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.