The human brain is an extraordinarily complex biological system underpinning cognition and experience. This complexity is evident at all levels, from genetics to molecular, cellular, network and systems constituents. This article provides an overview of these constituents, their organization and the processes in which they are engaged. We discuss the shaping influences of development and evolution, and describe the brain’s structure and function at several levels: cellular features, the organization of neurons into functional systems, the gross anatomy of the nervous system and the specific structural and functional properties of the cerebral cortex. There is considerable evidence that cortical activity – though not all cortical activity – is correlated with conscious experiences, but exactly which activities constitute consciousness is unclear.
The fundamental role of the visual system is to analyze properties such as form, color and motion in the environment, facilitating the generation of behaviors conducive to survival. A (happy) outcome of these computations is that humans are endowed with conscious visual perception. Despite the complexity of processing in the visual system, we experience a single, unified and continuous percept. This review describes the general anatomy and physiology of the primate visual system, emphasizing four organizational principles and processing strategies that ultimately inform perception and behavior: information processing is functionally segregated; information is encoded in a multiplexed manner; information is hierarchically processed, dependent on feedback and feedforward connectivity; vision is an active sense, with perception and eye movements tightly integrated.
Contributions from 19th Century scholars to binocular rivalry research are well recognized, however, observations concerning the phenomenon commenced centuries earlier and suggest a rich seam of research that is much less well known. This chapter discusses these early investigations, along with conflicting views and observations thereafter. We also discuss the early application of notions of attention and consciousness to rivalry. Such notions have more recently been the subject of concerted investigation into distinguishing brain activity mediating the rivalling states from that underlying visual stimulation. Observations in the literature that preceded this key principle are discussed. We also trace the rivalry studies that followed and note their relevance to current thinking on the phenomenon.
For a given visual stimulus, much can be inferred about its neural representation by measuring an observer’s responses on simple behavioral tasks. This is the essence of psychophysics, the method of examining sensory processing by studying the relation between stimulation and perception or behavior. Binocular rivalry is the phenomenon of alternating perception that occurs when the two eyes receive conflicting images. Psychophysical techniques have been used extensively in combination with rivalry, both to investigate the phenomenon itself, and using rivalry as a tool for addressing other questions. Recent techniques have permitted major advances in both areas, as we discuss here. We will also summarize the value and limitations of rivalry for consciousness research.
Our understanding of the inner workings of the human brain is increasing exponentially. This is due in no small part to the rapidly advancing technology that has evolved from the application of engineering to neuroscience. This chapter reviews some of the more influential tools that are in widespread use in research institutes throughout the world. Beginning with the basics of electrophysiology, a broad overview of the current methods for resolving and modulating neural activity in the fields of imaging and brain stimulation is presented. Special attention is paid to temporal and spatial resolution, i.e., the capacity of the technologies to resolve small detail in time and space. The chapter concludes with a discussion of technical obstacles and future directions.
Ever since Horace Barlow (1972) proposed his neuron doctrine for perceptual psychology, the holy grail for neurophysiologists has been to find individual neurons or groups of neurons whose firing correlates with specific percepts or even a state of mind or consciousness. Binocular rivalry is a particularly attractive paradigm for this approach because a stable visual stimulus causes an ever-changing subjective perceptual experience. The publication of Blake’s neural theory of binocular rivalry (Blake, 1989) inspired numerous attempts to identify neurons in various areas along the central visual pathways whose firing rate might signal dominance or suppression. Collectively these studies have shown that depending on the type of stimulus, rivalry is resolved at both lower and higher levels in the visual system.
Binocular rivalry has intrigued researchers for over two centuries, but research into its neural mechanisms was until recently limited to behavioral and animal studies. The availability of functional magnetic resonance imaging since the 1990s has boosted the neuroscientific investigation of binocular rivalry in humans. Functional neuroimaging has revealed an involvement of all levels of the brain’s visual processing hierarchy in rivalry dynamics, including early subcortical and cortical stages, functionally specialized visual areas, and non-sensory frontoparietal regions. Moreover, variants of binocular rivalry have helped to elucidate the neural fate of unconscious information during binocular rivalry suppression. The findings from neuroimaging research are integrated into a comprehensive view on how different processing stages interact to resolve perceptual conflict in the human brain.
