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Chapter 7

Sensation and Perception Psych 367 Chapter 7.docx

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University of Alberta
Douglas Wylie

Chapter 7 taking action The ecological approach to perception - Ecological approach to perception: focuses on how perception occurs in the environment by o Emphasizing the moving observer (how perception occurs as a person is moving through the environment) o Identifying information in the environment that the moving observer uses for perception The moving observer and information in the environment - Gibson began studying how pilots land airplanes o Book: perception of the visual world o What we know about perception from testing people fixed in place in the lab cannot explain perception in dynamic environments that usually occur in everyday experiences o Information for perception is located not on the retina, but “out there” in the environment - Optic array: the structure created by the surface, textures, and contours of the environment, and he focused on how movement of the observer causes changes in the optic array - Optic flow: the movement of elements in a scene relative to the observer o Movement of the surroundings - Optic flow has two characteristics o The flow is more rapid near the moving observer o There is no flow at the destination toward which the observer is moving - Gradient flow: The different speed of flow (fast near objects) (slow farther away objects) - The gradient of flow provides information about the observers speed - Focus of expansion: absence of flow at the destination point - Invariant information: property that remains constant under different conditions - Optic flow provides invariant information because it occurs no matter where the observer is, as long as they are moving Self-produced information - Self produced information: an observers movement provides information that the observer uses to guide further movement - We need to perceive to move, and we also need to move to perceive - Expert gymnasts perform somersaults more poorly with their eyes closed - Closing the eyes did not affect the performance of novice somersaulters as much as it affected the performance of experts - Experts learn to coordinate their movements with their perceptions, but novices have not yet learned to do this The senses do not work in isolation - Gibsons ideas was that the sense do not work in isolation - Each provides information for the same behaviour - Your ability to stand up straight, and to keep your balance while standing still or walking depends on systems that enable you to sense the position of your body - These systems include the vestibular canals of your inner ear and receptors in the joints and muscles - Gibson’s argued that information provided by vision also plays a role in keeping our balance - Vision provides a frame of reference that helps the muscles constantly make adjustments to help maintain balance - David lee and Eric Aronson: placed children in a swinging room - The flow is associated with moving forward, it creates the impression in the observer that he is swaying forward, this causes the toddler to sway back to compensate - Adults also affected by swinging room - The swinging room experiments show that vision is such a powerful determinant of balance that it can override the traditional sources of balance information provided by the inner ear and the receptors in the muscles and joints Navigating through the environment - Optic flow provides information about where a moving observer is heading - Observers task is to judge, based on optic flow stimuli, where he would be heading relative to a reference point (vertical line) - Observers viewing the stimuli such as this can judge where they are heading relative to the line within 1 degree Other strategies for navigating driving experiment - Land and Lee - Fitted cars with instruments to record the angle of the steering wheel and the speed, and measured where the diver was looking with a eye tracker - Gibson: the focus of expansion provides information about the place toward which a moving observer is heading - Drivers look straight ahead while driving, but they do not look directly at the focus of expansion - When going around a curve, drivers don’t look directly at the road, but look at the tangent point of the curve on the side of the road Walking experiment - An important strategy used by walkers that does not involve flow is the visual direction strategy o Observers keep their body pointed toward a target, if they go off course, the target will drift to the left or right - Flow information is not always necessary for navigation because we can find our way even when flow information is minimal, such as at night or in a snowstorm - Philbeck, Loomis, and Beall: demonstrated this by eliminating flow altogether, with a blind walk o Which people observed a target located 12 meters away, then walk to the target with their eyes closed - People are able to walk directly toward the target - The fact that a person stopped close to the target shows that we are able to accurately navigate short distances in the absence of any visual stimulation at all - One talk is to determine what information is available for perception - Another task is to determine what information is actually used for perception - The information that is used may depend on the specific situation The physiology of navigation Optic flow neurons - Neurons that respond to optic flow patterns are usually found in the medial superior temporal area (MST) - Britten and Van Wezel: demonstrated a connection between the response of neurons in MST and behaviour by first training monkeys to indicate whether the flow of dots on a computer screen indicated movement to the left or right of straight ahead - They electrically stimulated MST neurons that were tuned to respond to flow associated with a specific direction - They found that stimulation shifted the monkeys judgments toward the direction favoured by the stimulated neuron - This link between MST firing and perception supports the idea that flow neurons do in fact help determine perception of the direction of movement Brain area for navigation - There is more to navigating through the environment than perceiving the direction of movement - An essential part of navigation is knowing what path it takes to reach your destination - People often use landmarks - Parahippocampal place area (PPA) respond to buildings, the interiors of rooms, and other things associated with location - Maguire: observers viewed a computer screen to see a tour through a virtual town - Observers first learned the layout and as they were scanned with a PET, given the task of navigating from one point to another in the town - Navigating activated the right hippocampus and part of the parietal cortex - Acti
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