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All moving objects generate sequential retinotopic activations representing a series of discrete locations in space and time(motion trajectory).Visual motion is fundamentally different from physical motion,because the former represents sequential retinotopic neuronal activations in time generated by a physical moving object.Traditionally cortical direction-selective neurons are regarded as motion detector whiles orientation-selective neurons as contour detector.However,orientation-selective neurons also respond rigorously to motion stimuli.What is then the common neural mechanism underlying early motion processing in high mammalians? The visual brain must work as a whole not only of high efficiency but also of energy saving and economics.Different types of neurons may encode and process the same visual information.Therefore,any visual neuron shall be regarded as visual motion detector/processor,as long as it can code and deal with retinotopic sequential activations in time on the retina.For example,for an object moving fast in high speeds along a fixed direction,besides direction-selective neurons other type of neurons might be needed to process a high-speed motion.This hypothesis is famously authorized with a concept of motion streak by Geisler firstly in psychophysical experiments(Geisler,Nature,1999)and later single-unit recordings of the primary visual cortex of both macaque and cat(Geisler et al,Visual Neuroscience 2001),in which he demonstrates that the motion streak generated by a fast moving spot can effectively activate orientation-selective neurons.Motion streak is essentially the axial or trajectory information of a fast moving object.Here we ask how do cortical neurons particularly those orientation-and direction-selective neurons in early visual cortices encode these discrete retinotopic positions of a moving object at low and high speeds? This is a fundamental question of early visual motion processing,and we have investigated it consecutively bycombining in vivo simultaneous intrinsic-signal optical imaging along with electrophysiological electrode recordings and computer simulations: We firstly investigated what is the functional role of orientation-selective neurons in motion information processing at low and high speeds across V1,V2,and V4? By studying the orientation population responses to moving noises,we demonstrated that for a given motion direction,two groups of orientation-selective cells with orthogonal preferences encode motion direction and motion streak at low and high speeds,respectively.Unlike direction-selective responses encoded in the dorsal stream(Adelson&Movshon 1982; Born & Bradley 2005; Rust et al.2006; Bradley &Goyal 2008),the orientation population responses recorded in V1,V2,and V4,may serve as a separate linear processing stream contributing directly to motion perception as has been suggested from human psychological studies(Geisler 1999; Burr & Thompson 2011).This work was published in J Neurosci.(An et al.,2012).We next re-investigated how direction-selective neurons process motion information at low and high speeds.In comparison with macaque V1 and V2,cat visual areas 17 and 18 provide an excellent model to study different aspects of motion signal(direction,speed and motion axis)and their inter-relationships(Hubel & Wiesel 1962,Movshon 1972).Using single-cell recording and optical imaging of intrinsic signals along with mathematical simulation,we studied response properties of cat areas 17 and 18 to random dots moving at various speeds.We found that the motion trajectory at low speed was encoded as a direction signal by groups of neurons preferring that motion direction.Above certain transition speeds,the motion trajectory is processed by other groups of direction-selective neurons with perpendicular preferences,as a spatial orientation(streak)representing the motion axis of the moving dots in both areas were studied.This applied to both simple and complex cells.This work was published in PloS One(An et al.,2014a).Our results in cat and macaque early visual cortices demonstrate that,associated with speed,the combined processing of motion direction and axis by orientation-and direction-selective neurons with orthogonal preferences may serve as a common principle of early visual motion processing.We tested this assumption by investigating population responses of neurons in macaque V1 and V2 to stimuli closely mimicking natural camouflaged movements.Essentially,we found that low speed camouflage-breaking movements are encoded by both direction-and orientation-selective cells corresponding to the direction of motion of the concealed animal,while high speed camouflagebreaking movements generate a motion–streak signal that is encoded by a complementary set of direction-and orientation-selective cells within macaque early visual cortices.This work was published inProc.R.Soc.Bas “Breaking cover: neural responses to slow and fast camouflagebreaking motion”(Yin et al.,2015).Taketogether,here we demonstrate that motion trajectory only at low speed was encoded primarily as direction signal by both direction-and orientation-selective neurons preferring that motion direction,but at high speed,other groups of direction-and orientation-selective neurons with perpendicular preferences were activated to encode the motion trajectory as motion streak information.Thus,depending on motion speed,the combined processing of motion direction and axis/trajectory by neurons with orthogonal direction and orientation preferences may serve as a fundamental principle of visual motion processing in early visual areas of high mammalians.