4.13 Visual Processing and Face Recognition

In previous discussions, the primary visual cortex was described as the initial processor of visual information.
At the stage of processing in the primary visual cortex, no true perception has occurred yet.
Specifically, users cannot identify what they are looking at, such as recognizing a face.

To achieve perception and understanding, signals must travel through distinct visual streams in the brain.

Location: Runs along the underside and sides of the brain to the temporal lobes.
Often referred to as the 'what' stream because it is involved in recognizing and identifying objects.
Essential for face processing, which is critical for meaningful social interactions.

Location: Moves through the back and top of the brain.
The term 'dorsal' is likened to the dorsal fin of a fish or whale, which is located on the top side of the body.
This stream's function is less about identifying objects and more about spatial awareness and movement.

The ability to recognize faces is vital for social interactions.
The fusiform face area (FFA) is a specialized brain region dedicated to processing faces.
Humans have a significant amount of neural tissue devoted to face recognition; this capability allows the identification of complex configurations of facial features.

Sometimes the brain's efficiency in processing faces leads to pareidolia, where individuals see faces in inanimate objects.
Common examples include:
- Seeing a face of Jesus in toast.
- Reporting alien faces in structures on Mars.
This phenomenon illustrates the brain's pattern recognition tendency, sometimes leading to erroneous perceptions.

Definition: Prosopagnosia is commonly referred to as "face blindness", though this term is a misnomer.
It is not a visual problem, but rather a perceptual one affecting the ability to perceive and recognize faces.
Individuals with prosopagnosia may struggle to recognize even familiar faces, such as friends and family.
Instead of a holistic view, those with this condition rely solely on specific features (e.g., a trademark nose).

People typically perceive faces holistically; they recognize faces as a whole rather than focusing on individual parts.
An example demonstrating this is the face inversion effect or Thatcher effect:
- When shown an upside-down image of a face, distortion may not be immediately recognized.
- Once flipped right-side up, the gross distortion becomes apparent, revealing the challenges of holistic perception when the orientation is altered.
Disruption in recognizing faces in an upside-down position necessitates reliance on individual features rather than a holistic view.

Evidence suggests that the fusiform face area is not exclusive to facial recognition.
This was demonstrated in the Greeble Experiment:
- Participants were trained to differentiate between uniquely shaped figures called Greebles.
- Before training, the FFA showed minimal activation when viewing Greebles compared to faces.
- Post-training, participants exhibited increased FFA response to Greebles, indicating that this brain region also processes visual expertise and is not confined to face processing.
Similar results can be seen with individuals who have expertise in other areas, such as birdwatching or automotive knowledge, suggesting that visual expertise is trainable within the brain's perception systems.

Understanding the ventral and dorsal streams contributes to a broader knowledge of visual perception, particularly in how humans recognize and process faces.
The fusiform face area serves as a flexible visual expertise area rather than a domain strictly for face recognition, paving the way to understand how expertise in various visual domains can influence brain activity.