Transcription topic 6 HC 6 perception neuropsychology
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Course
Neuropsychology
Institution
Radboud Universiteit Nijmegen (RU)
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Visual perception is really interesting because a large part of our cortex is dedicated to our visual
system.
You mainly see coffee beans but you can also so a face
in it. Once you it’s there it’s difficult to ignore it.
Sensation and Perception
Sensation is the biological part that is
simply the registration of the stimuli from
the environment by the sensory organs.
So sensory organs are not only the eye.
Today we talk about the eye, in the next
lecture we talk about the sensory motor
system and about the auditory system. So
we have the registration of the physical
stimuli from the environment. And we
have perception. Perception is the
subjective interpretation of sensations by the brain. So our visual experience is not only an objective
reproduction of what is out there, but it’s also a subjective reconstruction of our reality.
So sensation is the biological registration of the physical stimuli by our sensory organs, today we talk
about the eye. And perception is a subjective interpretation of sensations by the brain.
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, one example of perception is that we also have
perceptual illusions. So here you can flip the image
to see the white vase and you can also see the
black faces. What we see here below is called the
Müller-Lyer illusion. This illusion means that you
perceive the top line as longer than the bottom
line.
Here you see different types of the Müller-Lyer illusion. The
top line is perceived as the shortest, the middle line as the
longest and the bottom line something in between. Usually
people can not help but perceive this top line as being
shorter even though we all know that all lines have the
same length,
what’s interesting is that this illusion varies
across cultures. There are researchers that
compared the illusion in three different
populations, Caucasians, Africans and
Philippines. The mean length of this
misperception differs a lot from only 1.4% to
20.3%. so there seems to be a lot of variation
in the misperception of the lengths of the lines.
European were the most susceptible to see this
illusion. And people in the Kalahari desert were
the least susceptible. One possible explanation is that European and American city residents have a
much higher percentage of living in rectangular environments. And in the desert you have more round
shapes. And one explanation could be that our environment triggers this illusion. When we are in an
environment with more rectangular lines and shapes that we are more susceptible to have this
illusion and people living in environments with more round houses or round shapes or living in the
desert that you are less susceptible to having this illusion. So this is also an example of perception, the
interpretation of what we see. Sensation is the physical stimulus from the outside world that is
perceived by our sensory organs.
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, So our brain receive input from our
outside world as a series of action
potentials. Maartje has talked about
it. These action potentials are passed
along the neurons to our sensory wire,
our sensory pathways, to our cortex
which is dedicated to our senses.
We have sensory receptors and that
are specialized cells that convert
sensory energy into neural activity. So
today we talk about the visual system and that is light. But we also have other sensory receptors.
Next week we talk about the sensory motor system so we have receptors on our skin for example. The
week after we talk about the auditory system. So we have different sensory receptors.
Our sensory system’s receptor cells are designed to respond to a specific band of energy. So vision is
light energy and auditory is air pressure and somatosensory is mechanical energy. We also have taste
and olfaction, this is transported by chemical molecules. So our different senses respond to different
energy band.
What is also important is that the
receptors have wary in their density
and that is important in determining
the sensitivity of this specific organ.
For example we have more tactile
receptors on our fingers than on our
arm. You can also test this, when you
have two pins and you have them
close together, on the fingers you can
still detect that they come from a
different location whereas you put the same difference of the pin on your forearm you perceive them
as coming from the same location. Because the receptors differ in their density, so we have higher
density in the fingers for example.
One other example is that dogs for example have higher receptors for olfactory abilities.
Another terminology is the receptive field. This is the specific part of the world to which sensory-
receptors respond to. The higher receptive density usually goes hand in hand with smaller receptive
fields. So the higher the density the more accurate is our perception.
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