Why So Few Motion-Perception Related Problems?
Motion perception in humans is remarkably robust, meaning that even with some damage to
motion-sensitive areas, we rarely experience a complete loss of motion perception. This robustness
comes from:
1. Many motion-sensitive areas – The brain does not rely on just one area to process motion.
Multiple brain regions contribute, making the system resilient.
2. Bilateral damage is needed – To completely lose motion perception (a condition known as
akinetopsia, or "motion blindness"), damage must occur in both hemispheres, particularly
in area V5/MT (middle temporal visual area).
3. Redundancy and parallel processing – The brain has multiple pathways that help
compensate for minor damage.
Is There One Motion System?
• Motion perception is not handled by a single system. Instead, multiple neural pathways
contribute to detecting motion.
• The way motion is processed varies across species, suggesting that different animals may
have evolved distinct mechanisms to detect and interpret motion.
Motion Sensitivity in Different Species
The study of motion perception across species reveals that motion-sensitive mechanisms are
widespread, but they vary in their anatomical locations and underlying processes.
• Reichardt Detector Model (1961) – A classic model of motion detection that suggests
neurons detect changes in light intensity over time and space.
• Retinal Motion Detection in Various Animals: detect motion on retina level
o Rabbits (Barlow & Levick, 1965)
o Frogs (Maturana, Lettvin, McCullach & Pitts, 1960)
o Turtles (Jensen & Devoe, 1983)
o Birds (Maturana & Frenk, 1963)
o Squirrels (Michael, 1968)
• Humans (Bach & Hoffmann, 2000) – Unlike some animals, humans do not rely solely on
retinal motion detectors but use a combination of retinal and cortical processing.
Key Observations:
• Not all animals use the same mechanisms for motion perception.
• Motion sensitivity – everyone seems to have it, many cell respond to change
• Transient effect – when you move something through the receptive field, it prefers motion
because it is transient in and out you get a high response – simple
1
, • By motion sensitivity you want the stimulus more complex like motion or direction or
speed selectivity
• Compound eye (flies) - > if you stimulate 2 of the cells in the compound eye in sequence
then you get a motion signal
• Despite anatomical differences, motion-sensitive mechanisms show similarities in function.
• A common principle emerges: a similar motion detection mechanism is implemented in
different brain regions across species.
Motion Sensitivity in Humans - - How Does Motion Perception Work?
Motion perception in humans involves several interconnected brain regions:
1. Retina – Some basic motion detection occurs here, but higher-level processing happens in
the brain.
2. Lateral Geniculate Nucleus (LGN) – Acts as a relay station for visual information from the
eyes to the brain.
3. Primary Visual Cortex (V1) – The first cortical processing center for visual input.
4. Middle Temporal (MT/V5) and Medial Superior Temporal (MST) Areas – These areas
are critical for perceiving motion. Damage to V5/MT can cause akinetopsia, where a
person sees the world as a series of still frames.
5. Dorsal Stream ("Where Pathway") – The pathway leading from V1 to V5/MT and then to
the parietal lobe, helping with motion perception, object tracking, and spatial awareness.
What Is Motion, anyway? - Motion can be defined as a change in the position of an object over time
relative to its surroundings. In the brain, motion is detected through:
• Motion opponency – Cells in the visual cortex compare motion signals from different
directions.
• Temporal integration – The brain combines multiple snapshots of an object's position to
infer motion.
• Feature tracking – Higher-order processing allows us to track moving objects even when
they momentarily disappear from view.
Key Takeaways
✔ Motion perception is robust because it involves multiple brain areas.
✔ Bilateral damage to V5/MT is needed for complete motion blindness.
✔ Different species use different anatomical pathways for motion detection, but the
fundamental mechanism is similar.
✔ Humans rely on a combination of retinal, subcortical, and cortical processing to perceive
motion effectively.
2
,What is Motion?
Motion is the change in position of an object over time. Mathematically, this means that for
motion to be perceived, an object must be identified at two different points in time and
recognized as the same entity.
This has an important implication: motion perception is closely linked to object perception. If
we need to recognize an object as the same before detecting motion, then our ability to separate
objects from their background is essential for motion processing.
However, there’s an interesting paradox:
✔ Objects can be defined by motion – When an object moves, its movement helps us perceive it
as distinct from the background.
✔ Motion can be perceived before object recognition – In some cases, we see motion without
recognizing an object first (as seen in dorsal vs. ventral stream processing).
Motion & Objects - How is Motion Related to Object Perception?
• We often define objects by their motion (e.g., a camouflaged animal becoming visible
when it moves).
