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Facial identity and expression perception in the human visual system

Facial identity and expression perception in the human visual system. NANOS 2011 Vancouver. Human Vision and Eye Movement Laboratory Medicine (Neurology) Ophthalmology and visual sciences Psychology University of British Columbia. DISCLOSURES: NO COMMERCIAL/PROPRIETARY INTERESTS.

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Facial identity and expression perception in the human visual system

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  1. Facial identity and expression perception in the human visual system NANOS 2011 Vancouver Human Vision and Eye Movement Laboratory Medicine (Neurology) Ophthalmology and visual sciences Psychology University of British Columbia

  2. DISCLOSURES: NO COMMERCIAL/PROPRIETARY INTERESTS Canada Research Chairs FUNDING SUPPORT: NIMH 1R01 MH069898 CIHR MOP-77615, MOP-85004, MOP-102567, MOP-106511 NSERC RGPIN 355879-08 Michael Smith Foundation for Health Research CI-SSH-035(03-1) Canada Research Chairs 950-202111 Student support from MSFHR, CIHR, Alzheimer’s Foundation

  3. Common concept: perception of identity and expression emerge from divergent streams of face processing Bruce and Young (1986) cognitive model

  4. Common concept: perception of identity and expression emerge from divergent streams of face processing EXPRESSION Encode facial dynamics Invariant for static structure • allow generalization across people IDENTITY Encode static structure Invariant for dynamic changes •allow stable recognition despite changes in expression and age • Are expression and identity functionally and structurally independent? If so, this would imply that the human brain has evolved highly specific systems for extracting different structural properties of the same object.

  5. 1. Behavioural studies • 2. Anatomic fMRI studies • 3. Patient studies

  6. 1. Behavioural investigation use face-adaptation to probe the functional relationship between the perception of facial expression and perception of facial identity

  7. ..and ask a question: “Did you see fear or anger?” 1. Behavioural adaptation a. Expression adaptation: are these invariant for the identity of the face? Method - perceptual bias technique - create a morph continuum between two expressions: anger fear 90/10 70/30 50/50 30/70 10/90 ambiguous stimuli - stare at one ‘end-face’ for 5 sec.. ..then flash a 300ms ambiguous morph face.. “EXPRESSION AFTER-EFFECT”: Subjects are more likely to perceive the other expression

  8. 1. Behavioural adaptation 5-second Adapting stimulus 300 ms Probe stimulus (*three expression pairs: Angry/afraid; happy/sad; disgusted/surprised)

  9. 1. Behavioural adaptation } } • Changing identity reduces but does not eliminate the expression after-effect. • Expression representations may have two components: Aftereffect magnitude (%) identity-dependent component Different person, Same gender Different person, Different gender identity-invariant component Same person

  10. 1. Behavioural adaptation b. Identity adaptation: is it invariant for the expression of the face? Method - create a morph continuum between two different people’s faces: “Joe” “Bob” 90/10 70/30 50/50 30/70 10/90 - after adaptation to BOB, subjects are more likely to respond that a following ambiguous face is more like JOE.

  11. 1. Behavioural adaptation Is the identity aftereffect partially dependent on expression? Different expression Same expression Aftereffect magnitude Answer: NO. In contrast to expression aftereffects, there is no expression-dependent component of identity aftereffects.

  12. 1. Behavioural adaptation Would we find expression-dependency in the identity after-effect for more familiar faces? Answer: NO Aftereffect magnitude very familiar culturally familiar not familiar minimally familiar

  13. 1. Behavioural adaptation There is an interesting asymmetric relationship between identity and expression! One possible (speculative) interpretation, influenced by network models…. Both contribute to expression adaptation identity adaptation

  14. 1. structural investigation Use fMRI-adaptation to probe the structural relationship between perception of facial expression vs. identity Superior temporal sulcus Fusiform face area

  15. 2. fMRI adaptation 2-D Morph Matrix with “categorical boundaries”: Expression morphing EXPRESSION BOUNDARY Identity morphing IDENTITY BOUNDARY • Ultimately, what mattered most in this experiment was not the stimulus but the perceptual decision - whether the subject said that they saw the face as similar or different.

