Chapter 1 Notes (pg.3-29):
Sensation: The ability to detect a stimulus and, perhaps to turn that detection into a
Perception: The act of giving meaning to a detected sensation.
The variety of methods used to study the senses:
Method 1: Thresholds
This is concerned with the different variations of sound one can hear and how it
works, often involving loud sounds or faint sounds.
Method 2: Scaling (Measuring Private Experience)
There is no direct way to experience someone else’s experiences.
Some people do have different sensory worlds so that their experience of a color
for example might be different from my experience of that color. Nevertheless
people are able to understanding these experiences through the scaling method.
Quale (pl. Qualia): In philosophy, a private conscious experience of sensation or
Method 3: Signal Detection Theory (Measuring Difficult Decisions)
This theory allows scientist to study how people make tough decision.
Method 4: Sensory Neuroscience
Tries to explain how one’s perception of the world depends on the activity of
one’s sensory nerves at least as much as it depends on the world itself.
Method 5: Neuroimaging (An Image of the Mind)
In binocular rivalry one is presented with two images for each eye, these images
differ however, and in observing them one sees the images switch. For example:
My right eye is presented with a face while my left eye is presented with a house,
what happens is that I can see the face and then the house and then the face and
then the house. It thus appears that the two images are competing for my
attention. It is through neuroimaging that we are able to see how this experience is
THRESHOLDAND THE DAWN OF PSYCHOPHYSICS: Gustav Fechner: AGerman scientist-philosopher often considered to be the true
founder of experimental psychology.Absorbed with the relationship between the
mind and body he came up with a new approach of understanding their relation
called Panpsychism: The idea that the mind exists as a property of all matter, that
is that all matter has consciousness which extended not only to animals but
inanimate objects. 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 method and theory Psychophysics: The science of defining quantitative
relationships between physical and psychological (subjective) events.
His idea of Panpsychism was presented during the time of two famous proposals
called Dualism and Materialism.
Dualism: The idea that the mind has an existence separate from the material world
of the body
Materialism: The idea that the only thing that exists is matter, and that all things,
including the mind and consciousness are the results of interaction between bits of
Ernst Weber: An anatomist and physiologist who was interested in touch.
Two-point touch threshold: The minimum distance at which two stimuli (e.g. two
simultaneous touches) are just perceptible as separate.
Just noticeable difference (JND) or difference threshold: The smallest detectable
difference between two stimuli, or the minimum change in a stimulus that enables
it to be correctly judged as different from a reference stimulus.
Weber fraction: The constant of proportionality in Weber’s law.
Weber’s law: The principle describing the relationship between stimulus and
resulting sensation that says the just noticeable difference (JND) is a constant
fraction of the comparison stimulus. The size of the detectable difference (ΔI) is a
constant proportion (K) of the level of the stimulus (I)
Fechner’s law: Aprinciple describing the relationship between stimulus and
resulting sensation that says the magnitude of subjective sensation increases
proportionally to the logarithm of the stimulus intensity. S = k log R
S in the psychological sensation, which is equal to the logarithm of the physical
stimulus level (log R) multiplied by a constant k.
Absolute threshold: The minimum amount of stimulation necessary for a person
to detect a stimulus 50% of the time.
1) Method of constant stimuli: a method of measuring absolute threshold, which requires
creating many stimuli with different intensities, in order to find the tiniest intensity that
can be detected. There is no hard boundary that exists in measuring the weakest detectable
stimulus. Because of the variability in the nervous system, stimuli near the
threshold will be detected sometimes and missed other times.
The method of constant stimuli is simple to use, but it can be somewhat
inefficient in an experiment because much of the subject’s time can be spent with
stimuli that are clearly well above or below threshold.As a more sufficient
approach is the:
2) Method of limits: In this method the experimenter begins with the same set of stimuli-
in this case, tones that vary in intensity. Instead of random presentation, tones are
presented in order of increasing or decreasing intensity. When tones are presented in
ascending order, from faintest to loudest, listeners are asked to report when they first hear
the tone. With descending order, the task is to report when the tone is no longer audible.
They 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 the threshold.
3) Method of adjustment: This method is just like the method of limits, expect the subject
is the one who steadily increases or decreases the intensity of the stimulus.
