Understanding Eye Movements & the Optokinetic System: Gaze Stabilization & Self-Motion Per, Quizzes of Speech-Language Pathology

Download Understanding Eye Movements & the Optokinetic System: Gaze Stabilization & Self-Motion Per and more Quizzes Speech-Language Pathology in PDF only on Docsity! TERM 1 Why we need eye movements DEFINITION 1 To stabilize the angle of gazeTo change the angle of gaze: the saccadic and smooth pursuit systems serve to do this TERM 2 Our Visual Angle DEFINITION 2 We can see about 200 degrees TERM 3 Pulse Vs. Step DEFINITION 3 Pulse: velocity commandStep: position command, obtained from the velocity command via neural integrator TERM 4 Gaze-Evoked Nystagmus DEFINITION 4 when the step process doesn't work, the eye is carried to its new position by the pulse by cannot be held there and drifts back to the primary position TERM 5 VOR Latency DEFINITION 5 less than 16msec TERM 6 Optokinetic System (OPK) DEFINITION 6 stabilizes gaze during sustained head rotation. stimulus: retinal slip that occurs once VOR compensation declinesVOR declines and visual drive takes over and maintains compensatory slow component eye movements during sustained rotationoutput: compensatory nystagmus and a sensation of spinning TERM 7 Circularvection DEFINITION 7 the sensation of self-motion even though there is no peripheral vestibular inputAn optical illusion is characterized by visually perceived images that differ from objective realityPart of the OPK system TERM 8 Optokinetic Nystagmus (OKN) DEFINITION 8 reflexive, nystagmic eye movement to an optokinetic stimulusboth the smooth pursuit and OPK systems contribute to the OKN responsesmooth pursuit most important at the onset of the stimulusOKN is decreased by fixation TERM 9 OKN Gain DEFINITION 9 about .8 for velocities less than 60 degrees/sec. greater for an upward moving stimulus than for a downward moving stimulusGreater if a person passively looks at the surround rather than actively looks at the moving stimulus TERM 10 Optokinetic after-nystagmus (OKAN) DEFINITION 10 once the optokinetic response begins, the OKN continues for some time after the stimulation stopsproduced by the velocity storage mechanism similar to that found in the VOR TERM 21 Saccadic Step DEFINITION 21 follows the saccadic pulsethe agonist eye muscles and ocular motoneurons hold the eye in its new position against orbital elastic restoring forcesstep command generated by the neural integrator TERM 22 "Slide of Innervation" DEFINITION 22 the transition between the pulse and the steptakes up to several hundred milliseconds TERM 23 Tracking DEFINITION 23 aka smooth pursuitallows continuous, clear vision of objects moving within the visual environmentgoal is to match eye velocity to the angular velocity of the targetexamples: watching a pendulum swing, or a single bird flying across a persons visual field TERM 24 Characteristics of Smooth Pursuit DEFINITION 24 trajectory of target must be predictable, and frequency of movement less than 1.2Hzmost efficient range is for frequencies less than 1 Hzlatency = 100msecstimulus used = sinusoidal waveMeasured in gain (peak eye velocity/peak target velocity= 1 unity)Measured in phase TERM 25 Breakdown in Smooth Pursuit Characterized by what? DEFINITION 25 a decrease in gainappearance of phase lagusually doesn't deteriorate until target velocity of about 100 degrees/secondinfluenced by alertness, drugs, and age TERM 26 Visual Fixation DEFINITION 26 the active process of maintaining a fixed line of gaze on a stationary target of interestshares neurological substrates with the smooth pursuit system TERM 27 Microsaccades DEFINITION 27 high-frequency, low-amplitude oscillations that can interrupt a visual fixation TERM 28 Congenital Nystagmus DEFINITION 28 patients who show normal fixation of stationary target but whose eyes break into oscillations during smooth pursuit TERM 29 Eccentric Position DEFINITION 29 when the eyes move away from the primary position (0 degrees) to a different position in the orbit (20 degrees to the R. or L.) TERM 30 Neural Integrator for Horizontal, conjugate eye movements DEFINITION 30 the medial vestibular nucleus (MVN) and nucleus prepositus hypoglossi (NPH) TERM 31 Cerebellum's responsibility DEFINITION 31 calibrates saccadic amplitude and the saccadic pulse-step match for optimal visuo-ocular motor behavior TERM 32 Classes of Eye Movements DEFINITION 32 1. Reflexive: gaze stabilization a) VOR: stabilize for head movement b) optokinetic: stabilize for image motion2. Voluntary: gaze shifting a) saccades: acquire stationary targetb) smooth pursuit: acquire moving targetc) vergence: acquire target in depth