Visual Feedback to Control Voluntary Motor Actions

Visual Feedback to Control Voluntary Motor Actions in Motor Control and Learning

Lecture Details

• Course: KNES 251 Introduction to Motor Control and Learning
• Institution: University of Calgary
• Date: November 7, 2025
• Presenter: Tyler Cluff, PhD

Sensory Information and Exteroception

• Dominance of Visual Information:
  • Visual information serves as the most significant source of exteroceptive feedback utilized for motor control.
• Exteroception Defined:
  • Exteroception refers to sensory information that informs us about the condition of our body concerning the surrounding world.
  • Major forms of exteroceptive information include:
  • Vision
  • Audition (hearing)
  • Smell

Receptors and Their Roles

• Eye Receptors:
  • Receptors in the eyes encode information concerning both the body and the environment.
  • Examples of real-world applications of visual feedback include:
  • Driving in traffic
  • Cycling in traffic
  • Refereeing in a hockey game
  • Hitting a fastball in baseball

Visual Tracking and Motion Detection

• Tracking Moving Objects:
  • Visual feedback plays a critical role in tracking the speed, spin, and location of objects.
  • Example scenario: Skating on the Rideau Canal requires vigilant visual tracking.
  • The importance of visual feedback fluctuates depending on the surrounding environment, with some environments demanding more than others.

Lecture Objectives

• Key Takeaways:
  1. The dorsal visual stream is essential for controlling actions.
  2. The ventral visual stream is crucial for perceptual judgments.
  3. Identification of basic receptors involved in visual processing.
  4. Understanding the functional properties of visual pathways.
  5. Recognizing behavioral impairments linked to lesions in dorsal and ventral visual streams.

Eye Structure and Function

• Photoreceptors in the Human Eye:
  • Mammalian eyes contain specialized cells known as photoreceptors, which absorb photons and instigate changes in the cell's membrane potential.
  • Types of photoreceptors:
  • Rods:
    • Population: Approximately 90-120 million in the human retina.
    • Location: Concentrated primarily in the peripheral parts of the retina.
    • Function: Specialized for low-light vision, contributing to motion detection yet offering low visual acuity.
  • Cones:
    • Population: Approximately 4.5 million in the human retina.
    • Location: Concentrated in the fovea, the retinal center.
    • Function: High spatial resolution and specialization in color vision, assisting in perceptual judgments.

Visual Processing: Receptive Fields

• Receptive Fields:
  • The receptive field refers to the specific area of the sensory space to which a neuron responds.
  • In the retina, these fields are distributed such that:
  • Higher spatial resolution is observed for cells in the fovea.
  • Periphery cells are more adept at motion detection.
  • Receptive fields expand as one moves away from the fovea, indicating specialization of visual pathways for action and conscious perception originating in the retina.

Dorsal vs. Ventral Visual Stream

• Visual Streams Overview:
  • The brain processes visual feedback via distinct pathways and circuits in the cerebral cortex:
  • Dorsal Stream: Known as the "Where" pathway - crucial for action guidance.
  • Ventral Stream: Known as the "What" pathway - essential for perception related to object and face recognition.
  • Ventro-dorsal Stream: Facilitates visuomotor transformations necessary for grasping and interpreting the actions of others.

Functions of Dorsal and Ventral Streams

• Dorsal Stream:

  • Input and Output:
  • Stimulus Identification (Perception)
  • Response Selection (Decision)
  • Response Programming (Action)
  • Characterized by rapid, unconscious processing of visual information for ongoing action corrections.

• Ventral Stream:

  • Input and Output:
  • Stimulus Identification (Perception)
  • Response Selection (Decision)
  • Response Programming (Action)
  • Characterized by slow, conscious processing of visual information primarily for object identification and recognition.

Clinical Implications of Visual Pathway Damage

• Form Agnosia due to Ventral Stream Damage:

  • Damage to the ventral stream can lead to impairments in conscious object perception while allowing intact movement control.
  • Example: Patient DF underwent tests demonstrating intact visuomotor 'posting' tasks with a deficit in perceptual orientation matching.

• Optic Ataxia due to Dorsal Stream Damage:

  • Damage in the dorsal stream, resulting from stroke or trauma, may lead to optic ataxia, characterized by an inability to use visual information to guide reaching movements.

Optic Flow and Movement Analysis

• Optic Flow:

  • Defined as the flow of light patterns across the retina. This flow occurs due to either self-motion or motion within the environment, providing crucial information about:
  • Time to contact
  • Direction of movement relative to surrounding objects
  • Velocity of movement through the environment
  • Overall movement dynamics of objects
  • Stability and balance determined by changes in the size of an object's retinal image, which changes at a faster rate when items are closer to the eye.

• Time to Contact:

  • The rate of expansion of the visual field is directly correlated to time-to-contact, whereby:
  • High Rate of Expansion = Decreased Time to Contact
  • Low Rate of Expansion = Increased Time to Contact

Importance of Visual Feedback in Goal-Directed Actions

• Vision's Role in Movement Accuracy:
  • Vision enhances the accuracy of slow, deliberate movements but has less impact on rapid movements. It is crucial for refining and correcting movement accuracy during slower actions.

Conclusion: Visual Feedback and Control

• Dorsal vs. Ventral Influence:
  • The dorsal visual stream facilitates fast, stimulus-dependent control of visual feedback during movement.
  • The ventral visual stream governs a somewhat slower, task-dependent control of visual feedback in broader contexts.