Motion Sensitivity and Brain Disorders
Neurological examinations present significant data on the realizing pathophysiological mechanisms of motion perception distinguishing different motion attributes disorders connected with a damage in a given part of the nervous system. The very 'motion' brain structures localization faces complexity, but various 'motion' disruption phenomena might be seen in conjunction with the damage localization.
It was reported (Vaina LM, Cowey A, 1996) first order motion (sensation) and second-order motion (spatiotemporal variation of motion attributes based on the luminance) may have the different extent of disorder in the patient with a small unilateral cortical lesion adjacent to human cortical area MT (V5). The disorder in perceiving several forms of second-order but not first-order motion in his contralateral visual field was detected. Authors conclude that separate pathways for motion perception exist, i.e. as divergent pathways from area MT or from primary visual cortex, or as separate pathways from subcortical areas to extrastriate visual areas.
The disability to discriminate the direction of motion (perceiving motion in depth) when presented in the hemianopic field in patients with partial or complete cerebral hemispherectomy was shown (King SM, Frey S, Villemure JG, Ptito A, Azzopardi P, 1996). The idea forward is the subcortical visual pathways which survive after hemispherectomy are unable to process visual information relating to motion in depth.
To localize brain structures responsible for motion perception (presumably in the lateral occipitotemporal cortex) and to distinguish them from others, when unilateral cerebral hemispheric lesions (Barton JJ, Sharpe JA, 1997), the motion direction discrimination with random dot cinematograms projected into the contralateral homonymous visual field defects was used. It was found the putative motion area and its input fibers distruction is not a sufficient condition for residual direction discrimination (blindsight) in homonymous visual field defects.
The pesented effect of induced percept in the 'blind' hemifield (when hemianopic visual field) from the movement in the normal visual hemifield (Finlay AL, Jones SR, Morland AB, Ogilvie JA, Ruddock KH, 1997) was shown to be dependent on the irection of movement, the contrast and the velocity of a grating presented to the normal hemifield. Interesting that this effect was indistinguishable from responses caused by moving stimuli when the direct stimulation within the 'blind' hemifield. And also no such induced effects were detected in response to color or to flickering stimuli. It may appoint on the difference in mechanisms and anatomical structures underlaying color, flicker and motion sensitivity.
The opthtalmic visual evoked potentials (VEPs) studies (Kubov Z, Kuba M, Juran J, Blakemore C., 1996) contribute the above investigations by the interesting observation on the ambliopic eyes. It was demonstrated that regardless of the type of amblyopia, the amplitude of the pattern-reversal VEP for full-field stimulation (P1 peak) was significantly smaller and its latency significantly longer through the amblyopic eye. In contrast, neither the amplitudes nor the latencies of the motion-onset (N2 peak) VEPs differed significantly between amblyopic and non-amblyopic eyes. Authors propose the source of motion-onset VEPs (probably an extrastriate motion-sensitive area) is less affected in amblyopia than that of pattern-reversal VEPs (probably the striate cortex).
Vaina LM, Cowey A.
Impairment of the perception of second order motion but not first order motion in a patient with unilateral focal brain damage. Proc R Soc Lond B Biol Sci, 1996, 22, 263:1374, 1225-32.
King SM, Frey S, Villemure JG, Ptito A, Azzopardi P.
Perception of motion-in-depth in patients with partial or complete cerebral hemispherectomy. Behav Brain Res, 1996, 76:1-2, 169-80.
Barton JJ, Sharpe JA.
Motion direction discrimination in blind hemifields. Ann Neurol, 1997, 41:2, 255-64.
Rorden C, Mattingley JB, Karnath HO, Driver J.
Visual extinction and prior entry: impaired perception of temporal order with intact motion perception after unilateral parietal damage. Neuropsychologia, 1997, 35:4, 421-33.
Finlay AL, Jones SR, Morland AB, Ogilvie JA, Ruddock KH.
Movement in the normal visual hemifield induces a percept in the 'blind' hemifield of a human hemianope. Proc R Soc Lond B Biol Sci, 1997, 22, 264:1379, 267-75.
Kubov Z, Kuba M, Juran J, Blakemore C.
Is the motion system relatively spared in amblyopia? Evidence from cortical evoked responses. Vision Res, 1996, 36:1, 181-90.
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