Chapter 5

• Our sensory education begins before birth, & we use our experiences with the world to make hypotheses abt what new info means
• Sensations


  Elementary parts of the environment that the brain uses to create meaning
• Perception


  Processing of stimuli to create sensory understanding of the world
• Bottom-Up Processing


  Neural processing that starts with the physical message or sensations
• Top-Down Processing 


  Integration of a person's beliefs, memories, & expectations into their sensory experiences to create perception
• Personal experience informs top-down processing & allows us to derive meaning from otherwise ambiguous information
• 20% of the cortex plays a role in interpretation of visual information
• Retina


  Thin layer of tissue on the back of the eye that contains photosensitive receptor cells
• Cornea


  Transparent covering of the eye that performs abt 80% of the focusing of the visual image
• Pupil


  Hole in the center of the eye that allows light to enter
• Iris


  Ring of pigmented tissue responsible for controlling the diameter & size of the pupil
• Lens


  Flexible piece of tissue located behind the pupil that focuses light onto the retina
• Accommodation


  Process through which the lens change shape to bring objects into focus on the retina
• Individuals with Myopia

  • Eyes that are longer than average, resulting in the lens focusing the image before the retina
  • Can see objects more clearly up close
• Individuals with Hyperopia

  • Eyes that are short than average, resulting in the image not focusing when it arrives at the retina
  • Can see objects more clearly at a distance
• Photoreceptors


  Cells specifically sensitive to light exposure
• Rods


  Photoreceptor most responsive to low-levels of light
• Cones 


  Photoreceptors most responsive to bright light conditions, & communicates information about acuity & colour
• Back of each retina contains ~126 million photosensitive cells
• Fovea


  Portion of the retina directly behind the pupil, containing a high concentration of cones
• Dark Adaptation


  Occurs as rods & cones adapt to changes in light
• Process of Dark Adaptation

  1. Cones rapidly respond to change in light until they can't get more sensitive (~8 minutes)
  2. Rods continue to increase sensitivity for 20 minutes after
• Cones are the only cells that communicate information about the wavelength, perceived as colour, of an object
• Retinal image initially hits our eye upside down as a result of refraction, but we use context & our understanding of the world to present a conscious perception of the visual world as right-side up
• Rods help compile early processing about locations of objects & motion in the environment
• Wavelength

  • Physical distance from one energy cycle to the next
  • Changes are often perceived as changes in colour
• Longer wavelengths create perception of red, medium create perceptions of greens, & shorter create perceptions of blues
• Our brain uses information to create colour as an evolutionary adaptation to help us survive in the environment, but in reality colour doesn't exist
• Short cones


  Cones in the visual system that respond to short wavelengths (blues)
• Medium Wavelength Cones


  Cones in the visual system that respond to medium wavelengths (greens)
• Long Wavelength Cones


  Cones in the visual system that respond to long wavelengths (oranges & reds)
• Trichromatic Theory


  Theory of colour vision that proposes that colour information is identified by comparing the activation of different cones in the retina
• What our brain interprets as sound is actually many small vibrating air molecules that collide with other molecules, & the pressure travels across distance
• Frequency


  Physical measurement of pitch, measured in Hz
• Intensity


  Physical measurement of the loudness of sound, measured in dB
• The ear is a pressure sensor
• Pinna


  External part of the ear, shaped specifically to filter sound into the ear canal
• Tympanic Membrane

  • aka eardrum
  • Structure transfers energy to 3 smallest bones called ossicles
• Ossicles

  • Malleus, incus, & stapes
  • Responsible for amplifying vibrations arriving at the eardrum & transmitting 3 signals to the oval window of the cochlea
• Cochlea


  Snail-shaped structure in the inner ear responsible for processing sound into the neural language of the brain