Anomalous motion illusions

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Anomalous motion illusions
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Outline

• -google Akiyoshi Kitaoka
• -ANOMALOUS MOTION illusions
• Peripheral Drift
• Central Drift
• Moving Insets
• Miscellaneous
• -Neural basis?

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Peripheral Drift
-illusory motion in peripheral vision -notice
that there is no illusory motion where you
foveate -as you make saccades to various parts
of the image, wherever you are looking, there is
never any motion - its only in the
periphery -has to do with PATTERNS OF CONTRAST
(more explanation later)
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Central Drift
-illusory motion in central and peripheral
vision -no positional changes -also has to do
with PATTERNS OF CONTRAST (more explanation later)
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Moving Insets
-illusory motion in central and peripheral vision
(stronger in peripheral?) -no positional
changes -has to do with RETINAL SLIP (more
explanation later - but not much!)
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Explanations
Peripheral Drift
-PATTERNS OF CONTRAST -higher-contrast signals
produce faster responses in visual system than
lower-contrast signals -because cells that
respond to the higher-contrast jumps are
activated faster than (before) cells that respond
to lower-contrast jumps, this accidentally
activates motion detectors -motion is seen as
going from higher-contrast element to
lower-contrast element -apparent motion!
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high contrast black to slightly-less contrast
dark grey
high contrast white to slightly less contrast
light grey
both lower contrast than overall average gray
both higher contrast than overall average gray
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Explanations
Peripheral Drift
-theres also evidence for REVERSE APPARENT
MOTION, originally discovered by our own Stuart
Anstis
high contrast black to other (light) gray
high contrast white to other (dark) gray
opposite contrasts relative to overall average
gray
opposite contrasts relative to overall average
gray
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Explanations
Peripheral Drift
forward-phi illusory motion comprise elements
with same signs of contrast relative to overall
mean gray luminance reverse-phi illusory
motion comprise elements with opposite signs
of contrast relative to overall mean gray
luminance -both of these happen, but forward-phi
seems more common/stronger of an effect, and
were not quite sure yet exactly what dictates
when one versus the other happens
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Explanations
Central Drift
-higher contrast border appears to move -moves
low-to-high contrast, toward higher contrast
border (blurry border kind of drags behind)
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Explanations
Central Drift
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Explanations
Central Drift
-not dependent on contrast POLARITY!
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Explanations
Moving Insets
-RETINAL SLIP -we learned earlier in the quarter
that the reason we dont see the world as moving
when we move our eyes, is because our perception
of motion depends on the motor commands our brain
sends to our eyes -when we move our eyes, even
though there is retinal motion from whatever
were looking at, our brain knows to cancel it
out in respect to how far we moved our
eyes -e.g. left to right eye movement, right to
left retinal motion -here, we are moving our
eyes, but we dont realize we are (jitter), so
the retinal motion is perceived as motion out
there (as opposed to self-induced)
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Neural Basis
-kind of old studies TMS and fMRI
-illusions of moving displays are correlated by
activation in MT, but not V1 -(however, the
illusions used were not nearly as powerful and
vivid as the peripheral drift illusion made by
Kitaoka) -NEW single-unit physiology, with
ROTATING SNAKE -V1 cells show some response to
illusory motion in their preferred direction
(but only the ones that are highly
directionally-selective) -MT cells show a much
stronger response (than V1 cells) to illusory
motion in their preferred direction -current
understanding is that effect of illusory motion
becomes more evident by the level of MT,
probably because signals from V1 are pooled in
MT -but occurs as early as V1!
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Miscellaneous
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Thank you!