Binding problem
Encyclopedia
The binding problem is one of a number of terms at the interface between neuroscience
and philosophy
which suffer from being used in several different ways, often in a context that does not explicitly indicate which way the term is being used. Of the many possible usages, two common versions may be useful anchor points. Firstly, there is the practical issue of how brains segregate elements in complex patterns of data. This can be illustrated by the question "When I see a blue square and a yellow circle, what neural mechanisms ensure that the sensing of blue is coupled to that of a square shape and that of yellow is coupled to that of a circle?" Secondly, there is the more fundamental problem of "how the unity of conscious perception is brought about by the distributed activities of the central nervous system." The first question is a difficult but conventional question within physical science that could equally be applied to a mechanical computer or any complex system with an input and output. The second question is metaphysical in the sense that the "unity of conscious perception" may be an idea outside physical science that requires a metaphysical or ontological underpinning, of the sort on which physics is generally agnostic. Thus "unity" in this sense has no physical meaning, but it does have a crucial meaning in subjective experience.
These two meanings of "binding problem" can be found in a well-defined form, chiefly in the neuroscience and philosophy literature respectively. However, there are also many instances where the two issues are conflated in ways that are difficult to be sure about. Perhaps the clearest exposition of the second meaning comes in William James
's Principles of Psychology where he refers to it as the combination problem.
specialize in processing the different aspects of colour
, motion
, and shape
. This type of modular coding yields a potential for ambiguity
in many instances. Thus, when humans view a scene containing a blue square and a yellow circle, some neurons signal in response to blue, others signal in response to yellow, still others to a square shape and a circle shape. Here, the binding problem is the issue of how the brain represents the pairing of colour and shape, i.e. is the square blue or yellow?
Presumably somewhere further down the line of interneural signalling the output of the blue sensitive cells and the square sensitive cells are allowed to interact by converging in the inputs of further cells in a way that the output of the blue sensitive cells and the circle sensitive cells are not. Whether this is achieved by timing or some form of gating still appears to be wide open to debate. Relevant to this issue is the work of Pylyshyn, which suggests that incoming visual (and other) data get allocated "object labels" in some way, such that "blue" and "square" get tagged as "object number 1". In fact this labelling is so potent that if a blue square goes behind a screen and a yellow square appears at the other side the perception is that "object number 1 changed colour".
A popular hypothesis is that features are bound via synchronisation of the firing of different neurons in the cortex. Andreas K. Engel and his coworkers have found that two different neuron
s with a different receptive field
produce divergent correlogram
s according to whether the stimuli were bound together or not. However, Thiele and Stoner found that perceptual binding of two moving patterns had no effect on synchronisation of the neurons responding to the two patterns. In the primary visual cortex, Dong et al. found that whether two neurons were responding to contours of the same shape or different shapes had no significant effect on neural synchrony.
A number of people, including Marcus have pointed out that phase of oscillation would only allow segregation of very few aspects of a visual image. At the very most ten phase states might be distinguishable, and even that would require stable oscillation rates over time. A much more plausible explanation would seem to be some sort of gating of allowed connection paths by short-term modulation of the weighting of synaptic inputs from "colour and shape cells" to downstream cells by signals from "object label cells".
In this form the binding problem is also an issue in memory
. How do we remember the associations among different elements of an event? How does the brain create and maintain those associations? Both the hippocampus
and prefrontal cortex
seem to be important for memory binding. There is an implication that the behaviour of "object label" or perhaps "event label" cells, can be converted into some form of long-term reinforcement capacity.
In her feature integration theory
, Anne Treisman suggested that binding between features is mediated by the features' links to a common location. Psychophysical demonstrations of binding failures under conditions of full attention provide support for the idea that binding is accomplished through common location tags.
—a putative inner "little man" who is the true subject within the brain. The question is how coloured squares and circles can be "experienced together" as a single scene. The implication is that something is experiencing all these data. It has become popular to deny any need to give a physical account of what it is that has the experience, often with the suggestion that it is the "person as a whole" or the "system". However, to ascribe input to such vague physical domains is not without problems. Such suggestions appear to arise from the common misconception that there cannot be a limited internal physical domain that has access to, for instance, data from blue sensitive and square sensitive cells. This domain is often equated with a "paradoxical" homunculus, but it is often not appreciated that a homunculus is only paradoxical under limited conditions. Sutherland denotes the fear of the homunculus as "homuphobia": "But if you look inside the brain you can't find any little green men and this has given rise to a fear of homunculi, agents and Cartesian theatres. All this has resulted in some desperate and flawed attempts to build a bottom-up theory."
The homunculus concept is often equated with someone "watching a wonderfully integrated internal TV screen" and, as René Descartes
noted, nothing is more certain than that there is an internal observer ("Cogito ergo sum
"), so the only alternative option to the homunculus is infinite regress (who is watching the screen inside the homunculus?). Some materialists refuse to accept the reality of subjective consciousness and so are led to conclude that infinite regress and homunculi are equally repugnant or absurd and so adopt the third alternative: eliminativism. Daniel Dennett maintains that "homunculi are only bogey men if they repeat entirely the talents they are rung in to explain". Limited domains within brains supporting percepts based on signals that have undergone several transductive steps almost certainly have to be postulated because much of brain activity appears to be outside consciousness. How signals are finally transduced into percepts in these domains remains a major mystery but there need be no further regress (again the regress/homunculus/eliminativism alternatives). What is much less clear is whether there is one such domain per brain or many, as in Dennett's "Multiple Draft" hypothesis.
