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Sensation & Perception
• Exam 3: Review
© Takashi Yamauchi (Dept. of Psychology, Texas
A&M University)
Sensation & Perception
Ch. 7: Action
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Ecological approach
Optic flow
The physiology of navigation
Skilled action
Linking sensory and motor functions
Perception reconsidered
• J. J. Gibson’s ecological approach
– All the studies we have seen so far are
conducted in laboratory settings, in which
stationary stimuli were given.
– Perception is not a stationary experience.
– Perception should be studied as it occurs in the
natural environment.
Optic flow and a gradient of flow
• A gradient of flow gives a strong cue for
motion and depth perception
Demonstration:
http://www.rdg.ac.uk/arl/clips/demo_of_displays.htm#opticflow
The Physiology of Navigation
• Optic flow neurons - neurons in the medial
superior temporal area (MST) of monkeys
respond to flow patterns
Neuron 1 in the monkey’s MST responds to an expanding stimulus
but not a stimulus with circular movement. Neuron 2 responds to
circular movement but not to expansion.
Physiological Links Between Sensory and
Motor Functions
• Optic ataxia
– Patients suffering from this syndrome produce
inaccurate reaching movements towards a
target or object in space.
Experiment by Schindler et al.
• Participants:2 groups
• Patients with parietal lobe damage and normal control
participants.
• Participants performed two tasks
• Bisection task - point to position between cylinders
• Reaching task - reach between cylinders and touch a gray
strip
Bisection task
In each trial, you saw
two cylinders that were
shifted different
positions.
You had to point a
place exactly midway
between the cylinders.
Experiment by Schindler et al.
Trial 1
Bisection task
In each trial, you saw
two cylinders that were
shifted different
positions.
point
You had to point to a
place exactly midway
between the cylinders.
Trial 2
So, for each trial, you
had to point different
positions.
point
Experiment by Schindler et al.
Trial 1
Reaching task
touch
In each trial, you saw
two cylinders that were
shifted different
positions.
You had to touch a gray
strip that were 20 cm
behind the cylinders.
Trial 2
touch
So, for each trial, you
had to extend your
hand to different
positions.
Results
Trial 1
• Pointing task
touch
– The patients with
parietal lobe damage
and normal control were
equally accurate
• Reaching task
Trial 2
touch
– The patients kept
reaching the same place
even though cylinders
were shifted in each
trial.
Mirror neurons
Mirror neurons
• Mirror neurons respond to a particular
“kind” of action (e.g., grasping) AND
observing someone doing the action.
The activity of a particular neuron in the
premotor area of a monkey.
• Video clip from NOVA (PBS)
– 15 min
– http://www.pbs.org/wgbh/nova/sciencenow/320
4/01.html
Sensation & Perception
Ch. 8: Motion
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
The functions of motion perception
The direction of movement
4 different ways to create the
perception of movement
• Real movement
– The object is physically moving
• Apparent movement
– Displacement of objects
• Induced movement
• Movement aftereffect
Functions of Movement Perception
• Survival in the environment
– Predators use movement of prey as a
primary means to location in hunting
– Motion agnosia
• Damage to the cortex resulting in
inability to perceive movement
• Extremely debilitating and dangerous for
the patient
Functions of Movement Perception continued
• Perceiving objects
– Movement of objects or the observer’s
movement through objects help perceive
the 3D organization of stimuli
– Kinetic depth effect - movement of an
object’s 2-D shadow can change into
perception of a 3-D object
• This is an example of structure-frommotion
– Perceptual organization
Figure 9.4 Setup similar to the one used by Wallach and O’Connell (1953) to demonstrate the kinetic depth
effect.
– Demonstration: structure-from-motion
• http://www.cs.ubc.ca/nest/imager/contributions/flinn
/Illusions/Illusions.html
Visual Pathway (MT)
The Physiology of Navigation
• Optic flow neurons - neurons in the medial
superior temporal area (MST) of monkeys
respond to flow patterns
• Neurons that are
sensitive to a
specific direction of
motion.
• Inhibitory
connections
The intelligence of movement
perception
• Top-down processes
– Certain stimuli (like the human body) have
special meaning that affects perception
Figure 9.18 Frames from the stimuli used by Grossman and Blake (2001). (a) Sequence from the pointlight walker stimulus. (b) Sequence from the scrambled point-light stimulus.
Biological Motion (Demonstration)
http://www.biomotionlab.ca/
Depth and size
• Monocular depth cues
• Binocular depth cues
Monocular pictorial cues
•
•
•
•
•
•
Occlusion
Relative height
Relative size
Familiar size
Atmospheric perspective
Linear perspective
Leonardo da Vinci (1452-1519)
Mona Lisa (1503)
There has never been an artist who was more
fittingly, and without qualification, described
as a genius. Like Shakespeare, Leonardo were
from an insignificant background and rose to
universal acclaim. Leonardo was the
illegitimate son of a local lawyer in the small
town of Vinci in the Tuscan region….
The Dreyfus Madonna:
da Vinci 1469
The Santa Trinita
Madonna: Cimabue
(1260/80)
Linear perspective
Things get smaller
when they are
away.
