~Chapter 14 - Lecture Section 14.2 Flashcards by Rebecca Temple

What is Tactile Acuity?

Our ability to detect details on the skin. Important for coding object shape and texture by touch.

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How is Tactile Acuity psychophysically measured?

Using the two-point threshold, where two probes/pencils are poked into your skin, and you are asked if you perceive one point or two.

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In order to perceive two points, each point has to stimulate a ___ pool of receptive fields.

significantly different

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If the two points stimulate ___ receptive fields, they’ll be perceived as a single point being pushed into your skin.

overlapping

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The parts of the body that have the lowest two-point thresholds have the ___ receptive fields, and the ___ representation in Somatosensory Cortex.

smallest // largest

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The hands, lips, nose, cheek and face have a very ___ two-point threshold

low

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When you reach areas which have a ___ representation in the Cortex, such as the back, the calf, thigh, or arms, they have ___ two-point thresholds.

smaller // very large

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What is the two-point threshold of your pointer finger?

Your pointer finger has a two-point threshold of around 3mm

So if you got the two points pressed into your finger at 1mm apart, you couldn’t tell the difference between 1 or 2 points

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For the center of your back, in order for the two points to be detected as two distinct areas of the skin being stimulated, those probes have to be separated by about ___.

4cm

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What are two methods of testing Tactile Acuity?

Two-Point Threshold and Grading Acuity

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How is Grading Acuity performed?

A textured probe is pressed into the skin, and you’d have to determine whether the grating is vertically or horizontally orientated.

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When performing Grading Acuity, in order to perceive the orientation of the grating as horizontal or vertical you must detect the spacing between the ___ and the ___.

bars // elongated contour

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In terms of perceiving details, ___ have ideal response properties to signal shape.

Merkel Receptors (SA1 afferents)

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There is a good correlation between ___ and the spacing of ___.

Tactile Acuity // SA1 afference

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There is ___ Tactile Acuity where there is ___ spacing at the fingertip, where there is ___ packing.

high // low // very dense

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At the base of the finger where there is ___ dense packing, there is ___ high Acuity.

less // less

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At the palm of the hand, there is the ___ Acuity, where the packing of the receptors is the most ___.

lowest // sparse

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What is one thing which makes Merkel Receptors really good at detecting details?

They respond linearly to static skin indentation.

This means that the relationship between the amount that the skin is pressed in and the number of action potentials that the receptor is firing make a nice straight line relationship.

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Likely due to the branched structure of the Merkel Receptors, that for stimuli that are smaller than the ___, these are likely just stimulating a ___ terminal branch.

receptive field (2-5mm) // single

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When the corner of a probe is being pressed into the Merkel Receptor, there is a ___ in spike.

large elevation

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When the flat bit of a probe is being pressed into the receptive field of a Merkel Receptor, the response is fairly ___.

low

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The Merkel Receptor (SA1) detects each ___ of the stimulus.

gap/bump

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The Pacinian corpuscle (RA2) responds ___ to all parts of the stimulus.

equally

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___ are capable of carrying information about fine details of the probe, whereas the ___ are not capable of transmitting the details of the probe.

Merkel Receptors // Pacinian Corpuscles

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2-point stimulation (arrows) needs to activate ___ pools of cortical neurons to be perceived as 2 locations on the skin.

different

There is a relationship between the Receptive Field size at the ___ and the ___.

Skin // Cortex

The Finger, which has small receptive fields, in response to the two points of stimulation, there are ___ receptive fields between the two points, which means that when we go to the neural activation anatomically, there are ___ neurons that reside between the two populations of ___ neurons, and so they will perceive ___ point(s).

non-stimulated // non-activated // activated // 2

The Forearm, which has large receptive fields, the two points which are the same spacing are now activating ___ receptive fields. In the Cortex, this will produce activation of a cluster of neighbouring Neurons with no ___ neurons in-between, and therefore, it will be perceived as ___ point(s).

overlapping // non-activated // a single

Pacinian Corpuscle (RA2 afferents) is ___, and responds really well to ___.

extremely sensitive // vibration

The Pacinian Corpuscle can respond to as little as ___ of skin motion as long as its vibrating fast enough, in the range of ___.