The synchronisation of oscillating cellular potentials has also been invoked as a solution to the combination problem. Thus it was never very clear whether Francis Crick was trying to solve the segregation or the combination problem in his book The Astonishing Hypothesis However, one criticism of the synchronisation idea is that experiential combination of information in separate neurons is incompatible with any standard biophysical explanation of the brain, whether or not there is any synchrony. One possible explanation for binding is that the information is integrated in each of many individual downstream neurons. This requires that percepts exist in multiple complete copies. This difficulty has led many to suggest unconventional physical explanations for percepts, often invoking quantum theory (e.g. the approach of Freeman and Vitiello). Also, multiply experiencing neurons seems to make no sense if their experience is not pooled in a "global workspace" (see Bernard Baars
or Cartesian theatre). And indeed they may be another example of a "desperate and flawed attempt" to build a bottom up theory.
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
and philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...
which suffer from being used in several different ways, often in a context that does not explicitly indicate which way the term is being used. Of the many possible usages, two common versions may be useful anchor points. Firstly, there is the practical issue of how brains segregate elements in complex patterns of data. This can be illustrated by the question "When I see a blue square and a yellow circle, what neural mechanisms ensure that the sensing of blue is coupled to that of a square shape and that of yellow is coupled to that of a circle?" Secondly, there is the more fundamental problem of "how the unity of conscious perception is brought about by the distributed activities of the central nervous system." The first question is a difficult but conventional question within physical science that could equally be applied to a mechanical computer or any complex system with an input and output. The second question is metaphysical in the sense that the "unity of conscious perception" may be an idea outside physical science that requires a metaphysical or ontological underpinning, of the sort on which physics is generally agnostic. Thus "unity" in this sense has no physical meaning, but it does have a crucial meaning in subjective experience.
These two meanings of "binding problem" can be found in a well-defined form, chiefly in the neuroscience and philosophy literature respectively. However, there are also many instances where the two issues are conflated in ways that are difficult to be sure about. Perhaps the clearest exposition of the second meaning comes in William James
William James
William James was a pioneering American psychologist and philosopher who was trained as a physician. He wrote influential books on the young science of psychology, educational psychology, psychology of religious experience and mysticism, and on the philosophy of pragmatism...
's Principles of Psychology where he refers to it as the combination problem.
The practical segregation problem
In the case of visual perception, the brains of humans and other animals process different aspects of perception by separating information about those aspects and processing them in distinct regions of the brain. For example, Zeki and coworkers have shown that different areas in the visual cortexVisual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
specialize in processing the different aspects of colour
Color vision
Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths of the light they reflect, emit, or transmit...
, motion
Motion perception
Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs...
, and shape
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
. This type of modular coding yields a potential for ambiguity
Ambiguity
Ambiguity of words or phrases is the ability to express more than one interpretation. It is distinct from vagueness, which is a statement about the lack of precision contained or available in the information.Context may play a role in resolving ambiguity...
in many instances. Thus, when humans view a scene containing a blue square and a yellow circle, some neurons signal in response to blue, others signal in response to yellow, still others to a square shape and a circle shape. Here, the binding problem is the issue of how the brain represents the pairing of colour and shape, i.e. is the square blue or yellow?
Presumably somewhere further down the line of interneural signalling the output of the blue sensitive cells and the square sensitive cells are allowed to interact by converging in the inputs of further cells in a way that the output of the blue sensitive cells and the circle sensitive cells are not. Whether this is achieved by timing or some form of gating still appears to be wide open to debate. Relevant to this issue is the work of Pylyshyn, which suggests that incoming visual (and other) data get allocated "object labels" in some way, such that "blue" and "square" get tagged as "object number 1". In fact this labelling is so potent that if a blue square goes behind a screen and a yellow square appears at the other side the perception is that "object number 1 changed colour".
A popular hypothesis is that features are bound via synchronisation of the firing of different neurons in the cortex. Andreas K. Engel and his coworkers have found that two different neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s with a different receptive field
Receptive field
The receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron. Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system....
produce divergent correlogram
Correlogram
In the analysis of data, a correlogram is an image of correlation statistics. For example, in time series analysis, a correlogram, also known as an autocorrelation plot, is a plot of the sample autocorrelations r_h\, versus h\, ....
s according to whether the stimuli were bound together or not. However, Thiele and Stoner found that perceptual binding of two moving patterns had no effect on synchronisation of the neurons responding to the two patterns. In the primary visual cortex, Dong et al. found that whether two neurons were responding to contours of the same shape or different shapes had no significant effect on neural synchrony.
