ch8 Perception of Motion
Perception of Motion
Definition and Importance
Perception of motion is crucial for:
Guiding action
Capturing attention
Helping define objects
Motion can reveal hidden aspects in visual stimuli, as exemplified in a notable TED talk discussing the phenomenon of motion (reference: begins at 4:09).
Overview of Topics
The following topics will be covered:
Kinds of motion
Eye movements
Corollary discharge theory
Motion detectors
Perception of biological motion
Kinds of Motion
Real Motion
Illusory Motion
Apparent Motion:
Example: Movie marquee effects, where stationary images appear to move due to rapid succession.
Induced Motion:
Example: Observing the moon moving against a stationary horizon while seated in a moving train.
Autokinetic Effect:
When a small, stationary light in a dark room appears to move due to small involuntary eye movements.
Motion Aftereffect:
Example: The waterfall illusion, where prolonged viewing of motion in one direction causes perception of motion in the opposite direction upon looking away.
Exploration of Perception Demos:
Refer to Sinauer website for demos related to motion perception.
Eye Movements
Muscles Controlling Eye Movement:
Each eye is controlled by 6 muscles:
Two Oblique Muscles:
Superior oblique
Inferior oblique
Four Rectus Muscles:
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
Visual representations are included (refer to SENSATION AND PERCEPTION, Figure 7.13).
Types of Eye Movements
Saccades:
Eye movements that can be both voluntary and involuntary.
Smooth Pursuit:
Tracking a moving object smoothly with eye movements.
Vergence:
Convergence and divergence of the eyes to maintain single vision at varying distances.
Optokinetic Nystagmus:
Involuntary eye movement occurring when the whole visual environment moves past the observer.
Other Movements:
Tremors, microsaccades, and nystagmus (involuntary eye movement).
Demos concerning eye movements can be found on the Sinauer website.
Neural Control of Eye Movements
Nuclei and Cranial Nerves Involved:
Midbrain Structures:
Oculomotor nucleus
Trochlear nucleus
Abducens nucleus
Cranial Nerves:
Cranial nerve III
Cranial nerve IV
Cranial nerve VI
Visual representation details included (refer to SENSATION AND PERCEPTION, Figure 7.13).
Corollary Discharge Theory
Definition:
Corollary Discharge Theory explains how motion is perceived under various circumstances related to eye movements.
Mechanism:
When an image moves across the retina, a signal called the Image Displacement Signal (IDS) is triggered, leading to perceived motion.
Tracking a moving object with the eyes may produce motion on the retina without a perception of the object moving.
Contradictions:
Eye movements initiate retinal movement; however, the surrounding room remains perceived as stationary despite the retinal motion.
Movement Systems in Corollary Discharge Theory
Systems Involved:
Retinal Image Displacement System (IDS)
Eye-Head Movement System
Signals flow to the brain via:
Efferent signals (to muscles)
Afferent signals (from sensory input)
Comparator Interpretations
Three conditions for the comparator to determine motion:
No IDS Movement but Yes Motor Signal: Target is perceived as moving.
Yes IDS Movement but No Motor Signal: Target is perceived as moving.
Yes IDS Movement and Yes Motor Signal in Opposite Directions: Target is perceived as not moving.
Comparison with Gibson’s View
According to Gibson,
Global Optic Flow:
Serves as a direct signal for an individual's movement.
Local Disturbance in Optic Flow:
Indicates the movement of objects.
Accretion and Deletion of Background Signals:
Help determine the direction and speed of motion.
Motion Detectors
Functionality:
A motion detection circuit composed of excitatory and inhibitory connections is designed to signal motion in one direction, while remaining inactive for the opposite direction.
Biological Motion
Additional resources and demos can be found on the Sinauer website that explore the perception of biological motion.