As per my understanding binocular summation occurs in V1 and everything above i.e, extrastriate cortex is mostly binocular. How much does the effect of amblyopic eye affect the motion coherence threshold of fellow eye and where does the binocular summation or inhibition ( if any ) occurs for motion perception.
We found equally poor global motion coherence thresholds in unilaterally deprived patients. See Ellemberg et al., 2002
Thank you Terri. I will look at the paper but studies are not consistent in the literature regarding this finding, are they?
Regards,
Nabin
Strabismic amblyopes show small deficits in the nondeprived eye for many aspects of vision. In deprivation amblyopes, the extent of the deficit in the nondeprived eye depends on the aspect of vision studied. For example, the deprived eye shows subtle deficits in acuity but large deficits (as large as those in the deprived eye) for global motion. We are the only group that has tested sensitivity to global motion in the nondeprived eye of deprivation amblyopes.
Hi Terri, your response sounds interesting. I saw couple of your papers on deprivational amblyopia as well. They are very impressive. But there must be a reason why such discrepency is found between deprivational and other types of amblyopia (aniso, strabismic). Also, are there monocular cells in Extrastriate regions in cases of amblyopia, if not why is there a difference in Global motion perception while tested with amblyopic eye and the fellow eye. Ideally, the coherence should be similar, shouldn't it, if a single ( binocular) center is driving the function.
Hi Mahesh, I totally agree that global MCT is affected more than the contrast defects in fellow eye of amblyopia which proves that these functions are binocularly driven. As Terri mentioned that they found similar level of global motion coherence in fellow eye of deprivational amblyopia which is very interesting but that might not be the case in strabismic and anisometropic amblyopia. Regarding the summation, http://www.tsolab.com/jclub/20070820/hess-binocular-motion.pdf this paper mentions that summation in global motion is mostly contrast dependent which mostly occurs in level V1.
Thanks!
I have been using the "ball in the grass" computer program (developed by Wattam-Bell, Atkinson and Braddick) within my optometric practice. In particular I have found reduced performance in both static form and motion processing (in children with educational difficulties, (with grater reduction in motion processing. which itself can be linked to Functional (dynamic) visual fields, speed of eye movement, accommodation and convergence performance as well as SAT results in school.(results undergoing peer review at present) Due to time constraints i always test binocularly, however starbismic children do have reduced functional (dynamic) fields cf to their "normal eye". This suggests they have less cortical input from the peripheral magno system which would reduce motion processing?? I don' t know if this helps with your thinking process
Hi Geoff,
Nice to hear that you are applying motion perception test in clinical practice which is very impressive. Your explanation makes sense to me. Keep on doing what you are doing. Just wondering if you can provide me a reference of the paper that designed the ball on the grass computer game.
Best wishes.
Nabin
There is a paper to be presented at CRVS conference you may be interested in http://cvrsoc.org/docs/CVRS2013-web.pdf
Motion Perception Deficits and Occlusion Therapy for Amblyopia Presenting Author: Deborah Giaschi, Ophthalmology and Visual Sciences, University of British Columbia , Canada Co-Author(s): C Chapman ; S Narasimhan ; C Ho ; C Lyons ; D Regan, Psychology, York University, Canada Purpose Amblyopia is characterized by reduced visual acuity in a clinically normal, optimally refracted eye. Visual acuity and other aspects of form perception are usually normal in the fellow eye. We found that following treatment, many children also have deficits in motion perception in the amblyopic and the fellow eye. Bilateral motion deficits may reflect a visual system that is more compromised and more difficult to treat than one with only unilateral form perception deficits. Standard treatment - occlusion of the fellow eye - fails to restore visual acuity in up to 33%, and post-treatment slippage of visual acuity occurs in up to 25% of patients. Treatment failures may occur because occlusion treats only some of the problems in amblyopia. The purpose of this study was to determine the effect of occlusion therapy on motion deficits in children with amblyopia. Methods We measured motion coherence thresholds for orientation discrimination of motion-defined rectangles, using standard psychophysical methods disguised as computer games. Children with strabismic or anisometropic amblyopia (4-8 years old) were tested at 3 time points during at least 1 year of part-time occlusion; age-matched controls were tested at the same intervals. Visual acuity was measured on each visit. Results Initially, the amblyopic group showed elevated motion thresholds in each eye relative to the control group (p.05), despite an average improvement in amblyopic eye visual acuity of two lines. Children with poorer final visual acuity tended to have higher initial motion thresholds. No new fellow-eye deficits were induced by treatment. Discussion & Conclusions These results suggest that deficits in motion-defined form perception are not caused by, and are somewhat resistant to, occlusion therapy. There are many negative effects associated with occlusion therapy; therefore it is important to identify children with visual deficits that are unlikely to be treated successfully. These children may benefit from recently successful alternative treatments, such as dichoptic antisuppression therapy.
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