Crossing a synapse takes at least half a millisecond, so the more neurons are
involved in a given process, the longer that process takes
Metzinger: experience requires there to be unity in what is experienced as
temporally present
Binding problem: how the different features of objects are brought together to
make a single object
Multisensory integration: how the different senses are brought together to
make a unified experienced world
Substance dualists: consciousness as intrinsically unitary, each person having
their own single consciousness distinct from their physical brain
‘the unity of conscious experience is provided by the self-conscious mind and not
by the neural machinery of the liaison areas of the cerebral hemisphere’
- Mind plays active role in selecting, reading out, and integrating neural
activity, moulding it into a unified whole according to its desire or interest
Problem (for Popper and Eccles & all dualists): how this mind-brain interaction
takes place
The theory provides no explanation of how the separate mind carries out its
selecting and unifying tasks = why few people accept it
Benjamin Libet: dualist (not substance dualist) - believed that conscious unity
was achieved through the effects of a conscious mental field (CMF)
Experiment: take isolated piece of cortical tissue that is completely cut off from
the rest of the brain but kept fully functioning and alive, then activate it
electrically or chemically
- If there’s a CMF = this stimulation should produce a conscious experience
in the person who has the rest of the brain “communication would have to
take place in fields that doesn’t depend on nerve pathways
Approaches:
- Part of progressive research programme for exploring all kinds of
questions about consciousness (incl. Its unity)
- Try to find out how the brain & rest of body manage to integrate and unify
their functions and the majority of the examples considered attempt this
- Reject the idea that consciousness is unified
1. THE BINDING PROBLEM
Visual system: info extracted from pattern of excitation in the rods and cones of
the retina takes one route through the superior colliculus to the eye-movement
system and thereby controls your visual tracking of moving object
- Other info from same retinal patterns takes a different route through the
lateral geniculate nucleus to visual cortex
- V1: retinotopic maps: the organisation of cells reflects the layout on the
retina
- Hierarchical processing of edges, lines and other basic features
- Higher visual cortical areas - original mapping lost and features are dealt
with regardless of where on the retina they originally fell
Color is processed faster than orientation
Orientation faster than motion
Dorsal stream: control fast action of catching the coin deftly
, Ventral stream: more time-consuming process of perceiving (a coin as a coin)
- The 2 Streams in complex dynamic interaction with each other - No single
place and time in the brain which everything comes together
Problem for consciousness: How this kind of binding happens dynamically in real
time
- Memory and attention
Attention: required for binding - when people’s attention is overloaded or
diverted, the wrong features can be bound together to produce illusory
conjunctions
Bilateral damage to parietal cortex: affects attention can cause binding deficits
and in visual search tasks focused attention is necessary for finding unknown
conjunctions
Feature integration Theory (Treisman): when we attend to objects,
computationally understood temporary object files bind groups of features
together on the basis of their spatial locations
- (treisman) binding= central to conscious experience and conscious access
in perception is always to bound objects and events not to free-floating
features of those objects or events
2. BINDING BY SYNCHRONY
Crick and Koch: studies of cat’s visual cortex: oscillations in which large numbers
of neurons all fired in synchrony: “gamma oscillations”
- All neurons dealing with attributes of a single object would bind these
attributes together by firing in synchrony
- This synchronized firing on, or near, the beat of a gamma oscillation might
be the neural correlate of visual awareness
- Thalamus controls attention by selecting the features to be bound
together by synchronisation of firing.
