Chapter 13: Touch Flashcards Preview

PSYCH 3310: Sensation & Perception > Chapter 13: Touch > Flashcards

Flashcards in Chapter 13: Touch Deck (76):
1

Components of Touch:

Tactile (mechanical displacement of skin)

Temperature

Pain (including itch and tickling)

Kinesthetic body sensations (where body parts are)

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Components of Touch:

Tactile (mechanical displacement of skin)

Temperature

Pain (including itch and tickling)

Kinesthetic body sensations (where body parts are)

3

Components of Touch:

Tactile (mechanical displacement of skin)

Temperature

Pain (including itch and tickling)

4

Proprioception

Perception mediated by kinesthetic and vestibular receptors

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Somatosensation

A collective term for sensory signals from the body (also includes vestibular system).

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skin

Largest sensory organ

About 1.8 square meters (19 square feet)

About 4 kg (9 pounds)

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Touch receptors

Embedded in outer layer (epidermis) and underlying layer (dermis) of skin

Multiple types of touch receptors

Each touch receptor can be categorized by 3 criteria:
1. Type of stimulation to which the receptor responds
2. Size of the receptive field
3. Rate of adaptation (fast versus slow)

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Each touch receptor can be categorized by 3 criteria:

1. Type of stimulation to which the receptor responds

2. Size of the receptive field

3. Rate of adaptation (fast versus slow)

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Each touch receptor can be categorized by 3 criteria:

1. Type of stimulation to which the receptor responds

2. Size of the receptive field

3. Rate of adaptation (fast vs. slow)

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Merkel cell neurite complex

SA I

Located at boundary between epidermis and dermis.

Responds best to steady downward pressure.

Small receptive field size

Used to detect fine spatial detail.

Sensitive to very low frequency of vibrations (

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SA I

Merkel cell

12

Meissner corpuscles

FA I

Located at boundary between epidermis and dermis.

Sensitive to low frequency vibrations between 5 Hz and 50 Hz.

Fast adapting (FA I).

Small receptive field size.

Important to detect slip of objects across skin.
E.g. to correct grip around object.

When stimulated electrically, people feel “wobble” or “flutter.”

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FA I

Meissner corpuscles

14

Ruffini Endings

SA II

Embedded deeply in the dermis.

Responds best to sustained downward pressure and lateral skin stretch.

Responds to finger position and grasp.

Slowly adapting (SA II).

Large receptive field size.

When stimulated, people experience no tactile sensation.

More than one SA II fiber needs to be stimulated in order to be detectable.

15

Ruffini Endings

SA II

Embedded deeply in the dermis.

Responds best to sustained downward pressure and lateral skin stretch.

Responds to finger position and grasp.

Slowly adapting (SA II).

Large receptive field size.

When stimulated, people experience no tactile sensation.

More than one SA II fiber needs to be stimulated in order to be detectable.

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SA II

Ruffini Endings

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Pacinian Corpuscles

FA II

Embedded in subcutaneaous tissue.

Respond best to high frequency vibrations of 50 – 700 Hz.

Active when object makes first contact with skin.
E.g., mosquito landing on skin, or hitting key on keyboard.

Fast adapting (FA II).

Large receptive field size.

When electrically stimulated, people report “buzz.”

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Slow Adapting

Merkel & Ruffini

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Fast Adapting

Meissner & Pacinian

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Small Receptive Field

Merkel & Meissner

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Large Receptive Field

Ruffini & Pacinian

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Texture Perception

Merkel

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Pattern/Form Detection

Ruffini

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Texture Perception

Merkel

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Pattern/Form Detection

Merkel

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Finger Position, Stable Grasp

Ruffini

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Small Receptive Field

Merkel & Meissner

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Low-Frequency Vibration Detection

Meissner

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High-Frequency Vibration Detection

Meissner

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Pacinian Corpuscles

FA II

Embedded in subcutaneaous tissue.

Respond best to high frequency vibrations of 50 – 700 Hz.

Active when object makes first contact with skin.
E.g., mosquito landing on skin, or hitting key on keyboard.

