Lecture 12- Visual Perception and Physiological Psychology

Review of Key Concepts in Physiological Psychology - Visual Perception

Alcohol Effects

  • Mechanism of Action:
    • Antagonist to glutamate and NMDA receptors
    • Impacts learning and memory (particularly in the hippocampus)
    • Danger of up-regulation of NMDA receptors and increased glutamate release during withdrawal
    • Agonist for GABA
    • Chronic use leads to reduced GABA receptor activity

LSD and Related Substances

  • LSD Creation:
    • Synthesized by Hoffmann with unexpected psychotropic effects.
  • Mechanism of Action:
    • Acts as a 5-HT2A receptor agonist
    • Implications regarding addiction and the mesolimbic pathway.
    • Highly potent; effects similar to psilocybin, bufotenine, mescaline, all increasing 5-HT receptor activity.

Dissociative Anesthetics

  • Substances: PCP and Ketamine
  • Mechanism:
    • Antagonize/block NMDA receptors
    • PCP inhibits reuptake of dopamine (DA), norepinephrine (NE), and serotonin (5-HT), which increases their production.

Perception vs Sensation

  • Definitions:
    • Sensation: Raw data from sensory systems.
    • Perception: Interpretation of sensory information.
  • Transduction:
    • The conversion of physical energy into electrochemical patterns.
    • Relevant to the mechanism of sensation.

The Retina

  • Light Sensory Receptors' Structure:
    • Contains rods and cones distributed non-uniformly.
  • Functionality:
    • Rods contribute to vision in dim light; cones are responsible for color and detail.

Rods vs Cones

  • Rods:
    • Approximately 100 million in the retina; high convergence (up to 100 rods per ganglion cell).
    • More prevalent in peripheral retina; specialized for low light (scotopic vision).
  • Cones:
    • About 4 million in the retina; lower convergence (one-to-one in fovea).
    • Focus on high acuity under bright light and color perception.

Foveal Anatomy

  • Fovea:
    • Center of focus in the eye, containing only cones, maximizing visual acuity.
    • Directly behind the pupil.

Visual Perception - Filling In Blind Spots

  • Experiment:
    • Observing how blind spots fill in visual information when focusing on specific areas.
    • Explains how the brain compensates for areas of no visual reception due to lack of photoreceptors.

Dark Current and Phototransduction

  • Mechanism:
    • In darkness, rods and cones release glutamate, inhibiting bipolar cells
    • Light absorption leads to hyperpolarization, stopping release of glutamate, activating bipolar cells.
  • Types of Bipolar Cells:
    • On-center bipolar cells activated by light; Off-center cells activated by darkness.

Color Coding: Trichromatic Theory

  • Mechanism:
    • Color vision arises from the relative activation of three types of cones (short, medium, long wavelengths).
  • Color Perception:
    • Depends on the pattern of activity among the three cone types.
  • Physiological Evidence:
    • Spectral pigments measured for their absorption maxima in different wavelengths leading to the discovery of the cone types.

Conclusion

  • Understanding the structure and function of photodetectors (rods and cones) is crucial for grasping the mechanisms of visual perception. This includes the principles of sensation, transduction, and color vision, which correspond to the physiological properties of the retina.