Crick conclude: Consciousness exists only if certain cortical areas have
reverberatory circuits that project strongly enough to produce significant
reverberations
- Distinguishes between explicit and tacit (conscious and unconscious) info
and thought that consciousness is real not illusory
LATER WORK - Crick and Koch: instead features of a single object or event are
bound together when they form part of one temporary coalition of neurons and
primary role of synchrony: help ine coalition in the competition for consciousness
C. Tallon-Baudry: gamma oscillations much stronger during feature-binding
tasks and for tasks in which participants had to hold the representation of an
object in short-term memory while searching a display than during control tasks
- Any stimulus elicits locally synchronous activity in early visual areas,
sufficient for coarse and unconscious identification
- Local oscillations could be more strongly synchronised between areas to
provide a much more detailed representation of the stimulus and maybe
conscious experience of it
Binding in synchrony doesn’t necessarily involve gamma oscillations
Engel& Singer:
involved in a given process, the longer that process takes
Metzinger: experience requires there to be unity in what is experienced as
temporally present
Binding problem: how the different features of objects are brought together to
make a single object
Multisensory integration: how the different senses are brought together to
make a unified experienced world
Substance dualists: consciousness as intrinsically unitary, each person having
their own single consciousness distinct from their physical brain
‘the unity of conscious experience is provided by the self-conscious mind and not
by the neural machinery of the liaison areas of the cerebral hemisphere’
- Mind plays active role in selecting, reading out, and integrating neural
activity, moulding it into a unified whole according to its desire or interest
Problem (for Popper and Eccles & all dualists): how this mind-brain interaction
takes place
The theory provides no explanation of how the separate mind carries out its
selecting and unifying tasks = why few people accept it
Benjamin Libet: dualist (not substance dualist) - believed that conscious unity
was achieved through the effects of a conscious mental field (CMF)
Experiment: take isolated piece of cortical tissue that is completely cut off from
the rest of the brain but kept fully functioning and alive, then activate it
electrically or chemically
- If there’s a CMF = this stimulation should produce a conscious experience
in the person who has the rest of the brain “communication would have to
take place in fields that doesn’t depend on nerve pathways
Approaches:
- Part of progressive research programme for exploring all kinds of
questions about consciousness (incl. Its unity)
- Try to find out how the brain & rest of body manage to integrate and unify
their functions and the majority of the examples considered attempt this
- Reject the idea that consciousness is unified
1. THE BINDING PROBLEM
Visual system: info extracted from pattern of excitation in the rods and cones of
the retina takes one route through the superior colliculus to the eye-movement
system and thereby controls your visual tracking of moving object
- Other info from same retinal patterns takes a different route through the
lateral geniculate nucleus to visual cortex
- V1: retinotopic maps: the organisation of cells reflects the layout on the
retina
- Hierarchical processing of edges, lines and other basic features
- Higher visual cortical areas - original mapping lost and features are dealt
with regardless of where on the retina they originally fell
Color is processed faster than orientation
Orientation faster than motion
Dorsal stream: control fast action of catching the coin deftly
, Ventral stream: more time-consuming process of perceiving (a coin as a coin)
- The 2 Streams in complex dynamic interaction with each other - No single
place and time in the brain which everything comes together
Problem for consciousness: How this kind of binding happens dynamically in real
time
- Memory and attention
Attention: required for binding - when people’s attention is overloaded or
diverted, the wrong features can be bound together to produce illusory
conjunctions
Bilateral damage to parietal cortex: affects attention can cause binding deficits
and in visual search tasks focused attention is necessary for finding unknown
conjunctions
Feature integration Theory (Treisman): when we attend to objects,
computationally understood temporary object files bind groups of features
together on the basis of their spatial locations
- (treisman) binding= central to conscious experience and conscious access
in perception is always to bound objects and events not to free-floating
features of those objects or events
2. BINDING BY SYNCHRONY
Crick and Koch: studies of cat’s visual cortex: oscillations in which large numbers
of neurons all fired in synchrony: “gamma oscillations”
- All neurons dealing with attributes of a single object would bind these
attributes together by firing in synchrony
- This synchronized firing on, or near, the beat of a gamma oscillation might
be the neural correlate of visual awareness
- Thalamus controls attention by selecting the features to be bound
together by synchronisation of firing.
Crick conclude: Consciousness exists only if certain cortical areas have
reverberatory circuits that project strongly enough to produce significant
reverberations
- Distinguishes between explicit and tacit (conscious and unconscious) info
and thought that consciousness is real not illusory
LATER WORK - Crick and Koch: instead features of a single object or event are
bound together when they form part of one temporary coalition of neurons and
primary role of synchrony: help ine coalition in the competition for consciousness
C. Tallon-Baudry: gamma oscillations much stronger during feature-binding
tasks and for tasks in which participants had to hold the representation of an
object in short-term memory while searching a display than during control tasks
- Any stimulus elicits locally synchronous activity in early visual areas,
sufficient for coarse and unconscious identification
- Local oscillations could be more strongly synchronised between areas to
provide a much more detailed representation of the stimulus and maybe
conscious experience of it
Binding in synchrony doesn’t necessarily involve gamma oscillations
Engel& Singer:
