Direction Of Image Motion Research Articles

Spatiotemporally Asymmetric Excitation Supports Mammalian Retinal Motion Sensitivity.

SummaryThe detection of visual motion is a fundamental function of the visual system. How motion speed and direction are computed together at the cellular level, however, remains largely unknown. Here, we suggest a circuit mechanism by which excitatory inputs to direction-selective ganglion cells in the mouse retina become sensitive to the motion speed and direction of image motion. Electrophysiological, imaging, and connectomic analyses provide evidence that the dendrites of ON direction-selective cells receive spatially offset and asymmetrically filtered glutamatergic inputs along motion-preference axis from asymmetrically wired bipolar and amacrine cell types with distinct release dynamics. A computational model shows that, with this spatiotemporal structure, the input amplitude becomes sensitive to speed and direction by a preferred direction enhancement mechanism. Our results highlight the role of an excitatory mechanism in retinal motion computation by which feature selectivity emerges from non-selective inputs.

Dendro-dendritic cholinergic excitation controls dendritic spike initiation in retinal ganglion cells

The retina processes visual images to compute features such as the direction of image motion. Starburst amacrine cells (SACs), axonless feed-forward interneurons, are essential components of the retinal direction-selective circuitry. Recent work has highlighted that SAC-mediated dendro-dendritic inhibition controls the action potential output of direction-selective ganglion cells (DSGCs) by vetoing dendritic spike initiation. However, SACs co-release GABA and the excitatory neurotransmitter acetylcholine at dendritic sites. Here we use direct dendritic recordings to show that preferred direction light stimuli evoke SAC-mediated acetylcholine release, which powerfully controls the stimulus sensitivity, receptive field size and action potential output of ON-DSGCs by acting as an excitatory drive for the initiation of dendritic spikes. Consistent with this, paired recordings reveal that the activation of single ON-SACs drove dendritic spike generation, because of predominate cholinergic excitation received on the preferred side of ON-DSGCs. Thus, dendro-dendritic release of neurotransmitters from SACs bi-directionally gate dendritic spike initiation to control the directionally selective action potential output of retinal ganglion cells.

An Approach to Star Map Simulation for Star Sensor Considering the Effect of Image Motion

To test high resolution and dynamic performance of star sensor, a method of consideration image motion on Modeling the motion blur of star sensor is proposed. Firstly, image motion geometric model based on the rotation of Starlight vector is studied. Secondly, with the help of the normal distribution of static star image energy model, introducing the star image motion speed, obtaining the energy distribution function of moving stars, implementing high dynamic simulation of star map. Finally, establishing the simulation environment, through adjusting input parameters such as integral time, rate of change of three attitude angle, the launch time, location, then, important simulation data of stars observed by star sensor in orbit can quickly be obtained, such as navigation stars information, value and direction of image motion, intensity distribution, signal to noise ratio. This work is very important to research and evaluate the star image motion compensation algorithm.

Visual response properties of neck motor neurons in the honeybee

Recent behavioural studies have demonstrated that honeybees use visual feedback to stabilize their gaze. However, little is known about the neural circuits that perform the visual motor computations that underlie this ability. We investigated the motor neurons that innervate two neck muscles (m44 and m51), which produce stabilizing yaw movements of the head. Intracellular recordings were made from five (out of eight) identified neuron types in the first cervical nerve (IK1) of honeybees. Two motor neurons that innervate muscle 51 were found to be direction-selective, with a preference for horizontal image motion from the contralateral to the ipsilateral side of the head. Three neurons that innervate muscle 44 were tuned to detect motion in the opposite direction (from ipsilateral to contralateral). These cells were binocularly sensitive and responded optimally to frontal stimulation. By combining the directional tuning of the motor neurons in an opponent manner, the neck motor system would be able to mediate reflexive optomotor head turns in the direction of image motion, thus stabilising the retinal image. When the dorsal ocelli were covered, the spontaneous activity of neck motor neurons increased and visual responses were modified, suggesting an ocellar input in addition to that from the compound eyes.

The temporal impulse response function during smooth pursuit

Recent studies indicate that the extent of perceived motion smear is attenuated asymmetrically during smooth pursuit eye movements, based on the relative directions of the target and eye motion. We conducted two experiments to determine if the reduction of perceived smear during pursuit might be associated with an acceleration of the temporal impulse response function (TIRF). In Experiment 1, two-pulse increment sensitivity was determined during fixation and rightward pursuit for sequential flashes of a long horizontal line, presented with stimulus-onset asynchronies between 5.9 and 234 ms. In Experiment 2, temporal contrast sensitivity was measured during fixation and rightward pursuit for a vertical 1 cpd grating with retinal image velocities between 4 and 30 Hz. During pursuit, grating motion was either in the same or the opposite direction as the eye movement. TIRFs were modeled as the impulse responses of a second-order, low-pass linear system, fit to the two-pulse increment sensitivity data by an optimization procedure and to the temporal contrast sensitivity results by iterative Fourier synthesis. The results indicate that the natural temporal frequency of the fitted TIRFs was approximately 10% higher during pursuit than fixation. In Experiment 2, the increased natural frequency of the TIRF was restricted to the condition in which the grating moved spatially in the opposite direction of the pursuit eye movement. The results are consistent with the hypothesis that extra-retinal signals reduce the extent of perceived motion smear during pursuit, in part by increasing the speed of visual processing preferentially for one direction of image motion.

