Motion Information Generated By Selfmotion

Moving through complicated environments is an everyday necessity that depends critically on visual motion information. Humans, like other animals, are able to perceive and control their motion precisely through complex environments. We have two main types of sensory inputs that help us perceive self-motion: vestibular and visual. Vestibular input from the semicircular canals in the ears directly sense certain types of self-motion by detecting accelerations. Here, we focus on the ability of humans to perceive self-motion from purely visual cues, which are produced by the changing images (motion) our eyes receive as we move.

When a person moves, the environment generates a pattern of motion across the retina, which is called optic flow. As J. J. Gibson described, if the person is moving along a line without rotating (translating), the object toward which he or she is moving stays fixed on the retina but all other objects move in an outward radially expanding pattern that is centered about the direction of translation (Fig. 10A). For pure translation, this stationary point is called the focus of expansion (FOE), and the direction of self-motion is toward its location. When the person is translating slightly to the left of straight ahead, the resulting optic flow pattern is shown in Fig. 10B. Many studies have presented stationary observers with various types of translational optic flow patterns and found that humans can accurately (to within approximately 1°) determine the simulated direction of self-motion under a wide range of conditions. A different type of optic flow pattern results when the observer's position remains fixed but he or she rotates his or her eyes (or body). This rotation produces the optic flow pattern shown in Fig. 10C. If the self-motion is a combination of translation and rotation, resulting from the observer rotating his or her eyes to maintain fixation of an object while walking in a straight line in a different direction, the resulting optic flow pattern is the sum of the translational and rotational optic flow patterns

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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