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Chapter 12

PSYB51H3 Chapter Notes - Chapter 12: Bony Labyrinth, Angular Acceleration, Vestibular System


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
12

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PSYB51: Perception and Cognition Clara Rebello
PSYB51 Chapter 12: The Vestibular System and Our Sense of
Equilibrium
When you spin around until you feel dizzy
oYour dizziness arose from contributions of the vestibular organs to your sense of
equilibrium
oVestibular organs: The set of five sense organs (three semicircular canals and two
otolith organs) located in each inner ear that sense head motion and head orientation
with respect to gravity
oEquilibrium: Our vestibular sense comprised of spatial orientation perception
(encompassing our perception of linear motion, angular motion, and tilt), combined
with reflexive vestibular responses like posture, vestibule-autonomic reflexes, and
vestibule-ocular reflexes
oThe senses of tilt and self-motion comprise our sense of spatial orientation: A sense
consisting of 3 interacting modalities
Perception of linear motion
Angular motion
Tilt
Vestibular system: The vestibular organs and the neural pathways directly associated with these
sense organs
oContributes to clear vision when we move and helps us maintain balance when we stand
The fundamental nature of this system is emphasized by the fact that the vestibular organs
appeared very early in evolutionary history and have remained relatively unchanged
oVestibular perception is often relegated to the attentional background, and many
responses evoked by the vestibular system are reflexive
oOnly when we experience problems like dizziness, vertigo, spatial disorientation,
imbalance, blurred vision, illusory self-motion are we likely to become more aware of
our equilibrium sense
Vertigo: A sensation of rotation or spinning  Term often used more generally to mean any form
of dizziness
oAristotle didn’t include equilibrium or vestibular sense when he catalogued our sensory
systems  Why?
It wasn’t until the 19th century that scientists understood that the vestibular
system is a specialized set of sense organs
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PSYB51: Perception and Cognition Clara Rebello
Until then, the vestibular system had been considered an entrance to the
cochlea
Not entirely satisfactory explanation  Aristotle had catalogued other senses
without detailed anatomical or physiological knowledge
Another explanation  Inconspicuous nature of the vestibular sense (vestibulo-
ocular reflex VOR: A shot-latency reflex that helps stabilize vision by
counterrotating the eyes when the vestibular system sense head movement)
You don’t typically perceive your head motion, because the vestibular system usually performs
its job automatically (little conscious awareness)
Vestibular Contributions to Equilibrium
The vestibular system makes crucial contributions to balance but doesn’t provide the sensory
foundation for balance
oKinesthesia does
oBalance: The neural processes of postural control by which weight is evenly distributed,
enabling us to remain upright and stable
It also helps stabilize our eyes during head motion
oMakes crucial contributions to clarity of sight but doesn’t provide the sensory
foundation
Our eyes and visual system do
Also helps maintain blood flow to the brain via contributions to cardiac regulation but isn’t
foundational there
oSomatosensation is
Our equilibrium sense combines information flowing from our brain to our muscles with
information flowing inward to the brain from various sensory systems (especially the
kinesthetic, visual, and vestibular systems)
oKinesthetic: Perception of the position and movement of our limbs in space
oActive sensing balances information derived from efferent commands flowing outward
from the brain to the periphery with information from various afferent signals flowing
from sensors inward to the brain
Active sensing: Sensing that includes self-generated probing of the environment
 Humans (vision, touch, equilibrium), animals (includes the use of echoes by
whales and bats, the use of electrical signals by some fish, and the use of
whiskers/antennae)
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PSYB51: Perception and Cognition Clara Rebello
Efferent commands: Information flowing outward from the central nervous
system to the periphery  Example: motor commands that regulate muscle
contraction
Afferent signals: Information flowing inward to the central nervous system from
sensors in the periphery  Passive sensing would rely exclusively on such
sensory inflow, providing a traditional view of sensation
Our equilibrium is composed of many fundamental reflexes and perceptual modalities, but the
vestibular system doesn’t exclusively provide the sensory foundation for any perceptual
modality
Modalities and Qualities of Spatial Orientation
Our perception of spatial orientation includes 3 sensory modalities
oSense of angular motion: Perceptual modality that senses rotation
oSense of linear motion: Perceptual modality that senses translation
oSense of tilt: Perceptual modality that senses head inclination with respect to gravity
Why are they called modalities?
oKey lies in the energy transduced: To convert from one form of energy to another
oColour and brightness are different interpretations of the same energy (qualities)
oSeeing and hearing  Perceiving angular motion, linear motion, and tilt requires that 3
different stimuli (angular acceleration, linear acceleration, gravity) be transduced
Semicircular canal: Any of three toroidal tubes in the vestibular system that sense angular
motion
oSenses angular acceleration: The rate of change of angular velocity
oThis signal makes a predominant contribution to our sense of angular motion
Otolith organs: Either of two mechanical structures (utricle and saccule) in the vestibular system
that sense both linear acceleration and gravity
oThey transduce both linear acceleration (The rate of change of linear velocity) and
gravity
oProvide a predominant contribution to sense of head tilt and to sense of linear motion,
also referred to as sense of translation
The semicircular canals and otolith organs establish at least two sensory modalities
oPerception of tilt results from the brain’s estimate of orientation with respect to gravity,
and perception of linear motion results from the brain’s estimate of linear acceleration
oTilt perception is fundamentally different from translation perception
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