1 Basics and Psychophysics Flashcards
What is sensation?
simple processes that occur at the beginning of a sensory system
usually no interpretation is needed
e.g. light reaches the eye
What is perception?
the organisation, identification, and interpretation of sensory information in order to udnerstand the presented info or environment
brain activity is involved
e.g. identify the food you’re eating
What is going on here?
Deciding what is sensation and perception is not always obvious and may be context-dependent
What is the perceptual process?
7 steps + knowledge inside the person’s brain
describes the process of perception
sensation -> eyes -> processed -> perception <-> recognition <-> action -> sensation
is a cycle
How can we measure perception?
psychophysics
What is psychophysics
methods that relate sensations/perceptions to the physical characteristics of the stimulus
What are 2 measures of interest of psychophysics?
- threshold (limits of sensory systems)
- magnitude (above threshold)
What is absolute threshold
the smallest stimulus level that can be detected
What are 3 psychophysical methods to measure absolute threshold proposed by fechner?
- method of limits
* stimuli of diff intensities are presented in ascending or descending order, reapt, average cross-over point = threshold - methods of constant stimuli
* stimuli of diff intensities are randmized, many trials, calc detection of each intensity, threshold is intensity that results in detection 50% of trials - method of adjustment
* participants continuously adjust the stimulus intensity until they detect it
What is the difference threshold?
the minimum difference that exists between 2 stimuli that a participant can detect
What is weber’s law
the difference threshold (DT) depends on the base magnitude (S)
* K=DT/S
* K is a constant called Weber’s fraction
* K is relatively constant for a sensory domain
* may be different between different domain
What can weber’s law be used to do?
measure the difference threshold
What is magnitude measurement?
stimuli above threshold
focus on the relationship between the perception and magnitude, instead of the limits of perception
What is the magnitude estimation paradigm?
- experimenter presents standard stimlus and assigns it a value (e.g.10)
- participant hears other sounds and assigns a rating to each of these sounds relative to the standard sound (e.g. if twice as loud, rating = 20)
loudness = perceived magnitude of the stimulus
What are 2 directions of magnitude estimation for different stimuli?
Response compression
* as stimulus intensity increases, the perceived magnitude increases more slowly than the intensity (e.g. brightness)
Response expansion
* as stimulus intensity increase, the perceived magnitude increases more quickly than the intensity (e.g. electricity)
What is the relationship between intensity and perceived magnitude?
a power function
What is steven’s power law?
N less than 1.0 are associated with response compression
N greater than 1.0 are associate with response expansion
What is a limitation of Fechner’s methods?
- other factors other than sensitivity may influence threshold estimation
- like personality
How is personality a limiation of fechner’s method?
liberal vs conservative
* different decision criterion for saying yes
* not taken into account in fechner’s methods
* doesnt mean ones visual system is more sensitive to light than the other
What is the signal detection theory?
- takes individual decision criterion into account
- can be used to measure true sensitivity
What is a standard signal detection experiment?
- participants asked to indicate whether a tone (signal) is present or not
- the tone is presented on some trials (noise + signal) and absent on other trials (noise)
- 2 normal distributions are used to represent the 2 conditions
How does liberal vs conservative affect decision criterion?
- conservative -> criterion shifts to right, low false alarm and low hits
- liberal -> criterion shifts left, high false alarm, high hits
What are the 4 diff results of SDT?
What is true sensitivity?
d’ = z(hit) - z(false alarm)
What is the receiver operating characteristic (ROC) curve?
- a plot that reflects the relationship between the % of hits vs the % of false alarms at diff decision criteria
- when the curve is closer to the top left corner, the true sensitivity (d’) is higher
- Thus, increasing the distance (d’) between the (N) and the (S 1 N) probability distributions changes the shape of the ROC curve.
- When the person’s sensitivity (d’) is high, the ROC curve is more bowed.
- calculating d’ enables us to determine a person’s sensitivity by determining only one data point on an ROC curve, thus using the signal detection procedure without running a large number of trials
