👁️Perception Unit 8 – Motion perception and optic flow

What's Motion Perception?

• Motion perception involves detecting and interpreting changes in the position of objects over time
• Relies on complex neural processes in the visual cortex to integrate information about object location, speed, and direction
• Allows us to navigate through the environment, avoid obstacles, and interact with moving objects
• Utilizes both central vision (fovea) and peripheral vision to gather motion information
• Plays a crucial role in everyday activities (driving, sports, walking)
• Influenced by factors such as contrast, luminance, and size of the moving object
• Can be affected by certain neurological conditions (akinetopsia) that impair motion processing

How Our Eyes Track Movement

• Eye movements, particularly smooth pursuit, enable us to track moving objects
  • Smooth pursuit involves continuously adjusting eye position to keep a moving target on the fovea
  • Requires coordination between the oculomotor system and visual cortex
• Saccades, rapid eye movements, help quickly shift gaze to different points of interest
• Optokinetic nystagmus (OKN) stabilizes gaze during head or body movement
  • Consists of slow phases (tracking movement) and fast phases (resetting eye position)
• Vestibular-ocular reflex (VOR) compensates for head movement to maintain stable vision
• Vergence eye movements adjust the angle between the eyes to maintain binocular vision
• Combination of these eye movements allows for efficient tracking and processing of motion

The Basics of Optic Flow

• Optic flow refers to the pattern of apparent motion of objects in the visual field as an observer moves through the environment
• Provides information about the relative motion between the observer and the environment
• Radial optic flow occurs when moving forward or backward, with the focus of expansion indicating the direction of heading
• Laminar optic flow occurs during lateral motion, with parallel flow lines
• Rotational optic flow results from head or eye rotations, causing the visual field to rotate
• Optic flow patterns are processed in specialized brain regions (medial superior temporal area)
• Helps in determining self-motion, estimating time-to-collision, and controlling locomotion

Types of Motion We Can Detect

• Local motion: movement of individual objects or features within the visual field
  • Detected by motion-sensitive neurons in the primary visual cortex (V1)
• Global motion: overall pattern of motion across the entire visual field
  • Processed in higher-level visual areas (middle temporal area, medial superior temporal area)
• Biological motion: movement patterns characteristic of living organisms (human gait)
  • Detected from minimal visual information (point-light displays)
  • Processed in specialized brain regions (superior temporal sulcus)
• Apparent motion: perception of motion created by rapidly presenting static images in succession (flip-book animation)
• Motion aftereffect: illusory motion perceived after prolonged viewing of a moving stimulus in the opposite direction
• Second-order motion: movement of texture or contrast boundaries without corresponding luminance changes

Tricks Our Brain Plays: Motion Illusions

• Motion illusions demonstrate the complex nature of motion perception and the brain's interpretations
• Peripheral drift illusion: stationary patterns appear to move in the peripheral vision due to differences in contrast sensitivity
• Motion-induced blindness: stationary objects seem to disappear when surrounded by moving patterns
• Rotating snakes illusion: static repeated patterns create the illusion of rotation due to asymmetric luminance gradients
• Illusory contours: motion can be perceived along edges that are not physically present (Kanizsa triangle)
• Wagon wheel effect: continuous motion appears to reverse direction under certain conditions (stroboscopic lighting)
• These illusions highlight the role of top-down processing and expectations in motion perception

Real-World Applications of Motion Perception

• Driving: detecting the movement of other vehicles, pedestrians, and obstacles
  • Helps maintain safe distances and avoid collisions
• Sports: tracking the motion of balls, opponents, and teammates
  • Essential for intercepting, catching, and hitting moving targets
• Virtual reality: creating immersive experiences by simulating realistic motion cues
  • Requires accurate tracking of head movements and updating of visual displays
• Motion graphics and animation: conveying dynamic information and engaging viewers
  • Used in films, video games, and user interfaces
• Robotics and machine vision: enabling autonomous systems to navigate and interact with the environment
• Medical imaging: detecting abnormalities in moving structures (heart, lungs) through techniques like ultrasound and MRI

Key Experiments and Findings

• Hubel and Wiesel (1959): discovered motion-sensitive neurons in the cat's visual cortex
  • Laid the foundation for understanding the neural basis of motion perception
• Newsome and Pare (1988): demonstrated the role of the middle temporal area (MT) in motion perception using random dot kinematograms
• Johansson (1973): introduced point-light displays to study biological motion perception
  • Showed that humans can recognize actions from minimal motion information
• Gibson (1950): proposed the concept of optic flow and its role in perceiving self-motion and the environment
• Nakayama and Loomis (1974): investigated the perception of heading direction from optic flow patterns
• Braddick (1974): studied the perception of apparent motion using random dot kinematograms
• These experiments have shaped our understanding of the mechanisms and neural substrates underlying motion perception

Wrapping It All Up: Why This Matters

• Motion perception is a fundamental aspect of visual processing that enables us to interact with a dynamic world
• Understanding the principles and mechanisms of motion perception has implications for various fields
  • Improving transportation safety by designing better collision avoidance systems
  • Enhancing virtual reality experiences by optimizing motion cues and reducing motion sickness
  • Developing more effective visual aids and therapies for individuals with motion perception deficits
• Studying motion illusions provides insights into the limitations and biases of the visual system
  • Helps refine models of motion processing and perceptual decision-making
• Advances in motion perception research contribute to the development of artificial intelligence and computer vision systems
• Interdisciplinary collaborations between vision scientists, engineers, and designers can lead to innovative solutions and technologies
• Ultimately, a deeper understanding of motion perception enriches our knowledge of how the brain makes sense of the dynamic visual world around us