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understanding the brain |
The behavioural meanings of cortical receptive field detections
3rd April 2021
The behavioural meanings of cortical receptive field detections
The behavioural meanings of cortical receptive field detections
The cortex gets a lot of information about the external environment from the senses. It also gets information about the state of the body, and plenty of information flows internally about the state of the cortex itself. The cortex defines conditions within all this information and detects any of the conditions that are currently present. A condition is essentially a list of inputs from different sources, and some algorithm that specifies what states of those inputs result in a condition being detected.
Each cortical hemisphere is divided up into about 150 areas. A few of these areas get inputs fairly directly from one of the senses. A more typical area gets most of its inputs from a small number of other areas. Each cortical area defines and detects conditions within its inputs. Areas are divided up into cortical columns, and each column defines and detects a group of relatively similar conditions within the inputs to the area. Columns are divided up into layers, and each layer within a column defines and detects a group of somewhat more similar conditions, with the deeper layers detecting somewhat more complex conditions. A layer of a column is divided up into pyramidal neurons, and each pyramidal neuron defines and detects a group of even more similar conditions. A pyramidal neuron is divided up into dendrites, and different dendrites define and detect groups of similar conditions within inputs to the area from other areas. A dendrite is divided up into branches, and each branch detects a group of very similar conditions. A synapse on a branch signals detection of a condition by another pyramidal neuron, these conditions are the components of conditions defined by the branch. Chemical receptors within a synapse define the degree to which an input from another neuron contributes to the definition of branch conditions.
The group of conditions defined and detected by a pyramidal neuron is called the receptive field of the neuron. The group of conditions defined and detected by a cortical column is called the receptive field of the column.
Each cortical hemisphere is divided up into about 150 areas. A few of these areas get inputs fairly directly from one of the senses. A more typical area gets most of its inputs from a small number of other areas. Each cortical area defines and detects conditions within its inputs. Areas are divided up into cortical columns, and each column defines and detects a group of relatively similar conditions within the inputs to the area. Columns are divided up into layers, and each layer within a column defines and detects a group of somewhat more similar conditions, with the deeper layers detecting somewhat more complex conditions. A layer of a column is divided up into pyramidal neurons, and each pyramidal neuron defines and detects a group of even more similar conditions. A pyramidal neuron is divided up into dendrites, and different dendrites define and detect groups of similar conditions within inputs to the area from other areas. A dendrite is divided up into branches, and each branch detects a group of very similar conditions. A synapse on a branch signals detection of a condition by another pyramidal neuron, these conditions are the components of conditions defined by the branch. Chemical receptors within a synapse define the degree to which an input from another neuron contributes to the definition of branch conditions.
The group of conditions defined and detected by a pyramidal neuron is called the receptive field of the neuron. The group of conditions defined and detected by a cortical column is called the receptive field of the column.
CORTICAL RECEPTIVE FIELDS HAVE AMBIGUOUS BEHAVIOURAL MEANINGS
The detection of one cortical receptive field has an information meaning and a behavioural meaning. The information meaning is that one or more of the conditions making up the receptive field have been detected. The behavioural meaning is a range of recommendations in favour of different behaviours, each recommendation having a different weight.
Individual cortical receptive fields do not correspond exactly with cognitive situations. For example, no receptive field is always detected when one type of visual object is seen, and never detected when looking at a different type. However, groups of fields can discriminate between different categories. The groups of receptive fields detected in response to a visual object of one type are fairly similar to the groups detected in response to another object of the same type. The groups of receptive fields detected in response to a different type of object are more different. This is not to say that the same receptive field can never be detected in response to both types. It is only that the groups detected in response to the same type must be sufficiently similar, and sufficiently different from the groups detected in response to response to a different type. “Sufficiently” means that it is possible to assign recommendation weights to some set of receptive fields so that category identifications are almost always correct. Such a set has the capability to discriminate between the different categories. A set with this capability for different types of visual objects is labelled ≈visual objects.
The detection of one cortical receptive field has an information meaning and a behavioural meaning. The information meaning is that one or more of the conditions making up the receptive field have been detected. The behavioural meaning is a range of recommendations in favour of different behaviours, each recommendation having a different weight.
Individual cortical receptive fields do not correspond exactly with cognitive situations. For example, no receptive field is always detected when one type of visual object is seen, and never detected when looking at a different type. However, groups of fields can discriminate between different categories. The groups of receptive fields detected in response to a visual object of one type are fairly similar to the groups detected in response to another object of the same type. The groups of receptive fields detected in response to a different type of object are more different. This is not to say that the same receptive field can never be detected in response to both types. It is only that the groups detected in response to the same type must be sufficiently similar, and sufficiently different from the groups detected in response to response to a different type. “Sufficiently” means that it is possible to assign recommendation weights to some set of receptive fields so that category identifications are almost always correct. Such a set has the capability to discriminate between the different categories. A set with this capability for different types of visual objects is labelled ≈visual objects.
