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Visual Perception Week 7 Notes

by: Freddi Marsillo

Visual Perception Week 7 Notes PSYC 3124

Marketplace > George Washington University > Psychlogy > PSYC 3124 > Visual Perception Week 7 Notes
Freddi Marsillo
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About this Document

These notes cover the two articles we discussed this week, along with additional information Dr. Philbeck pointed out in these studies.
Visual Perception
Dr. John Philbeck
Class Notes
Visual perception
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This 11 page Class Notes was uploaded by Freddi Marsillo on Thursday February 25, 2016. The Class Notes belongs to PSYC 3124 at George Washington University taught by Dr. John Philbeck in Spring 2016. Since its upload, it has received 30 views. For similar materials see Visual Perception in Psychlogy at George Washington University.


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Date Created: 02/25/16
Visual Perception Week 7 Notes 2/25/16 1:27 PM Nakayama Paper James Gibson – did research at Princeton during 50s-60s Nakayama’s Appreciation • Nakayama’s appreciation of Gibson grew over time • Gibson’s ideas were philosophical, not research based • In Nakayama’s time many researchers were concerned with physiology, not specific functions Gibson’s Physics • Scale comparable to the animal • Gibson is interested in the physical world’s possible interactions with animal life • Surfaces o The surface is what touches the animal, not the interior • Gibson’s 2 interests: o 1) How locomotion with respect to the physical environment is controlled o 2) The consequences of locomotion for perception (optic flow) Psychology of Information Pickup • How do our eyes interact with our environment? o Prior to vision, it was thought that vision is static o Gibson suggests that it is more dynamic – “even a slight movement of a photographer’s camera will shift the image and ruins the picture” comparison o Light is not just a stimulus, but also a carrier of information o Light as a medium Relative Motion and the Control of Locomotion • Optic flow provides sense of direction during movement Final Thoughts Despite: • 1) Not participating in research • 2) lack of interest in psychophysiology • 3) refusal to talk about mental images, Gibson was able to provide a framework for the field of visual perception He has encouraged us to focus more on real-world situations and stimuli; more ecological stance Talked about the importance of motion-based vision; the importance of the observer being able to actively interact with the world – actively engaging with the environment and not just passively observing Summary • Gibson was radical because he went against popular notion of vision at the time and shunned formal protocol in experiments on vision (Population notion at the time: vision is static; we rely on memory to see and recognize) • Said vision is a dynamic and active process, which he explained using his “Gibson Physics” o He compared cameras to our eyes. If even the slightest movement throws a camera or video camera off, our eyes are obviously not working like them. It’s more active o Instead of constantly taking pictures and analyzing them, Gibson said visual process is up the information we need from constant optic flow • Biggest point was information pickup (how do humans take in visual cues) o Said our eyes constantly pick up information about gradient, texture, motion, etc. because our eyes have properties that can observe these (never actually said neurons) o Theorized all this before visual physiology was fully known or broken down – that’s why Nakayama appreciates him o Think of fighter jets and pigeons as examples – if prior thought about memory directly linked to vision is true, how would pilots and pigeons fly around without colliding into everything around them? • Legacy – visual experiments that mimic the real world, changed the static notion of vision into a dynamic and active one Perception and Action The “what” stream is the ventral stream The “where” stream is the dorsal stream • When monkeys had dorsal damage, they did poorly on the landmark test • Monkeys with damage in the dorsal stream had the opposite problem; they could do the landmark task, but could not do the match to sample task Milner & Goodale then proposed that dorsal stream controlled action – in their book, they wrote that action and location might be confounded in some way • Patient DF – someone who had damage in her ventral stream, so had trouble using vision to recognize objects, but she could use her vision to reach out for something (the “where” factor) • You might find that the ventral stream is activated during certain tasks and the dorsal stream is activated during certain tasks Haffenden, Schiff, & Goodale Paper (2001) The dissociation between perception and action in the Ebbinghaus illusion: Nonillusory effects of pictorial cues on grasp Background 1) Recently proposed distinction: vision for perception and vision for action • Visually guided movements should be largely immune to