Chapter 12 Notes

Chapter 12 Notes - Chapter 12 The Visual System Depth...

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Chapter 12: The Visual System: Depth Perception and Stereopsis Binocular vision: the ability to see the world through two eyes Cyclopean vision: a single, unified vision of the world Having binocular vision has many benefits, the most important being depth perception! A. Extrapersonal space We first need to understand how to specify the spatial relationship with an object. Then we need to understand how we obtain and process information about the changing orientation of our own body in a 3-dimensional world. 1. Spatial Frames of Reference Two ways of specifying the location of objects: 1. Allocentric: specify the spatial location of an object independent from the viewer a. Thus, spatial locations are defined in an external manner b. Objects are described in relation to each other (a pen is next to a book) c. The pen will always be next to the book no matter how it’s viewed. 2. Egocentric: a viewer-dependent system a. Implies that we have a reference point on our body for judging the direction of objects ( visual egocentre ) b. Objects are usually visually perceived as a point midway between the 2 eyes (point of reference where the two eyes operate together) 2. Head and Body Movements In Space Human Dynamics Any movement of the body must be defined within a frame of reference!
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We define the principle axes of the body first with respect to gravity in an upright stance. X axis – transverse planes (divides the body into the lower and upper halves) rotations along this axis are referred to as roll Y axis – coronal planes (divides the body into the front and back halves) rotations along this axis are referred to as pitch Z axis – median planes (divides the body into the left and right halves) rotations along this axis are referred to as yaw Proprioceptive and efferent signals Proprioceptive system: a system of detectors of muscle contraction and movement around a joint. Every time we move a muscle or part of the body voluntarily, our motor centers in the brain send the command to our muscles. HOWEVER, a COPY (efference copy or corollary discharge) is also sent out to know limb position and movement as it happens. The vestibular system Vestibular apparatus is the balance organ, composed of the semicircular canal and the otoliths. Fluid movement in the vestibular organs is generated by the movement of the head and the body. Rotational movement fluid displacement in the semicircular canals Linear body movement stimulates the otolith organ In order to move fluid, you need acceleration! 3. Perception of Absolute Depth Location of an object comes from where it falls on the retina, but distance is not so easily found. There are 3 cues needed for depth perception: 1. Optical cue – retinal image size Changing the distance of an object does affect its size. If we know the object’s usual size (such as human height), we would have an idea of how close the object is to us.
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