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Chapter 7

PSYB51 Chapter 7


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
7

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Chapter 7: Motion Perception
-Shape, location in space, color her fundamental perceptual dimensions
-Motion as a low-level perceptual phenomenon–cells in primary visual cortex
selectively respond to motion in one particular direction
Motion aftereffect
-The illusion of motion of a stationary object that occurs after prolonged exposure to
moving objects
-Just as color after effects are caused by opponent processes for color vision, the
motion after effect is caused by opponent processes for motion detection
Computation of Visual Motion
-Page 171 look over
-Promotion detector is velocity sensitive in their direction sensitive
Apparent Motion
-One possible objection to this neuronal circuit is that it does not, in fact, require
continuous motion in order to fire
-The Reeichardt model provides an excellent explanations were visual illusions that
modern humans experience on a daily basis
-Apparent motion that illusory impression of smooth motion resulting from the rapid
alternation of objects that appear in different locations and rapid succession
First demonstrated by Sigmund Exner in 1875
The Correspondence and Aperture Problems
-Aperture - an opening that allows only a partial view of the object
-Correspondence problem the problems faced by the motion detection system of
knowing which feature in frame two corresponds to a particular feature in frame one
example on page 173 figure 7.5
-Aperture problem the fact that when a moving object is viewed t through an
aperturer, the direction of motion of a local feature or part of the objects may be
ambiguous
-Every V1 cell sees the world through a small aperture therefore none of them can tell
with certainty which visual elements correspond to one another when an object
moves
-Solution to this problem is to have another set of neurons listen to the V1 neurons
integrate the potentially conflicting signals
Detection of Global Motion and Area MT
-Lesions in the magnocellular layers of the LGN impaired perception of large, rapidly
moving objects
-The vast majority of neurons in MT our selective promotion in one particular
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direction, but they show little selectivity for form or color
-Newsome and Pare trained monkeys to respond to correlated dot motion displays
-No single dot in these displays is sufficient to determine the overall direction of
correlated motion; so to detect the correlated direction, neurons must integrate
information
-Monkeys could recognize a correlated motion direction on only 2 to 3% of the dots
are moving in the direction; once there brings release and they needed about 10
times as many correlated dots in order to correctly identify the direction of motion
The ability to discriminate orientation of stationary patterns was unimpaired
-Lesions may be incomplete or may influence other structures this may have led to a
third variable affecting the outcome
-Another experiment in which the researchers searched for groups of neurons that
responded to one particular direction showed to monkey a new set of stimuli and
electrically stimulated the identified MT neurons
The monkeys showed a strong tendency to report motion in the stimulated
neurons preferred direction, even when the dogs they were seeing were actually
moving in the opposite direction
-These show a strong case that the MT business site of global motion direction
Motion Aftereffects Revisited
-Neurons sensitive to upward motion fire at the same rate as neurons sensitive to
downward motion, so the signals cancel out and no motion is perceived
-The detectors are sensitive to downward motion become fatigued and when we
switch our gaze to a stationary object in nonsense to the upward motion fire faster
-Interocular transfer - the transfer of an effect from one night to the other
-The fact that a strong motion after effect is obtained with one eye is adaptive and the
other tested means that the effect must be reflecting activities in their arms in a part
of the visual system or information collected from the two eyes is combined the V1
area
-The emerging evidence suggests that the motion after affecting humans is caused
by the same brain region shown to be responsible for global motion detection and
monkeysthe cortical area MT
-First-order motion the motion of an object is defined by changes in luminance
-Luminance defined object object that is delineated by changes in reflected light
-Second-order motion the motion of an object is defined by changes in contrast or
texture, but not by luminance
-Texture defined object, and object is defined by changes in contrast for texture, but
not by luminance
Second Order Motion
-Nothing actually moves in second-quarter motion there is nothing to move in
second order motion
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