PSY 105 Lecture 4: CHAPTER 4 Sensation and Perception

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4 Aug 2016
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Saturday, November 7, 2015
Chapter 4: Sensation and Perception
Synesthesia
-SYNESTHESIA: A subjective experience of an aspect of a sense other than the one being stimulated
-Psychological and neurobiological reality
-Brain regions for different sensory modalities cross-activate each other
The Power of Perception
-The basketball tracking task
-Door Study
Basics of Sensation and Perception: Definitions
-SENSATION: the act of using out sensory systems to detect environmental stimuli
once acquired, the information must be interpreted in the context of past and present stimulus
-PERCEPTION: recognizing and identifying sensory stimuli
For example: realizing that you recognize the smell in a restaurant as pizza
Raw Sensory Data:
Vision Light Waves
Hearing Sound Waves
Smell Airborne Chemicals
Taste Food Chemicals
Touch Pressure
Features of Sensation and Perception
-What do we need to do to the raw sensory data so that our brain can understand it?
-Each of our sensory systems are set up to convert the physical stimuli we receive from the world into neural information
-sensation and perception occur differently in each of our sensory modalities, but all share specialized cells
SENSORY RECEPTOR CELLS: specialized cells that convert a specific form of environmental stimuli into neural
impulses (form of communication used in our brains and nervous systems)
-SENSORY TRANSDUCTION: the process of converting a specific form of sensory data into a neural
impulse that our brain can read
Thresholds: Testing the Limits
-Sensory receptors can be activated by weak stimuli, but the stimulus has to reach a certain level of intensity before being
detected because the conversion processes can only occur at that level
-ABSOLUTE THRESHOLD: the smallest amount of stimulus needed to be detected
For example: what is the dimmest light you can see? (A candle flame 30 miles away on a clear, dark night)
in other words, this is the difference between “sensing” and “not sensing”
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Saturday, November 7, 2015
Difference Threshold
-Absolute threshold varies from person to person
-JUST NOTICEABLE DIFFERENCE (JND): the minimal change in a stimulus that can just barely be detected (also known as
difference threshold)
the difference of what you need to add to the existing threshold to be detected
-how much do you have to turn up the radio to notice a change?
-WEBER’S LAW: the just noticeable difference of a stimulus is a constant proportion despite variations in intensity
the amount you need to add or takeaway from the existing to be detected
-the amount is 2%
-for salt, you need to add/take away 33.33% or 1/3 to notice
-Example 1: you're blindfolded and have something in your hand that is 100 grams. How much do you
need to add or takeaway to notice?
the proportion for Weber’s law is 1/50
2% of 100 grams is 2 grams (100/50 = 2)
-Example 2: you now have 1000 grams
the weight is heavier, so you have to add/take away more
2% of 1000 grams is 20 grams (1000/50 = 20)
the stronger the stimulus, the larger the change will have to be in order for this change in stimulus intensity to
be noticeable
-For example: if the radio is really loud, it’ll take a larger increase in volume to notice a difference
Sensory Adaptation
-senses are organized to detect change, since most stimuli we are exposed to are not important enough to warrant our
attention
-SENSORY ADAPTATION: the process where repeated stimulation of a sensory cell leads to a reduced sensory response
can be overcome by providing a stronger stimulus
some sensory stimulus in our surrounding stays the same for a period of time, such as the pressure of our
clothing on our skin
-sense of smell especially prone to this
Processing Sensory Information
-Sensation and perception almost always happen together
-BOTTOM-UP PROCESSING: the raw sensory data that is sent to the brain and your brain uses all of that data to build a
perception
begins with the physical stimuli from the environment, and proceeds through transduction of those stimuli into
neural impulses
-TOP-DOWN PROCESSING: you use previously learned information to help recognize and interpret the data coming into your
brain
affected by our knowledge and beliefs
-For example: if something furry brushes your leg, and you have a pet, you'll use top-down processing to
find out that its your pet. If you don't have a pet, you use bottom-up processing to figure out what’s
touching you
-PERCEPTUAL SETS: readiness to interpret a certain stimulus in a certain way
our expectations prepare us to perceive certain things in a certain way
-For example: would a dish taste the same to you if you thought it was chicken, or if you thought it was a
snake
AMBIGUOUS STIMULI: stimuli that can be interpreted in different ways (illusion pics)
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