Scaling Methods and Supertasters:
Magnitude estimation:Apsychophysical method invented by S.S Stevens in
which the participant assigns values according to perceived magnitudes of the
stimuli. (E.g. rating sugary solutions from a scale of 1-10 depending on how
sugary they are.)
The relationship between stimulus intensity and sensation is described by what is
now known as Stevens’ power law (S=al): which states that the sensation (S) is
related to the stimulus intensity (I) by an exponent (b).
Weber’s law: involves a clear objective measurement. We know how much we
varied the stimulus, and either the observers can tell that the stimulus changed or
Fechner’s law: begins with the same sort of objective measurements as Weber’s,
but the law is actually a calculation based on some assumptions about how
sensation works. In particular, Fechner’s law assumes that all just noticeable
differences (JNDs) are perceptually equivalent which is incorrect.
Steven’s power law: describes rating data quite well, but notice that rating data are
qualitatively different from the data that supported Weber’s law. We can record
the subjects’ ratings and we can check whether those ratings are reasonable and
consistent, but there is no way to know whether they are objectively right or
Cross-modality: Is a useful scaling method, which can show that different
individuals can live in different sensory worlds, even if they are exposed to the same stimuli. In this method, an observer adjusts a stimulus of one sort to match
the perceived magnitude of a stimulus of a completely different sort. This means
that two different stimuli are presented and the observer is to make them equal to
one another. For example: one might ask a listener to adjust the brightness of a
light until it matches the loudness of a particular tone, which result is the same
pattern of matches among people with “normal” vision and hearing.
Though the relationship between vision and hearing seems to be similar across
individuals, the case differs when it comes to the sense of taste. The molecule
called propylthiouracil (PROP) is experienced as very bitter by some people,
while others experience it as almost tasteless. Some people match the taste of
PROP to very weak sensations like the sound of a whisper, however a group of
supertasters assert that the bitterness of PROP is similar to the most intense pain
Supertasters: Individuals whose perception of taste sensations is the most intense.
Signal Detection Theory
Signal Detection Theory: Apsychophysical theory that quantifies the response of
an observer to the presentation of a signal in the presence of noise. Measures
obtained from a series of presentations are sensitivity (d’) and criterion of the
To better illustrate this theory, take for example the noise you hear in the shower,
at times this noise sounds louder to you and sometimes it seems softer. Now
imagine being in the shower and the phone rings, which will act as our signal.
What you hear now is a combination of the shower and the phone ringing, thus
adding a signal (ringing) to the noise (shower). Now we have a noise-alone
distribution and a signal-plus-noise distribution. What this means is that we have
two options either we are simply just hearing noise or we are hearing noise
coming from the shower but also a phone ringing. How do we then decide
whether to go and answer the phone or dismiss it? Well, we must first decide
whether we are hearing noise alone or noise plus signal. To do so we must decide
on a criterion level of response.
Criterion: In signal detection theory, an internal threshold that is set by the
observer. If the internal response is above criterion, the observer gives one
response (e.g. “yes, I hear that”). Below criterion, the observer gives another
response (e.g. “no I hear nothing”).
Aresponse inside the observer, above criterion will be taken as evidence that a
signal is present. Aresponse below the level will be treated as noise.
After we decided whether what we heard was a noise or a noise plus signal there
are four possible outcomes in regards to our actions.
1) You say “no” when there is no ring, known as correct rejection
2) You might say “yes” when there is a ring, known as a hit
3) You might say “yes” when there is no ring, known as false alarm
4) You say “no” when there is a ring, known as a miss
How sensitive are you to the ring? To determine one’s sensitivity there must be a
greater separation between the noise-alone and signal-plus-noise distribution. In simple terms, the closer the signal is to the noise the harder it is to detect a signal,
they must be distinct or separate from one another in order for one to be sensitive
to a difference. If the distributions completely overlap, d’= 0 and you have no
ability to detect the signal. If the distributions mediate, you have some sensitivity
but your performance will be imperfect, in this situation for example d’= -1. If d’
is big then distinguishing signal from noise is trivial, and in this situation d’= - 4
Sensitivity: In signal detection theory, a value that defines the e