations in the balance of perceptual processes in the two hemispheres of central origin are commonly observed (Kinsbourne, 1974;Trevarthen, 1974;Trevarthen & Sperry, 1973). In the intact brain, it would be expected that asymmetric activation would be, in part, maintained via callosally mediated inhibition or shunting. ...
Four commissurotomy patients were tested for ability to match tachistoscopi-cally presented stimuli with pictures in free vision, according to either struc-tural appearance or functional/conceptual category. Patients were given ambiguous, structural, or functional instructions on any given run of trials with simultaneous double stimulus input to the two cerebral hemispheres. With ambiguous instructions, appearance and function matches were per-formed by the right and left hemispheres, respectively. When instructions were specific, appearance instructions tended to elicit appearance matches and right-hemisphere control. When function instructions were given, left-hemisphere control and function matches tended to be elicited. In three of the four patients, however, there was a significant number of dissociations be-tween controlling hemisphere and strategy of matching. Previous studies of split-brain patients have revealed that the right hemisphere is superior for visual-spatial transformations (Bogen & Gazzaniga, 1965; Levy-Agresti & Sperry, 1968; Nebes, 1971) and for the rec-ognition of complex visual patterns (Levy, Trevarthen, & Sperry, 1972), while the left hemisphere is superior for speech and calcu-lation (Sperry, Gazzaniga, & Bogen, 1969),. The subjects examined were patients of Doctors Philip Vogel of the California College of Medicine and Joseph Bogen of the Ross-Loos Medical Group, Los Angeles. The authors express their apprecia-tion to Professor Roger W. Sperry in whose lab-oratory of psychobiology this study was conducted. We are much indebted to him for his encourage-ment and advice. Requests for reprints should be addressed to Jerre Levy, Department of Psychology, 3813 Wal-nut Street, University of Pennsylvania, Philadel-phia, Pennsylvania 19174.
Conducted 3 experiments with a total of 36 right-handed 18-25 yr olds with normal or corrected vision. Ss decided as quickly as possible whether dot patterns were or were not symmetrical about a line. Their decision times were shortest when the line was vertical and increased as the angle between the line and the vertical increased. This orientation function was essentially the same whether or not Ss knew in advance what the orientation of the line would be. When Ss tilted their heads, the function shifted in the direction of the head tilt, indicating that it was tied more closely to retinal than to gravitational coordinates. These data can be interpreted to mean that people mentally rotate patterns to a vertical orientation before judging their symmetry. This is turn suggests that the "template" for detecting symmetry may itself be embedded symmetrically in the brain. (21 ref)
The idea that the mind might be composed of distinct conscious entities goes back at least to the mid-19th century, and was at first based on the bilateral symmetry of the brain, with each side seemingly a mirror-image replica of the other. This led to early speculation as to whether section of the forebrain commissures might lead to separate, independent consciousnesses. This was not put to the test until the 1960s, first in commissurotomized cats and monkeys, and then in humans who had undergone commissurotomy for the relief of intractable epilepsy. Initial results did indeed suggest independent consciousness in each separated hemisphere, but later findings have also revealed a degree of mental unity, especially in some perceptual functions and in motor control. Some of these findings might be interpreted in terms of subcortical connections or external cross-cuing, and also address questions about the nature of consciousness in a more concrete way.
In a recent series of experiments, Pinto and colleagues found that the split-brain patient D.D.C. was able to respond accurately to stimuli in either visual field, whether using his right hand, his left hand, or verbally. Pinto and colleagues argue that this demonstrates that a split-brain patient remains a unitary agent and thus continues to possess a unified consciousness. This paper provides a critical evaluation of that claim. First, we argue that two conceptions of the unity of consciousness need to be distinguished: an agency-based conception and an experience-based conception. Second, we argue that it is an open question whether the data presented by Pinto and colleagues is best understood in terms of the unity of agency. Whether that interpretation is correct depends not only on the mechanisms that produce split-brain behaviour, but also on what is involved in being a single agent. Third, we argue that even if the behavioral data indicated that D.D.C has a unified consciousness in the agency-based sense of the term, it is difficult to reconcile them with the claim that his consciousness is fully unified in the experience-based sense.
A Tutorial serving as an introduction to the much larger "Processes in Biological Vision" in 20 Chapters. Updated to 2020 from its original publication in 2004.
Objective:
A bi-modal visual processing model is supported by research to affect dysfunction following a traumatic brain injury (TBI). TBI causes dysfunction of visual processing affecting binocularity, spatial orientation, posture and balance. Research demonstrates that prescription of prisms influence the plasticity between spatial visual processing and motor-sensory systems improving visual processing and reducing symptoms following a TBI.
