Chapter 12: Spatial Orientation and the Vestibular System Flashcards Preview

PSYCH 3310: Sensation & Perception > Chapter 12: Spatial Orientation and the Vestibular System > Flashcards

Flashcards in Chapter 12: Spatial Orientation and the Vestibular System Deck (31)
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1
Q

Vestibular organs

A

Set of 5 organs
— 3 semicircular canals
— 2 otolith organs

Located in each inner ear.

Sense head motion and head orientation with respect to gravity

Also called the “vestibular labyrinth” or the “vestibular system”

An often overlooked sense:
The vestibular “sixth sense”
Evolutionarily very old

2
Q

The vestibular organs help us in many ways:
Provide a sense of spatial
Allow for the vestibulo-ocular reflex
Stabilizes visual input by counter rotating the eyes to compensate for head movement

A

Provide a sense of spatial orientation, consisting of

  • Linear motion
  • Angular motion
  • Tilt

Allows for the Vestibulo-Ocular Reflex:
Stabilizes visual input by counter rotating the eyes to compensate for head movement

3
Q

vestibulo-ocular reflex

A

Stabilizes visual input by counter rotating the eyes to compensate for head movement

4
Q

Semicircular canals

A

The 3 toroidal tubes in the vestibular system that sense angular acceleration, a change in angular velocity

5
Q

Otolith organs

A

The mechanical structures in the vestibular system that sense both linear acceleration and gravity.

Source of our sense of linear velocity and gravity

6
Q

The vestibular organs do not respond to constant velocity

A

They only respond to changes in velocity, aka acceleration

7
Q

Push-pull symmetry

A

Hair cells in opposite ears respond in a complementary fashion to each other

When hair cells in the left ear depolarize, those in the analogous structure in the right ear hyperpolarize

8
Q

Coding of direction in the semicircular canals

A

3 semicircular canals in each ear

Each canal is oriented in a different plane

Each canal is maximally sensitive to rotations perpendicular to the canal plane

9
Q

Hair cell responses

A

In the absence of stimulation, hair cells release neurotransmitter at a constant rate

When hair cell bundles bend, change in hair cell voltage is proportional to the amount of deflection

Bending toward tallest stereocilia: Depolarization

Bending away from tallest stereocilia: Hyperpolarization

Hair cells increase firing to rotation in one direction and decrease firing to rotation in the opposite direction

10
Q

Semicircular canals

A

Each one is about 3/4 of a toroid (donut) shape, measuring 15mm long and 1.5mm in diameter

Canals are filled with a fluid called perilymph

A second, smaller toroid is found inside the larger toroid, measuring 0.3mm in diameter

Formed by a membrane filled with fluid called endolymph

Cross section of each canal swells substantially near where the canals join the vestibule: Ampulla

11
Q

Ampulla

A

Cross section of each canal swells substantially near where the canals join the vestibule

12
Q

Semicircular canals (cont’d)

A

Within the endolymph space of each ampulla is the crista

When the head rotates, the inertia of the endolymph causes it to lag behind, leading to tiny deflections of the hair cells

13
Q

Cristae

A

The specialized detectors of angular motion located in each semicircular canal in a swelling called the ampulla

Each crista has about 7000 hair cells, associated supporting cells, and nerve fibers

Cilia of hair cells project into jellylike cupula which forms an elastic dam extending to the opposite ampulla wall, with endolymph on both sides of dam.

14
Q

Semicircular canal dynamics

A

Canal afferent neurons are sensitive to back and forth rotations of the head, as well

Greatest sensitivity to rotations at 1 Hz or less

Faster rotations than 1 Hz would be dangerous

Firing rate goes up and down as the head rotates back and forth

The overall normalized amplitude of the canal neuron response scales with head rotation frequency

15
Q

Otolith

A

Otolith organs sense acceleration and tilt

There are 2 otolith organs in each ear:
Utricle: Contains about 30,000 hair cells
Saccule: Contains about 16,000 hair cells

Each organ contains a macula: A specialized detector of linear acceleration and gravity

16
Q

Utricle

A

Contains about 30,000 hair cells

17
Q

Saccule

A

Contains about 16,000 hair cells

18
Q

macula

A

Each Otolith organ contains a macula:
A specialized detector of linear acceleration and gravity.

Each macula is roughly planar and sensitive primarily to shear forces

19
Q

Hair cells

A

encased in a gelatinous structure that contains calcium carbonate crystals called otoconia (“ear stones” in Greek)

20
Q

Coding of amplitude in the otolith organs

A

Larger accelerations (or larger gravitational shear forces) move the otolith organ’s otoconia more

This leads to greater deflection of the hair cell bundles

Change in receptor potential is proportional to magnitude of linear acceleration or gravitational shear

21
Q

3 experimental paradigms are typically used to investigate spatial orientation perception:

A

Threshold estimation:
What is the minimum motion needed to correctly perceive motion direction?

Magnitude estimation: Participants report how much (e.g., how many degrees) they think they tilted, rotated, or translated.

Matching:
Participants are tilted and then orient a line with the direction of gravity.
This is done in a dark room with only the line visible to avoid any visual cues to orientation.

22
Q

Threshold estimation:

A

What is the minimum motion needed to correctly perceive motion direction?

23
Q

Magnitude estimation:

A

Participants report how much (e.g., how many degrees) they think they tilted, rotated, or translated.

24
Q

Matching:

A

Participants are tilted and then orient a line with the direction of gravity.

This is done in a dark room with only the line visible to avoid any visual cues to orientation.

25
Q

Rotation perception

A

At first, constant rotation (in the dark) is perceived accurately

Soon, however, subjects feel as if they are slowing down

After 30 seconds, they no longer feel as if they are rotating

Time course of habituation for perceived velocity is slower than time course of habituation for velocity neurons:
“Velocity storage”

When rotation stops, subjects feel as if they are rotating in the opposite direction

26
Q

Vestibulo-ocular reflexes (VORs):

A

Counter-rotating the eyes to counteract head movements and maintain fixation on a target

VORs are accomplished by 6 oculomotor muscles that rotate the eyeball

27
Q

Angular VOR:

A

The most well-studied VOR

Example: When the head turns to the left, the eyeballs are rotated to the right to partially counteract this motion

28
Q

Torsional eye movements:

A

When the head is rolled about the x-axis, the eyeballs can be rotated a few degrees in the opposite direction to compensate

29
Q

“The Spins”

A

Ingesting a great deal of alcohol in a short amount of time causes alcohol to quickly enter the bloodstream

The alcohol causes the cupula to become lighter than the surrounding endolymph.

This causes the system to become sensitive to gravity in addition to rotational acceleration.

30
Q

Visual–vestibular integration

A

Vection: An illusory sense of self motion produced when you are not, in fact, moving

Example: The feeling of flying while watching an IMAX movie

Example: Being stopped in your car at a light next to a semi. The semi begins to roll forward and you press on the brake because you feel as if you are rolling backwards

Sometimes a mismatch between visual and vestibular information can cause motion sickness

31
Q

Since the vestibular system has such a widespread influence, what happens when it fails?

A

Possible problems:

Spatial disorientation
Imbalance
Distorted vision unless head is held perfectly still
Motion sickness
Cognitive problems