Face Recognition Lecture Notes - 3

Face Recognition

  • Specialized topic following object recognition.
  • Learning Objectives:
    • Understand neural processes for face recognition.
    • Identify dedicated brain regions for facial information.
    • Understand the psychological basis of caricatures.
    • Recognize limited accuracy in recognizing unfamiliar faces and its implications for eyewitness testimony.

Neuropsychology of Face Recognition

  • Prosopagnosia: Failure to recognize faces.
    • Differentiated from failure to recognize objects.
  • Brain regions:
    • Process faces.
    • Process sight of bodies.
  • Grandmother Cells: Theoretical concept of individual cells responding only to specific people (e.g., one's grandmother).
  • Neural processing of faces is biased.
  • Eyewitness testimony accuracy is limited.

Disorders of Face Recognition

  • Prevalence:
    • Developmental prosopagnosia affects approximately 3% of people.
    • Can also result from brain damage.
  • Catastrophic Recognition Loss: Inability to recognize oneself, family members.
  • Brain Lesions:
    • Typically disrupt outputs from the visual cortex to the temporal lobe.

Symptoms and Interpretations of Face Agnosia

  • Symptoms:
    • Failure to recognize individual faces.
    • Recognition of others possible through cues like clothes, voice, or gait.
  • Visual system in prosopagnosia:
    • Face signals are not processed correctly.
  • Interpretations:
    • Specialized brain system for face recognition exists.
    • Damage to this system compromises face recognition.
    • Controversy exists regarding recognition of other object classes.

Challenges in Face Recognition

  • Faces share common components.
  • Differentiation relies on feature configuration.
  • Patients with prosopagnosia may struggle to differentiate objects within a class (e.g., car models).
  • Examples:
    • Mechanic failing to recognize car models after brain lesion.
    • Birder losing ability to recognize bird species.

Evidence for Specialized Face Recognition

  • Patient WJ:
    • Severe face recognition impairment (50% accuracy).
    • Could recognize sheep from his flock.
  • Study by McNeil and Warrington:
    • Politician-turned-sheep farmer with impaired face recognition but intact sheep recognition.
  • Farmers as a control group:
    • Showed normal face recognition abilities.

Double Dissociation

  • Patient C.K. (reported by Moskovitz):
    • Could recognize faces but not the component vegetables in a face made of vegetables.
  • Double Dissociation:** Demonstration of preserved ability in one domain and impaired ability in another, and vice versa in another patient.
  • Evidence for separate brain mechanisms for faces and objects.

Brain Imaging and Face Recognition

  • Functional Magnetic Resonance Imaging (fMRI):
    • Identifies active brain areas.
  • Nancy Kanwisher's Study:
    • Scanned individuals viewing faces and objects.
    • Subtracted brain activation to objects from activation to faces.

Fusiform Face Area (FFA)

  • FFA responds more to faces than objects, houses, or scrambled faces.
  • Located in the right hemisphere on the fusiform gyrus in the temporal lobe.
  • Active during comparisons between profile faces and hands.
  • Small region (fingernail-sized) present in most individuals.
  • Properties: Responds more to faces than other object classes, even those requiring expertise.

Extra Striate Body Area (EBA)

  • Discovered by Paul Dunning in Cardiff.
  • Responds to the sight of bodies, body parts (arms, feet, hands), people, line drawings, stick figures, silhouettes, and recumbent people.
  • Does not respond to:
    • Tools.
    • Jumbled stick figures or silhouettes.
    • Whole faces (intermediate responses to parts of the face).
    • Bodies of other species (intermediate response).

Brain Regions and Specialization

  • Orange region: Extra striate body region.
  • Purple region: Fusiform face area.
  • Parahippocampal place region (in the hippocampus): Responds to buildings and aids navigation.
  • Different brain systems are specialized to respond to different stimuli.

Neural Processing Hierarchy

  • First visual area:
    • Simple, complex, and hypercomplex cells.
  • Temporal cortex:
    • Cells responding to elaborate shapes.
  • Suggests a hierarchy of processing.

Selfridge's Pandemonium Model

  • 1970s model describing potential brain function.
  • Demons:
    • Feature demons: Detect component lines of letters.
    • Cognitive demons: Recognize combinations of lines.
    • Decision demon: Identifies the letter based on strongest activation.
  • Strictly hierarchical.
  • Cognitive demons feed on to decision demon.
  • More complex as you move up the hierarchy.

Grandmother Cells Revisited

  • Hypothetical cells responding only to a specific individual (e.g., one's grandmother).
  • Problem: Perceived lack of sufficient brain cells.
  • Refutation: Cubic millimeter of brain contains approximately one million cells.
  • Recognition vocabulary is limited (e.g., 20,000 words).
  • Specificity makes finding these cells difficult.

Historical Developments in Monkey Brain Studies

  • Areas analogous to the human fusiform face area exist in monkey brains.
  • Doris Tsao's Recordings:
    • Used micro electrodes to record from cells in this region.
  • Tested selectivity of cells with different stimuli:
    • Faces, fruits, bodies, gadgets, hands, and scrambles.

Selectivity of Cells in Monkey Brains

  • 97% of cells in the recorded region were selectively responsive to faces.
  • Correlation between fMRI studies and single-cell recordings:
    • Active cells corresponded to active brain regions in fMRI.
  • Back of the brain feature detectors.
  • Posterior temporal cortex elaborate cells.

