KANDEL PRINCIPLES OF NEURAL SCIENCE CHAPTER 23: INTERMEDIATE-
LEVEL VISUAL PROCESSING AND VISUAL PRIMITIVES
Contour integration = integration of information into a representation of specific objects.
Intermediate-level visual processing involves assembling local elements of an image onto a unified
percept of objects and background.
Three features of visual processing help overcome ambiguity in the signals from the retina:
1. The way in which a visual feature is perceived depends on everything that surrounds it the
response of a neuron in the visual cortex is context-dependent.
2. The functional properties of neurons in the visual cortex can be altered by visual experience or
perceptual learning.
3. Visual processing in the cortex is subject to the influence of cognitive functions, specifically
attention, expectation, and ‘perceptual task’.
Visual primitives = the local features in a visual scene (contrast, line orientation, brightness, color,
movement, and depth).
Analysis of visual primitives:
- Retina detection of brightness and color
- V1 analysis of orientation, direction of movement, and stereoscopic depth. Contour
integration and surface segmentation.
- V2 analyzes properties related to object surfaces
- V4 integrates information about color and object shape
- V5/MT integrates motion signals across space.
In the visual cortex neurons respond selectively to lines of particular orientations.
Each V1 neuron receives input from several neighboring geniculate neurons whose center-surround
receptive fields are aligned so as to represent a particular axis of ortientation.
There are two types of orientation-selective neurons:
1. Simple cells have receptive fields divided into ON and OFF subregions discharge briskly
when a bar of light leaves and OFF region and enters an ON region.
2. Complex cells are less selective for the position of object boundaries. They lack discrete ON
and OFF subregions and respond similarly to light and dark at all locations across their
receptive field.
Visual perception requires eye movement!
End-inhibition = inhibitory regions along the axis of orientation restrict a neuron’s responses to lines
of a certain length.
End-inhibition cells are selective for line curvature and also respond well to corners.
To define the shape of the object as a whole, the visual system must integrate the information on local
orientation and curvature into object contours.
Contextual modulation = the responses of a visual cortex neuron can be modulated by stimuli that
themselves do not activate the cell and therefore lie outside the receptive field’s core.
Association field = the interactions across visual space required to perceptually link contour elements
into global contours.
LEVEL VISUAL PROCESSING AND VISUAL PRIMITIVES
Contour integration = integration of information into a representation of specific objects.
Intermediate-level visual processing involves assembling local elements of an image onto a unified
percept of objects and background.
Three features of visual processing help overcome ambiguity in the signals from the retina:
1. The way in which a visual feature is perceived depends on everything that surrounds it the
response of a neuron in the visual cortex is context-dependent.
2. The functional properties of neurons in the visual cortex can be altered by visual experience or
perceptual learning.
3. Visual processing in the cortex is subject to the influence of cognitive functions, specifically
attention, expectation, and ‘perceptual task’.
Visual primitives = the local features in a visual scene (contrast, line orientation, brightness, color,
movement, and depth).
Analysis of visual primitives:
- Retina detection of brightness and color
- V1 analysis of orientation, direction of movement, and stereoscopic depth. Contour
integration and surface segmentation.
- V2 analyzes properties related to object surfaces
- V4 integrates information about color and object shape
- V5/MT integrates motion signals across space.
In the visual cortex neurons respond selectively to lines of particular orientations.
Each V1 neuron receives input from several neighboring geniculate neurons whose center-surround
receptive fields are aligned so as to represent a particular axis of ortientation.
There are two types of orientation-selective neurons:
1. Simple cells have receptive fields divided into ON and OFF subregions discharge briskly
when a bar of light leaves and OFF region and enters an ON region.
2. Complex cells are less selective for the position of object boundaries. They lack discrete ON
and OFF subregions and respond similarly to light and dark at all locations across their
receptive field.
Visual perception requires eye movement!
End-inhibition = inhibitory regions along the axis of orientation restrict a neuron’s responses to lines
of a certain length.
End-inhibition cells are selective for line curvature and also respond well to corners.
To define the shape of the object as a whole, the visual system must integrate the information on local
orientation and curvature into object contours.
Contextual modulation = the responses of a visual cortex neuron can be modulated by stimuli that
themselves do not activate the cell and therefore lie outside the receptive field’s core.
Association field = the interactions across visual space required to perceptually link contour elements
into global contours.
