Course Description
An introduction to the study of the human senses and higher order
perceptual processes. Data gathered from psychophysical research
and studies of the nervous system in both humans and other animals
will be discussed. The course will review the mechanisms and
principles of operation of vision, hearing, touch, taste and smell
Antirequisites: Psychology 115a/b and the former Psychology 212a/b, 213a/b, 211E.
Prerequisite: At least 60% in a 020-level Psychology course.
Course Web
http://instruct.uwo.ca/psychology/215b-002/
• most recent version of syllabus
• Powerpoint slides from lectures
Examination Schedule
• Mid-term Exams:
– Thursday February 7
– Tuesday March 19
– Final exam period
• Format:
– In class: 2 hrs
• Multiple choice
• Short answer
• Definitions
• Further details announced in class and on website
• Final Exam: Date to be announced
My content
The common wisdom:
• “Do not read the textbook if you can learn it from the lectures.
Textbooks are boring.”
• “Do not go to class if you can learn it from the textbook.
Professors are boring.”
My philosophy:
• Come to class. Use the text as a reference and refresher.
• If a name is important, I will emphasize it.
• Videos are fair game for exam questions.
Other lecturers may differ!
WHAT IS PERCEPTION?
The study of perception, especially vision and hearing,
has allowed psychology to grow from its philosophical
roots into an experimental science.
Yet deep philosophical questions remain - especially
over the role of consciousness. It is puzzling that we are
aware of so little of perception - and that we have any
awareness at all.
WHAT IS PERCEPTION?
The astonishing hypothesis is...
“that `You,' your joys and your
sorrows, your memories and
your ambitions, your sense of
personal identity and free will,
are in fact no more than the
behavior of a vast assembly of
nerve cells and their
associated molecules."
-- Francis Crick
Visual awareness is an
excellent case study in the
attempt to understand
consciousness
• What does it mean "to perceive"?
• literally (Latin), "to seize what is in front of us”
• to survive, we must acquire useful (though not
necessarily accurate) information about the objects and
events in our world
• perception constructs a reality (a conscious, experiential
view of the world) for the perceiver
perception is process of organizing sensory data,
deriving structure from the complex patterns of energy
impinging on our sensory receptors
WHY STUDY PERCEPTION?
“To be is to perceive” -- George Berkeley, philosopher
SUBJECTIVE REASONS
Intellectual curiosity: Why do we sense things the way we do?
WHY STUDY PERCEPTION?
OBJECTIVE REASONS
1.
Help the design of sensory environments (lighting,
acoustics, cockpit design)
2.
Build prosthetic devices to overcome sense organ
defects (glasses, hearing aids)
Build devices to fool the senses - create artificial
realities (movies, TV, sound reproduction systems,
artificial flavors, virtual reality displays)
Medicine: repair broken sense organs and nervous
systems, prevent defects
Engineering: Design perceiving machines
3.
4.
5.
WHAT IS INVOLVED IN STUDYING
PERCEPTION?
In a tribute to Hermann von Helmholtz, James Clerk
Maxwell (1877) stated the plight of the perception
researcher:
In no department of research is the combined and
concentrated light of all the sciences more necessary
than in the investigation of sensation.
HOW CAN WE STUDY PERCEPTION?
Main Approaches
1. Psychological
Phenomenology
Psychophysics
2. Biological (Neurological)
Anatomy
Single neuron recording
Neuroimaging (e.g. fMRI)
Lesions in brain damaged patients
3. Theoretical
4. Computational
PHENOMENOLOGY
“What does it feel like…?”
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Movie: MAE_demo_15sec.mov
PHENOMENOLOGY
Waterfall Illusion (Motion Aftereffect)
And also when persons turn away from
looking at objects in motion, e.g. rivers, and
especially those which flow very rapidly, they
find that the visual stimulations still present
themselves, for the things really at rest are
then seen moving.
--Aristotle
Falls of Foyer, Scotland
(Robert Addams, 1834)
PHENOMENOLOGY
Pros
• Fun
• Can be very enlightening
• Good starting point
Cons
• limited to verbal report
• can’t study other species or development
• verbal reports may be inaccurate, subjective
• doesn’t necessarily tell you how perception works
PSYCHOPHYSICS
Involves control and careful manipulation of the stimulus.
Allows one to identify exactly what aspect of the stimulus
underlies some perceptual experience and attempt to relate
results to underlying mechanisms.
PSYCHOPHYSICS
Strength of Motion
Aftereffect
What are the limits of ability?
How do the limits change as parameters are varied?
