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Module 16: Basic Principles of Sensation and Perception

16-1: What are sensation and perception? What do we mean by bottom-up processing and top-down processing?

  • ^^Sensation:^^ process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
  • ^^Perception^^: process of organizing and interpreting sensory information, enabling us to recognize meaningful object and events
    • Like remembering hair, gait, voice, or physique
  • Sensation and Perception are parts of one continuous process
  • ^^Bottom-up Processing:^^ analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information
    • Enables our sensory systems to detect the lines, angles, and colors that form the flowers and leaves (Figure 16.1)
    • Breaking things down to form something
  • ^^Top-down processing^^: information processing beginning with our higher-level mental processes, as when we construct perceptions drawing on our experience and expectations
    • Interpret what our senses detect

Selective Attention

16-2: How much information do we consciously attend to at once?

  • ^^Selective attention:^^ focusing of conscious awareness on a particular stimulus

    • Cocktail party effect: ability to attend to only on voice among many (while also being able to detect your own name in an unattended voice)

    • We selectively attend to, and process, a very limited portion of incoming information, blocking out much and often shifting the spotlight of our attention from one thing to another

      Figure 16.1

Selective Inattention

  • ^^Inattentional blindness^^ (Figure 16.2): failing to see visible objects when our attention is directed elsewhere

    • Figure 16.2: Testing Selective Attention; In this classic experiment, viewers who were attending to basketball tosses among the black-shirted players usually failed to notice the umbrella-holding women sauntering across the screen, (From Nasser, 1979)
    • A by-product of what we are really good at: focusing attention on some part of our environment

  • ^^Change blindness^^ (Figure 16.3): failing to notice changes in the environment

Transduction

16-3: What three steps are basic to all our sensory systems?

  • Everyday our sensory systems convert one form of energy into another
    • ex: vision processes light energy, hearing processes sound waves
  • All our senses:
    • Receive sensory stimulation, often using specialized receptor cells
    • Transform that stimulation into neural impulses
    • Deliver the neural information to our brain
  • ^^Transduction^^: process of converting one form of energy into another our brain can interpret
    • ex: stimulus energies like sights, sounds, and smells into neural impulses
  • ^^Psychophysics:^^ study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience

Thresholds

16-4: What are the absolute and difference thresholds, and do stimuli below the absolute threshold have any influence on us?

Absolute Thresholds

  • ^^Absolute Threshold:^^ minimum stimulation necessary to detect a particular light, sound, pressure, taste, or odor 50% of the time

  • Detecting a weak stimulus, or signal, depends not only on the signal’s strength but also on our psychological state–our experiences, expectations, motivation, and alertness

    • ^^Signal Detection Theory^^ (Figure 16.5): theory predicting how and when we detect the presence of a faint stimuli amid background stimulation, assumes that there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness

  • ^^Subliminal^^ (Figure 16.6): below one’s absolute threshold for conscious awareness (Stimuli you cannot detect 50% of the time)

    • Under certain conditions, you can be affected by stimuli so weak you don’t notice them

    • ^^Priming^^: activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response

    • ex: an unnoticed image that reaches your visual cortex and briefly primes your response to a later

    • ^^Backmasking^^: purposefully recording a message on a tape backward

    • ^^Reverse speech:^^ looking for messages while playing a recording backwards

  • Much of our information processing occurs automatically, out of sight, off the radar screen of our conscious mind

Difference Thresholds

  • To function effectively, we need our absolute thresholds low enough to allow us to detect important sights, sounds, textures, tastes, and smells
    • We also need to detect small differences among stimuli
    • ^^Difference Threshold:^^ minimum difference between two stimuli required for detection 50% of the time. We experience the difference threshold as a just noticeable difference
      • Increases with the size of the stimulus
      • ex: If you add 1 ounce to a 10-ounce weight, you will detect the difference; add 1 ounce to a 100-ounce weight and you probably will not
  • ^^Weber’s law^^: principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage, rather than a constant amount
    • Exact proportion varies, depending on the stimulus

Sensory Adaptation

16-5: What is the function of sensory adaptation?

  • ^^Sensory adaptation:^^ diminished sensitivity as a consequence of constant stimulation
    • ex: entering your brother’s room, smelling a musty odor, wondering how they can stand it, but within minutes you no longer notice
    • When we are constantly exposed to a stimulus that does not change, we become less aware of it because our nerve cells fire less frequently