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Volledige colleges uitgeschreven, midterm S&P
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Alle hoorcolleges van chapter 1 tm 7 volledig uitgeschreven.
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, Hoorcollege 1The introduction: The senses
Sensation and perception = How we see and understand the world around us. This is important because it affects
how we behave in response to our environment, and how we understand and interact with everything in our world
Interactions between physical forces and our sensory organs produce patterns of neural activity, which cary
information about the world around us.
colored largely bits are
Within these sensory organs, there are specific sensory receptor neurons processing
information
involved in
Esensess
sensory
that interact with something physical in the outside world.
This separates these ‘true’ senses from perceptions we have like our
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‘sense’ of time, or feelings like our ‘sense’ of familiarity, etc. These are
not true senses, although they are things we feel, because they do not
come from a particular sensory organ interacting with something
physical in the world. Therefore, we will not study these other feelings.
There are other feelings and sensations that result from the internal
i
state of the body: thirst, hunger, fullness, heart rate, blushing. These are also feelings and not senses.
However, there is a true sixth sense that is often missed but does have a sensory organ interacting with
external physical forces in the world. This is our sense of balance, or vestibular sense. This relies on interaction
between our vestibular labyrinths of the inner ear and gravity and inertia. We will study this later.
Sense Sensory organ
Vision (sight) .
Eyes (retina)
Hearing (audition) Ears (cochlea)
-
-
.
Taste (gustation) Tongue (taste buds)
Smell (olfaction) Nose (olfactory epithelium)
.
Touch (somatosensation) Skin etc. (many)
.
Balance (vestibular) Vestibular labyrinths
Furthermore, our sense of touch is not a single sense at all. Although much of our sense of touch relies on the
skin, there are many distinct sensory receptors involved, each producing distinct sensations. For example we
use light touch to sense what a material is made of or to place our body precisely in relation to an object. This
feels quite different to deeper pressure, which does not give these fine details. We also feel stretch, a different
sensation that can come from our muscles and joints as well as our skin.
It is fair to say that these are all types of touch, although they feel different. For example:
-
Sense of heat.
Sense of cold.
.
Sense of pain. Extreme heat or cold, or damage to the body. There are several distinct types of pain: burning,
.
itching, and throbbing pain feel very different.
These are all types of touch. They are sensing different physical forces in the world. The main thing that unites
these very different sensations is that they mainly rely on one sensory organ, the skin, or sometimes the muscles,
and similar processing in the brain.
,Why so much vision?
Vision is the primary sense in humans.
Almost every action we make is guided by vision. It is our most used sense.
We do a lot of analysis of vision.
Object recognition.
Form & colour.
Space and motion.
Location, motion, distance and depth.
As a result, a huge proportion of our brain is devoted to visual processing, even more than is shown here.
Conversely, only relatively small specific brain areas are involved in human touch processing and auditory
processing. Very small areas are involved in taste, smell and vestibular processing.
In vision, it is particularly easy to control the inputs, because with the computers now it is easy to make the
image you want, to our brain, and to understand how the brain is processing these, and test what the observer is
perceiving and see which information they are not sensitive to. It is also relatively easy to make a fMRI of the
visual cortex. As a result, we understand vision in far more detail than the other senses. And because we do so
much with vision, there is a lot to understand.
In the early stages of vision, it is possible to examine the inputs and the responses of single neurons in so much
detail that we can follow how a pattern of activity in one set of neurons is analyzed by the next neuron to give a
new type of response. In other words, we can see how individual neurons are processing information to help us
understand the world. The single cells are only active together if the spatial responses are lined up in a
particular way. So we can see in the early stages of vision which calculations are made to see if a neuron is
responding. That is really difficult to see anywhere else in the brain. This field, neural computation and its basis
in neural physiology, involves a more technical way of thinking than almost any area of psychology, though it is
probably more comfortable for those studying AI. We think this is very important to understand because it
reveals how the brain is actually doing things: not just which area is involved, but what is actually happening in
the brain to allow us to understand our world.
Dualism = Mind and spirit are a separate entity from the physical body.
Monism = The idea that the mind is an aspect of the body, held in the brain and the nervous system. If you don’t
have a body you don’t have a mind. The concept is that the mind is a part of de body because our nervous system
runs through our whole body. Monism takes the view that the mind and body are manifestations of the same
physical thing.
Perception is actually the activity of the neurons in our brain and nervous system.
Sensation = A translation of the external physical force/environment into a pattern of neural activity (this is done
by a sensory organ).
Perception = Analysis of this neural activity resulting from our sensory organs to understand the environment and
guide behavior. It is our subjective conscious experience of the outside world.
or: The subjective conscious experience of the outside world. Perception is what we feel.
, We may feel that we perceive the world as it truly is. But in fact we don’t perceive the world accurately at all.
Understanding the physical and neural basis of perception often reveals why we perceive things the way we do.
Sensation and perception reflect interactions between our sensory organs and physical properties of the world,
so they are:
Dependent on physical properties of the world.
Limited by the physical properties of our sensors.
Visible light has a short wavelength and does not reflect from most surfaces, so light does not travel around
corners. However, sound has a longer wavelength and reflects more easily, so we can generally hear around
corners fairly well: we can hear this car around a corner, but can only see around the corner with a mirror. The
human eye is only sensitive to a short range of wavelengths of light, part of a much larger electromagnetic
spectrum going from gamma waves to radio waves.
Sensation and perception have evolved to help us survive and reproduce, so they are:
Perception is optimized for useful representations of the environment.
Influenced by interpretation of the world: context and experience.
Dependent on limited resources of attention and awareness.
Perception is sometimes inaccurate because it is influenced by our expectations an our sensory organs receive
more input than the brain can process. Therefore, we use attention to focus our limited resources on the input
that seems important for our goals. As a result, we do not perceive parts of our sensory input, typically those
that don’t seem important to us.
If we see sensation and perception as: “A translation of the physical environment into a pattern of neural
activity that can be used by our brain to guide behavior” Then to study sensation and perception
experimentally, we will:
Change the physical environment of a human or animal (sensory stimulus). It is to change what we perceive:
we need to change our sensory input or stimulus.
Measure the resulting behavior. So we can see how this changes behavior responding to the change in
perception. So what you say you saw.
Measure the resulting change in neural activity. Or we can see how this change in the stimulus changes
patterns of neural activity.
Psychological approach/behavioral approach = We ask people to do task and tell us what they perceive. Then we
characterize what the people did en did not see, so we look at their behavior. Quantitative measurements of
behavior resulting from our perception.
Biological approach = Correlate a neural activity measure with a change in the presented stimulus, change in the
environment or the animal’s behavior.
Psychophysics = The scientific study of the relation between stimulus and sensation. It is best understood as
testing whether subjects perceive a difference between two stimuli. This term comes from the view of perception
as in interaction of the brain/nervous system (psyche) with physical stimuli, so a physical force in the world
(physics). Weber and Fechner saw that sensory stimuli have physical effects on sensors, and they wanted to
investigate these using psychophysics.
If we determine the just noticeable difference, the change in the environment that we can only just perceive, its
size depends on the stimulus that is being compared. So the variability or error with which our perception
represents a stimulus feature increases with the magnitude of that feature, or the strength of the stimulus.
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