Lecture 24 - Touch and Pain Perception

Question 1

haptic perception

Answer 1

how we perceive objects through touch

going to involve 3 different systems:

1) sensory system (touch and pain)
2) motor system (movement and kinesthesis)
3) cognitive system (top-down info: what we think we should be feeling based on experience)

Question 2

Humans use____ rather than passive touch to interact with the environment.

Answer 2

active

Question 3

Psychophysical research
shows that people can
identify objects haptically in

Answer 3

one to two seconds.

Question 4

Klatzky et al. (1985) have
shown that people use
exploratory procedures
(EPs):

Answer 4

– Lateral motion
– Pressure
– Enclosure (grasping)
– Contour following

used ubiquitously: we use them for any type of object

Question 5

The firing pattern of groups of mechanoreceptors (mainly

Merkel receptors) signals…

Answer 5

… shape, such as the curvature of an object, or directions of motion.

if someone takes the pad of their finger and roll their finger over a small or large object there are different firing rates: small object, with sharper curvature = narrower firing pattern because it’s getting less lateral inhibition

feedback from the system coactivates cells at the periphery

more cells acting around the central cell: center surround cell organization

Question 6

Perceiving objects: design consideration

Answer 6

The use of piezo actuators in smartphones adds tactile feedback to handheld devices.

Adding haptic information:
• Decreases typing errors
• Reduces cognitive loading on other sensory channels (if you feel the tapping you don’t have to be as visually aware
• Allows more interface options

Question 7

tactile feedback

Answer 7

vibrating smartphone: giving you feedback that something is happing to the object

higher resolution of vibrations give specific feedback

videogames

secondary source of info that you can coordinate with vision or audition

Question 8

High definition haptics ….

Answer 8

….will go beyond simple vibration notification and provide more realistic tactile effects
(likely by manipulating rapid adapting mechanoreceptors).

use faster frequencies (vibration rates)

active diff cells to use greater ability to use the feedback

Question 9

Using ultrasound to create volumetric haptic shapes

Answer 9

• Uses acoustic radiation force (nonlinear effects of sound) to generate tactile feedback on skin.
• Frequency and amplitude of sound waves are focused to produce targeted sensations.
• Only works on the hands.

Question 10

Perceiving objects: Hierarchical representation

Answer 10

• As signals move forward from the mechanoreceptors (and thalamus), they become more complex.
• Cells in the Monkey’s thalamus show center-surround fields, as we saw in vision. As noted before, these retain a
somatotopic organization (areas nearby on the skin are represented near one-another in the thalamus).
• [Recall how this might affect your two-point acuity.]

Question 11

In somatosensory cortex, single cell recordings indicate…

Answer 11

….some cells respond maximally to orientations of stimuli and direction of movement.
• This is much like the simple and complex cells of vision.

orientation tuning curve

converge in a similar way to complex cells in vision: this kind of organize is preserved across modalities

Question 12

Monkey’s somatosensory and parietal association cortices also show neurons that respond best to ….

Answer 12

….grasping specific objects.

as you’re grasping them or INTENDING to grasp them
—> Before you grasp, you need to make a hand movement to fit the object. (TOP DOWN INFO)

cells more active when monkey reaching or intending to grasp: it’s not just physical contact BUT the intention to interact with it (when they recognize the object these cells are activated): because you’re anticipating how you’re going to grasp the object

Question 13

Although many types of mechanoreceptors will contribute to identifying an object, which receptor type might be most
involved with detecting the use and feel of a particular object?

Answer 13

corrdinated motor activity: position, action (a little bit like kinesthesis)

Ruffini cylinders!!!!

Question 14

Paying attention to the task

Answer 14

… increases the firing rate of somatosensory cells.

• Neurons in S1 may respond to stimulation of the receptors, but attending to the task increases that response.
• In the task below, ignoring the tactile information inhibited the response to a stimulus presented to a monkey’s finger.

Question 15

As you’re attending to how touch feels

Answer 15

you’re gunna be more accurate and more responsive : increases activity in cortical areas

Question 16

Skin uses pain receptors as a threat detection system:

Answer 16

“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

• Importantly, we don’t all experience or perceive it in the same way or to the same degree (diff thresholds), so we don’t show the behavioral aspects in the same way.

Question 17

homeostasis

Answer 17

maintaining equilibrium of bodily responses

Question 18

what is pain?

Answer 18

is a multimodal phenomenon containing a sensory component and an affective or emotional/cognitive
component.

you’re previous state all effects your perception of pain

the sensation is not enough, the interpretation (cognitive or emotional element) is essential

Question 19

The threshold for pain detection

Answer 19

must be balanced to warn of potential damage, but not respond to normal activity (don’t want everything to feel painful)

you don’t have to feel searing pain before you respond

Question 20

People with Congenital Insensitivity to Pain (CIP)

Answer 20

don’t experience pain and can unintentionally injure
themselves while performing normal activities.

lack a certain protein that allows pain receptors to function: no internal or external discomfort

pretty rare

Question 21

Sensory Processing Disorder (SPD)

Answer 21

can result when an individual is too sensitive to common sensations.

more common

can be global (sounds, touch, light) or modal (just one modality, like touch)

Question 22

Classic types of pain:

Answer 22

1) Nociceptive
2) Inflammatory pain
3) Neuropathic pain
4) Social pain

not exclusive categories: can interact with each other

Question 23

Nociceptive

Answer 23

signals when there is currently damage being done to the skin or it’s approaching damage to the skin

These signal impending damage to the skin.
• Specific nociceptors respond to heat, chemicals, severe
pressure, and cold (pulling hand away from a hot stove).

• These typically trigger a protective (withdrawal) response.

Question 24

Inflammatory pain

Answer 24

caused by damage or irritation within tissues
and joints.

• Additionally, infections or injury associated with immune responses make nociceptors more responsive (Hyperalgesia)
• Tumor cells (release toxins in the tissue causing immune response that makes the nociceptors more responsive: lowers the threshold of pain)

Question 25

Hyperalgesia

Answer 25

infections or injury associated with immune responses make nociceptors more responsive

Question 26

Neuropathic pain:

Answer 26

caused by damage to the central nervous system (axons transmitting info or in the actual cortex), including:

• Brain damage caused by stroke
• Repetitive movements which cause conditions like carpal tunnel syndrome

Question 27

social pain

Answer 27

This is perceived pain resulting from interactions with other
people (or lack thereof).

• Sometimes called ‘psychological’ or ‘mental’ pain.
• Typical cases involve depression and social rejection.
• No tissue damage, but a strong affective (aversive) element.

• May be linked to subsequent damage (e.g. self-injury,
autoimmune responses, fibromyalgia, etc.).

• Usually studied separately from the other 3 varieties of pain.

Question 28

direct pathway model of pain

Answer 28

you have these nociceptors looking for threats in the environment, as soon as they interact with that stimulus you get a withdrawl response (stimulus then response)

Question 29

Problems with direct pathway model of pain :

Answer 29

1. Pain can be affected by a person’s mental state.
   – If you are happy, you are more tolerant of pain.
2. Pain can occur when there is no stimulation of the skin.
   – Phantom limbs cause pain or pain may be ‘referred’ to another location.
3. Pain can be affected by a person’s attention.
   – If you are unaware of an injury, you may ignore the pain.