Lecture Sensation and Perception

Chapter 4: Sensation and Perception

Sensation vs. Perception

• Sensation: The stimulation of sense organs.

• Perception: The selection, organization, and interpretation of sensory input.

• Important Note: Perception does not always accurately reflect the sensation.

Visual Perception

• Optical illusions (e.g., counting empty dots, perceiving movement) demonstrate that perception can differ from reality.

Vision: The Stimulus

• Light: Represents electromagnetic radiation.

• Amplitude: Related to the perception of brightness.

• Wavelength: Corresponds to the perception of color.

• Purity: Affects the perception of saturation and richness of colors.

Eye Anatomy

• External Structures:

  • Cornea: Entry point for light.

  • Lens: Focuses light rays onto the retina.

  • Iris: Colored muscle that constricts/dilates based on light intensity.

  • Pupil: Regulates the amount of light hitting the retina.

Function of the Retina

• Components of Retina:

  • Rods: Enable black and white vision in low light.

  • Cones: Responsible for color and daylight vision; concentrated in the fovea, which contains only cones.

From Eye to Brain

• Optic Nerve transfers visual information to the brain.

• Optic Chiasm: Where the optic nerves cross.

• Information is processed bilaterally in both sides of the brain.

Visual Pathways in the Brain

• Ventral Pathway: Processes 'what' an object is (form, color, texture).

• Dorsal Pathway: Processes 'where' an object is located (motion, distance).

Color Vision

• Colorblindness:

  • Occurs in ~10% of men and ~1% of women.

  • Types:

    • Dichromats: Blind to red-green or blue-yellow.

    • Monochromats: See only shades of light and dark.

Theories of Color Vision

• Trichromatic Theory (Young and Helmholtz, 1860):

  • Proposes three types of receptors (red, green, blue) that mix to form other colors.

• Opponent Process Theory (Hering, 1878):

  • Proposes three pairs of antagonistic colors (red-green, blue-yellow, black-white).

Hearing: The Auditory System

• Sound Waves: Stimuli created by vibrations in air.

  • Amplitude: Determines loudness.

  • Wavelength: Determines pitch (measured in Hz).

The Ear: Anatomy

• Divisions of the Ear:

  • External Ear (Pinna): Collects sound.

  • Middle Ear: Contains ossicles (malleus, incus, stapes).

  • Inner Ear: Contains cochlea, a fluid-filled structure housing hair cells (auditory receptors).

Sound Processing

• Mechanism:

  • Sound waves vibrate through the ear, causing the stirrup to hit the oval window of the cochlea, stimulating hair cells.

  • Converts physical sound stimuli into neural impulses sent to the auditory cortex.

Taste (Gustation)

• Primary Tastes:

  • Sweet, sour, bitter, and salty (unevenly distributed on the tongue).

• Taste Buds: Receptors that help translate these tastes.

Variability in Taste Sensitivity

• Non-tasters and Supertasters: Differences that influence eating habits and health outcomes.

Pathway for Gustatory Information

• Taste buds activate three nerve pathways (facial, glossopharyngeal, vagus), relaying information to the brain and ultimately to the Primary Gustatory Cortex in the frontal lobe.

Smell (Olfaction)

• Physical Stimuli: Airborne substances that dissolve in nasal mucus.

• Olfactory Receptors: Located on olfactory cilia.

Pathway for Olfactory Information

• Olfactory signals travel through the olfactory cilia to the olfactory bulb, directly to the brain (not mediated by the thalamus).

Touch

• Touch Receptors:

  • Mechanoreceptors: Respond to mechanical stimuli.

  • Thermoreceptors: Respond to temperature changes.

  • Chemoreceptors: Respond to chemical stimuli.

Pain

• Adaptive Function: Alerts to injury; promotes protective actions.

  • Types of Pain:

    • Neuropathic Pain: Not adaptive; associated with nerve damage.

    • Inflammatory Pain: Related to activated immune processes.

    • Nociceptive Pain: Linked to tissue-damaging stimuli.

Pain Pathways

• Fast Pain Pathway: Carries signals for sharp, localized pain (Delta fibers).

• Slow Pain Pathway: Carries signals for dull, diffuse pain (C fibers).

Pain Processing in the Brain

• Processed in the somatosensory cortex, organized somatotopically for spatial representation.

Other Senses

• Kinesthetic Sense: Awareness of body positions via receptors in joints and muscles.

• Vestibular Sense: Equilibrium and balance, managed by semicircular canals in the inner ear.

Conclusions

• Sensation and Perception: Two distinct processes; sensation involves bodily receptors while perception is processed in the brain. They may not always align.