Perception Flashcards
Role of receptive fields
Respond to visual properties important for perceiving objects
Inferotemporal cortex
Part of the cerebral cortex in the lower portion of the temporal lobe, important for object recognition
What is a lesion?
A region of damaged brain
What happens when IT cortex is lesioned
Agnosia - failure to recognise objects in spite of the ability to se them
Receptive field properties of IT neurons
Large
Don’t respond well to spots or lines
Do respond well to stimuli such as hands, faces or objects
Grandmother cells
Could be a neuron responsible for recognising your grandmother
Mid level vision
A loosely defined stage of visual processing that comes after basic features have been extracted from the image (low level ) and before object recognition and scene understanding
Involves the perception of edges and surfaces
Determines which regions of an image should be grouped together into objects
Texture segmentation
Carving an image into regions of common texture properties
what does texture grouping depend on
the statistics of textures in one region versus another
Gestalt grouping rules
similarity - similar looking items tend to group
Promiximity - 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
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
Camouflage
Animals exploit Gestalt grouping principles to group into their surroundings
Rapid serial visual presentation
An experimental procedure in which stimuli appear in a stream at one location at a rapid rate
Attentional blink
The difficulty in perceiving and responding to the second of 2 target stimuli amid a RSVP stream of distracting stimuli
Second target is often missed if it appears within 200 to 500ms of the first target
Findings of Green and Bavelier (2003)
Reported that people who play first person shooter video games have a reduced attentional blink
Suggests that visual attention performance can be improved with practice
3 ways responses of a cell could be changed by attention
Response enhancement
Sharper tuning
Altered tuning
Fusiform face area
An area in the fusiform gyrus of human extra striate cortex that responds preferentially to faces, according to FMRI studies
Parahippocampal place area
A region of cortex in the temporal lobe of humans that appears to respond strongly to images of places
Visual field defect
A portion of the visual field with no vision or with abnormal vision, typically resulting from damage to the visual nervous system
Pariteal lobe
In each cerebral hemisphere, a lobe that lies towards the top of the brain between the frontal and occipital lobes
Damage to this lobe can cause a visual field defect such that one side of the world is not attended to
Neglect in visual attention
The inability to attend o respond to stimuli in the contralesional visual field
Typically neglect of the left visual field after damage to the right
Contralesional field
The visual field on the side opposite a brain lesion
Ipsilesional field
the visual field on the same side as a brain lesion
Extinction in visual attention
the inability to perceive a stimulus to one side of the point of fixation in the presence of another stimulus, typically in a comparable position in the other visual field
pathways to scene perception
selective pathway - permits the recognition of one or very few objects at a time
Nonselective - contributes information about the distribution of features across a scene as well as information about the fist of the scene
ensemble statistics
the average and distribution of properties such as orientation or colour, over a set of objects or region in a scene
spatial layout
the description of the structure of a scene without reference to the identity of specific objects in the scene
change blindness
the failure to notice a change between 2 scenes
if the change doesn’t alter the fist or meaning of the scene, quite large changes can pass unnoticed
inattention blindness
A failure to notice or at east to report - a stimulus that would be easily reportable if were attended
Definition of sound
Waves of changing pressure travelling through air
Features of a pure tone
An amplitude - the maximum air pressure in each cycle
A frequency - the number of cycles of changing pressure per second
What do natural sounds consist of
Pure tones of many frequencies added together
What does increasing amplitude by 10 x cause loudness to increase to
approx 4 x
What is the role of hair cells
They are mechanocreceptors that transduce vibration of the basilar membrane and send electrical signals to the brain through the auditory nerve
Place coding of sound frequency in cochlea
Each part of the balsiliar membrane vibrates to a particular frequency
What is perception of loudness based on
The firing rate of the hair cells
What is the maximum range of frequencies which a person can hear
Approx 20 Hzto 20 kHz
What is the fundamental frequency
the lowest frequency component of the sound
White noise
Consists of all audible frequencies in equal amounts; used in masking
3 physical dimensions of sound
frequency
amplitude
complexity
These determine what we hear (pitch, loudness and timbre)
What do psychoacousticians study?
How listeners perceive pitch
Explain the ambiguity and perceptual committees metaphor
metaphor for how perception works
committees must integrate conflicting opinions and reach a consensus
(many different principles in perception)
What is an ambiguous figure?
A visual stimulus that gives rise to 2 or more interpretations of its identity or structure
What is an accidental viewpoint?
Viewing position that produces some regularity in the visual image
Gestalt figure ground assignment principles
Surroundedness
size
symmetry
parallelism
relative motion
Spots and bars
Retinal ganglion cells and LGN - spots
Primary visual cortex - bars
Figure and round assignment
=Process of determining that some regions of an image belong to a foreground object and other regions are part of the background
Gestalt figure ground assignment principles
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 the figure
Dealing with occlusion- reliability
the degree to which 2 line segments appear to be part of the same contour
Non accidental figure
A feature of an object that is not dependent on the exact viewing position of the observer
Global and superiority effect
the properties of the whole object take precedence over the properties of parts of the objects
The Bayesian approach
A formal mathematical system that combines information about the current stimulus with prior knowledge about the world
Object recognition - subtraction method
comparing brain activity measured in 2 conditions: one with and one without the mental process of interest
the difference between the images may show the brain regions specifically activated by that mental process
object recognition - decoding method
takes scans of a participant looking at many different images from various known cateofires
train a computer model to recognise brain activity from each category then test the computer model to see if it can identify an untrained image based on what is has learned
deep neural network
a more modern version of selfirdges model
multi level neural networks that can be trained to recognise objects
faces
an illustrative special case
face recognition seems to be special and different from object recognition
prosopagnosia
an inability to recognise faces
template theory
the proposal that the visual system recognises objects by matching the neural representation of the image with a shred representation of the same shape in the brain
Structural description
A description of an object in terms of its parts and the relationship between those parts
The pandemonium model
Oliver self ridge’s simple model of letter recognition - perceptual committee made up of demons
demons loosely represent neurons
