Sensation and Perception: Smell and Taste Notes

Sensation and Perception: Smell and Taste

Big Questions for Sensation and Perception

  • How does perception emerge from sensation?
  • How are we able to see?
  • How are we able to hear?
  • How are we able to taste?
  • How are we able to smell?
  • How are we able to feel touch and pain?

Sensation

  • Definition: Detection of physical stimuli and transmission of that information to the brain.
  • Physical stimuli include:
    • Light waves
    • Sound waves
    • Molecules of food or odor
    • Temperature changes
    • Pressure changes
  • Key Point: Sensation involves no interpretation of the raw data experienced.

Perception

  • Definition: The brain’s processing, organization, and interpretation of sensory information.
  • Purpose: To construct useful and meaningful information about a particular sensation.

The Sensory Process

  • Example: A green light
    1. Physical stimulus in the form of photons (light waves).
    2. Sensory receptors in the eyes detect this stimulus.
    3. The stimulus is transduced into chemical and electrical signals that are sent to the brain.
    4. The brain processes the signals and interprets them as a green light ahead, indicating to continue driving.

Processing Sensory Information

  • Bottom-up Processing:
    • Perception based on the physical features of stimuli.
    • Example Question: "What am I seeing?"
  • Top-down Processing:
    • Interpretation shaped by knowledge, expectations, and past experiences.
    • Example Question: "Is that something I’ve seen before?"

The Five Classic Senses

  • Touch
  • Sight
  • Sound
  • Smell
  • Taste
  • Additional Senses:
    • Proprioception (body position and movement awareness)
    • Thermoception (sense of heat)
    • Nociception (sense of pain)
    • Vestibular (balance and spatial orientation)
    • Tension (sense of being stretched)
    • Time perception

Magnetoreception

  • Definition: Ability to detect the Earth's magnetic field for direction.
  • Examples in Animals:
    • Birds use field lines and inclination for compass navigation.
    • Sea turtles possess a map sense, detecting variations in magnetic strength.

Touch and the Brain

  • Involved Brain Regions:
    • Parietal lobe
    • Frontal lobe
  • Visual Processing Streams:
    • Dorsal ("where") stream
    • Ventral ("what") stream

Gustation: The Sense of Taste

  • Survival Functions of Tastes:
    • Sweet: energy source
    • Sour: could indicate potentially toxic acids
    • Umami: proteins for tissue repair
    • Bitter: indicates potential poisons
    • Salty: sodium is essential for physiological processes
  • Taste Buds:
    • 8,000-10,000 taste buds, each with 50-100 receptor cells.
    • Misconception: "Tongue maps" for taste are not accurate.
    • Taste experience is produced by the insula in the frontal lobe.

Supertasters

  • Definition: Individuals who have a heightened sense of taste.
  • Characteristics:
    • Extreme aversion to bitter tastes.
    • More taste buds and heightened pain sensitivity to spicy foods.

Development of Taste Preferences

  • Infant Taste Preferences:
    • Naturally prefer sweet and umami flavours.
    • Dislike sour and bitter tastes.
  • Influence of Mother’s Diet:
    • Infants develop food preferences based on what mothers eat during and after pregnancy.

Manipulating Taste

  • Taste Adaptation:
    • Taste buds can be trained with repeated exposure to particular flavors.
    • Example: Developing a preference for salty foods after regular exposure.
  • Miracle Berry:
    • Contains miraculin, which modifies taste receptors to make sour foods taste sweet.

Olfaction: The Sense of Smell

  • Process of Smell:
    • Odor molecules inhaled through the nose stimulate olfactory receptor cells.
    • Signals sent to the olfactory bulb in the brain.

Neural Pathways for Smell

  • Involved Brain Areas:
    • Olfactory bulb
    • Olfactory tract
    • Olfactory cortex (conscious perception of smell)
    • Hippocampus (olfactory memory)
    • Amygdala (emotional responses)
    • Hypothalamus (relay center)
    • Reticular formation (visceral responses to smell)

Impact of COVID-19 on Smell

  • Loss of Smell:
    • Parosmia: distorted sense of smell often temporary.
    • May last for 3-4 months post-illness, more common in young females.
    • Mechanism: Virus infects olfactory neurons causing immune responses that decrease olfactory receptor gene expression.

Major Histocompatability Complex (MHC)

  • Definition: A key marker of identity in the immune system.
  • Study Findings:
    • Women prefer scents from men with dissimilar MHC genetic combinations, especially when not on birth control.

Takeaways

  • Our brains sense much more than we consciously realize.
  • Emotions and environmental factors influence both smell and taste.
  • Perception relies on both bottom-up and top-down processing.