the perceptually compelling changes in size produced by pictorial illusions 2) Previous tests: small effects of illusion on action using Ebbinghaus illusion • There is a single presentation of size for perception and action – do not support the double dissociation 3) More recent findings: confounding variables • 2-D pictorial elements (comprising illusory background) influence vision for action: give rise to an effect on grasp 4) Gap between target and illusory-making elements is equidistant across different conditions • Grasp scaling, in contrast, appeared to be affected primarily by the physical proximity of the 2-D illusory elements to the target, irrespective of the size of the surrounding elements New Figures • Adjusted figures   Materials and Method • Subjects: 9 female and 9 male undergraduate students, all right- handed and had normal or corrected-to-normal visionMaterials • 1) The viewing period was controlled by PLATO goggles, whose lenses are liquid-crystal shutters that remain opaque until they receive a switch signal from the experimenter. The change from clear back to opaque takes 2.5 milliseconds so all participants should have enough practice before the task to make sure they can react in a short time • 2) Markers of three-camera Optotrak system were fastened to subject’s index fingers, thumbs, and wrists to record the finger and hand position Stimuli-target disks Traditional small: the traditional small circle had an inner diameter of 38 mm and consisted of 11 circles with 10 mm diameters   Adjusted small: the adjusted small circle had an inner diameter of 54 mm and consisted of 16 circles with 10 mm diameters Traditional large: the traditional large circle had an inner diameter of 54 mm and consisted of 5 circles with 54 mm diameters Procedure • Each subject performed two tasks: manual estimation task and grasping task • Subjects complete one set of trials for each of the two tasks • A trail set consisted of 60 individual trials and 5 trials for each of the 12 conditions (3 displays x 4 disks) Estimation task • In the estimation task, the experimenter first signaled the lens to become clear to enable the participants to view the display • After seeing the display, the subjects should move their hands to their body and manually estimate the size of the disk by separating their thumb and index finger until they felt the gap accurately match the width of the target disk they had just seen. • They should hold this position for the whole 2.5 milliseconds Grasping task • The grasping task had similar a similar procedure • After the display was clear to view, the subjects should immediately reach out their hands to grasp the target disk with a neutral movement • They should hold their grasping hand for the whole 2.5 milliseconds Effects of Illusory Displays on Estimations/Grasp Scaling • From smaller to larger surrounding circles in the manual estimation task, participants consistently guessed smaller • Similar trend in grasp task, except between the adjusted small and traditional large illusions • Primary finding of the study: grasp was influenced by the distance between the center circle and the surrounding circles, NOT the size of the surrounding circles • The difference between the adjusted small and traditional large was significant for estimation and negligible for grasp • The only difference that is greater for grasp than estimation is between the traditional and adjusted small Effects of Target Disk Size on Estimations/Grasp • Significant interaction between task and target disk size • The size of the grasp AND the size of the estimation increased as the target disk size increased Predicted Effects of the Illusory Display on Grasp Scaling • Performed this to show that effects were not just due to the fact that the two tasks required different response functions • The small effects of displays on grasp scaling could reflect the same perceptual effect seen in manual estimation • Based this calculation on the differences between the two tasks when looking at disk size – when both tasks showed an increase in size Future Research Why should grasp be sensitive to distance between target and the surrounding circles? • Could be that they are treated as “potential obstacles” • Maximum hand opening reduced when there is a gap between the target and surrounding elements – as opposed to target on its own • Reach-to-grasp movements directed toward 3D target altered by the presence of a light emitting diode (an obstacle) embedded in surface of display • Diode: What to take away from this • Franz et al. (2000) suggested that small changes in grasp reveal that there is a single representation of size for both perception (manual estimation) and action (grasp) • This experiment shows that this is not true • There is a distinction between how we perceive size as it relates to perception and action o Distance is a key variable • Furthermore, it may be because the circles in the surrounding ring are treated as potential obstacles when action is involved 2/25/16 1:27 PM 2/25/16 1:27 PM


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