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PSYB57H3 (300)
Chapter 1-2

PSYB57H3 Chapter 1-2: CHAPTER 1-2

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George Cree

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Only your own sensory experience is directly accessible to you.
Sensation: the ability to detect a stimulus and to turn that detection into a private experience.
Perception: the act of giving meaning to those detected sensations
Everything we feel, think, and do depends on sensations and perceptions reason why philosophers have
talked about it for over 2 millennia.
18th century French philosopher Etienne Bonnot de Condillac asked readers to imagine a statue with no
senses (thus no mental life. The he iagied addig the statue’s ose so the etal life ould osist of ol
that smell. By adding more senses and experience, he imagined a real mental life developing.
Researchers studying topics in sensation and perception can be found in biology, computer science,
medicine, neuroscience, and many other fields.
Eaple, hat’s the faitest/loudest soud ou a hea. You a hage the theshold fo the
faintest sound if you listened to sounds that are too loud and damage your auditory system.
Quale (pl. Qualia): in philosophy, a private conscious experience of sensation or perception
We still hae o diet a to epeiee soeoe else’s epeiees ut e a deostate
that people inhabit different sensory worlds.
a perceptual decision has real consequences. Example, if a radiologist screens a woman for
breast cancer and the X-ray shows sign of cancer but it is’t lea. If the adiologist deides that
it’s eig ut it’s atuall aeous, the patiet ill die. If the adiologist deides it is
aeous ad pefos oe tests ad suge ut it as’t aeous, thee ould e less
severe consequences, but there will be consequences.
sensory neuroscience explains how your perception of the world depends on the activity of our
sensory nerves at least as much as it depends on the world itself
METHOD 5: Neuroimaging An Image of the Mind
Suppose you view 2 different images with each of your 2 eyes (example a house and a face). The
result is an effect known as binocular rivalry, the 2 images would vie to dominate your
perception: sometimes you see a house, sometimes a face, ut ou’ll ee see the  togethe.
Gustav Fechner (invented psychophysics) is considered to be the true founder of experimental
psychology, but the title is usually given to Wilhelm Wundt.
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Fechner suffered severe eye damage from gazing at the sun while performing vision
Dualism: the mind has an existence separate from the material world of the body
Materialism: the only things that exists is matter, and all things, including the mind and
consciousness, are the results of interaction between bits of matter
Materialists hold that the mind is not separate. Dualists hold the mind has an existence
separate from material world of the body
A modern materialist position, majority view in scientific psychology, is that the mind is what
the brain does
Panpsychism: the mind exists as a property of all matter, extended not only to animals but to
inanimate things as well. That is to say, all matter has consciousness.
Fechner took on the job of explaining the relation between the spiritual and material worlds:
mind and body using mathematics.
His goal was to formally describe the relationship between sensation (mind) and the energy
(matter) that gave rise to that sensation.
He called both his methods and his theory psychophysics (psycho for mind, and physics for
Ernst Weber was an anatomist and physiologist who was interested in touch.
Weber tested the accuracy of our sense of touch using a device much like the compass to
measure the smallest distance between 2 points that was required for a person to feel 2 points
instead of one.
He called the distance between the points the two-point touch threshold.
Fo Fehe, Wee’s ost ipotat fidig ioled judgets of lifted weights.
o Weber asked people to lift one standard weight and one comparison weight.
o When the standard was relatively light, people were much better at detecting a small
difference when they lifted the comparison weight. When the standard was heavier,
people needed a bigger difference before they could detect the change
o He called the difference required for detecting a change in weight the just noticeable
difference or JND. Another term for JND is the difference threshold (smallest change in
a stimulus that can be detected).
Weber noticed that JNDs changein a systematic way.
o the smallest change in weight that could be detected was always close to 1/40th of the
standard weight. Example a 1 gram change could be detected when the standard
weighed 40 grams, but a 10 gram change was required when the standard weighed 400
o For judging the lengths of two lines, the ratio was 1:100.
o For every measure (brightness, pitch, time) a constant ratio between the change and
what was being changed could describe the threshold of detectable change.
The ratio holds true except when intensities, and size are very small or very large, nearing
minimum and maximum of our senses. Fechner called these ratios Weber Fractions.
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The size of the detectable difference (▲I) is a constant proportion (K) of the level of the
stimulus (I)Weber’s law.
Fechner assumed that the smallest detectable change in a stimulus (delta I) could be considered
a unit of the mind because this is the smallest bit of change that is perceived
He then mathematically extended Weber's law to create what became known as Fechner's
law: S = k log R
where S is the psychological sensation, which is equal to the logarithm of the physical stimulus
level (log R) multiplied by a constant, k.
this equation describes that psychological experience of the intensity of light, sound, smell,
taste, or touch increases less quickly than the actual physical stimulus increases.
This euatio is siila to Eistei’s euatio: E = mc^2. Like mind and body, energy (E) and
mass (m) were thought of as distinct things. Fechner provided us one way to think about mind
and matter as equivalent.
Absolute threshold: minimum intensity of a stimulus that can be detected
Method of constant stimuli: creating many stimuli with different intensities in order to find the
tiniest intensity that can be detected
In general, the intensity at which a stimulus would be detected 50% of the time is chosen as the
Why? Due to the variability in the nervous system, stimuli near threshold will be detected
sometimes and missed other times.
Method of constant stimuli is inefficient in an experiment. A more efficient approach is the
method of limits.
o In this method, the experimenter begins with the same set of stimuli, in this case, tones
that vary in intensity
o Instead of random presentations, tones are presented in order of increasing or
decreasing intensity.
o If the’e peseted fo faitest to loudest, the listees ae asked to epot when
they first hear the tone.
o With desedig ode, the’e asked he the toe is o loge audile.
o This kid of epeiet shos thee’s soe oeshoot i judgets. It usuall takes
more intensity to report hearing the tone when intensity is increasing, and it takes
more decreases in intensity before a listener reports that the toe a’t e heard.
o We take the average of these crossover points (when listeners shift from reporting
hearing the tone to not hearing the tone, and vice versa) to be threshold.
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