Module 08 - Motion Perception

Introduction to Motion Perception

• Professor: Marviene W. Fulton
• Login Requirement: Students must login to Poll Everywhere with their @charlotte email to participate.

Definition of Motion

• Motion: A primary perceptual dimension defined as a change in position over time.
  • Provides information about spatial relationships.
  • Aids navigation by detecting self and object movement.
  • Enhances object recognition by using kinetic cues to reveal shape.
  • Directs attention to important features in the environment.
  • Defines events over time.
• Motion Demonstration: Demonstrated in “Perceptual Shift” by Mike Murphy, highlighting how motion gives us more information.

Review of Motion in Depth Module

• Relative Motion: Perceiving depth based on how objects move relative to each other.
• Motion Parallax: Perception of depth based on relative movement; closer objects appear to move faster than distant ones.
• Self-motion (Optic Flow): Visual field shifts as we move, providing cues for trajectory and speed.
  • Without these cues, change blindness occurs, wherein critical spatial updates are missed.

Understanding Absolute Motion and Visual Ambiguity

• Absolute Motion: Aids depth perception when no background reference exists, making depth cues absent.
  • Example: Detecting the speed and direction of a flying bird against a blank sky.
  • Visual Ambiguity: Difficult interpretation of absolute motion due to lack of reference points, causing perceptual illusions like the spinning dancer illusion.

Motion Aftereffects (MAE)

• MAE Definition: Following prolonged exposure to motion, stationary objects appear to move in the opposite direction.
• Cause: Adaptation in direction-selective neurons reduces sensitivity to sustained motion.
  • Opponent process: Similar to color aftereffects where adaptation shifts perception opposite to sustained stimulus.
• Key Demonstrations: Illustrated through the Waterfall Illusion and Spiral Aftereffects.

Interocular Transfer and Motion Aftereffects

• Interocular Transfer: MAE persists when switching eyes, indicating higher-level motion processing.
  • Occurs in neurons that respond to both eyes, suggesting processing in V1 or beyond.
  • Confirmed through fMRI studies indicating adaptation in the MT/V5 area, critical for motion processing.

Double Dissociation and Types of Motion

• Two types of motion:
  • First-order motion: Detected by luminance changes, typical in laboratory settings.
  • Pathway: V1 to MT.
  • Second-order motion: Perceived through contrast, texture, or flicker without defined edges.
  • Related area: Extrastriate cortex beyond MT.

Motion Detection Mechanisms

• Receptive Fields: Motion detection requires spatially separated receptive fields.
• Reichardt Detectors: Explain how neurons compare motion signals from two locations.
  • Requires excitatory and inhibitory interactions to compute motion and responds to both real and apparent motion.

Opponent Motion Detectors

• Compare leftward versus rightward motion signals.
• Functionality: Excitatory-inhibitory interactions that enhance detection of actual movement while suppressing stationary responses.
  • Neural adaptation leads to MAE where fatigue in one direction results in the perception of motion opposite to that direction.

Apparent Motion

• Definition: The illusion of smooth motion perceived from separate static images.
• Media examples: Movies and stop-motion rely heavily on this effect.
  • The first movie consisting of 16 sequential images of horses was made in 1878.
  • Both apparent and real motion processed similarly as confirmed by fMRI studies (e.g., Larson, 2006).

Apparent Motion Illusion Examples

• Various media demonstrate apparent motion, including animations and visual tricks that illustrate the principle.
• Reference: Beau Deeley 2012 & Akiyoshi Kitaoka's site for more examples.

Effect of Object Spacing in Apparent Motion

• Apparent Motion Quartet: Perceived motion can depend on the spacing of objects.
  • Closer vertical spacing promotes perception of vertical motion.
  • Closer horizontal spacing promotes perception of horizontal motion.
• Applies the Gestalt Proximity Principle, which suggests motion perception minimizes distance traveled.

Beta Motion and Phi Phenomenon

• Beta Motion: Created by sequential lights that offer a perception of smooth motion.
  • Basis for movie projection and animation is sensitive to timing and spacing between flashes.
• Phi Phenomenon: Alternating objects appear to shift locations, creating an illusion of movement without actual motion.

Correspondence Problem in Motion Detection

• Challenge in Motion Detection: The correspondence problem refers to determining which features in frame 2 correspond to frame 1, leading to ambiguity.

Aliasing Problem in Motion

• Aliasing: Occurs when motion is sampled too slowly, causing perceptual errors.
  • Examples: Tire spokes or helicopter blades appearing still due to misalignment of motion speed and frame rate.

Aperture Problem in Motion Perception

• Definition: When viewing motion through a restricted area, such as receptive fields in V1, the actual motion direction can appear ambiguous.
  • Example: The Barber Pole illusion where upward motion is perceived even though diagonal stripes are moving.
• Neural Solution: The brain combines motion signals across larger receptive fields in the MT area to resolve these ambiguities.

Motion Components in V1

• Functionality of V1: Involves detecting horizontal and vertical stripe movements.
  • Plaid Motion Perception: Combines signals from different fields to form a perception of diagonal motion.
  • Neural Integration: V1 neurons have small receptive fields detecting partial motion, while MT neurons integrate multiple signals for comprehensive motion perception.

