Visual Object recognition Flashcards
Agnosia
broad range of deficits related to recognition
Visual Agnosia
involves deficits in visually-based object recognition, which occur in the absence of other accompanying problems with lower-level visual processing (i.e. those affected still have intact visual sensation
hierarchical nature of visual processing
We go through different stages of processing to recognize objects
amodal form of knowledge
independent of any one modality but able to be be accessed/retrieved on the basis of various kinds of sensory input?
modal form of knowledge
always tied to a particular modality and thus only accessible on the basis of modality-specific kinds of processing?
Amodal example
visual input can activate neurons in the visual cortex, which in turn can then activate neurons elsewhere in the brain (e.g. the hippocampus?), which is where the concept is actually stored/represented
Modal example
visual input can activate neurons in the visual cortex, which in and of themselves actually store/represent the concept
Apperceptive agnosia
Typically involves an inability to recognize familiar objects based on shape
a way to think about apperceptive agnosia
primarily affecting one’s ability to form a coherent mental representation (i.e. percept, or pattern, ‘putting the pieces together’)
global level
the whole object being perceived
Local level
small portions of stimuli being processed
what level do visual agnosia patients have trouble perceiving? (global or local)
the global level
what is a navon figure used for
used to test for impairments in local or global processing
lateralization related to global vs local processing
Global features tend to be preferentially processed when stimuli are presented to the left visual field, Local features tend to be preferentially processed when stimuli are presented to the right visual field
associative agnosia
Involves an inability to connect visual perceptions with meaning/memory
what stages are affected by apperceptive agnosia
May primarily affect earlier stages of visual processing related to sensation
what stages are affected associated agnosia
May primarily affect later stages of visual processing related to perception (higher-level meaning)
a way to think about associative agnosia
capable of ‘putting together the pieces’ of a stimuli to form a coherent mental representation (i.e. pattern, perception, etc.) of whatever they’re visually processing but then can’t connect that with any meanin
copying objects and apperceptive agnosia
pretty much entirely unable to copy the model objects
copying objects and associative agnosia
their drawings very clearly stand out as looking ‘abnormal’`
Anomia
impairments in object naming which can also occur in patients with visual agnosia
category specific visual agnosia
These involve more selective impairments in identifying objects belonging to a particular category
prosopagnosia
selective agnosia for faces
prosopagnosia can result from 2 things
damage (e.g. stroke) or be congenital (present from birth)
Type identification
higher-level (superordinate) category
Token identification
specific examples from a given category
One debate in the literature is whether or not the function of the FFA
is intrinsic (e.g. coded for in our genes), as compared to dependent on experience
Inversion effects
are strong for faces, and are said to occur for stimuli that people have difficulty noticing unusual details (anomalies) in when turned upside down
A neurological model (structural model)
Focuses on the physiology of the brain and Tend to be built on direct measurement (fMRI data)
A cognitive model (process model)
Focusses on the cognitive processes, and in particular the stages of information processing, Tend to be built on indirect inferences
Library model for visual object processing
we can look up an address (e.g. a numeric code) for a particular book in a database at a library, then use that address to locate the book within the library shelving system
two major stages in the library model
processing of structural representations , ‘Visual semantics
processing structural representations
involves forming a mental representation with a coherent pattern/perception
Visual semantics
during which those abstract structural representations get matched to stuff in memory, which allows you to extract/impose meaning on the stimuli
example of the cognitivie model
Library model
criticisms of a library model?
not quantitative, descriptive rather than explanatory, Not constrained by/does not incorporate what we know about the brain
dorsal stream
where pathway
ventral stream
what pathway
critisism of the what where pathway
Doesn’t necessarily always explain the behaviour. we want to explain relevant physiology and cognitive process
variations in prosopagnosia
dissociations, within catagory impairment
dissociations is prosopagnosia
one case study in which the patient could recognize facial expressions but not identify faces (e.g. recognize who they belonged to), another case study in which a patient could identify faces but not facial expressions
Within-category impairments
being unable to discriminate being objects in a category
what di deficits and and within category impairments suggest?
deficits in face perception may be the most likely/obvious symptom, what we refer to as prosopagnosia may more generally reflect a loss of perpetual expertise (which may be most obvious as it applies to facial processing for the average person)
the expertise hypothesis
FFA is more generally used to process any stimuli that one develops expertise in within the visual domain
greebles are processed
configurally
what stream is the FFA located within?
ventral stream
evidence for specialized modules in and around the ventral stream
FFA, Parahippocampal Place Area (PPA), Extrastriate Body Area (EBA)
Parahippocampal Place Area (PPA)
Selectively response to places/scenes/landscapes
Damage to the PPA is associated with what?
difficulty recognizing places/scenes/landscapes (topographic agnosia)
Extrastriate Body Area (EBA)
Selectively responds to body parts
Electrocorticography (ECoG)
records electrical signals directly from the cortex surface
using ECoG
can actually use this method to alter brain activity and ask patient what they are perceiving
