Only your own sensory experience is directly accessible to you.
Sensation: the ability to detect a stimulus and to turn that detection into a priva.e 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.
18 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 system.
METHOD 2: SCALING – MEASURING PRIVATE EXPERIENCE
Quale (pl. Qualia): in philosophy, a private conscious experience of sensation or perception
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 DECISIONS
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
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.
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.
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 1/40 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. 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 experienceof 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
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
o If they’re presented from faintest to loudest, the listeners are asked to report when
they first hear the tone.
o With descending order, they’re asked when the tone is no longer audible.
o This 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 be 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. 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
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
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).
o Example, 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.
o The 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.
Weber’s law: involves clear objective measurement. We know how much we varied the
stimulus, and either the observers can tell that the stimulus changed or they cannot.
Fechner’s law: begins with same objective measurements as Weber’s, but is a calculation based
on assumptions about how sensation works. This law assumes all JNDs are perceptually
equivalent, which is an incorrect assumption because electric shock example violates this law.
Steven’s power law: describes rating data well but the rating data are qualitatively different
from the data that supported Weber’s law. There’s no way to know whether the subject’s
ratings are objectively right or wrong.
A variant of the scaling method can show that different people can live in different sensory
worlds, even if exposed to the same stimuli. This method is cross-modality matching.
o An observer adjusts a stimulus of one sort to match the perceived magnitude of a
stimulus of a completely different sort.
o Example, asking a listener to adjust the brightness of a light until it matches the
loudness of a particular tone.
o The relationship of visual and auditory experience appears to be similar across
individuals, but not so much when it comes to the sense of taste.
A molecule called propylthiouracil (PROP) tastes bitter to some people, while others experience
it as almost tasteless. If observers are asked to match bitterness of PROP to other unrelated
sensations, we don’t find the agreement that is found when observers match sounds and lights.
o Some people (called nontasters) match PROP to weak sensations like whispering.
o A group of supertasters assert that the bitterness of PROP is similar to intensity of the
sun or the most intense pain ever experienced.
o Medium tasters match PROP to weaker stimuli like smell of frying bacon or pain of mild
headache. o The basis for this variation is genetic and has implications for food preferences and
SIGNAL DETECTION THEORY
Signal detection theory: holds that the stimulus you’re trying to detect is always being detected
in the presence of “noise”.
If you sit in a quiet place and wear noise-cancelling headphones, you’ll still hear something.
Similarly, if you close your eyes in a dark room, you still see something.
This is internal noise, the static in your nervous system.
When you’re trying to detect a faint sound or flash of light, you must be able to detect it in the
presence of that internal noise.
There is also external noise.
o Example when screening for breast cancer, the fuzzy white region is a danger sign, but
there are a lot of other similar regions. The cancer can be thought as the signal and by
the time it’s presented to the radiologist in an X-ray, it’s a signal plus noise. Elsewhere in
the image are stimuli that are just noise. The radiologist is trained to find these signals
but sometimes the signal is lost in the noise and missed, and sometimes some noise will
look enough like cancer to generate a false alarm.
o Signal detection theory exists to help us understand what’s going on when we make
decisions under conditions of uncertainty.
Example you’re in the shower and the water is making noise, now the phone rings which is our
signal. Now the signal is added to the noise, so we have 2 distributions of responses in the
o The noise-alone distri