Mechanistic understanding of binocular rivalry (BR) has drawn upon psychophysical, electrophysiological and brain-imaging studies. The first brain stimulation approach occurred in the late 1990s and assessed a new mechanistic proposal, the interhemispheric switch (IHS) hypothesis. Both caloric vestibular stimulation (CVS) and transcranial magnetic stimulation (TMS) modulated rivalry predominance when applied unilaterally. We describe the IHS model, its genesis and the brain stimulation evidence on which it rests. We also review more recent CVS and TMS rivalry studies, and discuss the findings of slow BR in bipolar disorder (BD) and genetic contribution to individual variation in BR rate. Finally, we describe a recent Drosophila model that can shed light on genetic, molecular and neurophysiological aspects of both BR and BD.
The selection and maintenance of a specific percept during binocular rivalry have often been considered to be relatively automatic and influenced primarily by low-level stimulus attributes such as contrast and luminance. However, numerous studies have identified other, higher-level, factors that substantially influence perceptual selection, dominance, and suppression in binocular rivalry. These factors include the configuration of stimulus elements, the spatial and temporal context in which the rivaling stimuli are presented, and manipulations of attentional and pharmacological state. The studies summarized in this chapter broaden traditional conceptions of binocular rivalry as a competition between populations of stimulus-selective neurons and demonstrate that multiple factors can operate over extended spatial and temporal scales to modulate the competitive processes underlying perceptual selection.
This chapter will first examine the neural circuitry necessary to generate binocular rivalry. Such neural circuits entail both neural cooperation within and competition between monocular images. Evidence will also be presented that rivalry must occur at multiple hierarchic levels in the visual system in order to explain relevant data. In light of this, the suggestion that rivalry can elucidate the neural correlates of conscious vision will be challenged. Following this, generalizations of rivalry to competition among multiple spatial patterns will be developed. It will be argued that such generalized rivalry can provide significant insights into the nature of high level visual decisions in the presence of ambiguous or incomplete information.
Binocular rivalry is often considered an experimental window on the neural processes of consciousness. We propose three distinct approaches to exploit this window. First, one may look through the window, using binocular rivalry as a passive tool to dissociate unaltered sensory input from wavering perceptual output. Second, the mechanisms underlying binocular rivalry may yield detailed knowledge of the neuronal underpinnings of binocular vision and increase the value of rivalry as a tool to study consciousness. Finally, smart experimental manipulations allow experimenters to ‘reach through the window’ and interact with mechanisms of conscious visual perception. Within this distinction, we discuss the major open questions in binocular rivalry research and examine how recent technological developments may be incorporated in future studies
The human brain is an extraordinarily complex biological system underpinning cognition and experience. This complexity is evident at all levels, from genetics to molecular, cellular, network and systems constituents. This article provides an overview of these constituents, their organization and the processes in which they are engaged. We discuss the shaping influences of development and evolution, and describe the brain’s structure and function at several levels: cellular features, the organization of neurons into functional systems, the gross anatomy of the nervous system and the specific structural and functional properties of the cerebral cortex. There is considerable evidence that cortical activity – though not all cortical activity – is correlated with conscious experiences, but exactly which activities constitute consciousness is unclear.
The fundamental role of the visual system is to analyze properties such as form, color and motion in the environment, facilitating the generation of behaviors conducive to survival. A (happy) outcome of these computations is that humans are endowed with conscious visual perception. Despite the complexity of processing in the visual system, we experience a single, unified and continuous percept. This review describes the general anatomy and physiology of the primate visual system, emphasizing four organizational principles and processing strategies that ultimately inform perception and behavior: information processing is functionally segregated; information is encoded in a multiplexed manner; information is hierarchically processed, dependent on feedback and feedforward connectivity; vision is an active sense, with perception and eye movements tightly integrated.
Contributions from 19th Century scholars to binocular rivalry research are well recognized, however, observations concerning the phenomenon commenced centuries earlier and suggest a rich seam of research that is much less well known. This chapter discusses these early investigations, along with conflicting views and observations thereafter. We also discuss the early application of notions of attention and consciousness to rivalry. Such notions have more recently been the subject of concerted investigation into distinguishing brain activity mediating the rivalling states from that underlying visual stimulation. Observations in the literature that preceded this key principle are discussed. We also trace the rivalry studies that followed and note their relevance to current thinking on the phenomenon.
For a given visual stimulus, much can be inferred about its neural representation by measuring an observer’s responses on simple behavioral tasks. This is the essence of psychophysics, the method of examining sensory processing by studying the relation between stimulation and perception or behavior. Binocular rivalry is the phenomenon of alternating perception that occurs when the two eyes receive conflicting images. Psychophysical techniques have been used extensively in combination with rivalry, both to investigate the phenomenon itself, and using rivalry as a tool for addressing other questions. Recent techniques have permitted major advances in both areas, as we discuss here. We will also summarize the value and limitations of rivalry for consciousness research.