Identification of Retinal Ganglion Cells and Their Projections Involved in Central Transmission of Information about Upward and Downward Image Motion

The direction of image motion is coded by direction-selective (DS) ganglion cells in the retina. Particularly, the ON DS ganglion cells project their axons specifically to terminal nuclei of the accessory optic system (AOS) responsible for optokinetic reflex (OKR). We recently generated a knock-in mouse in which SPIG1 (SPARC-related protein containing immunoglobulin domains 1)-expressing cells are visualized with GFP, and found that retinal ganglion cells projecting to the medial terminal nucleus (MTN), the principal nucleus of the AOS, are comprised of SPIG1+ and SPIG1− ganglion cells distributed in distinct mosaic patterns in the retina. Here we examined light responses of these two subtypes of MTN-projecting cells by targeted electrophysiological recordings. SPIG1+ and SPIG1− ganglion cells respond preferentially to upward motion and downward motion, respectively, in the visual field. The direction selectivity of SPIG1+ ganglion cells develops normally in dark-reared mice. The MTN neurons are activated by optokinetic stimuli only of the vertical motion as shown by Fos expression analysis. Combination of genetic labeling and conventional retrograde labeling revealed that axons of SPIG1+ and SPIG1− ganglion cells project to the MTN via different pathways. The axon terminals of the two subtypes are organized into discrete clusters in the MTN. These results suggest that information about upward and downward image motion transmitted by distinct ON DS cells is separately processed in the MTN, if not independently. Our findings provide insights into the neural mechanisms of OKR, how information about the direction of image motion is deciphered by the AOS.

The influence of object-image velocity change on perceived heading in minimal environments.

When human observers move forward and rotate their eyes, a complex pattern of light flows across the retina. This pattern is referred to as retinal flow. A model has been proposed to explain how humans perceive their direction of self-movement (or heading) from (1) static depth, (2) direction of image motion, and (3) whether image velocity undergoes acceleration or deceleration (Wang & Cutting, 1999). However, findings from past research in which sparse or minimalist stimuli were used have suggested that not all of the information to which participants are sensitive is captured within the scope of this model. In particular it has been suggested that the magnitude or size of image velocity change may be of significance beyond simply whether image velocity could be categorized as speeding up (i.e., accelerating) or slowing down (i.e., decelerating). In two experiments, the influence of this factor on heading judgments under minimal conditions was investigated. Evidence was found in support of the idea that the rate of image velocity change can influence judgments of the direction of self-movement in minimalist conditions.

Discrimination of the speed and direction of global second-order motion in stochastic displays

The ability to integrate local second-order motion signals over space and time was examined using random-dot-kinematograms (RDKs) in which the dots were defined by spatial variation in the contrast, rather than luminance, of a random noise field. When either the speeds or the directions of the individual dots were selected at random from a range of possible values, globally the stimulus appeared to drift either in a single direction or at a single speed in a manner analogous to that reported previously for first-order (luminance-defined) RDKs. To quantify the precision with which observers could extract the global stimulus motion, speed- and direction-discrimination thresholds were measured using pairs of RDKs, one of which (the comparison) comprised dots whose speeds or directions were assigned stochastically and the other (the standard) comprised dots that all had the same drift direction and speed. Speed-discrimination thresholds were of the order of 8% and changed little as the range of dot speeds (bandwidth) of the comparison increased, in that performance was almost as good when the individual dot speeds were selected at random from a range spanning 3.84 deg/s as when all the dots moved at the same speed. There was a tendency for the perceived global speed of the comparison RDK to decrease as the speed bandwidth was increased and perceived speed tended to coincide with the geometric mean speed of the dots rather than the arithmetic mean speed. Direction-discrimination thresholds were lowest (∼4°) when the range of dot directions was less than 90° but increased markedly thereafter. Observers were able to perform both discrimination tasks when the lifetimes of the dots comprising the RDKs was reduced from 25 to 2 frames, a manipulation that prevented observers from determining the overall speed or direction of image motion from the extended trajectories of individual dots within the display. Thresholds under these conditions were somewhat higher but were otherwise comparable to those obtained with a dot lifetime of 25 frames. The similarities between the present results and those of previous studies that have employed first-order RDKs suggest that the extraction of the global speed and direction of each type of motion is likely to be based on computationally similar principles.

Spatial organization of retinal information about the direction of image motion.

The visual stimuli that elicit neural activity differ for different retinal ganglion cells and these cells have been categorized by the visual information that they transmit. If specific visual information is conveyed exclusively or primarily by a particular set of ganglion cells, one might expect the cells to be organized spatially so that their sampling of information from the visual field is complete but not redundant. In other words, the laterally spreading dendrites of the ganglion cells should completely cover the retinal plane without gaps or significant overlap. The first evidence for this sort of arrangement, which has been called a tiling or tessellation, was for the two types of "alpha" ganglion cells in cat retina. Other reports of tiling by ganglion cells have been made subsequently. We have found evidence of a particularly rigorous tiling for the four types of ganglion cells in rabbit retina that convey information about the direction of retinal image motion (the ON-OFF direction-selective cells). Although individual cells in the four groups are morphologically indistinguishable, they are organized as four overlaid tilings, each tiling consisting of like-type cells that respond preferentially to a particular direction of retinal image motion. These observations lend support to the hypothesis that tiling is a general feature of the organization of information outflow from the retina and clearly implicate mechanisms for recognition of like-type cells and establishment of mutually acceptable territories during retinal development.

A robust procedure for visual stabilisation of hovering flight position in guard bees of Trigona (Tetragonisca) angustula (Apidae, Meliponinae)

1. In the stingless bee, Trigona (Tetragonisca) angustula, hovering guard bees keep their position relative to a moving stripe pattern mounted on the front face of the nest box constant by flying forwards and backwards parallel to the pattern movement (Fig. 2). 2. The response is guided by two cues: (1) image position and motion of the pattern and (2) the retinal position of the nest entrance (Figs. 2–5). 3. Guard bees react to an expanding and contracting pattern by moving away from and towards the nest box (Figs. 6, 7). Bees always fly away from an expanding pattern in a direction that is defined by a line connecting the centre of expansion with the bee's position at the time the movement starts (Fig. 8). 4. A procedure based on Collett's 2nd optomotor rule can explain the ability of the bees to determine visually the direction of compensatory thrust (Fig. 10). The procedure is robust in 3 respects: (1) there will be no thrust generated in response to animal rotations as long as a scene contains contrast elements throughout the visual field; (2) errors in the direction of compensatory thrust are small even if the local direction of image motion alone is taken into account and not its magnitude; (3) only very few pattern elements are needed for the procedure to work.

Simple striate neurons in the cat. II. Mechanisms underlying directional asymmetry and directional selectivity.

1. Directionally asymmetric (DA) units respond preferentially to one direction of image movement. If that preferred direction is independent of stimulus contrast then the DA unit is considered directionally selective (DS). We have analyzed receptive-field (RF) properties of striate units with these properties by presenting bar-shaped stimuli that are moved in a stepwise sequence. Short interstimulus durations for certain ranges of step size elicit DA responses similar to those from smooth movement, while still allowing identification of on- and off-components of the response. 2. We have been able to isolate three mechanisms underlying DA and DS. The simplest, superposition, explains the dependence of preferred direction on stimulus contrast found in some DA units. It relies completely on asymmetries in static RF regions to provide an advantage for one direction of image motion by means of the simultaneity of image elements leaving an apparently inhibitory region and entering an excitatory one. 3. For all DA and DS units we have encountered forward inhibition of otherwise excitatory influences that reduces the responsiveness in the antipreferred direction. The spatial specificity of inhibitory target RF regions and the nonlinearity of the effect suggest that lateral inhibition may be transmitted via sequence-detecting subunits. 4. Units that do not show superposition in the preferred direction exhibit forward facilitation of responses in a nonlinear and target-specific way which suggests that facilitation may also be transmitted via sequence-detecting subunits. 5. Each of these mechanisms depends on short-lived influences that are laterally transmitted between 0.125 and 0.5 degrees in visual space. These spatial and temporal values are appropriate for the analysis of smooth movement by the visual system. 6. Stepwise movement sequences using dark bars on a bright background demonstrate for some DA units exactly the same mechanisms as demonstrated using bright-bar sequences in other units or, in the case of DS units, in the same units. In such DS units, which do not normally exhibit strong stationary RF asymmetries, differential sensitivity of the nonlinear DS mechanisms to stimulus elements of either contrast will yield an effective preferred movement direction for complex stimuli.

Color-selectivity in simultaneous motion contrast

Thirty-two Ss were required to estimate the apparent motion of stationary vertical lines viewed against a background of moving vertical lines when both patterns were seen by the same eye (monoptic conditions) or the center pattern was seen by one eye and the surrounds by the other eye (dichoptic conditions). The stationary lines appeared to be moving from right to left as the surrounds moved left to right. The simultaneous motion contrast found under monoptic conditions was maximal when the center pattern and the surrounds were the same color and was reduced when they differed in color. The surrounds had limited influence on the apparent motion of the center section under dichoptic condition, and the color relationship was no longer important. Related color selectivity has been reported for the motion aftereffect (successive motion contrast), and both sets of data can be attributed to inlaibitory interaction (simultaneous in one case and successive in the other) among neural detectors tuned to wavelength as well as the direction of image motion.