Anterior Temporal Cortex

  • Cells respond to the sight of faces.
  • Construction of faces from selectively picking of particular features using elaborate shapes.
  • Cells generalize across:
    • Position
    • Size
    • Orientation
    • Lighting

Responses to Various Faces

  • Cells respond to various faces.
  • Sensitivity to perspective view:
    • Respond to front views but not back views.
    • Some cells respond only to profiles.

Criticism of Marr's and Biederman's Models

  • Models are incorrect in their description of how the brain recognizes faces.
  • Two-dimensional images analyzed from one perspective.

Selectivity for Individual Faces

  • Cells respond more to specific individual faces under different viewing conditions.

Recordings from Epilepsy Patients

  • Tom Otter's lectures discussed recordings from epilepsy patients.
  • Neurosurgeons placed electrodes to find the origin of seizures and found cells responding to faces.
  • Example: Cell responding to Jennifer Aniston's face.

Halle Berry Cell

  • Cell responded to various images of Halle Berry, including her role as Catwoman with a mask.
  • Responded to the name "Halle Berry" when written out.
  • Concept of a person accessed through name, face, and body.
  • Cells like this exist in the temporal cortex.

Sensitivity to Identity

  • Small number of cells are sensitive to identity.
  • Other cells are selective for:
    • Familiar objects (e.g., food items).
    • Famous buildings (e.g., Sydney Opera House).
  • An array of cells responds to highly specific items an individual is familiar with.

Visual Cues for Face Recognition

  • Facial features (eyes, nose, mouth).
    • Eyebrows are a crucial cue.
    • Eyes are less important than expected.

Internal vs. External Features

  • Internal features.
  • External features (hair) are important, especially for unfamiliar faces.
  • Configuration of features is important.

Importance of Internal vs. External Features

  • Unfamiliar faces: External features are crucial.
  • Familiar faces: Internal features are more important.

Thatcher Effect

  • Inverted faces with locally upright features appear normal until upright.
  • Features are processed with respect to gravity.
  • Recognition system is locked to gravity.
  • Features are analyzed independently.

Caricatures

  • Faces are marked with shape of the face and chin.
  • Average face shape is constructed from 50 female faces.
  • Original images are warped to align with the average face and create a grand average.
  • Represents distinctive features of the class of stimuli.

Construction of Facial Averages

  • Averages are made of white female adults and male politicians.
  • Resultant image contains all of those traits.
  • Can be recognized as a woman/white woman or a man.
  • Individual instances of politicians used.

Exaggerating Differences from Average

  • Faces are warped away from average.
  • Elongated faces become more elongated.
  • Exaggeration produces caricatures.

Caricatures and Recognition

  • Images presented with names in a recognition task.
  • Real photographs (no distortion): 1.35 seconds recognition time.
  • Caricatures: More efficient recognition.
  • Caricatures exaggerate deviations from average.
  • Help recognition system improve its speed of recognition.

Coding Differences from Average

  • Faces are coded individuals in the brain by codifying differences from average.
  • Differences from average form the basis of recognition when meeting people.

Biases in Face Recognition

  • Similarity Judgments:
    • When asked to choose which face is more similar, the left one or the right one.
    • Tend to pick based off of the majority because the right isn't like the other.
    • Splitting middle picture in half.
  • People use information on the left half of the face for similarity. Right half is not used.
  • A mirror that halves had the double left looks more like the target than the double right.
  • Face processing is biased.

Masculinity Judgments

  • Task: Decide which image looks more masculine.
  • Result: Most people pick the top image.
  • Split Stimuli:
    • Same image, one flipped over.
    • Blend between male and female face.
  • Conclusion:
    • Attention is paid to features on the left side of the face.

Hemispheric Specialization

  • Visual information from the left side projects to the right brain.
  • Fusiform face area is in the right brain.
  • Left side of the world has preferential access to the fusiform face area.
  • Pay more attention to the left side of faces, which projects more to the right hemisphere.

Implications of Biased Face Processing

  • Pay more attention to the left side of faces for:
    • Age judgments
    • Attractiveness judgments
  • Left half of face projects to right hemisphere.
  • Right hemisphere has specialized face processing equipment.

Challenges in Recognizing Unfamiliar Faces

  • Difficulty matching passport photographs to real people.
  • Matching Accuracy:
    • Security and identifying the images to the siblings.
    • Passport fraud.
    • Checking ID.

Limitations of Eyewitness Testimony

  • Eyewitnesses are not very accurate.
  • High error rates (30%).
  • No improvement with training.
  • Police officers perform no better than students in matching photos to CCTV images.
  • Super-recognizers exist, but normal training doesn't help.

Line-Up Identification

  • Task: Identify the person from an array of faces.
  • Problem: False positives can occur, even when the person is not present in the line-up.
  • Eyewitness testimony is not always accurate. People can get falsely accused.

Key Takeaways

  • Recognizing familiar individuals is excellent.
  • Recognizing unfamiliar faces is poor.
  • Beware eyewitness claims and false positives.

Further Exploration: Capgras Delusion

  • Neuropsychology literature is full of interesting case histories.
  • Capgras Delusion:
    • A delusion where individuals believe that familiar people have been replaced by imposters.
    • How do the symptoms of someone with Capgras resemble horror movies?
  • Invasion of the Body Snatchers has similarities to Capgras delusions.