Chapter 3: Sensation and Perception

Intro to Psychology

Sensation is awareness of our surroundings (sound, color, form). Perception is interpreting this.


  • Doctrine of specific nerve energies says that we have different senses because different signals received by sense organs stimulate different nerve pathways and go to different places in the brain.
  • Synesthesia is a rare condition where people’s senses cross. Scientists have hypothesized that it’s a result of additional nerve connections.
  • Absolute threshold: the smallest change in a sense (vision, hearing) that you can detect.
  • Selective attention: the ability to focus on some parts of the environment and not others.
    • We’re really good at not registering objects, to prevent sensory overload.


  • Light has three dimensions:
    • Hue: color, wavelength
    • Brightness
    • Saturation
  • The front of the eye is protected by the cornea. Behind it sits a lens, which subtly changes its shape to focus. The amount of light allowed in is controlled by muscles in the iris, which surrounds the pupil.
    • In the back of the eye, the retina, an extension of the brain (the tissue it’s formed from is from the brain).
    • The more numerous receptors, rods, are sensitive to light. The other receptors, cones, are sensitive to color.
      • Cones need lots lights, so color vision is worse in the dark.
    • The optic nerve leaves the eye at the optic disc, where there are no rods or cones, which causes a blind spot.
    • Feature-detector cells fire in response to specific features (horizontal lines, vertical lines, etc) to make up edges of objects.
      • Others respond specifically to faces, hands, tools, words, numbers.
    • Theories about vision:
      • Trichromatic theory: color perception comes from having separate cones that are sensitive to blue, green, and red.
      • Opponent-process theory: cells fire for opposite colors (blue/yellow, red/green).
        • The cells that switch on or off to signal “green” send the opposite signal (“red”) when green is removed.
      • Gestalt principles:
        • Things closer together are grouped together (Proximity)
        • The brain fills in gaps to create complete forms (Closure)
        • Things that are alike are perceived as belonging together (Similarity)
        • Lines and patterns are perceived as continuing in time or space (Continuity)
      • Judging distances:
        • Convergence: judging how much your eyes turn inward to focus on something close by.
        • Retinal disparity: how different the views from your two eyes are.


  • The organ of Corti is the actual organ of hearing, which contains hair cells which are receptors.
    • The hair cells rise and fall with sound, brushing against another membrane. The hair cells bending initiates a signal that’s sent along the auditory nerve.


  • Papillae: tiny bumps on your tongue, whose sides are lined with taste buds.
    • Actual taste receptors are inside taste buds (50-150 per taste bud).


  • Gate-control theory
    • Pain impulses must get past a (metaphorical) “gate” in the spinal cord.
      • Gate = neural activity that blocks pain messages or lets them through
      • When body tissue is injured, large fibers and damaged and small fibers open the gate, and pain messages can reach the brain.
      • Stimulation (ice pack, heat) can interfere with pain by closing the gate.
    • Phantom pain: pain experienced from parts of the body that have been amputated.
      • Theory: other neurons have invaded the neurons that correspond to the amputated body part, and they are sending signals.
      • Showing an amputee a mirror that creates the illusion of two healthy limbs can resynchronize signals and has been very effective.

Internal senses

  • Kinesthesis tells us where our body parts are.
  • Equilibrium is our sense of balance.
    • Relies on semicircular canals in the inner ear.