A number of people, including Marcus have pointed out that phase of oscillation would only allow segregation of very few aspects of a visual image. At the very most ten phase states might be distinguishable, and even that would require stable oscillation rates over time. A much more plausible explanation would seem to be some sort of gating of allowed connection paths by short-term modulation of the weighting of synaptic inputs from "colour and shape cells" to downstream cells by signals from "object label cells".
In this form the binding problem is also an issue in memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
. How do we remember the associations among different elements of an event? How does the brain create and maintain those associations? Both the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
and prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
seem to be important for memory binding. There is an implication that the behaviour of "object label" or perhaps "event label" cells, can be converted into some form of long-term reinforcement capacity.
In her feature integration theory
Feature integration theory
The feature integration theory, developed by Anne Treisman and Garry Gelade since the early 1980s, posits that different kinds of attention are responsible for binding different features into consciously experienced wholes...
, Anne Treisman suggested that binding between features is mediated by the features' links to a common location. Psychophysical demonstrations of binding failures under conditions of full attention provide support for the idea that binding is accomplished through common location tags.
The combination problem
The binding problem, as it applies to the "unity of consciousness" is related to the problem of the homunculusHomunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
—a putative inner "little man" who is the true subject within the brain. The question is how coloured squares and circles can be "experienced together" as a single scene. The implication is that something is experiencing all these data. It has become popular to deny any need to give a physical account of what it is that has the experience, often with the suggestion that it is the "person as a whole" or the "system". However, to ascribe input to such vague physical domains is not without problems. Such suggestions appear to arise from the common misconception that there cannot be a limited internal physical domain that has access to, for instance, data from blue sensitive and square sensitive cells. This domain is often equated with a "paradoxical" homunculus, but it is often not appreciated that a homunculus is only paradoxical under limited conditions. Sutherland denotes the fear of the homunculus as "homuphobia": "But if you look inside the brain you can't find any little green men and this has given rise to a fear of homunculi, agents and Cartesian theatres. All this has resulted in some desperate and flawed attempts to build a bottom-up theory."
The homunculus concept is often equated with someone "watching a wonderfully integrated internal TV screen" and, as René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...
noted, nothing is more certain than that there is an internal observer ("Cogito ergo sum
Cogito ergo sum
is a philosophical Latin statement proposed by . The simple meaning of the phrase is that someone wondering whether or not they exist is, in and of itself, proof that something, an "I", exists to do the thinking — However this "I" is not the more or less permanent person we call "I"...
"), so the only alternative option to the homunculus is infinite regress (who is watching the screen inside the homunculus?). Some materialists refuse to accept the reality of subjective consciousness and so are led to conclude that infinite regress and homunculi are equally repugnant or absurd and so adopt the third alternative: eliminativism. Daniel Dennett maintains that "homunculi are only bogey men if they repeat entirely the talents they are rung in to explain". Limited domains within brains supporting percepts based on signals that have undergone several transductive steps almost certainly have to be postulated because much of brain activity appears to be outside consciousness. How signals are finally transduced into percepts in these domains remains a major mystery but there need be no further regress (again the regress/homunculus/eliminativism alternatives). What is much less clear is whether there is one such domain per brain or many, as in Dennett's "Multiple Draft" hypothesis.
The synchronisation of oscillating cellular potentials has also been invoked as a solution to the combination problem. Thus it was never very clear whether Francis Crick was trying to solve the segregation or the combination problem in his book The Astonishing Hypothesis However, one criticism of the synchronisation idea is that experiential combination of information in separate neurons is incompatible with any standard biophysical explanation of the brain, whether or not there is any synchrony. One possible explanation for binding is that the information is integrated in each of many individual downstream neurons. This requires that percepts exist in multiple complete copies. This difficulty has led many to suggest unconventional physical explanations for percepts, often invoking quantum theory (e.g. the approach of Freeman and Vitiello). Also, multiply experiencing neurons seems to make no sense if their experience is not pooled in a "global workspace" (see Bernard Baars
Bernard Baars
Bernard J. Baars is a former Senior Fellow in Theoretical Neurobiology at The Neurosciences Institute in La Jolla, CA., and is currently an Affiliated Fellow there. He is best known as the originator of the global workspace theory, a theory of human cognitive architecture and consciousness...
or Cartesian theatre). And indeed they may be another example of a "desperate and flawed attempt" to build a bottom up theory.
See also
- AttentionAttentionAttention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
- ConsciousnessConsciousnessConsciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
- PerceptionPerceptionPerception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
- Philosophy of perceptionPhilosophy of perceptionThe philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or...
- Feature integration theoryFeature integration theoryThe feature integration theory, developed by Anne Treisman and Garry Gelade since the early 1980s, posits that different kinds of attention are responsible for binding different features into consciously experienced wholes...
- Hard problem of consciousnessHard problem of consciousnessThe hard problem of consciousness is the problem of explaining how and why we have qualitative phenomenal experiences. David Chalmers contrasts this with the "easy problems" of explaining the ability to discriminate, integrate information, report mental states, focus attention, etc...
- Quantum mysticismQuantum mysticismQuantum mysticism is a term that has been used to refer to a set of metaphysical beliefs and associated practices that seek to relate consciousness, intelligence or mystical world-views to the ideas of quantum mechanics and its interpretations...