  16. 2. Rapid event-related fMRI adaptation study Subject sees pairs of faces: establishes baseline of full adaptation In all of these, face 2 is 33% morph different from face 1. identical identity is identical (held constant): Do FFA and STS differ in adaptation effects induced by: • physical changes in expression vs identity? • perception of difference in expression vs identity? similar expression different expression expression is identical (held constant): similar identity Subjects perform 2 runs with the same stimulus set: •Expression task •Identity task different identity

  17. 2. fMRI adaptation FUSIFORM FACE AREA (FFA) Release from adaptation (area ‘detects’ a difference): * FFA is sensitive to any structural change # FFA adaptation release is more when subject perceives a difference in EITHER identity or expression Baseline = adaptation for repetition of identical face same diff diff same identity expression (as reported by subject)

  18. 2. fMRI adaptation SUPERIOR TEMPORAL SULCUS (STS) identity task • STS is modulated by TASK - differences only seen when subject is actively processing expression same same diff diff expression identity DURING EXPRESSION TASK: * STS is sensitive to any stimulus change, expression task # STS adaptation release is more when subject perceives a difference in EITHER identity or expression same diff same diff expression identity

  19. 2. fMRI adaptation Conclusions of fMRI experiment • FFA and STS activity is sensitive to physical properties of face, • Correlate with perceptual report of subject, for both identity AND expression • STS is recruited during expression task • Identity and expression specific signals not seen until later in cortical hierarchy: Identity – precuneus Expression – middle STS

  20. 1. NEUROPSYCHOLOGY Differential impact of lesions on the perception of facial expression and perception of facial identity

  21. fMRI localization data in patients 3. Lesion study Region of interest prosopagnosic Subject prosopagnosic prosopagnosic

  22. 3. Lesion study: are expression and identity differentially impaired? Using 2-D morph matrix, create 4 oddity paradigm tests: Identity varies Identity fixed expression Which face is the different expression? identity Expression varies Expression fixed Which face is the different person? We vary the level of difficulty by choosing morph faces of varying distance in the matrix

  23. 3. Lesion study Other dimension fixed Impaired Identity only normal • Identity but not expression impaired by lesions of: OFA/FFA Ant temporal lobe Medial fusiform • Expression but not identity impaired by lesion of: STS Impaired expression AND Impaired identity Impaired expression only Identity task Expression task • Expression constancy of identity judgments impaired by STS lesion! identity varying expression varying expression fixed identity fixed

  24. Summary Behavioural adaptation results: • identity representations are expression-invariant • expression representations have identity-dependent and identity-invariant components fMRI-adaptation results: • effects of perceptual decision for both expression and identity are REFLECTED in the activity of both FFA and pSTS (does NOT mean that they are encoded there). Lesion results: • “fusiform - anterior temporal stream” lesions impair identity perception but NOT expression perception • STS lesion impaired expression perception and impedes identity judgments when expression must be discounted.

  25. 1. Behavioural adaptation Insula Amygdala Precuneus? Anterior temporal Middle STS FFA Other fusiform regions Posterior STS

  26. Bicycle tour of Vancouver! Wednesday meet at registration desk 1200h

  27. Behavioural adaptation: • Fox CJ, Barton JJS. What is adapted in face adaptation? The neural representations of expression in the human visual system. Brain Res2007; 1127: 80-9. • Butler A, Oruc I, Fox CJ, Barton JJS. Factors contributing to the adaptation aftereffects of facial expression. Brain Res 2008; 1191: 116-26. • Fox CJ, Oruc I, Barton JJS. It doesn’t matter how you feel. The facial identity aftereffect is invariant to changes in facial expression. J Vision 2008; 8(3): 11.1-13. fMRI-adaptation: • Fox CJ, Moon S-Y, Iaria G, Barton JJS. The correlates of subjective perception of identity and expression in the face network: an fMRI adaptation study. Neuroimage 2009; 44: 569-80. Lesions: • FoxCJ, IariaG, DuchaineBC, Barton JJS. Behavioral and fMRI studies of identity and expression perception in acquired prosopagnosia. Vision Sciences Society, Naples 2008 PERSONNEL Andrea Butler Brad Duchaine Chris Fox Giuseppe Iaria So Young Moon Ipek Oruç

  28. 3. Lesion study CONTROL DATA: Desired test properties: • equivalent perceptual difficulty, • controls perform well but not at ceiling • low variance

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