Psychophysics -- Basics, Laws, and Methods Flashcards
definitions of psychophysics
science underlying nearly all clinical optometric test procedures
science of measurement of sensory and mental phenomena
involves mathematical relationships between perception and physical reality
Gustave Fechner
founder of classical psychophysics
classical phychophysical issues
detection
recognition
discrimination
scaling
discrimination of sensory stimuli
involves difference thresholds
two things are detected–are they different?
detection of sensory stimuli
involves absolute thresholds
“is something there?”
Ex: humphrey visual field (is a light there?)
scaling
internal vs external scales (or psychological vs physical)
answers question: how does physical stimulus intensity relate to subjective perception of stimulus intensity? (i.e. if i double physical stimulus intensity, will subjective perception of stimulus intensity double?)
recognition of sensory stimuli
something is there–what is it?
threshold
boundary between two different responses to a stimulus (such as perception/no perception)
how sensory thresholds must be measured and why
repeated and averaged
humans are not perfect observers and exact thresholds vary depending on motivation, focus, etc
examples of sensory thresholds
phorias, accomodative lag, vergence ranges, VA, VF measurement, auditory acuity tests
absolute threshold, and what is another term for it
minimum physical stimulus required to evoke a sensation
other term: absolute limen (subliminal means below the threshold)
difference threshold, and two other terms for it
least change in physical stimulus intensity to evoke a sensation of difference
other term 1: difference limen
other term 2: JND (just noticeable difference)
clinical significance of DT/JND
small DT/JND: can be diff to examine (too precise in noticing differences)
large DT/JND: sometimes can’t provide useful response during subjective procedures (large changes in stimulus intensity may not be perceived as different)
signal detection theory
there is no consistent sensory threshold
psychophysical laws and what issue they address
Weber’s law
Fechner’s law
Stevens’s law
they address the classical issue of scaling
Weber’s law
CONSTANT PERCENTAGE
stimulus must be changed by constant percentage of its value to be JND (ex: two hands holding weights. whatever weight is in one hand, the weight in other hand must be changed by constant percentage (such as by 5%) to perceive difference between hands)
Fechner’s law
LOGARITHMIC
to double sensation, stimulus intensity must be squared
Stevens’s law
EXPONENTIAL
intensity raised to some exponential power
Classical Psychophysical Methods
Method of limits
method of constant stimuli
method of adjustment
adaptive psychophysical methods (modern psychophysics)
Method of limits (how, terminal judgment, errors)
how: present stimulus intensities in ascending and descending trials, slightly above and below approximate threshold. take mean of test trials to get absolute threshold.
terminal judgment: one of difference
errors: expectation (saying yes before suprathreshold intensity), habituation (continuing to say yes when intensity is subthreshold)
method of constant stimuli (how, what it controls for)
how: similar to method of limits, but 4-8 preset stimulus values within interval of uncertainty are presented in random order
controls for: expectation (same level of expectation for each stimulus)
