sensation and perception introduction. what is a sensation? usually refers to the physical stimulus...
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Sensation and Perception
Introduction
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What is a sensation? Usually refers to the physical stimulus in
the environment (light, sound waves).
We convert physical energy from the world into neural energy our brains can process.
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What is perception? Refers to how we interpret the stimulus
information our nervous system takes in & processes.
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Does perception equal physical reality?
What do you think????
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The Perceptual Process
Step 1: Distal Stimulus (stimulus at a distance: me, a friend).
Step 2: Proximal Stimulus (stimulus in proximity to your receptors).
Step 3: Transduction (process by which physical energy is transformed into neural energy that can be processed).
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Step 4: Neural Processing (neural energy is processed by brain).
Step 5: Perception (Neural information is interpreted into a percept).
Step 6: Recognition (Do I recognize the person or object?).
Step 7: Action (Will you go over to the object?).
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Three approaches to studying perception 1. Stimulus-Perception Relationship- the
relationship between the physical stimulus & what we perceive.
2. Stimulus-Physiology Relationship – the connection between stimuli & nerve firing.
3. Physiology-Perception Relationship – how does neural processing in the brain effect perception.
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What is the most rudimentary concept in perception?
Stimulus detection
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How do we detect a stimulus in the environment?
We look for the least amount of stimulus energy needed in order for a stimulus to be detected.
The Absolute threshold is the smallest amount of energy required to detect a stimulus (50% of the time).
E.g., How many photons of light (light particles) are needed for you to detect a light source?)
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Myths in measuring thresholds 1. People can accurately tell us when they detected a
stimulus.
-Not true, people are often unsure of what they’ve perceived.
2. The subject shouldn’t report a response unless a signal was presented.
No, random neural firing might make them think something happened when it didn’t. You think you hear the phone ringing while taking a shower.
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Classical Psychophysical Methods for measuring thresholds.
1. Method of Limits – the S is presented with stimuli that either increase in intensity (ascending series) or systematically decrease in intensity (descending series) until the S reports that a stimulus was detected.
The point at which the S reports no longer being able to detect the signal is called the “crossover point.”
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Method of Limits Advantages 1. Its quick & easy to administer
Disadvantages 2. Habituation—S tend to make the same response.
3. Anticipation-the S anticipates their response before seeing or hearing the stimulus.
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2. The Method of Adjustment
The stimulus is slowly changed as the S adjusts the stimulus intensity until the stimulus is either no longer detectable or detectable.
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Method of adjustment
Advantages: 1. It’s quick to do. 2. The S is an active participant, so the experiment is
more interesting for them.
Disadvantages: 1. Ss may crank up the intensity too high &
desensitize their sensory systems. 2. Ss have knowledge about the stimulus, which may
change thresholds.
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3. Method of Constant Stimuli
The experimenter picks a range of intensities & randomizes the order of the stimuli.
Advantages 1. Removes anticipation bias which reduces bias
in the threshold measurement.
Disadvantages 1. This method is slow & time consuming. 2. The S may become easily bored.