Motion Binding

• Definition: Integrates individual motion signals into a unified perception of an object.
  • Importance: Essential for object recognition and differentiating self-motion from that of objects in motion.

MT Area and Motion Perception

• Middle Temporal Area (MT): Integrates local motion signals for global motion perception.
  • Resolved ambiguities and addresses aperture problems effectively.
  • Demonstrated capability to analyze large-scale movements, e.g., flocks of birds or crowds.

Lesion Studies on MT

• Findings from Newsome and Paré (1988): Lesions in MT impair motion detection significantly.
  • Monkeys needed ten times more synchronized dots to determine motion direction when MT was damaged.
  • Causal links identified through neuron stimulation biases in perceiving motion.

Akinetopsia

• Definition: A rare disorder characterized by complete loss of motion perception caused by severe bilateral damage to the MT area.
  • Affected individuals perceive life as static images or experience severe motion blur.

MST and Motion Processing

• MST (Medial Superior Temporal Area): Processes more complex motion patterns, including radial and circular motions.
  • Functionality: Tracks optic flow to discern self-motion within environments.

Optic Flow

• Definition: Changing structure of light in an environment as one moves.
  • Focus of Expansion (FOE): Indicates heading direction within optic flow patterns.
  • Optic flow patterns aid in navigation and balance.

Biological Motion

• Definition: Unique perception of movement associated with living organisms, revealing gender cues, body size, and species differences.
  • Point-Light-Walker Display: Demonstrates that even minimal cues can reveal motion coordination.

Biological Motion Processing Area

• The Posterior Superior Temporal Sulcus (STSp): Critical for processing biological motion.
  • Evidence: Activation observed in fMRI studies during point-light walker displays; TMS inactivation disrupts perception of social motion cues.

Time to Collision (TTC) Estimation

• Tau (τ): A critical concept related to predicting time to collision based on the retinal expansion rate, directly proportional to TTC.
  • Example: If a car appears larger suddenly, it indicates imminent collision requiring immediate braking.

Dorsal Stream Movement Processing

• Functionality: Processes spatial location and visually-guided actions, crucial for motion interaction.
  • MT tracks object motion speed/direction, MST integrates global motion via optic flow.

Brain Regions Involved in Motion Perception

• Overview Table:
  

• Definition: A phenomenon where stationary objects disappear when viewed against a moving background due to brain prioritizing motion.
  • Isoluminant stimuli (similar brightness) are more prone to MIB, as background movement suppresses stationary visual input.

Eye Movements and Their Types

• Importance in Scene Viewing: Facilitates high-resolution vision due to limited foveal vision.
  • Types:
  1. Vergence - Depth control; aligns eyes on moving object.
  2. Vestibulo-ocular Reflex (VOR) - Stabilizes gaze by countering head movements.
  3. Smooth Pursuit - Fluid voluntary tracking of moving objects.
  4. Saccades - Rapid shifts of gaze, can be voluntary or involuntary.

Strategies to Stabilize Vision and Reduce Blur

• Three Processes:
  1. Tracking and eye compensation to maintain stable vision.
  2. Differentiating external vs. self-motion to manage motion blur expectations.
  3. Saccadic suppression to minimize blur during eye shifts.

Mechanisms of Visual Blur

• Understanding Blur: Occurs when there is relative motion between stationary and moving objects, where fixations cause various blurring effects depending on object movement relative to one's gaze.

Eye Movement Challenges

• Retinal Location as Motion Cue: Not a reliable indicator in various moving scenarios where the positioning shifts through eye movement.
• Conclusion: Motion is detected only when true relative motion occurs across direction-sensitive receptive fields in the visual system.

Saccadic Movements and Visual Perception

• Saccades: Rapid eye shifts between fixations, where saccadic suppression prevents motion blur and aids in perceiving the world through snapshots of visual input.

Role of Corollary Discharge Signal (CDS)

• Function: Informs the brain of upcoming eye movements, allowing stabilization of vision and preventing perceived jumps in the visual scene.
  • Sends signals from the Superior Colliculus to maintain spatial coherence across eye movements.

Summary of Concepts Related to the Lilac Chaser Illusion

• Mechanisms:
  • Retinal Neuronal Fatigue: Fatigue of S (blue) & L (red) cones leads to negative afterimages creating a green impression during viewing due to color opponent processes.
  • Phi Phenomenon: Facilitates the perception of motion from transient gaps during fixation, leading to a seamless experience of perceived movement.

Eye Movement and Attention

• Attention Mechanisms: Determining where to saccade and the duration of fixation.
  • Bottom-up attention driven by motion salience often engages the gaze more compared to other features.
  • Top-down attention actively predicts and directs gaze based on prior knowledge of motion cues.

Main Topics to Concentrate On

• Key Concepts:
  • Salience in Attention & Motion
  • Motion Aftereffects
  • Motion Parallax, Optic Flow, Focus of Expansion
  • Areas of the brain involved in motion: MT, MST, STSp
  • Disorders such as Akinetopsia
  • Motion-Induced Blindness and its implications
  • Correspondence and aperture problems along with solutions
  • Differences between first-order and second-order motion
  • Saccades & their role in motion perception
  • Techniques for predicting collisions (TTC & Tau)
  • Role of the Corollary Discharge Signal in visual perception and eye movements