Anthony J Greene1 MOTION & EVENT PERCEPTION
2 Event Perception Because perception evolved to provide organisms with world information, our ability to perceive events is the purpose of perception Perception across both 3-d space and time The integration of motion, form and color perception Includes perceptual learning and locomotion Most treatments of event perception include information from all sense modalities
Anthony J Greene3 Motion Perception: Aperture Problem
4 Motion detection cells - recall that complex cells in v1 and thick stripes in v2 can detect motion in a very local receptive field of the retina
Anthony J Greene5 Motion Perception: Aperture Problem V5 contains cells which are selective for motion across the entire visual field - cooperation between v1 and v5 is necessary for motion perception to occur Some cells are in V5 respond selectively for straight line motion in a particular direction Others cells respond to expansion and contraction patterns Still others respond to rotation (in depth and in the picture plane)
Anthony J Greene6 The Case of Motion Blindness Damage to V5 may result in motion blindness Stationary objects appear normally When an object or a person moves, it simply disappears When the object stops moving, it simply reappears What does this imply about the interactions of V3 and V5 for normal perception of a moving object?
Anthony J Greene7 Waterfall afterimage
Anthony J Greene8 Spiral afterimage spinner/index.html
Anthony J Greene9 Structure From Motion
Anthony J Greene10 Biological Motion In less than 1/2 second, almost everyone perceives a human form walking Although only motion information is available, recursive connections between v3 and v5 allow a stable 3 -d form to be perceived The sex, approximate age, height, and weight of the walker are readily apparent
Anthony J Greene11 3-D Necker Cube
Anthony J Greene12 3-D Necker Cube As in a 2-d Necker cube, the depth is ambiguous In this case, however, 3-d form is bound to motion and the direction of rotation is therefore also ambiguous This is a classic example of unconscious inference Gibson would admit that unconscious inference is going on, but, asserts that this sort of ambiguity would not occur in the real world - this sort of ambiguity was never present in the environment in which visual perception evolved
Anthony J Greene13 Rotating Trapezoid
Anthony J Greene14 Rotating Trapezoid
Anthony J Greene15 Rotating Trapezoid Because there are strong depth cues (linear perspective) it is natural to interpret the shape as a rectangle in depth Even knowing that it is a trapezoid does not allow us to override the perception that it is a rectangle In order for motion information to be paired with 3-d form information we interpret the motion as oscillation instead of rotation Infants and depth, size and shape perception
Anthony J Greene16 Visual Cliff E. Gibson (Late 1960’s) The Test Is To See If The Infant Will Crawl Across The Plexiglas Covered Cliff Towards Her Mother On The Left What Dominates The Infants’ Decision? Tactile Or Visual Information
Anthony J Greene17 Visual Cliff Result: Infants 6 To 14 Months Would Not Venture Over The Cliff - Does Not Address Whether Or Not This Is Innate Or Learned (Or Both) Experiment Was Repeated With 2-3 Day Old Kittens Deprived Of Depth Information With The Same Result
Anthony J Greene18 Visual Cliff Infants Less Than One Day Old Were Placed Both On The Plexiglas And On The Platform, And The Infants That Were Over The Cliff Showed More Anxiety (Anxiety Was Measured By Galvanic Skin Response, Heart Rate, Etc.) Stereopsis Was Not The Determining Factor Because The Same Result Was Obtained When One Eye Was Covered
Anthony J Greene19 Pseudo Visual Cliff To determine if the visual cliff effect was due to pictorial depth cues, or dynamic depth cues, a control study was run where a visual cliff was simulated by changing texture gradients Result: the infants did venture out over the “cliff” Demonstrates that dynamic monocular cues, such as motion parallax are required for convincing depth perception