Chapter 2: Perception Flashcards
2½-D sketch
Book definition: “Marr’s proposal for a visual representation that identifies where surfaces are located in space relative to the viewer (p. 34)”
3-D model
Book definition: “Marr’s proposal for an object-centered representation of a visual scene (p. 34)”
Ventral stream (or ‘What’-pathway)
Book definition: “ – “
One half of the ‘two-streams hypothesis’; the ventral stream carries visual information from the primary visual cortex in the occipital lobe to the temporal lobe, and is involved with object identification and recognition.
The ventral stream has strong connections to the medial temporal lobe, which stores long-term memories, as well as the limbic system, which controls emotion.
Dorsal stream (or ‘Where’-pathway)
Book definition: “ – “
One half of the ‘two-streams hypothesis’; the dorsal stream carries visual information from the primary visual cortex in the occipital lobe to the parietal lobe, and is involved with guiding actions and the processing of spatial information.
The dorsal stream connects to the posterior parietal cortex, which is essential for perceiving and interpreting spatial relationships and accurate body image as well as learning tasks involving body coordination. Damage to this area can result in optic ataxia.
Agnosia
Book definition: “ – “
Agnosia (Greek for “without knowledge”) is a general term for the inability to process sensory information. It exists in a variety of different forms and is generally caused by stroke, dementia or other neurological disorders.
Examples include apperceptive agnosia, which is a failure in recognition due to a failure of perception; associative agnosia, which is a failure in recognizing or assigning meaning to an otherwise accurately perceived stimulus; and prosopagnosia (also called ‘face blindness’), which is failure in recognizing faces.
Agnosia is not limited to vision, but can affect other areas such as hearing, speech or touch.
Apperceptive agnosia
Book definition: “A form of visual agnosia marked by the inability to recognize simple shapes such as circles and triangles. (p. 27)”
Agnosia refers to the general inability to process sensory information and exists in a variety of different forms. Apperceptive agnosia, which can also apply to other areas such as hearing or touch, is a failure in recognition due to a failure of perception.
This is in contrast to associative agnosia, which is a failure in recognizing or assigning meaning to stimuli, even though they are accurately perceived.
Associative agnosia
Book definition: “A form of visual agnosia marked by the inability to recognize complex objects such as an anchor, even though the patient can recognize simple shapes and can copy drawings of complex objects. (p. 27)”
Agnosia refers to the general inability to process sensory information and exists in a variety of different forms. Associative agnosia, which can also apply to other areas such as hearing or touch, is a failure in recognizing or assigning meaning to an otherwise accurately perceived stimulus. As such, patients may be perfectly able to copy a drawing of an object, but unable to correctly identify the object itself.
This is in contrast to apperceptive agnosia, which is a failure in recognition due to a failure in the perception of stimuli.
Bar detector
Book definition: “A cell in the visual cortex that responds most to bars in the visual field. Compare edge detector. (p. 31)”
Bar detectors are a type of on-off / off-on cell. Cells of this type generally fire at some spontaneous rate, even when no light is received by the eye. If light falls on the sensitive area (indicated by a “+” in the image example), the cell’s rate of firing goes up, indicating the presence of a corresponding type of visual stimulus. If light falls on the region just outside the sensitive area (here marked by a “-“), the cell’s rate of firing goes down, indicating the presence of an inverse type of corresponding visual stimulus.
In the case of bar detectors, this would mean that if light fell on the sensitive center-area of figure (c), the cell’s firing rate would increase, indicating the presence of a light bar. If instead light fell just outside the sensitive area of figure (c), the cell’s firing rate would decrease, indicating the presense of a dark bar. If light were to fall further from these areas, the cell’s firing rate would remain unchanged, indicating no presence of any type of bar.
Bottom-up processing
Book definition: “The processing of a stimulus in which information from a physical stimulus, rather than from general context, is used to help recognize the stimulus. Contrast with top-down processing. (p. 47)”
When a problem or a task is presented, internal cognitive processes are triggered, which elicit a response. For instance, if the problem is hunger and the environmental stimuli are muffins, the bottom-up response is to eat the muffins.
This is in contrast to top-down processing, where information-processing is influenced by the individual’s expectations and knowledge (i.e. “But I can’t, cause I’m on a diet…”).
