RF

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.