Rationale:
The rationale demonstrates that visual processing underlies the functional aspects of binocularity, balance and posture. The bi-modal visual process maintains plasticity for efficiency. Compromise causes Post Trauma Vision Syndrome (PTVS) and Visual Midline Shift Syndrome (VMSS). Rehabilitation through use of lenses, prisms and sectoral occlusion has inter-professional implications in rehabilitation affecting the plasticity of the bi-modal visual process, thereby improving binocularity, spatial orientation, posture and balance Main outcomes: This review provides an opportunity to create a new perspective of the consequences of TBI on visual processing and the symptoms that are often caused by trauma. It also serves to provide a perspective of visual processing dysfunction that has potential for developing new approaches of rehabilitation.
Conclusions:
Understanding vision as a bi-modal process facilitates a new perspective of visual processing and the potentials for rehabilitation following a concussion, brain injury or other neurological events.
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.
The failure of growth of the corpus callosum as a commissural bridge between the cerebral hemispheres is a rare condition (Ettlinger, 1977), and it is particularly rare for such individuals to grow to maturity and to be otherwise essentially normal in cognitive and neurological terms. However the systematic behavioural study of these unusual individuals may contribute to both of the issues which constituted the subtitle of this conference: namely, the “unified functioning” and “specialization” of the hemispheres.
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 superior colliculus is a phylogenetically old cortex, but determination and measurement of its function in primates has proved to be a particularly difficult and challenging task. It has been known for over a century that stimulation of the colliculus produces eye movements (Adamuk, 1870), but no experimental design has yielded an adequate answer to the question of the exact functional role of the colliculus.
Progress in strabology can only be made by careful differentiation of clinical entities. Such clinical entities are microtropia, the accommodative convergent squint, the normo sensorial late convergent squint and the congenital squint syndrome.
Nobody knows how the brain works. Major issues are rarely resolved by a single idea, let alone a single experiment. Different hypotheses capture different aspects of a complex and unfamiliar reality, and a narrowly-pitched adversary posture in defense of one position would limit rather than foster the growth of human understanding.1
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.
During the decade following the first edition of this book, methodological advances in a number of related disciplines have greatly enriched our fund of knowledge concerning the role of the corpus callosum in higher brain functions. At the microanatomical level, new tracer techniques have provided a detailed picture of interhemispheric connectivity patterns among functionally specialized cortical areas in anthropoids (for review see Pandya and Seltzer 1986). At the gross anatomical level, magnetic resonance imaging (MRI) has provided multiplanar, high-resolution images of the living human brain by which to: 1) analyze callosal morphometry; 2) delineate precisely the extent of transection in commissurotomy patients; and 3) correlate in vivo the extent of transection with functional effects (e.g., Gazzaniga et al. 1985, 1989; Oppenheim et al. 1989). At the behavioral level, the facility with which microcomputers can be used to generate stimuli, manipulate specific stimulus features, monitor a variety of response modes, and measure response latencies has enhanced the fine-grained assessment of cognitive, perceptual, and motor functions in neurological patients. Meanwhile, increasing numbers of collaborations among cognitive psychologists and clinical neuroscientists have provided the impetus to combine these methods in pursuit of brain-behavior correlations.
This review of findings in brain research is concerned with the biological causes of perception.
Among 55 consecutive patients with drug-refractory epileptic seizures referred to the multidisciplinary Epilepsy Program of the Medical College of Ohio for possible neurosurgical intervention for seizure control, 17 (30.90%) of those completing the multidisciplinary assessment were found to have seizure mechanisms unsuitable for treatment by focal cortical excision. Because these patients had a clear need for additional antiseizure therapy, we felt compelled to reexamine our hesitation to perform corpus callosum section (CCS) for seizure control. Viewing CCS from a background in cortical resection for seizure control, with its defined case selection criteria, known outcome probabilities for seizure control, and low neurological and neuropsychological morbidity and operative mortality (Rasmussen, 1975; Talairach et al., 1974), we experienced concern over (1) the neuropsychological consequences of callosal commisurotomy (e.g., Gazzaniga, 1970), (2) the surgical morbidity and mortality in the early series (Van Wagenen and Herren, 1940; Akelaitis, 1941a,b, 1943; Akelaitis etal., 1942; Smith and Akelaitis, 1942; Bogen and Vogel, 1962, 1975; Bogen et al., 1965; Luessenhop, 1970; Luessenhop et al., 1970; Gordon
Though diverse, the contributions to this book have all focused on a common topic. Such diversity, whilst potentially enriching the depth of understanding afforded, at the same time makes the task of pulling together the various threads into a coherent pattern, unusually challenging. This final chapter attempts, first, to highlight the salient points contained within each of the main sections of this volume. Inevitably this requires radical selection and necessarily omitting some of the important points covered in detail in earlier chapters. This selection in turn affords the opportunity to look for recurring themes which may be running through the earlier specialist sections.