Categorical perception
Book definition: “The perception of stimuli being in distinct categories with gradual variations. (p. 45)”
Change blindness
Book definition: “The inability to detect a change in a scene when the change matches the context. (p. 50)”
Below is an example of change blindness. See if you can spot the change.
Edge detector
Book definition: “A cell in the visual cortex that responds most to edges in the visual field. Compare bar detectors. (p. 31)”
Bar detectors are a type of on-off / off-on cell. Cells of this type generally fire at some spontaneous rate, even when no light is received by the eye. If light falls on the sensitive area (indicated by a “+” in the image example), the cell’s rate of firing goes up, indicating the presence of a corresponding type of visual stimulus. If light falls on the region just outside the sensitive area (here marked by a “-“), the cell’s rate of firing goes down, indicating the presence of an inverse type of corresponding visual stimulus.
In the case of bar detectors, this would mean that if light fell on the sensitive center-area of figure (c), the cell’s firing rate would increase, indicating the presence of a light bar. If instead light fell just outside the sensitive area of figure (c), the cell’s firing rate would decrease, indicating the presense of a dark bar. If light were to fall further from these areas, the cell’s firing rate would remain unchanged, indicating no presence of any type of bar.
Feature analysis
Book definition: “A theory of pattern recognition that claims that we extract primitive features and then recognize their combinations. (p. 37)”
Feature map
Book definition: “A representation of the spatial locations of a particular visual feature. (p. 32)”
Fovea
Book definition: “The area of the retina with the greatest visual acuity. When we focus on an object, we move the eyes so that the image of the object falls on the fovea. (p. 29)”
Latin for ‘pit’, the fovea is responsible for the sharp, central part of vision needed for observing something in detail. Approximately half of the nerve fibers in the optic nerve carry information from this small point, while the other half is responsible for the remaining part of the retina.
Most of the eye’s cone-cells, which are sensitive to color, are concentrated closely around the fovea, while the rest of the retina instead contains rod-cells, which are sensitive to light. As such, the peripheral vision in a human eye has practically no sensitivity to color, but a higher sensitivity to light than the center of vision (which is why you might notice a small improvement in night vision, should you direct your attention slightly off the center of focus).
Fusiform gyrus
Book definition: “A region in the temporal cortex involved in recognition of complex patterns like faces and words. (p. 42)”
The fusiform face area located in the fusiform gyrus is thought to be responsible for facial recognition. In addition, the fusiform gyrus has been linked to various neurological phenomena such as synesthesia, dyslexia and prosopagnosia.
Geon
Book definition: “One of Biederman’s 36 primitive categories of sub-objects that we combine to perceive larger objects. See also recognition-by-components theory. (p. 40)”
Gestalt principles of organization
Book definition: “Principles that determine how a scene is organized into components. The principles include proximity, similarity, good continuation, closure, and good form. (p. 34)”
Proximity: Elements close together tend to organize into units.
Similarity: Objects that look alike tend to be grouped together.
Good continuation: Elements that look like continuations of eachother tend to be assumed as such.
Closure: Objects that appear obstructed or overlaid by other shapes will be assumed a whole shape.
Good form: Parts of objects that are hidden will be assumed to continue the form that is visible.
Place of articulation
Book definition: “The place at which the vocal tract is closed or constricted in the production of a phoneme. (p. 44)”
Top-down processing
Book definition: “The processing of a stimulus in which information from the general context is used to help recognize the stimulus. Contrast with bottom-up processing. (p. 47)”
When a problem or a task is presented, it is compared to and analyzed in the light of previous problems or tasks before a response is produced. For instance, if the problem is hunger and the environmental stimuli are freshly baked muffins, the individual’s knowledge may indicate that they are on a diet and that the muffins are unhealthy, eliciting the top-down response to not eat the muffins.
This is in contrast to bottom-up processing, where information-processing is directly influenced by environmental stimuli (i.e. “I am hungry, feed me muffins.”)
Visual agnosia
Book definition: “An inability to recognize visual objects that results neither from general intellectual loss nor from loss of basic sensory abilities. (p. 27)”
Although visual recognition in patients is impaired, simply touching a presented object often results in correct recognition. Visual agnosia can be caused by damage to the inferotemporal cortex in the ventral stream, i.e. the ‘What’-pathway used for object recognition.
See also apperceptive agnosia and associative agnosia.
Word superiority effect
Book definition: “The superior recognition of letters presented in a word context than when the letters are presented alone. (p. 48)”
