Chapter 4: Cortical Organization
● The importance of organization and how neurons in the visual system are organized
The Organized Visual System
● The need for organization is imp in the visual system due to the tasks it carries out
● 2 of the tasks that organization plays a central role in are:
○ Processing information about objects’ characteristics and features (i.e. size,
shape, orientation, color, movement, location in space)
■ Each characteristic is served by separate mechanisms in diff areas in the
brain
○ Combining information to create clear comprehensible perceptions
An Exploration of Spatial Organization
● Spatial organization: refers to the way stimuli at specific locations in the environment
are represented by activity at specific locations in the NS (nervous system)
○ E.g. see scene → things in it are organized across visual field/org. in visual space
→ org. in the eye (creation of image on retina) → image turns into electrical
signals → occurrence of new org. type: “electronic maps” of the retina in
structures in the higher levels of the visual system
The Electronic Map of V1
● Stimulating diff places on the retina and determining where neurons fire in the cortex
⇒ determines how points in the retinal image are represented spatially on area v1
● Explanation based on Figure 4.1:
○ Locations on the cortex correspond to locations on the retina
○ Retinotopic map: electronic map of the retina on the cortex
■ This map shows that 2 points close to e/o on an object and on the retina
will activate neurons close to e/o in the brain
■ Cortical magnification: a large space on the cortex is devoted/activated
when the fovea and areas near it are stimulated (this map on the cortex
is distorted)
Brain imaging:
● Various procedures that create images of the brain’s activity
○ PET (positron emission tomography)
○ fMRI (functional magnetic resonance imaging)
, ○ Was used to measure cortical magnification in humans’ cortex
● Larger cortical space ⇒ provides extra neural processing
○ In the example of looking at words or letters, the larger cortical space dedicated
to what you're looking at provides extra neural processing to help in the task of
reading since it requires high visual acuity
● Larger cortical space = better detail vision
The Cortex Is Organized in Columns
● We now move below the surface of the cortex
Location and Orientation Columns
● Experiment: inserting an electrode into the cortex perpendicularly
● Discoveries:
○ The striate cortex is organized into:
■ location columns:
● contain neurons that share the same receptive field locations on
the retina
■ orientation columns:
● contain neurons that fire best to stimuli with the same
orientation
○ Orientation columns that are next to e/o have neurons with slightly different
preferred orientations
One Location Column: Many Orientation Columns
● The size of 1 location column is 1-mm which means 1 location column is big enough to
contain orientation columns of all possible orientations
● Hypercolumn: a location column with all of its orientation columns
○ Fit to process info from a small area in the visual field
● Ocular dominance columns:
○ Ocular dominance: when a neuron responds better to one eye than the other
○ Neurons with the same OD are organized into OD columns in the cortex
○ There are 2 OD columns per 1 hypercolumn, 1 for the right eye 1 for the left eye
How Do Feature Detectors Respond to a Scene?
● An object is represented by separate location columns in the cortex (1) → tiling: these
columns (that are adjacent and often overlap) work together to cover the entire visual
● The importance of organization and how neurons in the visual system are organized
The Organized Visual System
● The need for organization is imp in the visual system due to the tasks it carries out
● 2 of the tasks that organization plays a central role in are:
○ Processing information about objects’ characteristics and features (i.e. size,
shape, orientation, color, movement, location in space)
■ Each characteristic is served by separate mechanisms in diff areas in the
brain
○ Combining information to create clear comprehensible perceptions
An Exploration of Spatial Organization
● Spatial organization: refers to the way stimuli at specific locations in the environment
are represented by activity at specific locations in the NS (nervous system)
○ E.g. see scene → things in it are organized across visual field/org. in visual space
→ org. in the eye (creation of image on retina) → image turns into electrical
signals → occurrence of new org. type: “electronic maps” of the retina in
structures in the higher levels of the visual system
The Electronic Map of V1
● Stimulating diff places on the retina and determining where neurons fire in the cortex
⇒ determines how points in the retinal image are represented spatially on area v1
● Explanation based on Figure 4.1:
○ Locations on the cortex correspond to locations on the retina
○ Retinotopic map: electronic map of the retina on the cortex
■ This map shows that 2 points close to e/o on an object and on the retina
will activate neurons close to e/o in the brain
■ Cortical magnification: a large space on the cortex is devoted/activated
when the fovea and areas near it are stimulated (this map on the cortex
is distorted)
Brain imaging:
● Various procedures that create images of the brain’s activity
○ PET (positron emission tomography)
○ fMRI (functional magnetic resonance imaging)
, ○ Was used to measure cortical magnification in humans’ cortex
● Larger cortical space ⇒ provides extra neural processing
○ In the example of looking at words or letters, the larger cortical space dedicated
to what you're looking at provides extra neural processing to help in the task of
reading since it requires high visual acuity
● Larger cortical space = better detail vision
The Cortex Is Organized in Columns
● We now move below the surface of the cortex
Location and Orientation Columns
● Experiment: inserting an electrode into the cortex perpendicularly
● Discoveries:
○ The striate cortex is organized into:
■ location columns:
● contain neurons that share the same receptive field locations on
the retina
■ orientation columns:
● contain neurons that fire best to stimuli with the same
orientation
○ Orientation columns that are next to e/o have neurons with slightly different
preferred orientations
One Location Column: Many Orientation Columns
● The size of 1 location column is 1-mm which means 1 location column is big enough to
contain orientation columns of all possible orientations
● Hypercolumn: a location column with all of its orientation columns
○ Fit to process info from a small area in the visual field
● Ocular dominance columns:
○ Ocular dominance: when a neuron responds better to one eye than the other
○ Neurons with the same OD are organized into OD columns in the cortex
○ There are 2 OD columns per 1 hypercolumn, 1 for the right eye 1 for the left eye
How Do Feature Detectors Respond to a Scene?
● An object is represented by separate location columns in the cortex (1) → tiling: these
columns (that are adjacent and often overlap) work together to cover the entire visual
