Sensation and Perception Introduction
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.
What is perception? • Refers to how we interpret the stimulus information our nervous system takes in & processes.
Does perception equal physical reality? • What do you think????
The Perceptual Process • Step 1: Distal Stimulus (stimulus at a distance: me, a friend). • Step 2: Proximal Stimulus (stimulusin proximity to your receptors). • Step 3: Transduction (process by which physical energy is transformed into neural energy that can be processed).
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?).
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.
What is the most rudimentary concept in perception? • Stimulus detection
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?)
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.
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.”
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.
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.
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.
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.