Psychology of visual perception C O M M U N I C A T I O N D E S I G N, A N I M A T E D I M A G E 2014/2015

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1 Psychlgy f visual perceptin C O M M U N I C A T I O N D E S I G N, A N I M A T E D I M A G E 2014/2015 EXTENDED SUMMARY Lessn #7: Nv. 10 th 2014 Lecture plan: CONTENTS OF VISUAL PERCEPTION MOTION PERCEPTION. Image-retina system Eyes-head system Relative and induced mtin Apparent mtin Extended lessn summary: INTRODUCTORY ASPECTS DEFINITION OF MOTION PERCEPTION: - PROCESS OF INFERENCE OF SPEED AND DIRECTION OF OBJECTS AND SURFACES THAT MOVE IN A VISUAL FIELD, GIVEN SOME KIND OF VISUAL INPUT; VERY IMPORTANT ASPECT OF THE KNOWLEDGE OF THE REALITY AROUND US; THE MORE PERIPHERAL AREAS OF THE RETINA ARE ONLY SENSITIVE TO MOTION. COMPLEXITY INHERENT TO MOTION PERCEPTION All the fllwing different three situatins can prduce a sense f mtin: Eye balls are fixed n the bird. The F1 car passes by. We see the car mving. Our eye balls are fixed n the F1 car that passes by. We turn ur head t fllw the car. We see the car mving. Eye balls are fixed n the F1 car that passes by. We mve ur eye balls t fllw the car. We see the car mving. EXTENDED LESSON SUMMARY Pag. 1/6

2 S The sense f mtin may result frm: Mvement f the prjectin f the bject image n ur retina (retina/image system); Mvement f ur eye balls r head (eye ball/head system) IMAGE-RETINA SYSTEM MOTION PERCEPTION RESULTS FROM INFORMATION PROVIDED BY PROXIMAL STIMULI; THE IMAGE MOVING IN THE RETINA SEQUENTIALLY FIRING THE RECEPTORS THAT ARE ON HIS TRAIL; THE FASTER THIS IMAGE MOVES (UP TO A CERTAIN LIMIT) FASTER WILL BE THE PERCEIVED MOTION. EYE-HEAD SYSTEM PERCEPTION OF MOTION RESULTS FROM THE MOVEMENT OF OUR EYES AND HEAD; EXTRAOCULAR MUSCLES: Active muscle: Superir rectus Inferir rectus Superir blique Inferir blique Lateral rectus Medial rectus Mvement: Upwards & tempral Dwnwards & tempral Dwnwards & nasal Upwards & nasal Sideways & tempral Sideways & nasal LECTURE PLAN_#7_NOV. 10 TH 2014 Pg. 2/6

3 MOVEMENT OF EXTRA OCULAR MUSCLES Why des the wrld remain stable when we mve ur eyes? The retinal images run acrss the receptrs whenever we mve ur eyes, and yet we d nt experience mvement: the wrld des nt usually spin rund when we mve ur eyes. This des happen when a cine r vide camera is panned rund. We have seen that there are tw neural systems fr signalling mvement: - the image-retina and the eye-head systems. It seems that during nrmal eye mvements these signals cancel each ther ut, t give stability t the visual wrld. Hermann vn Helmhltz ( ) thught that retinal mvement signals are cancelled by central 'utflw' signals frm the brain, cmmanding the eyes t mve. REAL AND APPARENT MOTION REAL MOTION: Very little infrmatin is required t detect mtin; Perceptin f mtin can lead t the perceptin f shape and bjects: Link mtin perceptin/perceptin f shape? Example frm Dnald d. Hffman Exempl frm Michael Bach michaelbach.de/t/mt_bimt/index.html Mre elabrated exemple frm Nichlas Trje Bilgical mtin: LECTURE PLAN_#7_NOV. 10 TH 2014 Pg. 3/6

4 RELATIVE AND INDUCED MOTION Relative mtin Perceptin f mtin in a mving bject having as a reference pint ther bjects in the visual field where that bject is lcated r any ther frame f reference. Vide example: Induced mtin Perceptin f mtin f an bject which is mtinless; Smetimes induced mtin is prduced by mvements f the backgrund r frame f reference. Exemples: Mn behind cluds: Vide: The mn is mtinless but we see an illusin f mtin induced by the mving cluds. Pigen head: Vides: In the walking pigen the head seems t g back and frth, but in reality the head nly ges frward. The backwards mtin is an illusin induced by the frward mtin f the bdy f the pigen as explained in the fllwing drawings: Induced aut mtin: Induced mvement is ur wn mvement; LECTURE PLAN_#7_NOV. 10 TH 2014 Pg. 4/6

5 Example: We are inside a train that is clse t anther train. In a very first mment we feel ur train is mving, but what is actually mving is the train in ther platfrm. APPARENT MOTION Perceptin f a successin f still images as ne mving image; Tw types f apparent mtin: Beta β and Phi φ mtin. See: AUTOKINETIC MOTION Illusry displacement f a static pint f light in a cmpletely dark backgrund. Yu might like t try the fllwing experiment. The apparatus is a small dim light (such as an LED) placed at the far end f a cmpletely dark rm. If yu lk at the light fr mre than a few secnds, it will wander arund, in a curius erratic manner, smetimes swping in ne directin, and smetimes scillating gently t and fr. Its mvement may seem paradxical: it may appear t mve, yet nt change its psitin. The usual wandering mvements f the autkinetic effect seem t be due t cmmand signals maintaining fixatin in spite f slight spntaneus LECTURE PLAN_#7_NOV. 10 TH 2014 Pg. 5/6

6 fluctuatins in the efficiency f the muscles, which tend t make the eyes wander. It is nt the eyes mving, but the crrecting signals applied t prevent them mving which cause the light apparently t mve in the dark. S, the autkinetic effect seem t be due t efferent signals that keep the fixatin f the gaze, in the absence f a frame f reference. Due t disturbances f the eye-head system. THE WATERFALL EFFECT Due t disturbances f the image-retina system Depends n the mtin aftereffect; Was first described by Aristtle. Just after watching a waterfall, he saw the bank f the river apparently mving. S it is knwn as the waterfall effect thugh it is prduced by any cntinuus mtin, including expansin r cntractin. The after-effect is always in the ppsite directin t the 'inducing stimulus. Yu can see a nice vide demnstratin in: And read a little abut at: Far, Prfessr in charge f CU: LECTURE PLAN_#7_NOV. 10 TH 2014 Pg. 6/6