Stopped
Slow Medium
Speed
Fast
PSYCHOPHYSICS
Can even be used to study the perceptual abilities of other species
ANATOMY
Study the arrangement of neural structures
and the connections between them
• Over 30 visual areas
• Complex organization
• Visual areas make up ~40% of
monkey brain
SINGLE NEURON RECORDING
Specify the response properties of single neurons
in different parts of the brain
SINGLE NEURON RECORDING
Visual neurons are tuned to specific parts of space (receptive
fields) and properties (e.g., the recording above is from a cell
with a preferred motion direction).
BRAIN IMAGING
Measure human brain activity in specific brain areas during different
perceptual tasks
Functional Magnetic Resonance Imaging
(fMRI)
MRI studies anatomy.
fMRI studies function.
fMRI and Positron Emission Tomography (PET)
• indirect measures of neural activity
• can be measured over time as stimulus or task changes
 neural activity
MRI
  blood   fMRI/PET signal
fMRI
e.g., Area MT: The “motion area”
• activated when the subject views motion
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Movie: VIMTmovie.mpg
• also activated when the subject perceives motion, even
during the waterfall illusion when there is no physical motion
“Motion area” MT is also activated when the subject perceives
motion, even during the waterfall illusion when there is no
physical motion
Subject perceives real
motion
Subject perceives
waterfall illusion
Subject does not
perceive waterfall
illusion
Study of brain damaged individuals
Lesion technique. The oldest method for relating brain
events to perception entails destroying some portion of the
nervous system and then measuring associated changes
in perceptual function.
Studying humans with ‘natural’ lesions may help tell us
what brain areas control certain aspects of perception.
Example: motion blind patient (video)
THEORETICAL VISION
Example:
Ecological approach
Perception evolved to use the relevant
information available in the real world.
The point towards which one is moving
has zero velocity. This point should play
a fundamental role in coding locomotion.
COMPUTATIONAL VISION
If the eye is like a camera, the brain is far more than the film!
COMPUTATIONAL VISION
COMPUTATIONAL VISION
Which is harder to program, vision or chess?
1997 -- Deep Blue beats Kasparov
2??? -- A computer can perceive?!
Do we see the world "directly"?
No!
Our perceptions are representations, created by
our sensory systems and brain, of the information
in the world. Of course there has to be a
systematic relation between these
representations and the world or we wouldn’t
have survived.
Consider:
1. The same image can look different to
different people, or different to the same
person from one moment to the next.
Necker Cube
2. Your brain can create perceptions that
aren't present physically.
Subjective Contours
3. What we see can be different from the physical
stimulus.
Caution
It is easy to get so carried away by illusions that one starts to
think of visual perception as grossly inaccurate and unreliable.
This is a mistake.
Vision is evolutionarily useful to the extent that it is
accurate—or, rather, as accurate as it needs to be.
Illusions may actually be relatively harmless side effects of the same
processes that produce veridical perception under ordinary
circumstances - may help us figure out those processes.
There is a long chain of processes between the
physical events going on in the world and the
perceptual registration of those events by a
human observer.
The processes include:
the generation of energy by some external object or event
the transmission of the energy through the space between
the event and the observer
the reception and processing of the energy by the
observer's sensory receptors
the transmission of signals to the brain, where still more
processing takes place
presumably, the end result is the formation of a
representation in the brain of what is going on in the
external world.
OVERVIEW OF VISION - 7 STAGES
(1) Light emitted by a source (e.g., sun) is
reflected from objects, and modified in
the process. Hence, it picks up
information about those objects
Sun (source)
Tree (object)
(2) Light from objects enters eye, forms an
optical image on the retina.
Retinal image
of tree
Tree
Eye
(3) Light in the retinal image is
absorbed by photoreceptor cells,
causing nerve signals ("Transduction")
Nerve signal out
Light in
Photoreceptors
sensory transduction - how the nervous system
converts the patterns of physical energy into neural
events.
(4) Nerve signals from receptors are transmitted to
other retinal cells, which "process" them (carry out
computations)
Receptors Post-receptor retinal neurons
(5) Signals (trains of nerve impulses) are relayed
from retinal ganglion cells to primary visual cortex
(via thalamus) and midbrain
Thalamus
Eyes
Visual
Cortex
(6) The retinal signal is "recoded" in visual
cortex, broadcast to other cortical regions.
Visual
Cortex
(7) Neural events somehow create
conscious experiences.
In studying perception we (our brains) are trying to understand the brain
We have a long way to go
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