Fast adapting (FA II).

Large receptive field size.

When electrically stimulated, people report “buzz.”

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FA II

Pacinian Corpuscles

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High-Frequency Vibration Detection

Pacinian

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Kinesthetic receptors

Play important role in sense of where limbs are and what kinds of movements are made.

Muscle Spindles: Convey the rate at which the muscle fibers are changing in length.

Receptors in tendons provide signals about tension in muscles attached to tendons.

Receptors in joints react when joint is bent to an extreme angle.

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Muscle Spindles

Convey the rate at which the muscle fibers are changing in length.

Receptors in tendons provide signals about tension in muscles attached to tendons.

Receptors in joints react when joint is bent to an extreme angle.

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Importance of kinesthetic receptors:

Strange case of neurological patient Ian Waterman:

Cutaneous nerves connecting Waterman’s kinesthetic mechanoreceptors to brain destroyed by viral infection.

Lacks kinesthetic senses, dependent on vision to tell limb positions.

Watch BBC documentary: http://www.youtube.com/watch?v=bGlZpZgwnAc

36

Thermoreceptors

Sensory receptors that signal information about changes in skin temperature

Two distinct populations of thermoreceptors:
warmth fibers and cold fibers

Body is constantly regulating internal temperature.

Thermoreceptors respond when you make contact with an object warmer or colder than your skin.

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typical skin temperature

30-36 C, 86-96 F)

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Nociceptors

Sensory receptors that transmit information about noxious (painful) stimulation that causes damage or potential damage to the skin.

Two groups of nociceptors:

A-delta fibers:
Fast transmission to brain.
Respond to strong pressure (crushing) and heat.
Initial and quick sharp burst of pain at injury time.

C fibers:
Slower response, sustained stimulation.
Throbbing sensation that evolves after initial surge of pain.

Remember: A before C

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A-delta fibers

Fast transmission to brain.

Respond to strong pressure (crushing) and heat.

Initial and quick sharp burst of pain at injury time.

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C fibers

Slower response, sustained stimulation.

Throbbing sensation that evolves after initial surge of pain.

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Benefit of pain perception:

Sensing dangerous objects (hot pots in the kitchen).

Case of “Miss C”:
Born with insensitivity to pain,
could not protect herself, did not sneeze or cough.
Died at age 29 from untreated infection.

This is a HUGE problem for diabetic patients, who often loose sensation of their feet and become invalids because of untreated minor injuries.

diabetic feet rot and gangrene because no pain sensation make injuries such as blisters or cuts or twisted ankles go UNTREATED.
Diabetics lose ability to walk.

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Responses to noxious stimuli

Responses to noxious stimuli can be moderated by anticipation, religious belief, prior experience, watching others respond, and excitement

Example: Wounded soldier in battle who does not feel pain until after battle.

Real-world application for managing pain:
http://www.youtube.com/watch?v=jNIqyyypojg

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Analgesia

Decreasing pain sensation during conscious experience

Soldier in example:
Experienced effect because of endogenous opiates—chemicals released in body to block release or uptake of neurotransmitters transmitting pain sensation to brain.

Endogenous opiates may be responsible for certain placebo effects.

Externally produced substances have similar effect:
Morphine, heroin, codeine

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The more synapses, the more chances we get at blocking the transmission of pain, by inhibiting the release of neurotransmitters along those synapses.

Morphine, heroin, and codeine DO NOT DEAL with the CAUSES of pain.

Ibuprofen, aspirin, and acetaminophen DO (they prevent the nociceptors receptors from firing in the first place).

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Gate control theory

A description of the system that transmits pain that incorporates modulating signals from the brain.

Feedback circuit located in Dorsal Horn of spinal cord.

Gate neurons that block pain transmission can be activated by extreme pressure, cold, or other noxious stimulation applied to another site distant from the source of pain.

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Touch sensations travel as far as 2 meters to get from skin and muscles of feet to the brain!

Information must pass through spinal cord = First Synapse

Axons of various tactile receptors combine into single nerve trunks.

