Chapter 1: Sensation and Perception Flashcards
What’s the major difference between sensation and perception?
- Sensation - stimulation of the sensory organs (ex. touching a fuzzy surface)
- Perception - Organizing sensory information into representations of the physical stimulus (ex. registering the fuzzy surface as a blanket).
What’s one thing to note about sensation and perception?
- Perception comes after sensation
- This makes sense since perception gives meaning to all the sensory signals we receive. It also occurs automatically
What’s an important step that occurs between sensation and perception?
- Transduction. Turns sensory stimuli into neural signals that can be sent to and interpreted in the brain.
- Turns physical dimensions into perceptual dimensions (ex. wavelength into colour)
What are the two types of environmental stimuli and their respective definitions?
- Distal - The thing in the world seen at a distance (ex. a tree)
- Proximal - The physical phenomenon that impinges on sensory receptor cells (the light waves reflecting off the tree and into your eyes)
What is the Principle of Neural Representation?
- All that we perceive is not based on direct contact with stimuli but on representations (neural codes) in the receptors and brain
- Same occurs when visualization in the mind is happening
What happens after a signal from a stimulus is transduced to the brain?
- They go to their respective primary receiving area in the brain.
- Each sense has its own general area, differing in size
What’s the difference between a primary processing centre and association areas?
- Primary processing centres is where the signal first travels to when it arrives in the brain
- Association areas are where the brain attempts to coordinate and organize the different senses in order to perceive the surroundings.
Why is neural processing so important?
- Required to form an integrated conscious experience, store it in memory etc.
*Some info may be sensed, but not attended to.
What are the two types of neural processing?
- Bottom-up processing - processing based on the stimuli reaching the receptors (ex. getting a paper cut)
- Top-down processing - an observers knowledge, expectations, and goals, all of which can affect perception (ex. reading)
Who is the scientist responsible for developing the field of psychophysics?
- Gustav Fechner (early to late 19th century)
What were the three ways that Fechner devised to empirically evaluate the mind?
1) Absolute threshold
2) Difference threshold
3) Magnitude estimation (correspondence between physical and perceptual magnitudes)
What was the initial definition of absolute threshold?
- The minimum stimulus intensity that can just be detected by the brain
- Meant to represent the boundary between sensing and not.
What were the three classical methods used for determining the absolute threshold for an individual?
- Method of limits
- Method of adjustment
- Method of constant stimuli
What’s the method of limits?
- A reasonably quick and fairly accurate way of classically measuring the absolute threshold.
- Experimenter presents a stimulus of a given intensity and continuously asks participants if they can detect the stimulus. They will increase or decrease the stimulus depending on their response.
- Boundary value is taken and process is repeated but this time started in the other direction
What’s the method of adjustment?
- A quick and dirty, classical estimate of the absolute threshold
- Start at a given stimulus intensity and the participant is able to increase or decrease the intensity of the stimulus until they identify the threshold level.
- Not as precise as the participant may overshoot the boundary since they may not be that sensitive
- The process is repeated, and the average is taken
What’s the method of constant stimuli?
- The most time-consuming but most accurate classical method in determining the absolute threshold
- 5-9 selected stimuli of ‘constant’ intensities are repeatedly presented in a random order. These results are then graphed as a probability of detection
What new definition of the absolute threshold was derived from the method of constant stimuli?
- Absolute threshold - lowest intensity necessary for a stimulus to be detected 50% of the time.
What does it mean to have a lower threshold?
- Means you are more sensitive to lower levels of stimulus
How does adaptive testing work?
- Builds off the method of limits but is much more efficient
- each time a response changes, the direction of the stimulus also changes (also called the staircase method)
- End up hovering/oscillating over a specific value, that being your threshold
- Everything depends upon the participant’s response
What’s the difference threshold?
- Also called the just-noticeable difference (JND)
- The smallest difference between two stimuli that people can detect (50% of the time)
- The minimum difference between 2 stimuli before you can tell they are different
How is the difference threshold/JND measured/determined?
- Using Weber’s law which states that the size of the JND is proportional to the magnitude of the first stimulus
- Each type of stimulus has its own constant fraction that’s used
- As stimulus get more intense, the difference must also increase for us to be able to perceive it (or constant difference get less and less noticeable)
What does psychophysical scaling involve?
- An attempt to discern whether perception matches/corresponds to the changes in sensation/environmental changes.
- Varies for each sense
What’s response compression vs. response expansion?
- Terms used in psychophysical scaling.
- Response compression - don’t perceive gradual increases in stimulus as to what the environment reflects (this is the case with brightness)
- Response expansion - Perceive the change in sensation much greater than it actually was (this is the case when experiencing pain)
What does Steven’s Power law describe?
- The relationship between physical and perceived intensity follows the same equation across all values of a stimulus type
- P = KS^n (the constant is not super relevant)
What’s the purpose of the Signal Detection Theory?
- Want to differentiate people’s perception to a change in stimulus as valid or not (are they actually super-sensitive or just less conservative?)
- A decision criterion is set to ensure the person is actually detecting the stimulus or not
- Sometimes the stimulus will change, sometimes it won’t. These are often referred to as catch trials.
What are other influences on threshold?
- Personality
- Level of fatigue/attention (too tired can cause you to miss the stimulus)
-Rewards/cost - Noise that interferes with the individual’s ability to catch the stimulus
True or false: There is a fixed level of sensitivity.
- FALSE
- Perception depends on sensation and cognitive processes (as indicated by the signal detection theory)
- There’s no fixed level of sensitivity
