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