PSYC 212 Lecture Notes - Lecture 5: Absolute Threshold, Posterior Grey Column, Xeroderma

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20 Jul 2016
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Lecture#5: Somatosensory Perception 17:25
Somatosensory system: Fairly accessible- Do some experiments on yourself
to get a feel for what it is and what various concepts we will discuss are, it is
a fairly simple system so it is a good starting point.
Overview:
What are the dimensions of touch?
Somatosensory includes not just touch but also proprioception and heat
sensation.-Focus on touch.
How can we measure these dimensions in the stimulus?
In our surroundings, stimulus.
How are these aspects of the stimulus sensed by our mechanoreceptors?
Receptors in our skin called mechanoreceptors- sensitive to mechanical
changes.
How are the mechanoreceptor signals transmitted to the brain?
How is touch represented in the brain?
Somatosensory perception is basically pressure sensation:
False. Touch is not just pressure sensation either.
It wouldn’t include pain.
Pressure alone is a brute force, to say that somatosensory perception is
simply pressure sensation is light saying vision is light vision- does not
describe the richness of the sensation.
We are going to be covering a lot on various dimensions on touch, what
happens/what is the sort of stimulus- rubbing your hand on the back of your
hand- what is particularly distinct in regards to the pressure changes both in
time and in space.
What does the feeling of touch involve?
A skin indentation somewhere on the body.
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A skin indentation at some point in time.
Sodium channels opening.- Because we need to generate action potentials.
Action potentials.
A spatio-temporal pattern of indentation.
Could describe the richness of sensation as being a spatio-temporal pattern
of skin indentation.
Pressure patterns?
-Two objects can be applied at the same pressure, but result in different
precepts. How?
They might have different surface properties- one could be a rock or a glass.
-Is the surface of a rock the same as glass?
In terms of frequency, spatial frequency on the skin, the difference between
the rough surface of a rock and glass.
The rock would have a lot higher frequency, the spatial frequency changes of
indentation are much higher than glass.
The roads in Montreal have really high spatial frequency, lots of bumps and
holes.
Temporal frequency- The bumps in the road are there, they will feel slow if
you drive slow you feel them less, if you start racing down any of the nasty
roads, the rate at which you will shake is much higher.
You are the constant in the car, moving, and the road bumps are shaking
you basically- the temporal frequency you are e experiencing is very high,
simply as a function of how fast the same surface your car is past over.
-Does rubbing your hand over a rock result in the same pattern of pressure
change as rubbing your hand on a piece of glass?
-What is the basis for pattern perception?
Somatosensory stimuli:
-A spatio-temporal pattern:
Touch the back of your fingers of your left hand with your right hand. Now
touch the back of your hand instead of the fingers. Which one exhibits a
higher spatial frequency?
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You can feel that the frequency of pressure change on your finger is higher
than touching the back of your hand.
With hair on your hands- extra high frequency features.
Every object, based on its surface features, has a conglomeration of diff.
frequency features on it.
The texture of the object is defined by those spatial features.
The texture on the top of your fingers- a medium spatial frequency,
compared to the hair on the back of your hand or your wrist. The
fluctuations are small and very fast.
Stroke the palm of your hand with your fingers, then stroke your hair. Which
has a higher spatial frequency? Which has a higher temporal frequency?
-Spatial frequency:
How much change you would experience or is present in a fixed
space/frame.
The area where my fingers are covering is about the same width as the back
of my hand- the frame of the two is about the same, but there are many
fluctuations in pressure when you rub the finger on the back of the finger-
the number of changes you would experience are much higher than when
you rub it on the back of your hand.
In general, you would feel the back of your hand as fairly infrequent change.
Hairs cause rapid fluctuations.
Frequency means how frequent something is.
Talking about the stimulus itself, if you take these two surfaces and you
think about the amount of change on one vs. the other, it is clear that one
surface changes more.
The back of my finger changes more than the back of my hand.-More
changes in depth- that is all spatial frequency is talking about- frequency of
change, over the same space.
-The spatial frequency is one of the key concepts to remember, it explains
and helps us describe our sensations, our stimuli rather.
Fine things, course things, medium things in a fixed space.
-In some ways, the somatosensory system, our sensation of touch, in order
for it to be useful in telling us what we are touching, must be useful in
differentiating these different frequencies/ diff. spatial frequencies and
possibly some temporal frequencies as well, some changes will be alive or
happening very quickly.
EX. Vibrations- If you ever carved something with a knife, you know whether
you hit something bad or whether your knife has slipped- the acceleration of
the knife tip and the scratching feeling that generates a fine vibration feeling
in your hand.
Holding a pen/pencil, the tip of the pencil has friction against the paper,
which is registered by our receptors.
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