Sensation and Perception: Notes on Smell and Taste

Big Questions for Sensation and Perception

  • How does perception emerge from sensation?

  • How are we able to see, hear, taste, smell, and feel touch and pain?

Sensation

  • Detection of physical stimuli and transmission of that information to the brain.

  • Physical stimuli include light and sound waves, molecules of food or odor, temperature changes, and pressure changes.

    • Involves no interpretation of the experience.

Perception

  • The brain’s processing, organization, and interpretation of sensory information.

  • Purpose is to construct useful and meaningful information about a particular sensation.

Example of Sensory Process

  • Scenario: A green light seen by a driver.

    • Stimulus: Green light emits physical properties (photons).

    • Sensation: Sensory receptors in the driver’s eyes detect this stimulus.

    • Transduction: Stimulus translated into chemical/electrical signals sent to the brain.

    • Perception: Brain processes signals to interpret the green light as a signal to continue driving.

Processing Sensory Information

  • Two-way Street: Sensory processing occurs through two main types.

    • Bottom-Up Processing: Perception based on the physical features of the stimulus (e.g., patterns of light and dark).

    • Top-Down Processing: Knowledge, expectations, and past experiences shape the interpretation of sensory knowledge.

Difference Between Top-Down and Bottom-Up Processing

  • Bottom-Up Processing asks "What am I seeing?"

  • Top-Down Processing asks "Have I seen this before? What does this picture represent?"

Human Senses

  • Classic Five Senses:

    • Touch

    • Sight

    • Sound

    • Smell

    • Taste

  • Additional Senses:

    • Proprioception

    • Thermoception

    • Nociception

    • Vestibular (balance)

    • Tension

    • Time perception.

Magnetoreception

  • Detection of the Earth's magnetic field for a sense of direction found in some animals (e.g., birds, sea turtles).

Touch and Brain Mapping

  • Key Brain Areas:

    • Parietal Lobe: Involved in sensory processing.

    • Frontal Lobe: Higher-order processing.

    • Dorsal Stream: 'Where' processing.

    • Ventral Stream: 'What' processing.

Gustation: Sense of Taste

  • Survival Functions of Tastes:

    • Sweet: Energy source

    • Sour: Potentially toxic

    • Umami: Provides proteins for tissue growth

    • Bitter: Signals potential poisons

    • Salty: Essential for bodily processes.

The Taste System

  • Humans have about 8,000-10,000 taste buds.

  • Taste buds contain 50-100 taste receptor cells each.

  • Myth: Tongue maps for taste are inaccurate.

  • Taste experiences occur in the insula of the brain's frontal lobe.

Supertasters

  • Have an extreme dislike of bitter substances due to genetics.

  • Possess more taste buds and may experience pain from spicy foods.

Development of Taste Preferences

  • Infants prefer sweet and umami, but dislike sour and bitter flavors.

  • Maternal diet influences infants' taste preferences before and after birth.

Emotion and Taste

  • Research by Rozin et al. explores emotional responses to taste contexts (e.g., sterilized cockroach in water).

Altering Taste

  • Taste buds can be “trained” with repeated exposure (e.g., high salt levels lead to preference).

  • Miracle Berry changes sour tastes to sweet through a protein called miraculin.

Olfaction: Sense of Smell

  • Airborne odor molecules inhaled through the nose stimulate olfactory receptor cells, which transmit signals to the olfactory bulb in the brain.

Neural Pathways for Smell

  • Olfactory pathways include:

    • Olfactory Bulb

    • Olfactory Tract

    • Olfactory Cortex: Responsible for the conscious perception of smell.

    • Hippocampus: Associated with olfactory memory.

    • Amygdala: Links scent to emotional responses.

Impact of COVID-19 on Sense of Smell

  • Parosmia: Distorted sense of smell that can occur during viral infections.

  • May persist for months post-infection due to immune responses affecting olfactory receptors.

Major Histocompatibility Complex (MHC)

  • Individual differences in MHC genes play a role in mate choice.

  • Women prefer scents of men with different MHC genes when not on birth control.

Conclusion: Interplay of Sensation and Perception

  • Perception is influenced by emotional factors and external conditions.

  • Bottom-up and top-down processing work together to shape experiences in our environment.