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35 Cards in this Set
- Front
- Back
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motion |
spatiotemporal event |
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speed of sight |
takes 80-120 milliseconds for visual signals to reach higher areas of the visual cortex takes another 80-100 milliseconds after that to make a motor response to that stimulus |
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temporal frequency |
the rate of change of a visual stimulus, given in cycles of change per second |
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flicker |
used to determine how fast we can follow a changing stimulus capable of detecting stimulus alterations at up to 60 Hx |
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critical flicker fusion |
frequency at which temporal changes become undetectable |
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temporal resolution |
how sensitive the visual system is to different temporal frequencies obtain contrast threshold of a flickering stimulus at different temporal frequencies greater our temporal resolving ability at a certain frequency, the lower the contrast needed to just observe the flicker temporal contrast sensitivity function shows that our visual system optimally detects temporal frequencies in the 10-15 Hz range and that scotopic vision is more sluggish compared to photopic vision |
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time to collision |
obtained by evaluating the absolute depth of the incoming object and making an estimate of its speed of approach |
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tau |
the ratio of retinal image size to the rate at which it is expanding provides accurate estimate of TTC without need for obtaining object distance or rate of movement responsible for our ability to make split-second reactions to avoid collisions |
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directional selectivity |
ability of a neuron to distinguish one direction of motion from all others neurons are found as early as area V1 display vigorous response only when light bar moves along the direction preferred by that neuron some are extremely specific, others are more broadly tuned, but the neurons together covers all possible directions of movement |
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The Reichardt detector |
simple convergence of two neurons upon a third does not endow it with the property of directional sensitivity insertion of an interneuron in one path of the circuit creates a delay that when matched to the delay of the stimulus movement in the correct direction, produces a synchronized convergence of neural signals, thus conferring directional selectivity upon the neuron relies only on temporal summation of signals provides a simple way of encoding speed selectivity |
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elaborated low-level detectors |
two Reichardt detections that are tuned in opposite directions and have their outputs subtracted to form a bidirectional motion detector |
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motion processing in area V1 |
precise location of directionally selective neurons: high directionally selective neurons found in bottom of layer 6 and along a middle band 4b |
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motion processing beyond V1 |
area MT (area V5) area MST |
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area MT (area V5) |
vast majority of neurons in this area are directionally selective |
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area MST |
processes more advanced properties of the motional signal |
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correlated dot motion |
created from a random field of dots in which a certain percentage of the dots move coherently in one direction, whereas the remainder move in random directions
produce a correlation threshold correlation thresholds increases after area MT is removed -> MT is involved in motion perception |
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kinetic depth effect |
the phenomenon that movement can enhance the 3D appearance of objects in space |
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biological motion perception |
point-light movements lead to an immediate and vivid perception of a person's movement |
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the motion aftereffect (motion adaption) |
a stationary object will appear to move when looked at immediately after viewing a moving scene prolonged viewing of a moving stimulus produces strong firing with specific directionally selective neurons once stimulation ceases, neurons that previously fired at a high level now enter temporary period of reduced responsiveness motion impression in the opposite direction arises |
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interocular transfer |
if neurons in only one eye experience adaption, the motion aftereffect is only viewed by the other eye shows that adaption effects responsible for motion aftereffect do not occur at the level of the retina or LGN motion aftereffect can only arise at a level where neural output from two eyes are combined |
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aperture problem |
global motion of an object is not faithfully represented by the motion that is only visible through an aperture if two non-parallel edges are part of the same moving object, they must be moving in the same direction true motion of the object is derived from the one motion vector that is common to all constraint lines |
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first-order motion |
luminance-defined object movement assumes that a luminance difference exists between a moving object and its background most commonly occurring type of motion in our natural world |
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second-order motion |
movement of isoluminant objects detectors found in areas MT and MST |
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apparent motion |
when a stimulus is presented at one location, turned off, and shown at a different location shortly afterwards foundation for all movement in television and film illustrates importance of space and time when generating motion |
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wagonwheel effect |
when a moving stage coach reaches a certain speed, the spoked wheels suddenly appear to rotate in the opposite direction |
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correspondence problem |
correspondence between image components in different frames of a sequential display is a challenge from a computational point of view |
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complex motion illusions |
induced motion vection motion |
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induced motion |
a large moving object/background induces movement in a smaller stationary object ex: moon through clouds |
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vection motion |
when moving objects impart a sense of self motion ex: inside a parked car -> movement of another vehicle outside leads to vection illusion |
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oculomotor response |
more sensitive in terms of object tracking |
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neurobiological mechanisms of eye movements |
cortical structures beyond V1 include parietal cortex and frontal cortex superior colliculus receives input from three major cortical areas, able to integrate sensory information from retina with descending cortical output, has a major output to motor areas of brain |
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position constancy |
stability of the visual world during self-generated eye movements |
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microsaccades |
involuntary movements of the eyes that are in continuous motion |
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retinal stabilization |
when an image is made to be perfectly stable on the retina, it disappears |
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the Purkinje tree |
a shadow is cast on photoreceptors by the retinal blood vessels present in the eye, but we don't see them because it is always fixed |
