Sensation & Perception

• Sensation
  • Detection of physical energy by sense organs (eyes, ears, skin, etc.).
• Perception
  • Brain’s interpretation and organisation of sensory inputs.
  • Our link to reality, but:
    • Often fills in gaps with imagination.
    • Not always accurate (illusions, biases).

Transduction & Adaptation

• Transduction
  • Conversion of sensory stimuli → neural impulses.
  • Done by specialised receptor cells (photoreceptors, hair cells, taste receptors, etc.).
• Sensory Adaptation
  • Receptors respond strongly at first, then decrease firing with continued stimulation.
  • Allows focus on changes, not constants.

Psychophysics & Signal Detection

• Psychophysics (Fechner, 1860)
  • Study of relationship between physical stimuli and subjective experience.
  • Measures:
    • Absolute threshold: lowest stimulus level detected 50% of the time.
    • JND (Just Noticeable Difference): smallest detectable change in stimulus intensity.
• Weber’s Law
  • JND is a constant proportion of the original stimulus.
  • Stronger stimulus → larger change needed to notice a difference.
• Signal Detection Theory (Green & Swets)
  • How we detect stimuli in uncertain conditions.
  • Detection depends on:
    • Stimulus intensity
    • Background noise
    • Expectations, motivation, decision criteria.

Cross-Modal Perception & Culture

• Cross-modal sensation
  • Brain integrates inputs from multiple senses into one percept.
  • Examples:
    • Flavour = taste + smell.
    • Synesthesia (stimulation in one sense → experience in another).
• Why we study perception
  • Brain can misinterpret sensory info (illusions, body ownership errors).
  • Cultures emphasise different senses, shaping beliefs/worldviews.
• Dadirri
  • Aboriginal concept of deep inner listening and quiet awareness.
  • Highlights cultural variation in perceptual emphasis.

The Visual System

Eye Anatomy & Function

• Sclera – white outer layer; structure & protection.
• Cornea – clear, curved; major light refraction.
• Iris – coloured muscle ring; controls pupil size.
• Pupil – opening that regulates light entry.
• Lens – changes shape (accommodation) to focus near vs far.
• Aqueous humour – fluid nourishing cornea/lens.
• Vitreous humour – gel maintaining shape & light transmission.
• Retina – photoreceptors (rods/cones), processes light → neural signals.
• Fovea – centre of retina; sharpest vision, many cones.
• Blind spot – optic nerve exit; no receptors.
• Optic nerve – carries visual info to brain.

Eye Shape & Focus

• Myopia (nearsightedness)
  • Image focuses in front of retina (steep cornea / long eye).
• Hyperopia (farsightedness)
  • Image focuses behind retina (flat cornea / short eye).
• Presbyopia
  • Lens loses flexibility with age → reduced near focus.

Retina, Rods & Cones

• Rods
  • Very light-sensitive; low-light vision.
  • No colour; peripheral, movement detection.
• Cones
  • Need bright light; colour + fine detail.
  • Concentrated in fovea.
• Dark adaptation
  • Rods regain sensitivity in dim light (~30 mins).
  • No rods in fovea → better to look slightly away from faint objects.
• Photopigments
  • Light-sensitive chemicals; rods contain rhodopsin (vitamin A dependent).

Visual Pathways & Feature Detection

• Retina → bipolar cells → ganglion cells → optic nerve
• Optic chiasm: partial crossing to opposite hemisphere.
• Major projections:
  • LGN of thalamus → V1 (primary visual cortex).
  • Superior colliculus: eye/head orienting reflexes.
• Hubel & Wiesel
  • Discovered simple cells (specific orientation + location)
  • Complex cells (orientation, less location-bound).
  • Basis of feature detectors (edges, lines, motion).
• Dual streams
  • Dorsal (“where”): V1 → parietal (spatial, movement).
  • Ventral (“what”): V1 → temporal (objects, faces, colour).

Colour Vision

• Trichromatic theory (Young–Helmholtz)
  • 3 cone types:
    • Short λ: blue
    • Medium λ: green
    • Long λ: red
  • Explains receptor-level colour mixing.
• Opponent-process theory
  • Opponent pairs:
    • Red vs Green
    • Blue vs Yellow
    • Black vs White
  • Explains afterimages & colour contrast.
• Integration
  • Trichromatic: cones.
  • Opponent-process: later neural processing (ganglion cells, thalamus).
• Colour vision variants
  • Monochromats – 1 cone type (near B&W).
  • Dichromats – 2 cone types (e.g. red–green colour blindness).
  • Trichromats – typical.
  • Tetrachromats – 4 cone types; extra colour distinctions.

