Psychology 3120 – Sensation and Perception.
Lecture 1
Definition
PSY 3120 is the study of our relatively automatic responses to the physical events and energies
of our environment.
Responses, i.e., behavior, to be studied will vary from the rudimentary to the complex
Sensation: Simple responses to external stimulation
Presence of a sound.
Brightness of a light.
Location of a touch.
Perception: Complex responses to external stimulation
A friend’s face
A piece of music
A spoken sentence
Automaticity
In general, the responses are automatic, mostly NOT under cognitive control.
We have little cognitive control of how we see what we see, how we hear what we hear.
We are not able to perceive a red car as being green, for example.
Stroop Test: Say the colors. Red Blue Yellow Green Orange Violet
Now again: Red Blue Yellow Green Orange Violet
We are unable to hear a low-pitched man’s voice as being high-pitched.
Processes within our brain force specific experiences on us.
If I don’t want to like someone, I can think about things that would make me not
want to like him/her and eventually, I could develop the response of “dislike”
whenever I saw that person.
I cannot do this with the color of grass, however. No matter how much I think
about how grass would be better if it had a different color, I’ll always perceive it
as I do now.
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Assumptions
The following specific assumptions have been made by most people in the field . . .
1) Neural activity. Perceptual experiences are associated with/correspond to/represented by
characteristic patterns of neural activity in the brain. Each different scene is represented by a
different pattern of activity. The philosophy underlying this assumption is called materialism.
2) Symbolic Process. The neural activity need not literally resemble the objects we perceive.
This means that perception is a symbolic process. The neural activity is a symbol of the object
perceived, not a replica of it.
About 80 years ago, some psychologists believed that a miniature 3-D image exactly like what
was being observed was created in the brain. We now know that is not the case. However,
everyone believes that the activity that occurs corresponds in some regular way to the external
stimulus although that activity is not exactly like the perceived scene. That brain activity is a
symbol of the external object.
3) Explainable, predictable, controllable. All behavior is in principle explainable,
predictable, and controllable.
Distinguish “In principle” from “In practice”
In principle,
The behavior of a falling leaf is in principle explainable, predictable, and controllable.
Think of the opening scene in Forest Gump.
But in practice,
the task of actually measuring all the variables that we would have to measure – air
pressure, shape of the leaf, air movements, temperature – would be daunting, so daunting that we
might never actually do it in practice.
4) Understanding in terms of Brain Processes. Finally, the explanations of sensory and
perceptual phenomena are in terms of brain processes. (This is a restatement of 1 above.)
This means that many scientists studying S&P believe that all experience corresponds to neural
activity in the brain. So, to understand perception we must understand the brain. We seek neural
mechanisms underlying perceptual phenomena.
Some of what we experience is based on the way our brains were created controlled by
our genetic makeup.
Some of what we experience is based on the way our brains have changed since birth,
due to the vagaries of the environment in which they have been put.
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Why Study Sensation and Perception?
What does S&P have to do with psychology?
1. Sensations and Perceptions are behaviors, so they’re qualified to be part of the study of
psychology, even though they’re so automatic that we hardly ever think of them and we may not
be interested in them.
Just as some people climb mountains because they’re there and not yet climbed, some
psychologists study S&P because it’s there and not yet understood.
2. It’s important to understand and perhaps control certain perceptual phenomena
a. Creation of perception in those for whom it doesn’t exist
Vision for the blind
Hearing for the deaf
Movement and sensation for persons without limbs:
http://www.cbsnews.com/video/watch/?id=50137987n
b. Color “blindness” - the inability of some persons to easily distinguish colors, such as
red and green, that most people can without difficulty.
c. Effects of early deprivation or unusual experience on development of sensory
capabilities.
d. Hallucinations – effects of certain drugs, such as LSD; phantom limb pain
e. Machine perception
Optical Character Recognition OCR: Being able to recognize text and convert it
to a Word document.
Being able to recognize speech - Siri
Teaching a car or Mars Rover to go from one place to another by itself.
Recognizing when a heart is beating correctly. Recognizing fibrillation.
Machine recognition of faces.
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3. S&P mechanisms may be similar to the mechanisms underlying other more complex or
elusive phenomena.
For example, the processing of wavelength of light leads to a categorization of wavelengths
into 6 rough categories – red, orange, yellow, green blue, and violet. Understanding this
categorization process may help us understand other categorizations that we make, such as . . .
The processes underlying the liking/disliking of people – categorization analogous to the
categorization that is color perception.
The processes underlying the experience of humor. Some things are funny. Others are
not.
The processes underlying the experience of beauty.
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The Perceptual Process G9 p. 5
1. What’s “out there”.
Need to understand a little bit of physics and chemistry
2. The stimulus on the receptors.
Vision – light rays
Audition – sound waves
3. The neural activity of the receptors.
Vision – rods and cones
Audition – hair cells
4. The processing of receptor activity by brain neurons.
Magnification of some of the receptor activity
Diminution of some of the receptor activity
Comparison of different receptor activities
5. The perception of “something”.
6. The recognition of specific entities.
7. Taking action.
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Approaches to the study of Perception
The Physiological Approach – G9 p 10
The physiological approach focuses on relationships between external stimuli and neural
structures and activity
Methods, some of which are gruesome
1. Single cell recording
2. Multiple cell recording
a. Evoked potential recording – electrode attached to skin and record activity.
b. Brain scan techniques
Computer Assisted Tomograph CAT scans
Positron Emission tomography (PET scans)
Magnetic Resonance Imaging (MRIs and fMRIs)
3. Lesion technique – destruction of parts of the brain and observation of results using scalpels
or chemicals.
Transcranial Magnetic Stimulation: (TMS) Brief, strong pulse of magnetic energy
thru the scalp – results in a temporary cessation of function of involved neurons. A
temporary lesion or cut, if you will.
4. Staining – injection of drugs which are absorbed by neural activity. The presence of these
drugs can be indicated either visually or using special equipment.
5. Brain stimulation – Stimulating parts of the brain and recording the sensations, if any, that
result from such stimulation. During surgery for reasons other than the brain stimulation.
Wilder Penfield – Neurosurgeon who discovered areas of the brain corresponding to
various senses using brain stimulation of surgery patients.
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The Behavioral Approach – Y p. 20
Psychological approaches involve the use of verbal reports or other overt behavior as the
gauge of perception.
Focus on relationship between external stimuli and overt behaviors, including verbal report
Behaviors include:
Verbal reports of experience: Much early research involved showing an object to a research
participant who then described the basic “sensations” he or she experienced when looking at the
object. The Gestalt Psychologists of the 1920s and 1930s.
Detection reports: “I hear it.” “I see it.” “I smell it.”
Discrimination reports: “These two are different.” “These two are the same.”
Magnitude estimation reports: “I’ll give it a 6.” “I’ll give him a 5.”
But wait!! If we’re interested in the brain, why are we studying external behaviors?
1) Inferences about brain activity can be drawn from psychophysical approaches
Careful behavioral research has yielded very good inferences concerning physiological
processes.
Example: Helmholtz postulated the existence and described the nature of the three types
of cones in the late 1800s, more than 100 years before first observations of cones
Ewald Hering in the early 1900s postulated the existence of opponent processes in color
perception many years before the first evidence of those processes was presented in the
1960s.
Use of dark adaptation curves (detection reports of faint lights) lead to postulation the
existence of two receptor classes.
2) Sometimes the practical results of such experiments, e.g., the difference in sodium content of
potato chips that’s just noticeable, is what we need.
Makers of potato chips have whole departments of persons whose goal is to figure out
how to make less sodium taste like the “usual amount” of sodium.
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