User:Prdillon/sandbox

Paul Dillon's Sandbox

5. Eye Movement and Attention
Eye movements are extremely important to the human beings visual perception of the world. For example, high acuity vision is only possible within the fovea consisting of only about 1/40th or 1% of the retinal surface area. Eye movements redirect incoming light onto specific regions such as the fovea allowing the visual system to operate correctly.

Eye Movement Types
Eye movements have been categorized in a variety of ways. The list provided below is neither a distinct nor comprehensive categorization of eye movements but a listing of the primary types along with their definitions.


 * Saccade: When we read or search for an object, the human eye doesn’t actually move continuously, rather many short and rapid eye movements are made; these movements are called saccades. Saccades are rapid movements of the eyes with velocities as high as 500 angular degrees per second. In fact even when we are simply viewing a scene, although it may seem that we are taking in the whole scene simultaneously our eyes are actually completing many saccadic movements.  These saccades allow our vision to transition between all of the important parts of the scene and stitch them together in order to attend the image as a whole.


 * Smooth Pursuit: Smooth pursuit eye movements allow primates to rotate their eyes smoothly so that the fovea remains pointed at slowly moving objects. This type of eye movement is experienced while tracking moving objects across your vision.  Smooth pursuit is impossible for most people to begin without a moving stimulus.


 * Vergence: Vergence is the simultaneous inward and outward movement of both eyes.  Like smooth pursuit, vergence allows primates to keep images of interest focused on the foveal region of the retina.  The process of vergence is most salient to humans as one attempts to focus on a close object and feels the eyes straining to turn inwards.


 * Vestibulo-ocular: Vestibular eye movements occur when the eyes rotate to compensate for head and body movements in order to maintain the same direction of vision. Without the vestibular system humans would be unable to remain upright as this system contributes largely to the process of balance.


 * Miniature Eye Movements: Miniature eye movements, also called microsaccades, are extremely small eye movements, so small that they are constantly happening yet we as human beings do not experience them in our vision.  Even when gaze is fixed on a specific object the eyes are physically moving ever so slightly. This area of eye movements comprises a category of vision that remains somewhat debated.  Some claim that miniature eye movements have no practical application and play no important role in vision.  However, others have hypothesized that these minute movements of the eyes prevent the process of adaptation that would be experienced if the eyes did not move at all.