Visual Disorders & Phenomena

• Blindness
  • Vision ≤ 20/200.
  • Causes: cataracts, glaucoma, other eye/nerve damage.
  • Plasticity: visual cortex can be recruited for touch (e.g. Braille).
• Blindsight
  • V1 damage → conscious blindness, but:
    • Can navigate obstacles, detect expressions, etc.
  • Suggests unconscious visual pathways still active.
• Visual agnosia
  • Can see features, but cannot recognise objects.
  • Shows separation between perception and identification.
• Rubber hand illusion
  • Synchronous stroking of real + fake hand → illusory ownership of rubber hand.
  • Shows how easily body representation can be altered.
• Alien hand syndrome
  • Limb performs involuntary, complex movements.
  • Person feels limb is foreign.

Chemical Senses: Taste & Smell

Taste (Gustation)

• Function
  • Acts as “gatekeeper” → prevents ingestion of harmful substances.
  • Preferences:
    • Sweet (energy), salty (minerals), umami (protein).
    • Avoid bitter (often toxic compounds).
• Basic tastes
  • Sweet, Sour, Salty, Bitter, Umami.
• Anatomy & Pathway
  • Taste buds in papillae on tongue + some on soft palate.
  • Saliva dissolves food chemicals → detected by taste receptor cells.
  • Signals via sensory nerves → brain (incl. insular cortex).
  • Taste receptor cells replaced every 1–2 months.

Smell (Olfaction)

• Taste–smell interaction
  • Flavour = taste + smell (+ texture, temperature).
  • Blocked nose → reduced flavour.
• Pathway
  • Odour molecules dissolve in nasal mucus.
  • Detected by receptors in olfactory epithelium.
  • Signals → olfactory bulb → directly to:
    • Cerebral cortex
    • Limbic system
    • Hypothalamus
  • Explains strong link to emotion & memory.
• Smell disorders
  • Anosmia – complete loss of smell (temporary or permanent).
    • Causes: tumours, polyps, deformities, Alzheimer’s, cancer, zinc deficiency.
  • Hyposmia – reduced smell ability.
  • Parosmia – incorrect smell identification.
  • Cacosmia – odours distorted as intensely foul.
  • Phantosmia – perceiving odours that aren’t present.

Somatosensation & Pain

Somatosensation

• Sensory experiences about the body’s condition & interactions with environment.
• Includes:
  • Touch
  • Proprioception (body position)
  • Pain
  • Temperature (thermoreception)
• Signals from skin, joints, muscles, tendons, ligaments → transduced → CNS.
• Somatosensory cortex
  • Located at top of brain, adjacent to motor cortex.
  • Larger cortical area for body parts with greater touch sensitivity (sensory homunculus).

Pain & Nociception

• Nociception
  • Detection of potentially harmful stimuli by nociceptors.
• Cognitive appraisal
  • Emotions, attention, and beliefs influence pain intensity.
  • Negative mood → can amplify pain.
• Acute → Chronic pain
  • Factors:
    • Stress, depression
    • Maladaptive coping strategies
    • Brain structural/functional changes
    • Nocebo effects (expecting pain → more pain)
• Pain modulation
  • Psychological interventions altering pain perception:
    • Relaxation techniques
    • Mindfulness
    • CBT

Vestibular System (Balance)

• Located in inner ear, next to cochlea.
• Components:
  • Semi-circular canals
  • Utricle
  • Saccule

Semi-circular canals

• Detect head rotation in 3 planes.
• Help maintain balance and stabilise vision during movement.

Utricle

• Detects:
  • Side-to-side movement
  • Horizontal linear acceleration

Saccule

• Detects:
  • Up-down movement
  • Gravity
  • Vertical linear acceleration

Hearing (Quick Overview)

• Sound = pressure waves in air.
  • Pitch = frequency (Hz)
  • Loudness = amplitude

Basic hearing pathway

• Sound waves → ear canal → eardrum vibrates
  → Ossicles vibrate → move fluid in cochlea → basilar membrane moves
  → Hair cells bend → transduction → impulses in auditory nerve → brain.