object recognition

• Modularity


  Fine-grained within the ventral visual ('what') pathway
• Evidence for specialised face processing system in ventral pathway


  • Behavioural evidence
  • Neuropsychological evidence – prosopagnosia
  • fMRI evidence – e.g. Fusiform Face Area (FFA)
• Prosopagnosia


  Acquired deficit in face recognition after brain damage
• Prosopagnosia


  • Lesion region of right ventral occipitotemporal cortex
  • Right hemisphere dominance
  • Hard to pinpoint a specific region that is always damaged
• Evidence from fMRI


  1. Functional localiser scan to identify face-selective voxels

  2. Subsequent scans to test the selectivity of voxels to other stimuli and rule out confounds
• Parahippocampal Place Area (PPA)


  A region in ventral visual cortex that activates selectively to scenes
• Extrastriate Body Area (EBA)


  A region in ventral visual cortex that activates selectively to pictures of human bodies
• No other category of objects shows a selective pattern of activation in a circumscribed cortical region
• Greebles


  Novel objects that subjects were trained to recognise
• FFA: Faces or Expertise?


  • Gauthier et al. (2000) showed bird experts and car experts pictures of birds, cars and faces
  • Stronger FFA activation to birds in bird experts and to cars in car experts
• Prosopagnosics can become experts at identifying other objects
• Challenges to the FFA module hypothesis - Multiple face-selective cortical regions


  • Every brain region needs inputs and outputs
  • Multiplicity and spatial separation of such regions does not argue against the functional specificity of each
• Developmental prosopagnosia


  • Impairment in face recognition that is not the result of a brain injury
  • Impairment is present from birth
  • No obvious pathology e.g. lesion in FFA
  • fMRI evidence inconclusive
• MVPA can pick up on differences in info represented in populations of neurons that show little sensitivity to differences in univariate analysis
• Haxby et al. (2001) study

  
  

  1. Measured activation in each voxel in the ventral visual cortex to each category of object

  2. Compared the within-category correlation and the between category correlation r values across pairs of runs
• Vuilleumier et al. (2002) findings:

  • Reduced activation in left fusiform cortex to the same object from a different viewpoint relative to when different objects were presented
• Yee et al. (2010) fMRI findings:

  • Regions in left temporal cortex showed adaptation to pairs of words with the same function
• Anatomically separate brain regions mediate different aspects of object recognition

  • Lateral occipital cortex – shape
  • Left fusiform cortex – object constancy
  • Left temporal cortex - function