Receptive fields are defined by different groups of similar circumstances that occur on a number of occasions. For example, a receptive field might be defined by something vaguely spherical in the visual environment. Such a receptive field might be detected when looking at balls, balloons, globes, or apples etc. Detection of such a receptive field could help discriminate between such objects and more linear objects like chairs, books, pens etc. but additional receptive fields are needed to discriminate between the different vaguely spherical objects. Another possible receptive field would be two vaguely spherical shapes, close together and one larger than the other. This type of field might be detected when looking at the head and body of many different animals, it could be detected when looking at dogs, cats or birds, but not when looking at plants. The requirement is that enough receptive fields of different types are defined so that discrimination between different visual objects is possible, whenever different objects have different behavioural implications.
A cortical area labelled TE defines receptive fields that are very effective for discriminating between different types of visual objects. No individual receptive field resembles any actual category of object. Each receptive field has a range of recommendation strengths in favour of different object recognition behaviours, and the predominant recommendation is almost always appropriate.
A cortical area labelled TE defines receptive fields that are very effective for discriminating between different types of visual objects. No individual receptive field resembles any actual category of object. Each receptive field has a range of recommendation strengths in favour of different object recognition behaviours, and the predominant recommendation is almost always appropriate.
CORTICAL RECEPTIVE FIELDS IN DIFFERENT AREAS HAVE DIFFERENT COMPLEXITIES
Information derived from the senses arrives at cortical areas labelled primary. Raw input from the eyes arrives at the primary visual area, input from the ears at the primary auditory area. Input from sensors in the skin and muscles arrives at the somatosensory area. Smell information arrives at the olfactory area, and taste at the gustatory area. Monomodal cortical areas get inputs ultimately derived from just one sense, either directly from the primary area or via other monomodal areas. Polymodal areas get inputs derived from more than one sense, from different monomodal areas or from other polymodal areas.
A receptive field within one area is defined by some combination of the available inputs from the three or four other areas that provide most of its inputs. A receptive field complexity can be defined as the total number of raw sensory inputs that contribute to the receptive field, either directly or via intermediate receptive fields in other areas. Each area will define receptive fields in a different range of complexity.
Information derived from the senses arrives at cortical areas labelled primary. Raw input from the eyes arrives at the primary visual area, input from the ears at the primary auditory area. Input from sensors in the skin and muscles arrives at the somatosensory area. Smell information arrives at the olfactory area, and taste at the gustatory area. Monomodal cortical areas get inputs ultimately derived from just one sense, either directly from the primary area or via other monomodal areas. Polymodal areas get inputs derived from more than one sense, from different monomodal areas or from other polymodal areas.
A receptive field within one area is defined by some combination of the available inputs from the three or four other areas that provide most of its inputs. A receptive field complexity can be defined as the total number of raw sensory inputs that contribute to the receptive field, either directly or via intermediate receptive fields in other areas. Each area will define receptive fields in a different range of complexity.
Receptive fields in different ranges of complexity are more effective for recommending different general types of behaviour. For example, area TE mentioned earlier is a monomodal visual area with receptive fields that are fairly effective for recommending behaviours that respond to the presence of different types of visual objects. An area defining receptive fields that are combinations of TE fields could be fairly effective for recommending behaviors in response to groups of objects. Even more complex receptive fields could be fairly effective for recommending behaviors in response to groups of groups.
However, an area that is fairly effective for one type of discrimination could also contribute to other types. For example, to discriminate effectively between a dog and a coyote, ≈visual features receptive fields detected in response to a collar around the neck of the animal could contribute recommendation strength in favour of identifying the animal as a dog. Receptive fieldsat the ≈groups of objects complexity that are detected in response to the animal on a lead walking next to a man could contribute similar recommendation strength.
The 150 cortical areas in each brain hemisphere each define and detect receptive fields in a different range of complexity. Higher levels define receptive fields able to discriminate between and recommend behaviours in extremely complex circumstances. Natural selection has ensured that together, fields defined heuristically at all these different complexity levels make it possible to discriminate between almost all situations which have different behavioural implications.
However, an area that is fairly effective for one type of discrimination could also contribute to other types. For example, to discriminate effectively between a dog and a coyote, ≈visual features receptive fields detected in response to a collar around the neck of the animal could contribute recommendation strength in favour of identifying the animal as a dog. Receptive fieldsat the ≈groups of objects complexity that are detected in response to the animal on a lead walking next to a man could contribute similar recommendation strength.
The 150 cortical areas in each brain hemisphere each define and detect receptive fields in a different range of complexity. Higher levels define receptive fields able to discriminate between and recommend behaviours in extremely complex circumstances. Natural selection has ensured that together, fields defined heuristically at all these different complexity levels make it possible to discriminate between almost all situations which have different behavioural implications.