Sensation & Perception - Key Concepts

LO 3.1 Sensation and the central nervous system

  • Sensation: activation of receptors in the sense organs.
  • Sensory receptors: specialized forms of neurons.
  • Sense organs: eyes, ears, nose, skin, taste buds.
  • Pathway: Stimulus energy → sensory receptors → neural impulses → brain (sensation); brain areas for perception include visual, auditory, olfactory regions.

LO 3.2 What is light

  • Brightness: determined by amplitude of the wave.
  • Color (hue): determined by wavelength.
  • Saturation: purity of the color.

LO 3.3 How eyes see and see color

  • Structure of the eye
    • Cornea: clear membrane; focuses most light.
    • Aqueous humor: clear, nourishing fluid.
    • Pupil: opening that lets in light; size controlled by iris.
    • Iris: colored muscle; adjusts pupil size.
    • Lens: focuses light; accommodation changes lens shape.
    • Vitreous humor: jelly-like fluid maintaining eye shape.
    • Retina: final stop for light; contains rods and cones; three layers: ganglion, bipolar, photoreceptors.
    • Rods: noncolor vision, low light.
    • Cones: color vision, sharpness.
  • Visual processing
    • Light → cornea → pupil → lens → retina → photoreceptors → bipolar/ganglion cells → optic nerve → brain.
    • Dark adaptation vs. light adaptation.
  • Color vision theories
    • Trichromatic theory: three cone types (red, green, blue).
    • Afterimages.
    • Opponent-process theory: red-green and blue-yellow pairs; LGN involvement.
  • Color blindness
    • Monochrome; Red-green colorblindness (X-linked).

LO 3.4 What is sound

  • Basic properties
    • Wavelength: frequency (pitch).
    • Amplitude: volume.
    • Purity: timbre.
    • Frequency unit:
    • Hz (cycles per second).
  • Structure of the Ear
    • Outer ear: auditory canal.
    • Eardrum (tympanic membrane): vibrates with sound.
    • Middle ear bones: hammer, anvil, stirrup; amplify vibrations.
    • Cochlea: fluid-filled inner ear; organ of Corti with hair cells (receptors).
    • Auditory nerve: carries neural signals to brain.
  • Theories of pitch
    • Place theory: different pitches stimulate different locations on the organ of Corti.
    • Frequency theory: pitch related to rate of firing of neurons in the auditory nerve.
    • Volley principle: for frequencies above ~100 Hz, groups of neurons fire in turns.

LO 3.5 Hearing impairment and improvement

  • Types of hearing impairments
    • Conduction: problems in outer/middle ear (eardrum or middle-ear bones).
    • Nerve (sensorineural): problems in inner ear or auditory pathways.
  • Cochlear implant
    • Microphone → speech processor → transmitter/receiver → electrode array in cochlea → brain.

LO 3.6 Senses of taste and smell

  • Taste (gustation)
    • Taste buds: receptor cells in the mouth.
    • Five basic tastes: Sweet, Sour, Salty, Bitter, Umami.
  • Smell (olfaction)
    • Olfactory receptors and olfactory bulbs.
    • Olfactory bulbs receive input; at least ~1000 olfactory receptors.

LO 3.7 Touch, pain, motion and balance

  • Somesthetic senses: skin senses, kinesthetic sense, vestibular senses.
  • Skin senses
    • Touch, pressure, temperature, pain.
    • Gate-control theory: pain signals can be modulated at the spinal cord gate.
  • Kinesthetic sense
    • Proprioceptors detect body position and movement.
  • Vestibular senses
    • Sensing movement, balance, and body position.
    • Sensory conflict theory explains motion sickness (conflict between visual and vestibular inputs).

LO 3.8 Perception and perceptual constancies

  • Perception: interpretation and organization of sensations.
  • Size constancy: objects perceived as same size despite distance changes.
  • Shape constancy: object shape remains constant though retinal shape changes.
  • Brightness constancy: apparent brightness remains similar under varying light.

LO 3.9 Gestalt principles of perception

  • Figure-ground: objects perceived as separate from background.
  • Reversible figures: figure and ground can switch.
  • Similarity: similar elements grouped together.
  • Proximity: nearby elements grouped together.
  • Closure: fill in missing parts to complete figures.
  • Continuity: perceive smooth, continuous patterns.
  • Contiguity: events that occur together in time are linked.

LO 3.10 Perceiving the world in three dimensions

  • Depth perception: 3D interpretation of the world.
  • Visual cliff: studies depth perception in infants.
  • Monocular cues
    • Aerial perspective: distant objects appear hazier.
    • Texture gradient: textures become finer with distance.
    • Motion parallax: closer objects move faster than distant ones.
    • Accommodation: lens shape changes with distance.
  • Binocular cues
    • Convergence: eye rotation increases as objects get closer.
    • Binocular disparity: different retinal images due to eye separation; greater for near objects.

LO 3.11 Visual illusions and other factors influencing perception

  • Perceptual illusions
    • Müller-Lyer illusion: line length misperception due to corner cues.
    • Moon illusion: moon appears larger on horizon.
    • Apparent distance hypothesis.
  • Illusions of motion
    • Autokinetic effect: light in dark appears to move.
    • Stroboscopic motion: rapid sequence of images appears to move.
    • Phi phenomenon: sequence of lights appears to move.
  • Factors influencing perception
    • Perceptual set: expectations influence interpretation.
    • Top-down processing: using prior knowledge to organize features.
    • Bottom-up processing: building perception from sensory input.
  • Applying psychology
    • Extrasensory perception (ESP): claims of perception without normal senses (telepathy, clairvoyance, precognition).
    • Parapsychology: study of ESP, ghosts, and related subjects.