10nm // 200Hz

The responses of the Pacinian Corpuscle are ___.

Transient

The Pacinian Corpuscle has an ___ structure which surrounds the ___.

onion-like // unmyelinated nerve ending

When there is stimulation from the outside to the Pacinian Corpuscle, the layers of the onion-like outer bulb contain a ___ which ___ static forces

viscous fluid // dampen

If a probe is pressed into the Pacinian Corpuscle, there will be a ___ as that energy is transmitted to the Mechanoreceptors along the unmyelinated part of the neuron. Then everything settles and that pressure is absorbed, so there's ___ firing. And then when the probe is removed, the layers shift again and cause a disruption to allow the Mechanoreceptors to shift and ___ ion flux, and so then there is a ___ of activity when the probe is removed. This is the ___.

burst // no more // allow // burst // Rapidly Adapting Response

What happens if you remove the onion-skin layers of the Pacinian Corpuscle?

The Transient responses of the axon are changed to sustained responses, and if you put a pressure stimulus on, the neuron keeps firing as long as the stimulus is present, until the probe is removed.

Why do we need to respond to vibration?

This is where the Duplex Theory of Texture Perception comes in.

What does Touch Perception depend on?

Spatial Cues & Temporal Cues

What are Spatial Cues?

This is where objects are pressed into the skin, and we can detect this pressure of the different features of an object.

Spatial Cues are useful for ___ (mainly conveyed by ___).

Tactile Acuity // Merkel Receptors

What are Temporal Cues?

Where objects move as we interact with them, and the movement across the skin creates/transmits vibrations through the skin

The combination of Spatial and Temporal cues for tactile perception is called the ___.

Duplex Theory of Texture Perception

Frequency of vibration is very important because different touch events have ___.

characteristic frequencies

When you’re holding something in your hand, small ___ occur between the object and your skin. This produces skin movement with vibration at ___Hz.

Microslips // 3-40

___ are perfectly suited for detecting Microslips to provide essential feedback to motor control of grip.

RA1 (Meissner Corpuscles) fibres

What is the function of Microslips?

To provide essential feedback to motor control of grip

When ___ frequencies are transmitted to the skin this is usually from when a ___ object is moved over the skin. This is within the range of ___Hz.

higher // textured // 10-500

As long as the ___ is correct, you don't have to be touching the object you are examining.

frequency of vibrations

___ alone are not good for detecting fine textures.

Spatial Cues

When vibrations produced by hand motion are available, texture discrimination ___.

improves

When subjects are not allowed to move their fingers, and can only touch and press their finger into the sandpaper, there is a ___ in the judgement of roughness between the very fine and fine sandpaper.

small difference

If the subjects are allowed to move their fingers over the sandpaper, or have the sandpaper moved over their fingers, the difference in perceived roughness is then magnified, such that the very fine sandpaper feels ___ smoother than the fine sandpaper.

much

___ Studies have been used, using ___ to show the importance of different frequencies of vibration.

Selective Adaptation // Two Alternative Forced Choice Protocol

When Subjects had to determine which sandpaper was rougher without any type of adaptation (as in, no senses vibrated away), what did researchers find?

Subjects guessed correctly 80% of the time

When subjects had to place their hand on a vibrating plate that shook at 10Hz for many minutes, this was to adapt the Meissner Corpuscles (RA1), what did researchers find?

When the RA1 fibres were adapted away, the response was still pretty accurate, and only fell by a few %.

Meissner Corpuscles are for ___, they are detecting ___.

grip aperture control // Microslips

When Subjects were asked to hold their hand over a plate that vibrated at 200Hz to adapt away the Pacinian Corpuscle responses, what did researchers find?

This affected texture perception. When the PC were adapted away, the texture judgement fell to chance, to 50%

Texture discrimination is most affected when the ___ activity are adapted, just as what is predicted by the ___.

