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Matthias Niemeier

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PSYB51 Notes are
Chapter 1:
Early Philosophy of Perception
-The allegory of the cave, written by Plato compares our ordinary sense of reality that of prisoners in a
cave. - It emphasizes how critically our conception of reality depends on what we can learn about the
world through our senses
-our sense of reality are the products of evolution
- Heraclitus was a Greek philosopher known for his famous statement you can never step into the same
river twice
- stresses his view that everything is always changing
- no two experiences can ever be identical, because experiencing the first event changes the way
we experience the same event the second time
- perceptual systems are keenly sensitive to change
- perception quickly comes to ignore anything that stays the same for very long, this is adaptation
- Democritus is had the radical idea that the world is made up of atoms that collide with one another
- are senses should be trusted because perception as a result of the physical interaction
between the world and our bodies
- the most reliable senses were those that detect the weight or texture of objects
- taste and olfaction, our sense of smell, come closest to Democrituss theory
- primary qualities are those that can be directly perceived, secondary qualities are those that
require interaction between atoms from objects and atoms in the perceiver
- sensory transducer is a substance or structure that changes energy from one form to another
- perception deals with the interpretation of the signals from sensory transducers, it depends more on
Nativism and Empiricism
- Plato believed that the body and the mind are separate entities, and that certain mental abilities must
be innate = nativism
-Rennee Descartes Believed that only humans have in mind, the dualist tradition–he considered the
mind separate from the body
- and mind is then extended it has no substance and it survives the death of the body
- monism the idea that mind and matter are formed from, or reducible too, a single ultimate substance of
principle or being
-materialism the idea that physical matter is the only reality, and everything including the mind can be
explained in terms of matter and physical phenomena. A type of monism
- mind-body dualism originated by Rene Descartes, the idea of positing the existence of two distinct
principles of being in the universe
- empiricism the idea that experience from the senses is the only source of knowledge
- Thomas Hobbes believed that only matter exists and rejected the concept of spirit, he argued that all
knowledge must arise from the senses
- a model of human nature relies entirely on experience
- memories are simply sensory experiences that were old and faded
- John Locke, the idea of the Tabula rasa
- suggested that all ideas must be created through experience
- first century impressions are called simple ideas
- blind people treated in late the adulthood that are not made happier by being able to see

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PSYB51 Notes are
- George Berkeley concluded that we learn how to perceive distance by experiencing many objects and
scenes in the world
- through experience we learn how to use multiple visual cues to arrive at a pretty good estimate
of where things are
- like Plato,he appreciated that there are limits on perception, and matter how much experience
the Perceiver has; like Hobbes and Locke, in contrast, Berkeley concluded that all of our knowledge
about the world must come from experience
- David Hume, the most significant British empiricist
- reliability refers to the consistency of measurements
- validity refers to the relationship of the measurement to what is measured
- he argued that the world, as portrayed through our senses, seems very real because
perception is highly reliable
The Dawn of Psychophysics
- Gustav Fechner, is the true founder of experimental psychology
- he proposed that the mine, or consciousness, was present in all of nature
- panpsychism the idea that mind exists as a property of all matter
- his goal was to formally describe the relationship between sensation [mine] and energy [matter]
that gave rise to the sensation
- psychophysics science of of defining the quantitative relationships between physical and
psychological events
- Ernst Weber tested the accuracy of our sense of touch
- two-point touch threshold: and minimum distance at which to stimuli are just perceptible as
- most important finding involves judgments of lifted weights; he found that the ability of the
subject to detect the difference between the standard and comparison weight depended greatly on the
weight of the standard. When the standard was relatively light, people were much better at detecting
small difference when they lifted the comparison weight
- he called the difference required for detecting a change in weight the just noticeable
difference or JND, or a difference threshold
- the smallest change in ways that could detect it was always close to 1/40 of the standard weight;
judging the lengths of two lines, the ratio was only 1 to 100
- fechner called these ratios Weber fraction and the general rule that the size of the detectable
difference is a constant proportion of the level of the stimulus Webers law
- this equation describes the fact that her psychological experience of the intensity of light,
sound, smell, taste or touch increases less quickly than the actual physical stimulus increases
- absolute threshold minimum intensity of the stimulus that can be detected
Psychophysical Methods
- method of constant stimuli: requires creating many stimuli with different intensities in order to find the
tiniest intensity that can be detected
- tones, varying in intensity, will be presented randomly. The listeners task would be to report
whether they heard a tone or not
- the point at which a stimulus could be detected 50% of the time is chosen as the threshold
- method of limits begins the same set of stimuli but instead of random presentation, tones are presented
in order of increasing or decreasing intensity
- when tones are presented in ascending order, listeners are asked to report when they hear the
first tone; with ascending order, they must report when the tone is no longer audible
- the crossover points other threshold

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PSYB51 Notes are
- method of adjustment the subject is the one who steadily increases or decreases the intensity of the
- is hard to get people to reliably adjust intensity to the same definition threshold across people in
Signal Detection Theory
- thresholds are probabilistic
- this is because subjects change from trial to trial, the stimulus presented to a subject is not the
only source of activity in the perceptual system, and people bring their own biases to the perception task
- page 15, look at diagrams
- correct rejection, hit, false alarm, miss
- page 16 figure 1.18
- for a fixed value of d, changing the criterion on changes that had been false alarms in
predictable ways
- receiver operating characteristics curve (roc) in studies of signal detection, the graphical plot the hit
rate as a function of the false Alarm rate. If these are the same, points fall on the diagonal, indicating
that the observer cannot tell the difference between the presence and the absence of the signal. as the
observers sensitivity increases, the curve bows upward toward the upper left corner. That point
represents a perfect ability to distinguish signal from noise
- signal detection Theory a psychophysical 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 and criterion of the Observer
- magnitude estimation play one tone and tell the listener to label this level of a specific value, all of the
responses should then be sensibly above or below the standard
- cross modality matching the subject at just the stimulus of one sort to match the perceived magnitude
of the stimulus of a completely different sort
- Stevens found cases in which the sensation grows more rapidly than the physical stimulus, this is
known as Stevens power law which states that the sensation is related to the stimulus intensity by an
- example, for electric shock the pain grows with an exponent of three, so an increase of 10 fold
in the voltage is 1000 V in the pain
- Webers law involves a clear objective measurement, fechners law also begins with the same sort of
objective measurement but the law is actually a calculation based on some assumptions, it assumes that
all just noticeable differences are perceptually equivalent
The biology of perception
- the key assumption of animal studies is that they tell us something about human senses
-rennee descartes claimed that animals were in most ways very similar to humans, as only distinction is
that humans have minds and souls
- he proposed the animal spirits enter the brain and exit your pores that guide this fluid through
nerves to muscles, like hydraulic machines
- the most powerful argument for a continuity between humans and animals came from Darwins theory
of evolution
- and inescapable implication is that we learn much but human sensation and perception by
studying our nonhuman relatives
- Johannes Mueller formulated the doctrine of specific nerve energies which states that the nature of a
sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated
- page 20 figure 1.23
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