Perception Flashcards
FFA: Fusiform Face Area
Responds to faces more than other objects
PPA: Parahippocampal Place Area
Responds
preferentially to places, such as pictures of houses
EBA: Extrastriate Body Area
Specifically involved in the perception of body parts
Dorsal vs Ventral Visual Stream
The ventral stream (also known as the “what pathway”) is involved with object and visual identification and recognition. It is Allocentric (where things are in relation to other things not us) and conscious.
The dorsal stream (or, “where pathway”) is involved with processing the object’s spatial location relative to the viewer and with speech repetition. It is Egocentric and unconscious.
Milner & Goodale (1995)
Studied patients with optic ataxia - damaged dorsal stream and found that they had difficulty with:
- moving towards targets
- pointing without delay
But no difficulty in identifying visual stimuli
Studied a patient (DF) with visual agnosia - damaged ventral stream
- Incapable of recognising faces objects, shapes and sizes
- incapable of copying pictures
- But could draw from memory
Evidence for the dual system theory
Describe the Primary Visual Cortex V1
Highly specialized for processing information about static and moving objects and is excellent in pattern recognition
It receives its main visual input from the lateral geniculate nucleus of the thalamus (LGN), and sends its main output to subsequent cortical visual areas
The basic operation that V1 is thought to perform on images is simple filtering to enhance edges and contours
Describe the V2 Cortex
It receives strong feedforward connections from V1 (direct and via the pulvinar) and sends strong connections to V3, V4, and V5
Better edge detection than V1
Object-recognition memory (ORM) alterations could result from the manipulation in V2
Describe the V3 Cortex
V3 is normally considered to be part of the dorsal stream, receiving inputs from V2 and from the primary visual area and projecting to the posterior parietal cortex
Describe the V4 Cortex
V4 is the first area in the ventral stream to show strong attentional modulation. Most studies indicate that selective attention can change firing rates in V4 by about 20%
Like V2, V4 is tuned for orientation, spatial frequency, and color. Unlike V2, V4 is tuned for object features of intermediate complexity, like simple geometric shapes
Describe the V5 Cortex
The V5 in primates is thought to play a major role in the perception of motion, the integration of local motion signals into global percepts, and the guidance of some eye movements
Describe the V6 Cortex
The dorsomedial area (DM) also known as V6, appears to respond to visual stimuli associated with self-motion and wide-field stimulation
For many years, it was considered that DM only existed in New World monkeys. However, more recent research has suggested that DM also exists in Old World monkeys and perhaps humans
Describe the Extrastriate Cortex
The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex
The extrastriate cortex encompasses multiple functional areas, including V3, V4, V5/MT, which is sensitive to motion, or the extrastriate body area (EBA) used in the perception of human bodies
What is meant by the 2 Streams Hypothesis (Occipital Lobe)?
Ventral stream = Travels to the lower levels of the temporal lobes, includes brain areas that represent an object’s shape + identity. (WHAT?)
Dorsal stream = Travels up to the parietal lobes, connecting with the areas that identify the location and motion of an object. (WHERE/HOW?)
Explain what is meant by Agnosia
Failure to recognize objects in spite of the ability to see them
What is the Inferotemporal Cortex (IT)?
Part of the cerebral cortex in the lower portion of the temporal lobe, important for object recognition
Part of the “What” Pathway
Lesions lead to Agnosia
What are the receptive field properties of IT neurons?
Very large—some cover half the visual field
Don’t respond well to spots or lines
Do respond well to stimuli such as hands, faces, or objects
What are Grandmother Cells?
The grandmother cell, sometimes called the “Jennifer Aniston neuron,” is a hypothetical neuron that represents a complex but specific concept or object. It activates when a person “sees, hears, or otherwise sensibly discriminates” a specific entity, such as his or her grandmother
Explain what is meant by Mid-level Vision
A loosely defined stage of visual processing that comes after basic features have been extracted from the image (low-level vision) and before object recognition and scene understanding (high level vision)
Involves the perception of edges and surfaces
Determines which regions of an image should be grouped together into objects
Define the term Illusory Contour
A contour that is perceived even though nothing changes from one side of the contour to the other
What are the main Gestalt Principles?
Good Continuation -> A Gestalt grouping rule stating that two elements will tend to group together if they lie on the same contour
Texture Segmentation -> Carving an image into regions of common texture properties
= Similarity -> Similar looking items tend to group
= Proximity -> Items that are near each other tend to group
= Parallelism -> Parallel contours are likely to belong to the same group
= Symmetry -> Symmetrical regions are more likely to be seen as a group
= Common region -> Items will group if they appear to be part of the same larger region
= Connectedness -> Items will tend to group if they are connected
Dynamic Grouping
= Common fate: Elements that move in the same direction tend to group together.
= Synchrony: Elements that change at the same time tend to group together
What is meant by Figure-Ground Assignment?
The process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground)
= Surroundedness: The surrounding region is likely to be ground.
= Size: The smaller region is likely to be figure.
= Symmetry: A symmetrical region tends to be seen as figure
= Parallelism: Regions with parallel contours tend to be seen as figure.
= Relative motion: If one region moves in front of another, then the closer region is figure
How does the brain deal with Occlusion?
Relatability: The degree to which two line segments appear to be part of the same contour
Nonaccidental feature: A feature of an object that is not dependent on the exact (or accidental) viewing position of the observer
= T junctions: Indicate occlusion. Top of T is in front and stem of T is in back.
= Y junctions: Indicate corners facing the observer.
= Arrow junctions: Indicate corners facing away from the observer.
Define the Global Superiority Effect
Global superiority effect: The properties of the whole object take precedence over the properties of parts of the object
What are the five principles of Middle Vision?
- Bring together that which should be brought together
- Split asunder that which should be split asunder
- Use what you know
- Avoid accidents
- Seek consensus and avoid ambiguity