• However, motion can also be perceived independently of objects (e.g., flickering lights,
flowing water, or abstract motion illusions).
• This suggests that motion perception does not always require prior object recognition.
Dorsal vs. Ventral Stream in Motion Perception
The brain has two visual processing streams:
• Dorsal stream ("Where Pathway") – Processes motion and spatial information; detects
motion before object identity.
• Ventral stream ("What Pathway") – Processes object recognition and detailed shape
analysis.
Since motion is mainly processed in the dorsal stream, we can detect movement even before fully
identifying the object.
3
, Structure from Motion: Seeing Shape Through Movement - - Some visual illusions and
perceptual phenomena show that motion itself can reveal object structure.
Examples:
1. Structure-from-Motion (SFM)
a. A set of moving dots can create the illusion of a 3D shape, even when no solid
object is present.
b. Example: A point-light walker (a set of moving dots arranged like a human body)
is recognized as a walking figure only when in motion.
2. Illusory Rotation
a. Some illusions give the impression of rotation or movement even when no real
motion is happening.
b. This is an example of how the brain interprets motion from visual cues alone.
c. Back and forth =linear
Motion Adaptation & Aftereffects - - One of the strongest proofs that motion perception is a
distinct system in the brain is the motion aftereffect.
What is the Motion Aftereffect?
• If you stare at moving stimuli (e.g., a waterfall or spinning spiral) for a while, then look
at a still object, you will see the illusion of motion in the opposite direction.
• This happens because motion-sensitive neurons in the brain adapt to the movement and
become "fatigued," causing a temporary imbalance in motion perception.
Extreme Example: Motion in Art
• Some paintings, such as Vincent van Gogh’s brushstrokes, create a strong illusion of
movement. - motion after effect – there much higher-level processing
• The way the brushstrokes flow can activate motion-sensitive neurons, making the painting
feel dynamic.
Summary: What is Motion?
✔ Motion = a signal inferred from position change over time.
✔ Object perception and motion perception are intertwined but not dependent on each other.
✔ Motion can define objects, and objects can define motion.
✔ The brain processes motion in a dedicated pathway (dorsal stream), allowing us to detect
movement even before recognizing objects.
✔ Motion adaptation and aftereffects reveal the existence of specialized motion-detecting
neurons.
4
Motion perception in humans is remarkably robust, meaning that even with some damage to
motion-sensitive areas, we rarely experience a complete loss of motion perception. This robustness
comes from:
1. Many motion-sensitive areas – The brain does not rely on just one area to process motion.
Multiple brain regions contribute, making the system resilient.
2. Bilateral damage is needed – To completely lose motion perception (a condition known as
akinetopsia, or "motion blindness"), damage must occur in both hemispheres, particularly
in area V5/MT (middle temporal visual area).
3. Redundancy and parallel processing – The brain has multiple pathways that help
compensate for minor damage.
Is There One Motion System?
• Motion perception is not handled by a single system. Instead, multiple neural pathways
contribute to detecting motion.
• The way motion is processed varies across species, suggesting that different animals may
have evolved distinct mechanisms to detect and interpret motion.
Motion Sensitivity in Different Species
The study of motion perception across species reveals that motion-sensitive mechanisms are
widespread, but they vary in their anatomical locations and underlying processes.
• Reichardt Detector Model (1961) – A classic model of motion detection that suggests
neurons detect changes in light intensity over time and space.
• Retinal Motion Detection in Various Animals: detect motion on retina level
o Rabbits (Barlow & Levick, 1965)
o Frogs (Maturana, Lettvin, McCullach & Pitts, 1960)
o Turtles (Jensen & Devoe, 1983)
o Birds (Maturana & Frenk, 1963)
o Squirrels (Michael, 1968)
• Humans (Bach & Hoffmann, 2000) – Unlike some animals, humans do not rely solely on
retinal motion detectors but use a combination of retinal and cortical processing.
Key Observations:
• Not all animals use the same mechanisms for motion perception.
• Motion sensitivity – everyone seems to have it, many cell respond to change
• Transient effect – when you move something through the receptive field, it prefers motion
because it is transient in and out you get a high response – simple
1
, • By motion sensitivity you want the stimulus more complex like motion or direction or
speed selectivity
• Compound eye (flies) - > if you stimulate 2 of the cells in the compound eye in sequence
then you get a motion signal
• Despite anatomical differences, motion-sensitive mechanisms show similarities in function.
• A common principle emerges: a similar motion detection mechanism is implemented in
different brain regions across species.
