biolpsy_10

Page 1: Introduction

• Biological Psychology Lecture 10: Sensory Systems III

• Instructor: Dr. Richárd Reichardt

  • Email: reichardt.richard@ppk.elte.hu

Page 2: Vision

• Definition: Vision is the sensation of electromagnetic radiation with a wavelength of 400-700 nm.

• This range constitutes the spectrum of visible light.

• Visible light is consistently reflected by dense materials.

Page 3: The Eye

• Vision begins in the eye.

• Light Path: Light enters through the pupil, is refracted by the lens, and reaches the retina.

• The retina translates light patterns into neural activation.

• Ciliary Muscles: Change the lens shape and visual focus.

Page 4: The Retina

• Composed of several layers:

  • Pigmented epithelium

  • Photoreceptor layer: Contains rods and cones

  • Bipolar cell layer

  • Ganglion cell layer

Page 5: Phototransduction

• Opsins: Proteins in receptor cells containing a light-sensitive molecule called retinal.

• When a photon hits retinal, it changes shape, leading to a chain reaction that:

  • Closes sodium (Na) channels.

  • Causes hyperpolarization of the cell.

Page 6: Distribution of Photoreceptors

• Photoreceptor distribution varies across the retina:

  • Fovea: Highest cone density; provides the most accurate vision.

  • Other retinal areas: Contain more rods for less detailed vision.

  • Blind Spot: Area where optic nerve exits the retina, lacking photoreceptors.

Page 7: The Fovea

• Foveal receptors are directly hit by light, bypassing other retinal layers, leading to improved visual clarity.

Page 8: The Optic Tract

• The optic nerve crosses at optic chiasm:

  • Information from the right visual field goes to the left hemisphere.

Page 9: The Visual System

• Pathway: Optic tract to thalamus (LGN), then to occipital cortex.

• Some axons project to the superior colliculus for reflexive eye movements.

Page 10: Brightness Perception

• Brightness is influenced by the visual system, not solely by light amount.

• Lateral inhibition enhances the perception of boundaries, creating the illusion of varying brightness among uniform gray bars.

Page 11: Lateral Inhibition

• Neurons in a region are interconnected, inhibiting each other.

• This causes edge photoreceptors to report receiving less light, creating the illusion of darker edges next to lighter areas.

Page 12: Receptive Fields of Ganglion Cells

• Ganglion cells possess concentric receptive fields:

  • This configuration increases sensitivity to patterned stimuli.

Page 13: Lateral Geniculate Nucleus (LGN)

• The LGN receives contralateral visual field info:

  • Different layers: Some for the contralateral eye, others for ipsilateral eye.

  • Parvocellular layers: Involved in color vision.

  • Magnocellular layers: Important for detecting movement.

Page 14: The Visual Cortex

• Cells in the LGN have concentric receptive fields, while V1 cells are most responsive to edges:

  • Simple Cells: Respond to specific edge orientations.

  • Complex Cells: Responsive to edges moving in specific directions.

Page 15: Simple and Complex Cells

• Simple cortical cells aggregate inputs to respond favorably to bars of light compared to single spots.

• Complex cortical cells receive inputs from simple cells, becoming more responsive to moving bars of light.

Page 16: Visual Processing

• Visual information is processed in areas beyond the occipital cortex:

  • Different areas are linked to specific stimulus features.

Page 17: Complex Stimuli Response

• Certain concentric and radial stimuli evoke strong responses in visual areas (e.g., V4).

• The anterior inferior temporal area cells react to highly specific stimulus features.

Page 18: Color Perception

• Same shade appearance: Gray eyes across different lighting.

• People perceive colors differently due to lighting interpretations (e.g., dress as white/gold or blue/black).

Page 19: Trichromatic Hypothesis

• Proposed by Hermann von Helmholtz:

  • Three types of receptor cells in the retina (blue, green, red sensitive) are responsible for color recognition.

  • Colors perceived based on activated receptor paths to the brain.

Page 20: Opponent-Process Theory

• Ewald Hering's theory suggests:

  • Four unique hues and three opposing pairs of colors (blue/yellow, green/red, black/white).

  • Color vision is based on processes with opposed values.

Page 21: Repeat of Opponent-Process Theory

• Reiteration of Hering's opposing colors concept.

Page 22: Color Detection

• Detection relies on three different cone opsins, or photopigments:

  • Each cone responds to a range of wavelengths, contributing to hue perception through activity levels.

  • Spectrally opponent retinal ganglion cells assess cone activity.

Page 23: Two Streams of Visual Information

• Visual information is processed through two pathways:

  • Ventral pathway: Experiences vision.

  • Dorsal pathway: Integrates vision with movement.

  • Blindsight: Ventral stream damage leads to obstacle avoidance without conscious visual experience.

Page 24: Blindsight and Optic Ataxia

• Lesion in ventrolateral occipital cortex causes visual agnosia (e.g., patient DF can guide movements but not recognize objects).

• Optic Ataxia: Impairment in visually guided movements.

Page 25: Restoring Vision

• Light-sensitive ion channels led to optogenetics, advancing neuroscience methods and restoring photosensitivity in experimental animals.

Page 26: Conclusion

• Thank you for attention!

• Next class: Sensory Systems IV.