object recognition Flashcards
ventral visual processing stream
in the occipitotemporal region
processing info related to object recognition
inferotemporal cortex
posterior
central
anterior
receive info coming from primary visual cortex
what do posterior regions respond to
simple stimuli
what do cells further along the ventral stream respond to
more complex stimuli
receptive fields
area of space to which a cell is sensitive
- if falls outside the cell will not respond
becomes larger as we move further along ventral stream
- inferotemporal has large, primary cortex has small
a large field allows an object to be identified regardless of its sizer and location. we can understand more of what we are looking at. recognizing what, not so much where
consequence of a large receptive field
some info about an item’s position in space is lost
lose ability to know location
agnosia
means without knowledge
visual agnosia
when things go wrong in the ventral stream
an inability to recognize objects in the visual modality (that cannot be explained by other causes such as problems with attention, memory, language etc)
object can be recognized by other senses therefore it is modality specific
two types: apperceptive and associative
apperceptive agnosia
can not perceive a whole
a fundamental difficulty in forming a percept (a mental impression of something perceived by the senses)
sensory info is still processed in a rudimentary way (ie/ distinctions between light and dark can be made), but the data cannot be put together to allow a person to perceive a meaningful whole
have trouble seeing integrated objects
associative agnosia
can copy and reproduce a figure
basic visual info can be integrated to form a meaningful perceptual whole, but that particular perceptual whole cannot be linked to stored knowledge
can see objects, but do not know what they are seeing
can perceive more detail
appreceptive agnosia is damage to where
occipital lobe
associative agnosia is damage to where
occipitotemporal regions of both hemispheres and subadjacent white matter
prosopagnosia
agnosia specific to faces
can occur with people losing the ability to recognize printed words
a selective inability to recognize or differentiate among faces
result of damage to the ventral stream of the right hemisphere
can usually determine basic info (its a face)
limited ability to recognize a face as belonging to a specific person
category specific deficits
trouble identifying a category of objects
ie/ fruits, vegetable
sparse coding
the theory that a small but specific group of cells responds to the presence of a given object
the grandmother cell theory
there is a particular cell in the ventral stream whose job is to fire when you see a particular object or person
a single cell responding to when you see your grandma
not thought to be correct
population coding
the theory that the pattern of activity across a large population of cells codes for individual objects
extreme version: every cell in the ventral stream is involved in coding for every object (all just firing at different rates)
the reality probably lies in between population and sparse, but eveidence leans more towards population
form- cue invariance
the brain’s categorization is constant regardless of the form of the cue that represents that object
ie/ drawn, physically there, cartoon, colour - can recognize it no matter what its form
perceptual constancy
the ability to recognize objects see from different angles, positions, sizes and kinds of illuminations
ie/ from above/below
lateral occipital complex
involved in form-cue invariance and perceptual constancy
- shows evidence of perceptual constancy across variations in size, location and form of the shape
may be the stage in visual representations are formed
- supports recognition of objects despite differing conditions
viewpoint dependency
can recognize objects from multiple viewpoints, but recognition is faster and more accurate when viewed from familiar viewpoint
neural representations
some ventral stream cells change depending on object orientation, other cells respond to an object in the same way regardless of orientation
neuroimaging studies have found viewpoint-dependence at earlier stages of the ventral stream and viewpoint-independence at later stages
left ventral stream
important in analyzing parts of objects
right ventral stream
important for analyzing whole parts (configuration of the parts)
inversion effect
especially effects faces
recognition is poorer when an object is turned upside down
suggests we tend to rely of the way features are put together/ related to each other (configural info) when identifying object
- especially important with object categories for which we have a lot of expertise
nonlogical binding
a whole object is represented by the co activation of cells that represent the part of the object in particular locations
no seperate unit that represents the whole, but rather the whole is perceived when the units are representing all the constituents parts are simultaneously activated
whole is exactly the sum of its parts
conjunctive encoding
lower level regions represent features and send output ot higher level regions representing the shapes that result from the joining of those features
seperate unit that represents the whole, beyond just the ones that respond to the parts
evidence leans in support of this
a whole is more than the sum of its parts
fusiform face area
greater response to faces than other objects
parahippocampal place area
process visual info related to places in the local environment
extrastriate body area
responds to images of the human body and parts of it
visual world form area
responsive to visual representations of the world
auditory agnosia
the inability to recognize the meaning of sounds
can hear smt but can not connect to what it is
somatosensory/ tactile agnosia
is the inability to recognize an item by touch (but can recognize the object in other modalities)
ie/ like a snag rug - can not connect to what it is
