Proprioception: Balance and Phantom Limbs

26 Visual Contributions to Balance

Learning Objectives

Be able to define optic flow.

Understand what information optic flow provides that the vestibular system cannot.

The utricle and the saccule sense head position, and the semicircular canals sense head movement, but balance is affected by more than just vestibular information. Both proprioceptive information (pressure sensors and kinesthetic information) and visual information become integrated and contribute to our sense of balance. Yet there is no place in the cerebral cortex that has been discovered thus far as being dedicated to interpreting balance. There are, however, vestibular nuclei in the brainstem (near the 4th ventricle and brainstem) that receive vestibular information as well as proprioceptive and optic flow information.

Optic flow is the perceived visual motion of objects as the observer moves relative to them. To an observer driving a car, a sign on the side of the road would move from the center of their vision to the side, growing as they approached. If they had 360 degree vision, this sign would proceed to move quickly past their side to their back, where it would shrink. This motion of the sign is its optic flow.

 

Fig.3.6.1. Optic flow gives these planets the illusion of passing by as the image approaches the point of expansion. (Credit: Jarod Davis. Provided by: University of Minnesota. License: CC-BY SA 4.0)

This allows a person to judge how close they are to certain objects, and how quickly they are approaching them. It is also useful for avoiding obstacles: if an object in front of an observer appears to be expanding but not moving, they are probably headed straight for it, but if it is expanding but moving slowly to the side, they will probably pass by it. Since optic flow relies only on relative motion, it remains the same when they are moving and the world remains still, and when they are standing still but everything they can see is moving past them. These properties have made the concept useful for robot designers writing visual navigation routines. It also appears to be used by certain insects, especially flying ones, where a large optic flow (indicating a quickly approaching obstacle) triggers muscles to move away.

When moving in a particular direction, an observer’s optical flow field expands from a singular point, called the focus of expansion (Fig.3.6.1). This point of expansion tells us our heading; this is the one place in our visual field where there is no motion when we’re moving (because we’re moving straight toward it).

Optic flow thus provides us with information concerning coordinated motion in the visual field. Whereas semicircular canals respond to rotations and otolithic organs (utricle, saccule) sense linear accelerations—thus contributing to our sense of balance—optic flow tells us about our motion when we’re not accelerating (i.e., when our vestibular and kinesthetic information is useless).

 

Exercises

  1. True or False: Balance is only affected by vestibular information.
  2. True or False: Optic flow applies when you are moving, and the world remains still, rather than when you are still, and the world is moving.
  3. True or False: Optic flow helps someone determine how quickly an object is moving towards them.
  4. Vestibular nuclei in the brainstem receive what kind of information?
    A. Proprioceptive Information
    B. Vestibular information
    C. Optic Flow Information
    D. All of the above
  5.  One example of optic flow is blank:
    A. When you are able to detect an object from your peripheral vision
    B. When you sit in front of a non-moving wall and stare at it
    C. When you’re sitting in a car and a train passes by, and the world around you (trees, buildings, etc.) appears to be moving backwards
    D. When you lose your balance after you close your eyes and spin in a circle
  6. Optic flow is necessary for balance because blank:
    A. When we are not accelerating, our vestibular and proprioceptive information is useless
    B. It sends signals to our brain when our eyes get fatigued, causing imbalance
    C. It provides us with information concerning where light is coming from in the visual field
    D. Its purpose is to determine what size a non-moving object is when the object is 5 feet or closer

 

Answer Key:

  1. False.
  2. False.
  3. True.
  4. D.
  5. C.
  6. A.

 

CC LICENSED CONTENT, SHARED PREVIOUSLY

Psychology Wiki, Optic Flow.
Provided by:  Wikipedia
URL: https://psychology.wikia.org/wiki/Optic_flow
License: CC-BY-SA 3.0

CC LICENSED CONTENT, SHARED PREVIOUSLY
Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
Download for free at http://vision.psych.umn.edu/users/caolman/courses/PSY3031/
License of original source: CC Attribution 4.0
Adapted by: Nika Khadem

References:
Huston, S. J., & Krapp, H. G. (2008). Visuomotor Transformation in the Fly Gaze Stabilization System. PLoS Biology, 6(7). doi: 10.1371/journal.pbio.0060173

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Introduction to Sensation and Perception by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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