Sensation and Perception Pt 1

• Sensation


  The process by which the sense organs (eyes, ears, skin) gather information about the environment. Sensation relates to the raw information we receive from the environment based on physical stimuli.
• Perception


  The process by which sensory information is selected, organized, and interpreted. Perception relates to what we do with the sensory information we receive, the way we use psychological processes to add meaning to the physical stimulus. Affected by factors including our expectations, past experiences, and motivation.
• Processes that apply to all senses

  • Transduction
  • Sensory adaptation
  • Thresholds
  • Signal detection
• Transduction


  The conversion of environmental energy (light, energy, sound), into neural impulses that we can interpret. Stronger environmental stimulus means sensory neurons will fire faster.
• Sensory adaptation


  The response to a particular stimulus declines over time. Decrease in firing rate when the stimulus is unchanged or held constant over time.
• Sensory adaptation examples


  • Bread in bakery decreases as you sit down in café as it becomes 'normal'
  • Swimming in cold water, skin receptors decrease as time goes on as the water temperature is not changing over time
• Psychophysics


  The study of the relationship between the physical characteristics of sensory stimuli and our psychological experience of them.
• Physical world


  • Electromagnetic energy - light
  • Electromagnetic energy - infrared
  • Pressure waves
  • Mechanical forces
  • Sugar
• Perceptual experience


  • Colour brightness
  • Heat
  • Sound volume pitch
  • Weight pressure
  • Sweetness
• Absolute threshold


  The lowest intensity level of a stimulus that we can detect 50% of the time
• Just Noticeable Difference (JND)


  The smallest change in intensity of a stimulus that we can detect 50% of the time. It depends on the level of intensity of new stimulus and the level of stimulation already present.
• Weber's Law


  The change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. The second must differ from the first by a particular constant proportion to be seen as different.
• Signal detection theory


  Sensation occurs when we judge whether a stimulus is present or not. Two processes contribute: initial sensory process (sensitivity to the stimulus) and decision process (the individual's readiness to report detecting a stimulus when uncertain).
• Attention


  The mental phenomenon of concentration and its shifts in focus. It is influenced by internal and external factors.
• Selective attention


  When we choose some input for further processing, but ignore other input. There is limited capacity to attention so we apply a selective filter to decide which channel of incoming information to focus on.
• Divided attention


  When we shift attentional resources from one task to another and back again. Complex tasks often require us to do more than one thing at a time.
• Inattentional blindness


  Where you don't notice something that is unexpected in an image or scene.
• Change blindness


  Refers specifically to when you don't notice obvious changes in a scene.
• Human vision


  1. Focusing light on the retina

  2. Transducing light into neural signals
• Light


  An electromagnetic energy which travels in waves. Wavelength determines colour, wave amplitude determines intensity of light.
• Accommodation


  The process where the lens changes shape to focus on objects at different distances. It becomes more difficult with age.
• Photoreceptors


  Cells in the retina that transduce light into neural signals. Photopigments in the cells respond to light by changing membrane potential.
• Types of photoreceptors


  • Cones (active in bright light, colour vision, central vision)
  • Rods (sensitive in low light, monochromatic, peripheral vision)
• Photoreceptors to optic nerve

  1. Cellular structure of mammalian retina

  2. Convergence of cones and rods
• Optic nerve to cortex

  Optic chiasm -> Lateral geniculate nucleus -> Primary visual cortex
• Visual cortex


  Different cortical cells respond best to different stimuli. Simple cells respond to light of specific orientation, complex cells respond to orientation but less dependent on location. Feature detectors respond to lines, edges, length, shapes, movement, colour.
• Trichromatic theory


  Vision is made up of 3 primary colours of light that matches up with the presence of 3 types of cones, each of which are the most sensitive to different wavelengths of light. The combination of signals from different cones allows vision of a full range of colours.
• Opponent process theory


  We view colour because pairs of colours are in competition with each other as opponents (red vs green, blue vs yellow). If we are seeing red, this inhibits green. This is likely part of the higher areas of the visual processing system.
• Seeing colour


  White light includes all parts of the physical spectrum. Parts of the visible spectrum are either absorbed or reflected back from objects, determining which wavelengths are received by the eye. Mixing light produces white (additive), mixing pigments produces black (subtractive).
• Colour attributes


  Brightness (intensity), Hue (colour), Saturation (purity of colour)
• Myopia (near-sightedness)


  Occurs when the cornea is too steep, or the eyeballs are too long. The result is that light is focused slightly in front of the retina and it is difficult to see far away objects.
• Hyperopia (far-sightedness)


  Occurs when the cornea is too flat, or the eyeballs are too short. The result is that the light is focused slightly behind the retina and it is difficult to see near objects.
• Cataracts


  A cloudy area that forms in the eye, resulting in overall blurring and haziness of vision.
• Macular degeneration


  Damages the central region of the retina where images are focused, leading to a loss of central vision and difficulty seeing detail. The leading cause of vision loss for older people.
• Glaucoma


  Excess pressure in the eye damages the optic nerve leading to a loss of peripheral vision, described as 'tunnel vision'.
• Diabetic retinopathy


  Occurs when diabetes damages the tiny blood vessels in the retina, resulting in overall blurred vision and blind spots from bleeding in the eye.
• Motion blindness


  Related to problems stitching visual frames together smoothly, can occur following damage to area V5 of the visual association cortex.
• Visual agnosia


  Related to difficulty in recognising objects, even though the viewer knows what particular objects are (their memory is intact). The viewer can describe features of the objects but cannot perceive it as a whole object.