Several nerve trunks from different areas of body.

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Once in spinal cord, two major pathways:

Spinothalamic:
- Slower, evolutionary older
- Heat and pain
- Multiple synapses = slower

Dorsal-column-medial-lemniscal: - Faster
- Tactile and proprioceptive information
- Fewer synapses = fast transmission

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Spinothalamic

- Slower, evolutionary older

- Heat and pain

- Multiple synapses = slower

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Once in spinal cord, two major pathways:

Spinothalamic:
- Slower, evolutionary older
- Heat and pain
- Multiple synapses = slower

Dorsal-column-medial-lemniscal:
- Faster
- Tactile and proprioceptive information
- Fewer synapses = fast transmission

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Dorsal-column-medial-lemniscal

- Faster

- Tactile and proprioceptive information

- Fewer synapses = fast transmission

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Spinothalamic

- Slower, evolutionary older

- Heat and pain

- Multiple synapses = slower

Several synapses in spinal chord

Slower information transmission

Provides mechanisms for pain inhibition

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Dorsal-column-medial-lemniscal

- Faster

- Tactile and proprioceptive information

- Fewer synapses = fast transmission

Synapse in Cuneate and Gracile nuclei, then ventral posterior nucleus of thalamus, then somatosensory area 1 (S1), somatosensory area 2 (S2)

Wider axons

Fewer synapses

Faster information transmission

Used for planning & execution of fast movements

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somatosensory details:
sleep

Remember that THALAMUS is mostly SHUT down during sleep, so somatosensory information about mild tactile sensations and limb movement is NOT passed to the BRAIN.

You don’t notice moving or the contact with your sheets.

54

Touch sensations are represented somatotopically in the brain:

Primary somatosensory cortex called S1; secondary somatosensory cortex called S2

Analogous to retinotopic mapping found in vision

Adjacent areas on skin connect to adjacent areas in brain

Homunculus:
Maplike representation of regions of the body in the brain.

Brain contains several sensory maps of the body in different areas of S1 and S2

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Homunculus

Maplike representation of regions of the body in the brain.

56

Touch sensations are represented somatotopically in the brain:

Primary somatosensory cortex called S1.
Secondary somatosensory cortex called S2.

Analogous to retinotopic mapping found in vision.

Adjacent areas on skin connect to adjacent areas in brain.

Homunculus:
Maplike representation of regions of the body in the brain.

Brain contains several sensory maps of the body in different areas of S1 and S2.

57

How sensitive are we to mechanical pressure?

Max von Frey (19th century) developed elegant way to measure this, using carefully calibrated stimuli:
Horse and human hairs.

Modern researchers:
Use nylon monofilaments of varying diameters.

Find a hair (or pluck one from your head), and try detecting a poke of your hair on your lips (easy), versus your thighs or upper arm or sole of your feet.
Try your thumb or different spots on the back of your hand.
You will feel differences on those surfaces.

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Homunculus

Maplike representation of regions of the body in the brain.

NOTE THE DISTORTIONS in the humunculus:
Bigger representations for more important parts of the body: THUMB > hip or leg
Lips > hand or neck (who cares about the neck!)

NOTE the DISCONTINUITY: next to hand is FACE!!!
This leads us to the phantom limb.

59

How sensitive are we to mechanical pressure?

Max von Frey (19th century) developed elegant way to measure this, using carefully calibrated stimuli:
Horse and human hairs.

Modern researchers:
Use nylon monofilaments of varying diameters.

Find a hair (or pluck one from your head), and try detecting a poke of your hair on your lips (easy), versus your thighs or upper arm or sole of your feet.
Try your thumb or different spots on the back of your hand.
You will feel differences on those surfaces.

60

2-point touch thresholds are determined primarily by _____

the concentration and receptive-field sizes of tactile receptors in an area of the skin.

The minimal separation between 2 points needed to perceive them as separate when the points are applied at different sites on the body

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How finely can we resolve temporal details?

