Visual Motion PDF

Types of motion Real motion: object in the world is moving through our visual field Apparent motion: static images presented in rapid succession if the images change fast enough, the motion appears indistinguishable from real motion i.e. animation moves, flip books, etc. Movies also nam...

Types of motion Real motion: object in the world is moving through our visual field Apparent motion: static images presented in rapid succession if the images change fast enough, the motion appears indistinguishable from real motion i.e. animation moves, flip books, etc. Movies also named motion pictures Induced motion: movement of part of the image causes perception of motion in another part (background) i.e. the moon through the clouds: moon seems to move but its the clouds The motion after-effect: after prolonged of viewing a moving stimulus, a stationary scene will appear to move in the opposite direction Also named the waterfall illusion Happens because our eyes have adapted for a certain motion Biological motion we are especially sensitive to the familiar motion of a moving person or animal when the motion is only represented by finite points of light apparent when looking at a "point-light walker" Reichardt motion detectors Motion detector Motion: the change in position over time Moving objects will activate one receptive field followed by adjacent receptive field Larger objects will activate 2 RFs simultaneously Motion detection: need to capture the output from 2nd RF and delayed output from 1st RF To detect motion in either direction, we need to mirror this circuit To detect motion in a larger area, we need several simple detectors joined together Allowing adaptation can also explain the motion after-effect Detection tuning Detectors are not perfectly selective for a specific direction Respond most strongly to their preferred direction Less strongly to other directions depending on how close they are to the preferred one Aperture problem Aperture problem: When moving object is viewed through a restricted window (aperture), direction of motion may be ambiguous The RFs of the neural motion detectors function as apertures Global motion detectors Combination of multiple local detectors With different preferred directions and different spatial locations Each local detector can respond to many possible directions of motion with a preferred one Some neurons in MT receive input from multiple motion-sensitive neurons in different RFs in V1 and are sensitive to the global motion of a stimulus Sources 1. Motion of our environment 2. Self-motion Self-motion: focus of expansion (FOE) informs us of the direction we are moving Causes optic flow, which depends on the direction in which we are moving 3. Eye-movements Fixation: micro-saccades, drift, tremor Looking at a single point; eye is almost still Smooth pursuit: voluntary tracking eye movement Nystagmus: reflexive eye movements Saccades: voluntary eye movement Vergence: turning eyes inwards or outwards Anatomy 6 muscles in 3 pairs Inferior/Superior rectus (Up & Down) Medial/lateral rectus (Left & Right) Inferior/Superior oblique (rotation of eyeball) Visual motion and eye movements when we make an eye movement (or any movement), we use a copy of the motor command (corollary discharge) to predict the sensory consequences of that movement uses this prediction when interpreting the retinal image if our eyes are moving, we know that a stationary retinal image means that the object is also moving Saccadic Suppression We don’t perceive the visual information from during the saccade we use the corollary discharge information to remap the receptive field of frontal eye field (FEF) neurons to their future target just before an eye movement has started