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Lecture 1

MDU 4830 Lecture Notes - Lecture 1: Gestalt Psychology, Proprioception

102 pages121 viewsFall 2015

Department
Health Outcomes & Policy
Course Code
MDU 4830
Professor
M C A T
Lecture
1

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Processing the Environment
Sensory Perception
Visual Cues
Depth, Form, Motion, Constancy
Binocular Cues - retinal disparity (eyes are 2.5 inches apart). Convergence – things far
away, eyes are relaxed. Things close to us, eyes contract.
Monocular Cues – relative size, interposition (overlap), relative height (things higher
are farther away), shading and contour, motion parallax (things farther away move
slower)
oConstancy – our perception of object doesn’t change even if it looks different on
retina. Ex. size constancy, shape constancy, color constancy.
Sensory Adaptation
Hearing - inner ear muscle: higher noise = contract.
Touch - temperature receptors desensitized
Smell – desensitized to molecules
Proprioception – mice raised upside down would accommodate over time, and flip it
over.
Sight – down (ex. Light adaptation, pupils constrict, rods and cones become
desensitized to light) and upregulation (dark adaptation, pupils dilate)
Weber’s Law
2 vs. 2.05 lb weight feel the same.
2 vs. 2.2 lb weight difference would be noticeable.
The threshold at which you’re able to notice a change in any sensation is the just
noticeable difference (JND)
So now take 5 lb weight, in this case if you replace by 5.2 weight, might not be
noticeable. But if you take a 5.5 lb it is noticeable.
I = intensity of stimulus (2 or 5 lb), delta I = JND (0.2 or 0.5).
Weber’s Law is delta I to intensity is constant, ex. .2/2 = .5/5 = .1.
oDelta I/I = k (Webers Law)
If we take Weber’s Law and rearrange it, we can see that it predicts a linear
relationship between incremental threshold and background intensity.
oDelta I = Ik.
oIf you plot I against delta I it’s constant
Absolute threshold of sensation
The minimum intensity of stimulus needed to detect a particular stimulus 50% of the
time
At low levels of stimulus, some subjects can detect and some can’t. Also differences in
an individual.
Not the same as the difference threshold (JND) – that’s the smallest difference that
can be detected 50% of the time.
Absolute threshold can be influenced by a # of factors, ex. Psychological states.
oExpectations
oExperience (how familiar you are with it)
oMotivation
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oAlertness
Subliminal stimuli – stimuli below the absolute threshold.
The Vestibular System
Balance and spatial orientation
Focus on inner ear - in particular the
semicircular canals (posterior,
lateral, and anterior)
Canal is filled with endolymph, and
causes it to shift – allows us to detect
what direction our head is moving in,
and the strength of rotation.
Otolithic organs (utricle and saccule)
help us to detect linear acceleration
and head positioning. In these are Ca
crystals attached to hair cells in
viscous gel. If we go from lying down
to standing up, they move, and pull on
hair cells which triggers AP.
Also contribute to dizziness and
vertigo
oEndolymph doesn’t stop spinning the same time as we do, so it continues moving
and indicates to brain we’re still moving even when we’ve stopped – results in
feeling of dizziness.
Signal Detection Theory
Looks at how we make decision under conditions of uncertainty – discerning between
important stimuli and unimportant “noise”
At what point can we detect a signal
oOrigins in radar – is signal a small fish vs. large whale.
oIts role in psychology – which words on second list were present on first list.
oReal world example – traffic lights. Signal is present or absent (red).
Strength of a signal is variable d’, and c is strategy
od’: hit > miss (strong signal), miss <hit (weak signal)
oc: 2 strategies – conservative (always say no unless 100% sure signal is present.
Bad thing is might get some misses). Or liberal (always say yes, even if get false
alarms).
For any signal, have noise distribution. And get a second graph – the signal distribution.
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oThe difference between means of the two is d’. So if signal shifted to right, d’
would be big and easy to detect. If left, d’ very small and more difficult to detect.
oX-axis have intensity.
oThe strategy C can be expressed via choice of threshold – what threshold
individual deems as necessary for them to say Y vs. N. Ex. B, D, C, beta, just dif
variables.
oIf we were to use B, let’s say choose this threshold – 2. So anything greater than
2 will say Y to, anything less say N. So probability of hit is shaded yellow, and
false alarm is pink.
oD = d’-B, so let’s say d’ in this example is 1, so 2-1=1. So if we use D strategy,
anything above 1 = Y.
oC strategy is an ideal observer. Minimizes miss and false alarm. C = B – d’/2. So
in our example, it’s 2- ½ = 1.5. So anthing above a 1.5
When C = 0, participant is ideal observer. If <1, liberal. If >1, conservative.
oBeta, set value of threshold = to the ratio of height of signal distribution to height
of noise distribution. lnbeta = d’ x C = 1 x 1.5 = 1.5
Bottom-Up vs. Top-Down Processing
Bottom up: stimulus influences our perception.
Top-down: background knowledge influences perception. Ex. Where’s waldo
Gestalt Principles
Similarity – items similar to one another grouped together
Pragnanz – reality is often organized reduced to simplest form possible (Ex. Olympic
rings)
Proximity – objects that are close are grouped together
Continuity – lines are seen as following the smoothest path
Closure – objects grouped together are seen as a whole
Sight (Vision)
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