week 4: psychophysics Flashcards
what is sensation
how our sensory organs (eyes, ears, etc) convert physical/chemical info into signals that our NS can understand
what is perception
how we acquire info from the environment
how we process that info to form internal representation of the environment
what is cognition
how we use the internal representation to do more complex things
examples of sensation
psychophysics
vision
hearing
examples of perception
pattern recognition
mental imagery
attention and performance
examples of cognition
memory
problem solving
reasoning and decision making
navigation
language
what is difference threshold
the smallest change in a stimulus that can be detected
what is absolute threshold
the minimum intensity of a stimulus that can be detected
what is webers law
weber found that the size of the JND (just noticeable difference) is a function of the magnitude of a reference stimulus
what was fechners idea
if a weber fraction is constant for a given stimulus dimension, then the mind might use the weber fraction as a unit for perceiving that stimulus dimension
implication of fechners law
fechners law relates to internal experience (psyche) and physical environment (physics)
(psyche+physics=psychophysics)
what is fechners law about
the absolute. not relative, intensity of a stimulus
fechners law asserts that our:
psychological experience of the intensity of a stimulus tends to change less quickly than the actual change in stimulus intensity
what does fechners law relate to
fechners law relates internal experience (psyche) and physical environment (physics)
what is fechners law about
fechners law is about the absolute, not relative, intensity of a stimulus
fechners law asserts that:
our physical experience of the intesity of a stimulus tends to change less quickly than the actual change in stimulus
why is it hard to measure thresholds
because humans are very good at perceiving
methods to measure thresholds
methods of constant stimuli
methods of limits
staircase procedures
method of constant stimuli
construct a set of stimuli with magnitudes ranging from above to below the presumed threshold value
present these stimuli a number of times in a random order
participants respond whether or not they detect the stimulus on each trial
plot the proportion of detections occurring at each stimulus magntitude
the threshold is taken as a magnitude at which the stimulus is detected a criterion proportion of the time (eg. 50%)
advantages to the method of constant stimuli
allows the shape of the psychometric function to be established
provides an accurate estimate of threshold
disadvantages to the method of constant stimuli
requires pre-testing to roughly estimate the threshold
wastes alot of trials which lie far from the threshold
it is difficult to measure changes in threshold over brief time periodss
methods of limits
measures the threshold without determining the shape of the psychometric function
types of series in method of limits
ascending and descending series in trials
what is descending series in method of limits
present the stimulus at a suprathreshold level
decrease stimulus intensity in small steps until participants can no longer detect the stimulus