cornell psych 205: day03
TRANSCRIPT
Psychology 205Perception
28 January 03
Day 03
Two Psychophysical Phenomena
Minds, Bodies, & FechnerMeasurement: 4 scalesAnisomorphism: Hayek and 4 cases
1. Broca-Sulzer effect2. Detection thresholds
teleologyabsolute vs. relative
Just noticeable differences - JNDs3 methods: limits, adjustment, constant stimuli
means, distributions, & “cheating”States of the nervous system
spontaneous neural activity
GustafFechner 1801-1887
Elements of Psychophysics1860
beginnings ofempirical psychology &psychophysics
a way to measure (in dealing
with the) mind-body problem
How do we measure?
in all of science, 4 ways (S.S. Stevens, 1951)
nominal: classifies gender
“this is different than that”“this is the same as that”
nested nominality = hierarchies, taxonomies
kingdom, family, order, genus, phyla, class, species
nominal: classifies gender
nested nominality = hierarchies, taxonomies
ordinal: classifies & class @ CUorders
“this is more than that”
nominal: classifies gender
nested nominality = hierarchies, taxonomies
ordinal: classifies & class @ CUorders
interval: classifies, °C, °Forders, &shows “measured” differences
“This difference is equal tothat difference”
“This difference is twice thatdifference”
nominal: classifies gender
nested nominality = hierarchies, taxonomies
ordinal: classifies & class @ CUorders
interval: classifies, °C, °Forders, &shows measured differences
ratio: classifies, orders, °K, m, s, kgshows measured differences, & has a true zero. “This value is twice as
much as that value”
psycho-physics
ordinate --> psycho- usually ordinal scale abscissa --> -physics usually ratio scale
Region of plotted function
Region of plotted function
ordinateordinate
abscissaabscissa
anisomorphism
an - notiso - samemorph -structureism - practice, theory
F.A. Hayek (1899-1992) The sensory order(1952), pp. 7-8
" ... psychology must take the physical world as represented by modern physics as given, and try to reconstruct the process by which the organism classifies the physical events in the manner which is familiar to us as the order of sensory qualities...
… In other words, psychology must start from stimuli defined in physical terms and proceed to show why and how the senses classify similar physical stimuli sometimes as alike and sometimes as different, and why different physical stimuli will sometimes appear as similar and sometimes as different.”
---> 4 cases
similar physical stimuliperceivedsometimes similar --->
Case 1 and sometimes different --->
Case 2
different physical stimuliperceived sometimes similar --->
Case 4 and sometimes different --->
Case 3
other examples of anisomorphism in psychophysics:
1. Broca-Sulzer effect2. Detection thresholds
Broca-SulzerBroca-Sulzer
anisomorphism (of order) between psychological scale and physical scale
anisomorphism (of order) between psychological scale and physical scale
Explanation: 2 types of cells in optic nerve
transient (on or off) and sustained cellstemporal summation (time window of “now”)
crude model: transient = 75 spikessustained = 1 spike/ms
Explanation:crude model: transient = 75 spikes
sustained = 1 spike/ms
50 ms stimulus: on (75) + duration (50) + off (75) = 200 spikes
100 ms stimulus: on (75) + duration (100) + off (75) = 250150 ms stimulus: on (75) + duration (150) + off (75) = 300
200 ms stimulus: on (75) + duration (200) or duration (200) + off (75) = 275
averaging window: >150 ms & <200 msapparent brightness is the sum of what’s in the “window”
additive model, but actually some inhibition (subtraction) is going on
Anisomorphism
2. detection thresholds in senses
absolute threshold
Explanation:
When there is not enough physical energy in the stimuli the receptors will not respond. All insufficient stimuli are alike.
more on detection thresholds in senses
the idea of an absolute thresholdand the remarkable sensitivity of
the senses
teleology: doctrine of final causes“why things are the way they are”
detection thresholds in senses
vision = a candle flame seen @ 30 mion a clear, dark night
~80 quanta entering eye ( w/in ~150 ms)
~8 quanta absorbed by receptors
any more sensitive in the infrared we would seebody heat at night
detection thresholds in senses
audition = tick of a watch @ 20 ft underextremely quiet conditions
vibrations on ear drum of ~1/10 width of hydrogen atom
any more sensitive we would hear jointmovement,and hear Brownian motion of air in ear canal
detection thresholds in senses
smell = one drop of perfume diffused into the entire volume of a 3-rm apt
~5-40 molecules, 1 per receptor cell; 1 molecule of bombykol for the
silkworm moth
detection thresholds in senses
smell = one drop of perfume diffused into the entire volume of a 3-rm apt
~5-40 molecules, 1 per receptor cell; 1 molecule of bombykol for the
silkworm moth
taste = .5 tsp sugar in 1 gallon water
detection thresholds in senses
smell = one drop of perfume diffused into the entire volume of a 3-rm apt
~5-40 molecules, 1 per receptor cell; 1 molecule of bombykol for the
silkworm moth
taste = .5 tsp sugar in 1 gallon watertouch = the wing of a bee falling on your
back from a distance of 1 cm
problem
statements of the absolute
perception doesn’t work that waybecause the nervous system doesn’t work
that way
Assumption:
as in text
as in text
:Reality
psychophysical function,
more later
From detection thresholds to difference thresholds
Just Noticeable Differences (JNDs)
increments (or changes) to a suprathreshold stimulus that are sufficient to make it appear different in a direct comparison of the two
e.g.
Stimulus B just detectably louder, brighter, different than
Stimulus Arelevant to signal detection theory
next time
Fechnerian psychophysical methods Elements of Psychophysics, 1860
1. Method of Limits2. Method of Adjustment3. Method of Constant Stimuli
1. Method of Limits
threshold value
2. Method of Adjustment
thresholdvalue
rapid; good in clinic settings
3. Method of Constant Stimuli
threshold value &distribution
3. Method of Constant Stimuli
same threshold value & differentdistribution
knowing means is important, but you can’t tell if there is a reliable difference between means without knowing the distributions of responses
method of constant stimuli is by far the most commonly used of the Fechnerian methods in psychophysics today
but there is a problem
“cheating”
observer says “yes” or “no” whether or not he or she sees/hears/etc. a stimulus.
With the method of constant stimuli there is always a stimulus present. Thus, the observer could rightfully say “yes, there is a stimulus present” even if it were not perceived.
Signal Detection Theory, Thursday
Fechernian Methods (Method of Constant Stimuli)
Response Yes No
Stimulus Present
Signal Detection Methods
Response __Yes No__
Yes | | |Stimulus |_______|_______|
No | | | |_______|_______|
A final relevant issue:
States of the Nervous System
hiddenassumptionof Fechnerian
Methods:
all-or-none neural spikes
all-or-none neural spikes
States of the Nervous System
Reality:
spontaneousneural activity
A peripheral neuron without spontaneous neural activity is (soon to be) a dead neuron.
Spontaneous neural activity is how the neuron maintains its readiness
---> Signal Detection Theory
Two Psychophysical Phenomena
Minds, Bodies, & FechnerMeasurement: 4 scales ---> ordinal:ratio
Anisomorphism: Hayek and 4 cases1. Broca-Sulzer effect --->
mappings can be
2. Detection thresholds unruly
teleologyabsolute vs. relative
Just noticeable differences - JNDs ---> TSD3 methods: limits, adjustment, constant stimuli
means, distributions, & “cheating” --> TSDStates of the nervous system
spontaneous neural activity ---> TSD