Pacinian Corpuscle // Duplex Theory of Texture Perception

What is Passive Touch?

- Where the contact force is provided by an outside source - Subject has objects poked/pressed into their skin - Passive Touch is experienced as a sensation located on the skin - e.g. knife-point = “I feel a pricking sensation on the skin”

What is Active Touch?

Where the contact force is provided by the subject - You’re allowed to move your hands and touch the object in question - Subject controls the pressure, direction, and speed with which the skin is stimulated - Active Touch is experienced as a property of the object - e.g. knife-point = “I feel a pointed object”

What is Haptic Perception?

Haptic Perception is the ability to explore three-dimensional objects with the hand and identify them.

Haptic Perception typically uses ___.

Active Touch

Haptic Perception involves ___, ___, and ___.

Cutaneous Sensory System // Motor System // Cognitive System

What is the Cutaneous Sensory System for in Haptic Perception?

Gives texture, pressure, temperature, finger position from Proprioception

What is the Motor system for in Haptic Perception?

Moving your fingers and hands based on the sensory feedback

What is the Cognitive system for in Haptic Perception?

Matching bottom up information from sensory-motor interactions with top-down information about potential candidates for what object you’re holding (e.g. memory).

Most people can identify common objects in ___ by touch alone. People use a set of ___. Specific movement patterns often give ___ information.

1-2s // stereotypical exploratory procedures // different

Texture info is usually determined by ___ and ___.

Lateral motion // contour following

Shape info can be reconstructed by ___, and ___, where you're grasping the object and getting a sense of its physical size and dimensions.

contour following // enclosure

The sponginess or rigidity of the object you're trying to identify can be explored using ___.

pressure

A combination of ___, ___, and ___ processes are all going on at the same time when exploring an object.

sensory // motor // cognitive

As we move from Mechanoreceptors on the skin, to the Thalamus and Cortex, Cutaneous information is represented in ___ ways (similar to visual and auditory systems).

increasingly complex

Thalamic Neurons in the Ventral Posterior Lateral Nucleus have ___ just like the visual system in the Thalamus.

center-surround receptive fields

There is an excitatory center where touch info would lead to ___ of the ___, and an inhibitory surround which is ___, and would lead to ___ of that neuron.

excitation // Thalamic neuron // antagonistic // inhibition

By the time we get to Primary Somatosensory Cortex, there is even more ___ information.

complex

Neurons in Primate Somatosensory Cortex respond to pressure from an ___ of a ___, and other neurons respond to ___ across the skin in a ___.

elongated edge // specific orientation // motion // specific direction

Neurons in the Primary Somatosensory Cortex have more ___.

advanced responses

Similar to visual neurons in area ___ responding only to particular ___ or ___, neurons in Somatosensory Cortex can be specific for a particular ___.

IT // shapes // objects // shape

Recordings from a Single Neuron in S1 show that the neuron responds ___ when the monkey grasps a ruler with a sharp edge, and responds ___ when the monkey grasps a rounded cylinder

strongly // poorly

Attention modulates Tactile induced activity in ___.

Somatosensory Cortex

___ can affect the firing of S1 neurons in response to ___.

Attention // Tactile stimulation

When the monkey was performing the Tactile attention task, when the letter was rolled over their finger, there was a ___ response of the neuron in the Somatosensory Cortex.

strong

When the monkey was performing the visual task, but the finger pad was stimulated with the exact same pattern of tactile info, there was a ___ response from the neuron in the Somatosensory Cortex.

weak

Why did the monkey have a strong response to the Tactile attention task but a poor response to the Visual attention task even though the bottom-up info was identical?

The monkeys attention was directed to different things in different tasks, so the bottom-up information only activated S1 when the task was appropriate.

The strong effect of attention very early on in Somatosensory processing is very indicative of strong ___.

top-down modulation

In some ways, this attention modulation for touch info seems to be much ___ than attention modulation in vision.

more powerful

Attention modulation for touch info and attention modulation in vision seem to work on ___ mechanism. Important stuff is flagged for ___, and non-important stuff is ___.

the same // amplification // dampened down