Object Recognition pt 2 (3b) Flashcards
(13 cards)
Outline the work by Tanaka & Farah (1993) on facial processing
Faces are processed HOLISTICALLY
Their study gave participants a house/face task
- face task: learn to associate faces with names
- house task: learn to associate houses with names
After learning, ppts had to identify 1. individual features or 2. whole faces/houses
Results:
–> house condition: really no difference - ppts equally good
–> faces: correct is MUCH lower for isolated parts
appears to be an advantage when we see the whole face
What is Prosopagnosia
ACQUIRED deficit in FACE RECOGNITION ABILITY AFTER BRAIN DAMAGE
- patients lose the ability to recognise friends and relatives
- and lose the ability to learn identity of new acquaintances
- patients can still recognise people by their voices
- remote memories of known people remain intact
- cognitive skills remain intact
Lesions are large and extend across lots of lobes and boundaries - predominantly a RIGHT SIDED DEFICIT
Outline the evidence from Kanwisher et al. (1997) for a face processing module
Fusiform Face Area (FFA): a face processing ‘module’
–> Kanwisher et al. (1997) very replicable research
–> ppts in scanner looking at pictures of faces
–> trying to get rid of alternative explanations
Used a REGION OF INTEREST (ROI) approach
- functional localiser scan to identify face-selective voxels
- subsequent scans to test the selectivity of voxels to other stimuli and rule out confounds
–> CONCLUDED: when subtracting other conditions (eg. faces, houses, scrambling): that the FFA is a region of the ventral visual cortex involved in facial processing
Additional fMRI evidence: outline the findings by Epstein et al. (1999) and Downing et al. (2001)
No other category of objects shows a selective pattern of activation in a circumscribed cortical region
- didn’t find for most categories
- DID FIND ONE FOR ‘SCENES’ (the PPA - Epstein)
- DID FIND ONE FOR BODIES (also in visual ventral cortex - Downing)
Only BIOLOGICALLY IMPORTANT STIMULI seem to have dedicated processing modules - for example identifying threats, spatial nav etc.
Challenges to the FFA module hypothesis - list all four
- Expertise-related activation
- Activation in other brain regions to faces
- Developmental prosopagnosia
- Distributed patterns of activation the idea of modularity in general
- Expertise-Related Activation in FFA (outline the work of Gauthier et al. 1999)
Trained subjects to recognise novel objects (GREEBLES) and found that in greeble experts (those that had been trained) - FFA activation
EVALUATION
- evidence if weak and inconsistent for this expertise approach –> increases are small and to replicate findings
- greeble experiment confounded by similarity of stimuli to faces
- prosopagnosics can become experts at identifying other objects
- part/whole behavioural effects are observed for faces but not for other ‘expertise’ objects
- Multiple Face-Selective Cortical Regions
Kanwisher - there are several areas that respond to faces
–> the question is, how do these regions interact?
–> BUT: this multiplicity doesn’t eliminate the idea of functional specificity
- Developmental Prosopagnosia
Impairment of face recognition that is NOT the result of a brain injury (impairment is present from birth)
–> neural basis is matter of debate
–> clearly no obvious pathology
–> functional imaging inconclusive
- Challenging the modularity of the ventral visual objective recognition system (MVPA evidence)
KEY: challenging the concept of modularity
MVPA fMRI: looks for patterns of activation rather than peaks
–> MVPA can ask what information is represented in patterns of activation across a brain region
Research by Haxby et al. (2001)
- presented ppts pictures of different categories in the scanner
- fMRI data included no spatial smoothing
- for each category: measured activation in each voxel in the ventral visual cortex
FOUND:
- within-category correlations were MUCH higher than between-category correlations (for all voxels)
more consistency comparing face-face than face-object
–> remained EVENT WHEN removing voxels that showed higher activation to each category
–> suggests that patterns of activation across the whole ventral visual cortex contain info about the CATEGORY of object someone is looking at
How did Nancy Kanwisher respond to the challenge to her idea of modularity
She acknowledges there is only so much research we can do with fMRI - what we want to be looking at is whether a region is ESSENTIAL or not (looking at the cause)
Attempting to find CAUSE: outline the work of Pitcher et al. (2009)
Used fMRI to identify 3 cortical regions that respond selectively to faces, objects, and bodies
–> then carried out TMS on these regions (attempting to deactivate neuronal processing)
FOUND:
OFA: saw a selective reduction in performance on discriminating face tasks
EBA: saw reduction in body identification task results
LOC: saw reduction in object discrimination ability
Outline the work of Schalk et al. (epilepsy)
Neurosurgical patients implanted with electrodes along fusiform gyri
–> responses showed selectivity to faces
–> electrical stimulation in region of FFA produced illusory experience of seeing a face (facephene)
–> causal evidence that FFA is involved in face perception
Summarise: what is the evidence for and against anatomically distinct ‘modules’ for processing different categories of objects in the ventral visual pathway
Evidence FOR:
- behavioural: holistic processing of faces
- neuropsychological: prosopagnosia
- fMRI: activation of the FFA (fusiform face area)
Evidence AGAINST:
- expertise-related activation in FFA
- activation in other brain regions to faces
- developmental prosopagnosia (no identifiable lesion?)
- distributed patterns of activation to different object categories in ventral visual cortex
