6.3

Introduction to Sensation and Perception

• Module 6 focuses on sensation and perception, building on previous concepts from vision.

• Vision is just one of the senses; the lecture will cover audition (hearing), olfaction (smell), gustation (taste), somatosensation (touch), and proprioception.

• Sensory systems work together to create a cohesive experience of reality.

Review from Previous Lecture

• Questions on visual processing pathways and cones sensitive to red light confirmed key concepts of visual system:

  • Echinatopsia (motion blindness) is related to the dorsal pathway.

  • L cones are sensitive to red light (564-580 nanometers).

Exploration of Audition (Hearing)

• The outer ear collects sound waves, which then vibrate the eardrum.

• Tiny bones in the middle ear (hammer, anvil, stirrup) amplify sound signals.

• The cochlea converts vibrations into neural signals:

  • Tiny hairs inside respond to sound frequencies, transforming them into electrical signals for the brain.

Pitch and Volume

• Pitch depends on the frequency of sound waves:

  • High frequency = higher pitch (e.g., whistle).

  • Low frequency = lower pitch (e.g., drum).

• Volume is determined by the amplitude of sound waves:

  • Larger vibrations = louder sounds.

Sound Localization

• The brain uses binaural cues to determine sound location:

  • Interaural time difference (sound hits one ear slightly before the other).

  • Interaural intensity difference (sound is louder in the ear closer to the source).

• Processed in the auditory cortex within the temporal lobe.

• Differences in hemispheric processing:

  • Left hemisphere: language processing.

  • Right hemisphere: emotional tones and music interpretation.

Olfaction (Smell) and Gustation (Taste)

Sense of Smell (Olfaction)

• Airborne molecules bind to olfactory receptors, sending signals to the olfactory bulb.

• The olfactory bulb connects directly to emotion (amygdala) and memory (hippocampus) areas, explaining strong emotional recollections triggered by smell.

Sense of Taste (Gustation)

• Taste buds on the tongue detect five basic tastes:

  • Sweet, sour, salty, bitter, umami (savory).

• Connection between taste and smell enhances flavor experience.

Somatosensation (Sense of Touch)

• Encompasses various sensations: pressure, temperature, pain, vibration; includes proprioception.

• Mechanoreceptors for pressure, thermoreceptors for temperature, and nociceptors for pain.

• Signals travel to the somatosensory cortex in the parietal lobe:

  • Somatosensory homunculus: non-proportional representation where sensitive areas (e.g., fingers) occupy more brain space.

Proprioception

• Refers to the body's ability to sense its position and movement in space (like touching your nose with eyes closed).

• Muscles/joints have receptors that continually inform the brain of their position.

• Vestibular system within the inner ear helps maintain balance and spatial orientation, comprising:

  • Semicircular canals (detect rotational movement) and otolith organs (detect linear movement and gravity).

Multisensory Integration

• The brain combines input from multiple senses for a coherent experience.

• Example: Flavor is perceived through a combination of taste, smell, temperature, and texture.

• McGurk Effect demonstrates how visual cues can override auditory perception.

Special Cases—Synesthesia and Phantom Limb Sensation

• Synesthesia: Stimulation of one sense may trigger another (e.g., seeing colors with music).

• Phantom limb sensation: Feelings from an amputated limb may occur due to the brain's outdated internal model of the body.

Conclusion

• Sensory systems build a model of reality that helps individuals navigate their environment.

• Important points to remember:

  • Each sense contributes uniquely, and perception is an active process.

  • Understanding the interplay of senses and contextual influences is critical in psychology.

• Reminder: "All models are wrong, but some are useful."

Review Questions

1. Which structure in the ear transforms sound vibrations into neural signals?

   • Answer: Cochlea.

2. Which condition is not associated with altered multisensory integration?

   • Answer: Congenital analgesia (loss of ability to feel pain).