Biological Bases of Face Recognition

• Importance of face recognition
• Researchers' insights into biological underpinnings
• Key area involved: fusiform gyrus
  • Specific region: fusiform face area
  • Role in recognizing faces
  • Consequence of damage: prosopagnosia
• Studies on prosopagnosia
  • Individuals born with prosopagnosia have compromised connections
  • Fibers of white matter connecting brain areas for facial recognition are affected (Cibu et al., 2009; Garrido et al., 2009)
• Limitations of brain plasticity
  • Persistent facial recognition impairments despite lifelong experiences
• Neuronal firing related to specific faces
  • Example: neurons in the hippocampus responding to celebrity faces (Quiroga et al., 2005)
• Concept of "grandmother cells"
  • Originated by Jerry Lettvin
  • Definition: a hypothetical neuron storing a specific memory (e.g., memory of grandmother)
  • Lettvin assumed it could be easily disproven
  • Reference to Horgan (2005) discussing this idea

Neuronal Networks in Face Recognition

• Current understanding on face recognition
  • Suggestion that individual neurons may contribute, but are not solely responsible
  • Many neurons across different regions are involved in the process
  • Brain recordings are limited in scope, preventing a complete understanding
  • Most plausible hypothesis: face recognition depends on networks of neurons rather than single cells

Perception of Motion

• Mechanism of motion perception
  • Brain compares visual frames to detect motion like frames in a movie
  • Example of real-world application: judging the distance of a car approaching while crossing the street
• Illusions of motion
  • Example: phi phenomenon, discovered by Max Wertheimer
  • Description: rapid flashing of images creates the illusion of continuous motion
  • Implication: brain interprets partial visual information to form perceptions of motion
• Motion blindness
  • Definition: disorder where patients cannot perceive continuous motion
  • Comparison to creating a movie: lacking many visual frames results in erratic perception
  • Everyday life challenges due to motion blindness:
  • Example 1: Judging distances inaccurately, e.g., a car jumping from 100 feet away to 1 foot
  • Example 2: Difficulty performing tasks like pouring coffee due to inability to perceive filling behavior

Perception of Depth

• Definition: ability to perceive spatial relations in three dimensions
• Importance for navigating physical environments, such as grasping objects
• Two types of depth cues:
  • Monocular depth cues
  • Binocular depth cues

Monocular Cues

• Utilizes only one eye to perceive depth
• Key pictorial cues to identify depth:
  • Relative size: more distant objects appear smaller
  • Texture gradient: texture diminishes with distance
  • Interposition: closer objects block further objects
  • Linear perspective: outlines converge at a vanishing point
  • Artists exploit this to create depth illusions
  • Height in plane: distant objects appear higher in a visual field
• Additional monocular cue:
  • Motion parallax: ability to assess distance of moving objects based on perceived speed
  • Closer objects seem to move faster
  • Example of experience while observing from a moving vehicle

Binocular Cues

• Our visual system uses both eyes for depth perception
• Axons in the optic nerve split to enhance depth perception
• Key binocular cues:
  • Binocular disparity: differences in image from each eye for near objects
  • Demonstrated by holding a pen close to the face and switching closed eyes
  • Illustrates how each eye offers a unique perspective to help judge depth