SOCB43H3 Chapter Notes - Chapter 1: Vitalism, Visual Cortex, Physical Law
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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). Then he imagined adding the statue’s nose so the mental life would consist of only 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.
METHOD 1: THRESHOLDS
•Example, what’s the faintest/loudest sound you can hear. You can change the threshold
for the faintest sound if you listened to sounds that are too loud and damage your auditory
METHOD 2: SCALING – MEASURING PRIVATE EXPERIENCE
•Quale (pl. Qualia): in philosophy, a private conscious experience of sensation or
•We still have no direct way to experience someone else’s experiences but we can
demonstrate that people inhabit different sensory worlds.
METHOD 3: SIGNAL DETECTION THEORY – MEASURING DIFFICULT
•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 isn’t clear. If the radiologist
decides that it’s benign but it’s actually cancerous, the patient will die. If the radiologist
decides it is cancerous and performs more tests and surgery but it wasn’t cancerous, there
would be less severe consequences, but there will be consequences.
METHOD 4: SENSORY NEUROSCIENCE
•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, but you’ll never
see the 2 together.
THRESHOLDS AND THE DAWN OF PSYCHOPHYSICS
•Gustav Fechner (invented psychophysics) is considered to be the true founder of
experimental psychology, but the title is usually given to Wilhelm Wundt.
•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
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•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 matter).
•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.
•For Fechner, Weber’s most important finding involved judgments of lifted weights.
o Weber asked people to lift one standard weight and one comparison weight.
oWhen 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
oHe 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.
othe 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 grams.
oFor judging the lengths of two lines, the ratio was 1:100.
oFor 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.
•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.
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•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 equation is similar to Einstein’s equation: 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 threshold.
•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.
oIn this method, the experimenter begins with the same set of stimuli, in this case,
tones that vary in intensity
oInstead of random presentations, tones are presented in order of increasing or
oIf they’re presented from faintest to loudest, the listeners are asked to report when
they first hear the tone.
oWith descending order, they’re asked when the tone is no longer audible.
oThis kind of experiment shows there’s some “overshoot” in judgments. It usually
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 tone can’t
oWe 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.
•The third classic measure of thresholds is the method of adjustment: it’s just like the
method of limits, except the subject is the one who steadily increases or decreases the
intensity of the stimulus.
SCALING METHODS AND SUPERTASTERS
•Magnitude estimation: participant assigns values according to perceived magnitudes of
the stimuli. Example, if a participant is given sweet solutions, sweeter solutions should be
assigned bigger numbers.
•S. S. Stevens invented magnitude estimation. Relationship between stimulus intensity and
sensation is described by Steven’s power law: S= a
•Sensation (S) is related to the stimulus intensity (I) by an exponent (b).
oExample, experienced sensation might rise with intensity squared (I x I). If the
exponent is less than 1, it means that the sensation grows less rapidly than the
stimulus, this is what Fechner’s law and Weber’s law would predict.
oThe exponent for brightness is about 0.3, for sweetness is 0.8, for length it’s 1. For
electric shock, the pain grows with I^3.5, so a 4x increase in the electrical current
is experienced as a 128x increase in pain.
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