AB015.Interocular normalization in monkey primary visual cortex(V1)

Background:The two images,slightly different,seen by the two eyes allow the brain to build a 3D representation of the world.Monocular signals enter the primary visual cortex through layer 4,where they are segregated and organized in ocular dominance stripes.They are later combined in upper layers.In order to study the integration of the information coming from the two eyes at this mesoscopical scale in V1,we use optical imaging in anaesthetized macaque monkey.Methods:Ocular dominance maps have been obtained with intrinsic optical imaging.Dichoptic interactions have then been studied with voltage-sensitive dye imaging(VSDI)with a frequency-tagging paradigm.Visual stimuli with different contrasts were respectively presented at 6 and 10 Hz to the two eyes,independently or simultaneously with a passive 3D screen.Frequency analysis thus allowed to identify each eye’s contribution to the signal.Results:We observed that V1 population activity generated by one eye stimulation is suppressed when the other eye is stimulated too.This integration of monocular signals at the population level can be accurately modeled with an interocular normalization model.Conclusions:This approach and this model confirm V1 implication in combining the signals coming from the two eyes.The mechanisms underlying this interocular normalization,through local,feedforward,feedback or long-range connections,are still to be determined.

AB013.The effects of monocular deprivation on the Pulfrich phenomenon

Background:Short term monocular deprivation allows for the modulation of ocular dominance,such that the previously deprived eye contribution will increase,while that of non-deprived eye will decrease.This study examines the effects of short monocular occlusion on the Pulfrich phenomenon,an illusory perception of a horizontally moving object moving in an elliptical orbit in depth.In addition,we will explore whether the modulation of the Pulfrich effect is produced in the magnocellular pathway or the parvocellular pathway,by comparing two protocols,each designed to activate one pathway at a time.Methods:The stimulus used throughout the experiment is made up of elements defining a cylinder rotating in depth,allowing to measure interocular delay.The task consists of reporting the direction of rotation of the stimulus presented.There are two different stimuli:the P stimulus is composed of small elements oscillating slowly,which stimulates the parvocellular pathway,and the M stimulus which is composed of large elements oscillating rapidly which stimulates the magnocellular pathway.One experimental session consists of pre-patch testing,one hour of patching,and a post-patch testing.Each participant performs four sessions,both stimuli for each eye.Results:The point of subjective equivalence(PSE)is extracted from psychometric functions obtained during pre-testing and post-testing.Following deprivation of the left eye the PSE shifts negatively,whereas deprivation of the right eye shifts the PSE positively on the psychometric function.This indicated that monocular deprivation slows the perceptual processes of the previously patched eye.The amplitude of this effect is larger for the M protocol than it is for the P protocol.Conclusions:Contrary to expectations,results showed that effects of monocular deprivation are not exclusively mediated by contrast gain mechanisms,as suggested by Zhou and colleagues(2014).The amplitude of the differences observed for the M protocole suggest that the plasticity induced by short term deprivation is equally subjected to dynamic components.

AB074.Link between interocular correlation sensitivity and stereoscopic vision

Background:Stereoscopic Vision uses the disparity between the two images received by the two eyes in order to create a tridimensional representation.With this study,we aimed at providing an estimate of binocular vision at a level prior to disparity processing.In particular,we wanted to assess the spatial properties of the visual system for detecting interocular correlations(IOC).Methods:We developed dichoptic stimuli,made of textures which IOC is sinusoidally modulated at various correlation spatial frequencies.Then,we compared the sensitivity to these stimuli to the sensitivity to analogous stimuli with disparity modulation.Results:We observed that IOC sensitivity presents a low-pass/band-pass profile and increases as a function of presentation duration and contrast,in a similar way as disparity sensitivity.Conclusions:IOC sensitivity is weakly-though significantly-correlated with disparity sensitivity in the general population,which suggests that it could provide a marker for binocular vision,prior to disparity processing.

AB066. Duration dependent visual plasticity via monocular deprivation

Background:Short-term monocular deprivation has been recently shown to temporarily increase the sensitivity of the patched eye.Many studies have patched subjects for an arbitrary period of 2.5 hours,but for no principled reason.Our goal is to show a relationship,if any,between the length of patching duration and the strength of its effect.Methods:We tested nine subjects with three different patching durations:1-,2-,3-hour.Four of the nine subjects were patched for 5-hour.Monocular deprivation was achieved by the use of a translucent eyepatch.A session included two rounds of baseline testing of interocular eye balance,patching,and post-patching tests.Each post-patching test occurred at 0,3,6,12,24,48,60 and 96 minutes after patching to track the patching effect over time.Every subject performed two sessions per condition.Results:One-hour patching produced a small shift in ocular dominance.A larger shift occurred from 2-hour patching,but 3-hour patching produced a comparable effect to the one measured after 2-hour patching.Conclusions:These results show a saturation of the patching effect beyond 2-hour patching.Hence,we believe that 2-hour patching duration is the optimal duration for eye dominance changes induced by monocular deprivation.