2 tactile pulses can be delivered over time, in a manner analogous to spatially separated 2-point threshold stimuli.

Touch: Sensitive to time differences of only 5 ms

Vision: Sensitive to time differences of 25 ms

Audition: Sensitive to time differences of 0.01 ms!

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How finely can we resolve temporal details?

2 tactile pulses can be delivered over time, in a manner analogous to spatially separated 2-point threshold stimuli.

Touch: Sensitive to time differences of only 5 ms

Vision: Sensitive to time differences of 25 ms.

Audition: Sensitive to time differences of 0.01 ms!

63

Phantom limb:

Perceived sensation from a physically amputated limb of the body.

Parts of brain listening to missing limbs not fully aware of altered connections, so they attribute activity in these areas to stimulation from missing limb.

Remember how close the hand was to the face?

Patients report feeling their missing hand OVER their face.

Real PAIN might be felt if they perceive their phantom limbs to be in uncomfortable positions.

64

Haptic perception:

Knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration.

ACTIVITY in mechanoreceptors is CRUCIAL to maintain our grasp of objects.

If anestheszied, we drop them even if we can look at them and feel the postion of our fingers and hand.

65

Haptic Perception....

Action for perception:
Using our hands to actively explore the world of surfaces and objects outside our bodies.

Exploratory procedure:
A stereotypical hand movement pattern used to contact objects in order to perceive their properties; each exploratory procedure is best for determining one or more object properties.

Example: To determine roughness of an object, use lateral motion

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Haptic Perception:
The What system of touch:

Geometric properties of objects are most important for visual recognition.

Material properties of objects are crucial for haptic recognition.

Two-dimensional pictures of objects are recognized easily visually but poorly haptically

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Haptic Perception:
The What system of touch:

Geometric properties of objects are most important for visual recognition.

Material properties of objects are crucial for haptic recognition.

Two-dimensional pictures of objects are recognized easily visually but poorly haptically.

68

LEGO perception

Cross modal LEGO perception (vision-haptic) performance better when stimuli are rotated 180 degrees.
Newell et al., (2001)

Perceptual equivalence between vision and touch is complexity dependent.

69

Tactile agnosia:

The inability to identify objects by touch.

Caused by lesions to the parietal lobe.

Patient documented by Reed & Caselli (1994):
Tactile agnosia with right hand but not left hand.
Could not recognize objects such as a key chain in right hand, but could with left hand or visually.
Other sensory abilities were normal in both hands.

70

Haptic perception of tabletop space

Task: Adjust left rod so that it is parallel to the right rod.

Result: Error by 40 degrees on average!

71

Body image:

The impression of our body in space

Our body image is highly changeable

It is possible to induce an out-of-body experience:

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Body image:

The impression of our body in space

Our body image is highly changeable

It is possible to induce an out-of-body experience:


Laboratory-induced out of body experience:http://www.youtube.com/watch?v=8oF8sQvnTlM

Rubber hand illusion video:http://www.youtube.com/watch?v=sxwn1w7MJvk

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Social Touch

The influence of touch can extend beyond perception and action in surprising ways.

Incidental touch can influence social judgments.
(Ackerman, Nocera, and Bargh, 2010).

Job candidates whose resumes were on heavy clipboards were judged to be more serious about the job.

People sitting in hard chairs while judging employees see them as more stable and less emotional than when they make the judgments in soft chairs.

74

Haptic virtual environments

A synthetic world that may be experienced haptically by operation of an electromechanical device that delivers forces to the hand of the user

Virtual surgery:
Efforts are underway to perfect force-feedback devices to allow surgeons to practice complex procedures or conduct remote operations via the Internet

75

Haptic virtual environments

A synthetic world that may be experienced haptically by operation of an electromechanical device that delivers forces to the hand of the user.

Virtual surgery:
Efforts are underway to perfect force-feedback devices to allow surgeons to practice complex procedures or conduct remote operations via the Internet

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A virtual surgical trainer

A novice surgeon receives high-precision graphics and force feedback about a blood vessel that is being repaired.