Lecture 3 - Psychophysics Flashcards
What is psychophysics?
The relation between subjective perceptual (experience) and the objective physical stimuli that give rise to that experience
comparing 2 things
How sensitive is that persons sensory system to stimulus (perceptual threshold/absolute)
What is method of constant stimuli?
psychophysical technique used to measure sensory thresholds by presenting a set of stimuli with different intensities, chosen beforehand, in a random order to a participant, who then judges whether each stimulus is detectable or not, allowing researchers to determine the threshold at which the stimulus is reliably detected at a specific percentage of the time;
essentially, it involves repeatedly exposing a subject to a fixed set of stimuli with varying intensities to find the point at which they can just barely perceive a stimulus.
What is a psychometric function to data on a graph?
Basically a line of best fit thru data points
(eg s shaped or..)
Common to see without the data points
You want this to find different points or relative thresholds (difference between stimuli that a person can detect)
What are relative thresholds?
Interested in the smallest difference between two stimuli that a person can detect
(JUST NOTICEABLE DIFFERENCE / JND) method used to calculate relative thresholds.
JND - The stimulus level that maps onto 75% point is the just noticeable difference
What is Weber’s Law?
Explains the observation (the pea and weight thing)
The JND is a constant proportion of the stimulus intensity
(TRIANGLE P / P = k)
delta p over p = k
so it’s proportional to the stimulus intensity
P= the intensity of the standard (we know in advance bc we chose the stimuli)
Delta p is the JND (calculated after the experiment)
k is the % change in the comparison that we need for stimulus to be detected
When the standard is more intense (in this case longer), discriminating differences is what?
More difficult
What is an Absolute threshold?
Limits of perception
Our sensory systems allow us to experience only a ___ part of what?
Limited part of our physical environment
What is a Perceptual threshold?
1 stimulus presented on each trial and p is asked if they detected it
could you tell it was there?
What are absolute thresholds more interested in now point wise?
50% of detection
to see the point where the p detects the stimulus
What are 3 threshold finding methods?
CLA
Method of Constant stimuli
Method of Limits
Method of Adjustment
What is the method of constant stimuli?
A way of finding thresholds requires fitting a psychometric function
P JUDGES A STIMULI ACROSS FIXED DURATIONS
stimuli are decided by experimenter and run in random order, psychometric function is fit to results and threshold is calculated from there
What do the methods of limits and method of adjustment not require that the method of constant stimuli requires?
Method of limits and adjustment do not require fitting a psychometric function
What kind of approach is the method of limits?
(like a step up step down approach)
Increase or decrease stimulus intensity until participant detects the stimuli
What is the step up procedure?
In method of limits,
increase stimulus intensity start off w weak intensity, until p detects it
What is the step down procedure?
Start w a high intensity, so p can detect it, decrease the intensity until p can no longer detect the stimulus presented
What is the method of adjustment?
Participant adjusts stimulus intensity themselves
Aim for perceptual threshold (until can detect its there)
can be repeated w different starting intensities
What is an advantage and disadvantage of choosing to use method of constant stimuli??
most precise
but the slowest
What is an advantage and disadvantage of using the method of limits?
Faster
May suffer from order effects
What is an advantage and disadvantage of choosing to use method of adjustment?
Quickest method
But more dependent on participant coordination
What are potential issues with Psychophysics?
Are people’s responses reliable?
Are they consistent?
Are they true reports?
All ps typically exhibit what?
Bias
What is the Signal Detection Theory?
Manage bias (ps responses not true to their true sensitivity of sensory system w stimulus)
Detect signal against noise
Separate ps sensitivity to their bias
What is bias influenced by?
Costs and benefits of the response outcomes
What is the benefit of signal detection theory?
Perceivers’ sensitivity can be distinguished from their bias
How can you measure magnitude?
Magnitude estimation
Use a standard (present p w a standard stimulus and ask p to assign perceptual value, eg 10)
Then researcher present p w other stimulis and ask p to give them a value but judge that relative to the standard presented at the beginning
so ask to rate magnitude with respect to standard
Magnitude functions can be used to what
Relationship between stimulus intensity and perceived magnitude
Normally there is a linear form that p s follow in perceived magnitude
There is a response compression w what stimulus?
light and brightness,
curve flattens out creating response compression
brightness follows a relationship referred to as response compression
What do electric shocks follow the relationship of?
Response expansion, inverse relationship
perception of magnitude increases as stimulus intensity increases, but w weaker shocks the perception of magnitude isnt increased as much in value
What is Stevens’ power law?
P = KS n (small n at top right, power of n)
P= Perceived magnitude
S= Stimulus intensity
K n = constants (specific to percept under investigation)
theyre values that are the same to specific type of stimulus, whatever sensory system we are trynna investigate
non-linear bc its how our sensory systems adapt to our env
