object recognition and sound localisation Flashcards
What does perceptual organisation mean?
the way information is received from our sense
What is the organisation like in retinal images?
they are not organised
What is necessary for object recognition?
perceptual organisation
What are the 2 aims of perceptual organisation?
perceptual segregation
figure background segregation
What does perceptual segregation mean?
the ability to distinguish which elements belong together and form separate objects
What does figure-background segregation mean?
where the visual system separates an image into figure and background by identifying one object as a figure so rest forms the ground
What type of driven is the bottom-up approach?
stimulus driven
What type of driven is a top-down process?
cognitive driven
What are the 6 laws of perceptual organisation?
law of…
similarity
pragnanz
continuity
closure
proximity
common region
What is law of similarity?
similar elements are grouped together perceptually
What is law of pragnanz (or good figure)?
group elements so that the resulting shape is the simplest
What is law of continuity?
where smooth curves are grouped together
What is law of closure?
group elements in a single, recognisable pattern
What is the law of proximity?
elements close together to one another grouped together
What is the law of common region?
elements within a boundary are grouped together
What is a criticism of the laws of perceptual organisation?
it’s provides a description not an explanation!!!
focus is on the cues the brain looks for not how an image is processed
What provides information for perceptual organisation?
natural scene statistics
What are physical regularities?
physical properties that commonly occur in the environment we live in
Marr’s theory of object recognition (Structuralist)
object recognition as a computational problem
What are generalised cones?
elementary units which objects are decomposed into
Biderman’s extended theory from Marr’s
the visual system extracts simple, non-accidental features
these features are invariant
used to infer which geons are present in image
What is a geon?
a simple 2D or 3D geometric shape
used to represent parts of an object
What do structuralist theories like Marr’s and Biderman assume?
assume viewpoint independence
but recognition also depends on viewpoint
What does modularity mean?
refers to how damage in a specific area impairs a specific function
What does Agnosia mean? (Lissauer, 1890)
not knowing
causes problems not recognising object (visual agnosia)
What are the 2 types of Agnosia?
apperceptive agnosia
associative agnosia
What is apperceptive agnosia?
impaired ability to consciously perceive and discriminate stimuli
in posterior right hemisphere
What is associative agnosia?
preserved ability to perceive stimuli but inability to interpret what was seen
e.g couldn’t say what an object it but can draw it
Gathier and Tarr: recognition
recognition at an individual level is more common for faces than objets
more experience with faces than other objects
What is prosopagnosia?
when face perception is selectively comprised after brain damage
What areas of the brain does face perception activate?
fusiform gyrus
What is visual imagery?
seeing with the mind’s eye
occurs when visual representation is present in STM but stimulus is not viewed
The retina is spatiotopic, what does spatiotopic mean?
means the retina corresponds to positions in space
The Cochlea is tonotopic, what does tonotopic mean?
means it corresponds to frequencies
What does interaural time difference mean (ITD)?
means the difference in the arrival time of a sound to two ears
What does interaural level difference mean (ILD)?
means the difference in the intensity of a sound between two ears
Why does sound reach 2 ears at different levels?
due to acoustic shadow
What are binaural cues?
auditory cues that help humans locate sound using both ears
Lord Rayleigh: Duplex theory
states that low frequency sounds (below 800Hz) are localised using ITD
whereas high frequency sounds (above 1600Hz) are localised using ILD
Are most sounds in the environment low or high frequency?
low frequency
so Interaural time difference is dominant cue
What is used to localise low frequency sounds?
interaural time difference (ITD)
What is used to localise high frequency sounds?
Interaural level difference (ILD)
What does cone of confusion refer to?
how all points on a surface provide same binaural cue
What are spectral cues?
a physical cue that helps us locate source of sound
but depends on frequency of sound
What is head-related transfer functions?
a description of how sound waves are modified by the head, ears and other parts of the body as they travel to the ear
What are 2 ways you measure sound localisation?
using an anechoic chamber
spectral cue manipualtion