The failure of growth of the corpus callosum as a commissural bridge between the cerebral hemispheres is a rare condition (Ettlinger, 1977), and it is particularly rare for such individuals to grow to maturity and to be otherwise essentially normal in cognitive and neurological terms. However the systematic behavioural study of these unusual individuals may contribute to both of the issues which constituted the subtitle of this conference: namely, the “unified functioning” and “specialization” of the hemispheres.
Callosotomy has played a unique role in the treatment of epilepsy and in the understanding of human brain function. The pioneering work of Dejerine and Liepmann presenting the first findings of callosal lesion pathology at the turn of the 20th century was accepted but then quickly forgotten. Two schools resurrected the phoenix of callosal syndromes: Roger Sperry and Michael Gazzaniga leading in experimental neuroscience, and Norman Geschwind leading in clinical neurology. Callosotomy remains an effective technique to treat atonic, tonic, and tonic–clonic seizures, especially in patients with symptomatic generalized epilepsies such as Lennox–Gastaut syndrome. Neurologic, cognitive, and behavioral complications limit its use given that precise characterization of these complications as well as their frequency is difficult. The high frequencies of developmental delays, severe seizures, head injuries, antiepileptic drug burden, and other factors limit the ability to attribute a specific change to surgical intervention, since surgery can change multiple factors. For example, subtle behavioral changes in executive function and personality are difficult to delineate in a population with preexisting neurologic and psychiatric disorders. Despite this, a clearer picture of the effects of callosotomy, as defined by clinical neurology and neuropsychology as well as cognitive neuroscience, is emerging.
This chapter focuses on the question, is it necessary for consciousness to be fully unified, or is it possible for consciousness to be only partially unified? The intuitive idea of togetherness or co-consciousness can be used to explain full unity. Full unity requires that if two conscious states are co-conscious at a time, then each is also co-conscious with all the states the other is co-conscious with at that time. A partially unified consciousness would not satisfy this assumption of transitivity. In a partially unified consciousness, two states that are not co-conscious with each other can nevertheless both be co-conscious with the same third state.
A considerable part of developmental brain research is concerned with how cellular mechanisms of perception are built. This chapter attempts a review of the field, but does not claim to cover all complex issues brought to light. There is good reason to be selective, as there are difficult conceptual problems. First, we must define perception so that this psychological function—the uptake of information by sensory systems—can be related to the many developmental processes that contribute to it. Somehow we must compare selective and organizing processes in perception with pattern-making and pattern-using systems in the growth of the entire behavioral system: body and brain.
If we are physical things with parts, then accounts of what we are and accounts of when composition occurs have important implications for one another. Defenders of restricted composition tend to endorse a sparse ontology in taking an eliminativist stance toward composite objects that are not organisms, while claiming that we are organisms. However, these arguments do not entail that we are organisms, for they rely on the premise that we are organisms. Thus, sparsist reasoning need not be paired with animalism, but could instead be paired with other accounts according to which we are composites. The embodied mind account—a version of the brain view—is one such account. Replacing the premise that we are organisms with the premise that we are embodied minds, in arguments that otherwise parallel those supporting animalist sparsism, yields an account according to which composite objects include thinkers, but perhaps nothing else. Since animalism has implausible implications about scenarios which are handled better by the embodied mind account, this approach is preferable to animalist sparsism. Furthermore, the role of mental features in sparsism makes embodied mind sparsism the more reasonable conclusion. Meanwhile, adopting sparsism allows the embodied mind account to dodge objections that may not be as easily avoided by it or other versions of the brain view if not paired with sparsism. These include objections about brains that are not persons, inorganic part replacement, and another form of part replacement that might seem to allow one to get a new brain.
Cerebral cortical mechanisms for limb praxis are reviewed, with an emphasis on lesion studies of humans and monkeys. There are multiple components in the cortical control of motor behavior. Prefrontal cortex is important for the direction of behavior when environmental demands are somewhat ambiguous. There are bifrontal and contralateral frontal and parietal mechanisms for the execution and exact control of movements. Premotor cortex and the supplementary motor area each appear to be involved in movement coordination as well as in the selection of movements. There is also a system for the bihemispheric integration of behavior, which involves at least the supplementary motor area and corpus callosum. In humans, there are left-hemispheric processes for the generation of specific movements from memory. Evidence supports the view that the human and monkey brain are organized very similarly, although published research has not addressed the issue of hemispheric specialization for motor tasks in the monkey.
Many research groups have developed outdoor mobile robots and have tested them on roads. Martin Marietta (Denver) has developed “ALVin,” an autonomous mobile robot of 2.7 m in width, 4.2 m in length, 3.1 m in height, and 6 tons in weight. It takes about 2 s to process an image. ALVin has reached about 20 km/h on an unobstructed road [15]. Carnegie—Mellon University (MU) has developed “NAVLAB,” which is based on a commercial van chassis of 4 tons in weight. NAVLAB has reached 1.6 km/h on driveways on the CMU campus. It takes about 20 s to process an image [16].