Occlusion
Relative height
Relative size
Atmospheric perspective
Texture gradient
• Two types of perspectives
– Linear perspective
– Atmospheric perspective
Belvedere
: Escher
Binocular disparity
• The binocular disparity arises when a given
point in the external world does not project
to the corresponding points on the left and
right retinae
– (Palmer, 1999, “Vision Science”)
Binocular disparity
• Your two eyes are getting
different images  disparity
 double images
Corresponding
points
Corresponding
points
No disparity
disparity
Small
disparity
Large disparity
No disparity
Horopter (ViethMuller circle)
small
large
distance
distance
Small disparity
large disparity
Sensation & Perception
Ch. 11: Sound, The Auditory System, and Pitch
Perception
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Sound stimuli, amplitude and frequency
Sound quality (timbre)
Ear (structure)
Place theory
Central auditory processing
Sound wave
• Figure 1: Graphic
representations of a sound
wave. (A) Air at equilibrium,
in the absence of a sound
wave; (B) compressions and
rarefactions that constitute a
sound wave; (C) transverse
representation of the wave,
showing amplitude (A) and
wavelength (taken from
Britannica Online)
A sound wave is determined by
two factors
• Magnitude
– Y axis
• Frequency
– X axis
Specifying a sound stimulus
• Amplitude
– Y axis
– Decibel (dB)
– Number of dB = 20 x log(P/P0)
– (P: the sound pressure of the
stimulus, P0: a standard pressure)
– P0:=the pressure of a 1000Hz
tone at threshold.
• Frequency
– X axis
– Hertz (Hz)  one cycle per
second
dB: Decibel
• dB? With p=200, p0(standard pressure
level)=20
dB=20 x log (200/20)= 20 x log (10)
= 20 x 1= 20
• with p = 2000
dB = 20 x log (2000/20)= 20 x log (100)
= 20x 2 = 40
With p = 20000
dB = 20 x log (20000/20)= 20 x log (1000)
= 20x 3 = 60
• create a complex
sound by
combining simple
sound waves
•  Additive
synthesis
• reduce a complex
sound wave into a
collection of
simple sound
waves.
•  Fourier
analysis
• A sound wave from
clarinet.
• Simple sound waves that
make a sound of clarinet
Figure 11.9 The frequency
spectrum for the tone in
Figure 11.8d. The heights of
the lines indicate the
amplitude of each of the
frequencies that make up
the tone.
Ear
Ear
Bekesy’s place theory
• A wave spreads.
• The wave reached the
peak at a particular
location.
The height of the wave
reaches the peak at P, and
then gradually subsides.
• Different locations of
vibration peak are
produced by different
spatial frequencies.
• Different frequencies of sound waves
activate hair cells in different locations
• A complex tone (440Hz,
880Hz, and 1320Hz)..
• The auditory system
basically carry out a
“Fourier analysis” 
treat a complex sound as
a composite of simple
waves.
Sensation & Perception
Ch. 12: Sound Localization
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Auditory localization
Perceptual grouping
ch 12
73
Identifying the sound source in
the horizontal coordinate
• Interaural differences
– Interaural time differences
• Capture the difference in the time that a sound
reaches the left and right ears
– Interaural level differences
• Capture the difference in the level of the sound
intensity (sound pressure level) that a sound reaches
the left and right ears
ch 12
74
ch 12
75
Sensation & Perception
Ch. 13: Speech Perception
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Phoneme
Speech spectrogram
The segmentation and variability problems
Categorical perception
Multimodal speech perception, Top-down process
Speech perception and the brain
Some major problems in speech
perception
• The segmentation problem
– How do we segment the individual
words?
• The variability problem
– Variability from different speakers
– Variability from a phoneme’s context
• E.g., /d/ differs in “dig” “dug”
Stimuli
• Phonemes:
• The smallest unit of the sound system in a language
– consonants and vowels
– If you change a phoneme in a word, the meaning of the word is
also changed. (e.g., hip  tip; cat  hat; dog  dig)
• English has about 40 different phonemes
– Every English word is produced by a combination of phonemes.
• Different languages have different phonemes
– E.g., Japanese does not distinguish r and l.
– E.g., rice / lice; election / erection
Some major problems in speech
perception
• The segmentation problem
– How do we segment the individual
words?
• The variability problem
– Variability from different speakers
– Variability from a phoneme’s context
• E.g., /d/ differs in “dig” “dug”
Question:
• How does the perceptual system handle
these problems, and give us a coherent
speech perception?
Using visual cues in speech
perception
• The McGurk effect (demonstration)
– http://www.media.uio.no/personer/arntm/McGurk_english.html
– What am I saying? Play the clip several times, alternating
between looking at the talking head while listening, and listening
with your eyes shut. Most adults (98%) think they are hearing
"DA" - a so called "fused respons" - where the "D" is a result of an
audio-visual illusion. In reality you are hearing the sound "BA",
while you are seing the lip movements "GA". The "McGurk
effect" was first described by Harry McGurk and John MacDonald
in "Hearing lips and seeing voices", Nature 264, 746-748 (1976).
Using visual cues in speech
perception
• The McGurk effect (demonstration)
– http://www.youtube.com/watch?v=I1XWDOwH47Y
– http://www.youtube.com/watch?v=jtsfidRq2tw&NR=1
– The "McGurk effect" was first described by Harry
McGurk and John MacDonald in "Hearing lips and
seeing voices", Nature 264, 746-748 (1976).
Speech perception and the brain
• Broca’s area
• Wernicke’s area
Speech Perception and the Brain
• Broca’s aphasia - individuals have damage in Broca’s area (in
frontal lobe)
– Labored and stilted speech and short sentences but they
understand others
– http://video.google.com/videoplay?docid=9178936581276081395
&q=Broca%27s+aphasia&total=6&start=0&num=10&so=0&type
=search&plindex=0
• Wernicke’s aphasia - individuals have damage in Wernicke’s
area (in temporal lobe)
– Speak fluently but the content is disorganized and not
meaningful
– They also have difficulty understanding others
– http://video.google.com/videoplay?docid=7590914168187986085
&q=Wernicke%27s+aphasia&total=3&start=0&num=10&so=0&t
ype=search&plindex=0