Our understanding of the inner workings of the human brain is increasing exponentially. This is due in no small part to the rapidly advancing technology that has evolved from the application of engineering to neuroscience. This chapter reviews some of the more influential tools that are in widespread use in research institutes throughout the world. Beginning with the basics of electrophysiology, a broad overview of the current methods for resolving and modulating neural activity in the fields of imaging and brain stimulation is presented. Special attention is paid to temporal and spatial resolution, i.e., the capacity of the technologies to resolve small detail in time and space. The chapter concludes with a discussion of technical obstacles and future directions.
Ever since Horace Barlow (1972) proposed his neuron doctrine for perceptual psychology, the holy grail for neurophysiologists has been to find individual neurons or groups of neurons whose firing correlates with specific percepts or even a state of mind or consciousness. Binocular rivalry is a particularly attractive paradigm for this approach because a stable visual stimulus causes an ever-changing subjective perceptual experience. The publication of Blake’s neural theory of binocular rivalry (Blake, 1989) inspired numerous attempts to identify neurons in various areas along the central visual pathways whose firing rate might signal dominance or suppression. Collectively these studies have shown that depending on the type of stimulus, rivalry is resolved at both lower and higher levels in the visual system.
Binocular rivalry has intrigued researchers for over two centuries, but research into its neural mechanisms was until recently limited to behavioral and animal studies. The availability of functional magnetic resonance imaging since the 1990s has boosted the neuroscientific investigation of binocular rivalry in humans. Functional neuroimaging has revealed an involvement of all levels of the brain’s visual processing hierarchy in rivalry dynamics, including early subcortical and cortical stages, functionally specialized visual areas, and non-sensory frontoparietal regions. Moreover, variants of binocular rivalry have helped to elucidate the neural fate of unconscious information during binocular rivalry suppression. The findings from neuroimaging research are integrated into a comprehensive view on how different processing stages interact to resolve perceptual conflict in the human brain.
Mechanistic understanding of binocular rivalry (BR) has drawn upon psychophysical, electrophysiological and brain-imaging studies. The first brain stimulation approach occurred in the late 1990s and assessed a new mechanistic proposal, the interhemispheric switch (IHS) hypothesis. Both caloric vestibular stimulation (CVS) and transcranial magnetic stimulation (TMS) modulated rivalry predominance when applied unilaterally. We describe the IHS model, its genesis and the brain stimulation evidence on which it rests. We also review more recent CVS and TMS rivalry studies, and discuss the findings of slow BR in bipolar disorder (BD) and genetic contribution to individual variation in BR rate. Finally, we describe a recent Drosophila model that can shed light on genetic, molecular and neurophysiological aspects of both BR and BD.
The selection and maintenance of a specific percept during binocular rivalry have often been considered to be relatively automatic and influenced primarily by low-level stimulus attributes such as contrast and luminance. However, numerous studies have identified other, higher-level, factors that substantially influence perceptual selection, dominance, and suppression in binocular rivalry. These factors include the configuration of stimulus elements, the spatial and temporal context in which the rivaling stimuli are presented, and manipulations of attentional and pharmacological state. The studies summarized in this chapter broaden traditional conceptions of binocular rivalry as a competition between populations of stimulus-selective neurons and demonstrate that multiple factors can operate over extended spatial and temporal scales to modulate the competitive processes underlying perceptual selection.
This chapter will first examine the neural circuitry necessary to generate binocular rivalry. Such neural circuits entail both neural cooperation within and competition between monocular images. Evidence will also be presented that rivalry must occur at multiple hierarchic levels in the visual system in order to explain relevant data. In light of this, the suggestion that rivalry can elucidate the neural correlates of conscious vision will be challenged. Following this, generalizations of rivalry to competition among multiple spatial patterns will be developed. It will be argued that such generalized rivalry can provide significant insights into the nature of high level visual decisions in the presence of ambiguous or incomplete information.
Binocular rivalry is often considered an experimental window on the neural processes of consciousness. We propose three distinct approaches to exploit this window. First, one may look through the window, using binocular rivalry as a passive tool to dissociate unaltered sensory input from wavering perceptual output. Second, the mechanisms underlying binocular rivalry may yield detailed knowledge of the neuronal underpinnings of binocular vision and increase the value of rivalry as a tool to study consciousness. Finally, smart experimental manipulations allow experimenters to ‘reach through the window’ and interact with mechanisms of conscious visual perception. Within this distinction, we discuss the major open questions in binocular rivalry research and examine how recent technological developments may be incorporated in future studies