Motion Sensitivity in Humans - - How Does Motion Perception Work?
Motion perception in humans involves several interconnected brain regions:
1. Retina – Some basic motion detection occurs here, but higher-level processing happens in
the brain.
2. Lateral Geniculate Nucleus (LGN) – Acts as a relay station for visual information from the
eyes to the brain.
3. Primary Visual Cortex (V1) – The first cortical processing center for visual input.
4. Middle Temporal (MT/V5) and Medial Superior Temporal (MST) Areas – These areas
are critical for perceiving motion. Damage to V5/MT can cause akinetopsia, where a
person sees the world as a series of still frames.
5. Dorsal Stream ("Where Pathway") – The pathway leading from V1 to V5/MT and then to
the parietal lobe, helping with motion perception, object tracking, and spatial awareness.
What Is Motion, anyway? - Motion can be defined as a change in the position of an object over time
relative to its surroundings. In the brain, motion is detected through:
• Motion opponency – Cells in the visual cortex compare motion signals from different
directions.
• Temporal integration – The brain combines multiple snapshots of an object's position to
infer motion.
• Feature tracking – Higher-order processing allows us to track moving objects even when
they momentarily disappear from view.
Key Takeaways
✔ Motion perception is robust because it involves multiple brain areas.
✔ Bilateral damage to V5/MT is needed for complete motion blindness.
✔ Different species use different anatomical pathways for motion detection, but the
fundamental mechanism is similar.
✔ Humans rely on a combination of retinal, subcortical, and cortical processing to perceive
motion effectively.
2
,What is Motion?
Motion is the change in position of an object over time. Mathematically, this means that for
motion to be perceived, an object must be identified at two different points in time and
recognized as the same entity.
This has an important implication: motion perception is closely linked to object perception. If
we need to recognize an object as the same before detecting motion, then our ability to separate
objects from their background is essential for motion processing.
However, there’s an interesting paradox:
✔ Objects can be defined by motion – When an object moves, its movement helps us perceive it
as distinct from the background.
✔ Motion can be perceived before object recognition – In some cases, we see motion without
recognizing an object first (as seen in dorsal vs. ventral stream processing).
Motion & Objects - How is Motion Related to Object Perception?
• We often define objects by their motion (e.g., a camouflaged animal becoming visible
when it moves).
• However, motion can also be perceived independently of objects (e.g., flickering lights,
flowing water, or abstract motion illusions).
• This suggests that motion perception does not always require prior object recognition.
Dorsal vs. Ventral Stream in Motion Perception
The brain has two visual processing streams:
• Dorsal stream ("Where Pathway") – Processes motion and spatial information; detects
motion before object identity.
• Ventral stream ("What Pathway") – Processes object recognition and detailed shape
analysis.
Since motion is mainly processed in the dorsal stream, we can detect movement even before fully
identifying the object.
3
, Structure from Motion: Seeing Shape Through Movement - - Some visual illusions and
perceptual phenomena show that motion itself can reveal object structure.
Examples:
1. Structure-from-Motion (SFM)
a. A set of moving dots can create the illusion of a 3D shape, even when no solid
object is present.
b. Example: A point-light walker (a set of moving dots arranged like a human body)
is recognized as a walking figure only when in motion.
2. Illusory Rotation
a. Some illusions give the impression of rotation or movement even when no real
motion is happening.
b. This is an example of how the brain interprets motion from visual cues alone.
c. Back and forth =linear
Motion Adaptation & Aftereffects - - One of the strongest proofs that motion perception is a
distinct system in the brain is the motion aftereffect.
What is the Motion Aftereffect?
• If you stare at moving stimuli (e.g., a waterfall or spinning spiral) for a while, then look
at a still object, you will see the illusion of motion in the opposite direction.
• This happens because motion-sensitive neurons in the brain adapt to the movement and
become "fatigued," causing a temporary imbalance in motion perception.
Extreme Example: Motion in Art
• Some paintings, such as Vincent van Gogh’s brushstrokes, create a strong illusion of
movement. - motion after effect – there much higher-level processing
• The way the brushstrokes flow can activate motion-sensitive neurons, making the painting
feel dynamic.
Summary: What is Motion?
✔ Motion = a signal inferred from position change over time.
✔ Object perception and motion perception are intertwined but not dependent on each other.
✔ Motion can define objects, and objects can define motion.
✔ The brain processes motion in a dedicated pathway (dorsal stream), allowing us to detect
movement even before recognizing objects.
✔ Motion adaptation and aftereffects reveal the existence of specialized motion-detecting
neurons.
4
