Notes on Perception and Visual Hallucinations

Perception and Visual Hallucinations

• Visual hallucinations are associated with an imbalance between bottom-up and top-down processing.

Bottom-Up vs. Top-Down Processing

• Bottom-up processing: Acquiring information directly from the environment.
• Top-down processing: The brain's interpretation of sensations, incorporating expectations and filling in missing information (e.g., blind spot).
• Hallucinations: Occur when bottom-up sensations are confusing, leading the brain to make mistaken predictions through top-down processing.
• Activation of higher-level brain areas during hallucinations supports the role of top-down processing.

Deafferentation and Hallucinations

• Deafferentation: Reduction or removal of sensory input from the outside world (afferent neurons).
• Deafferentation hypothesis: Decreased incoming sensory information increases the likelihood of producing hallucinations.
• Sensory losses (e.g., in vision or hearing) result in greater reliance on top-down processing to compensate for missing input.