Motion Streaks Research Articles

The kinetic Orbison illusion.

In the typical Orbison illusion, the sides of a square placed on concentric circles appear to be bending toward the center of the circles. We report a motion version of the Orbison illusion (namely, the kinetic Orbison illusion). When a dot moves along a square trajectory against a background of concentric circles, the sides of the trajectory appear to bend toward the center and the corners appear to be sharpened. In the present study, observers adjusted the shape of a comparison stimulus to the shape of the perceived trajectory by bending the sides. The amount of illusion was operationally defined as the largest discrepancy between the square and adjusted shape in the comparison stimulus. It was found that the illusory bending was more than twice the static Orbison illusion and reached a maximum of 7.3% of the length of one side. Experiments including a comparison between fixation and pursuit conditions revealed that the main cause of the kinetic illusion was not motion streaks of the dot crossing background circles. We propose an alternative hypothesis based on induced motion generated by background circle motion, the direction of which is misperceived owing to the aperture problem.

Computational Long Exposure Mobile Photography

Long exposure photography produces stunning imagery, representing moving elements in a scene with motion-blur. It is generally employed in two modalities, producing either a foreground or a background blur effect. Foreground blur images are traditionally captured on a tripod-mounted camera and portray blurred moving foreground elements, such as silky water or light trails, over a perfectly sharp background landscape. Background blur images, also called panning photography, are captured while the camera is tracking a moving subject, to produce an image of a sharp subject over a background blurred by relative motion. Both techniques are notoriously challenging and require additional equipment and advanced skills. In this paper, we describe a computational burst photography system that operates in a hand-held smartphone camera app, and achieves these effects fully automatically, at the tap of the shutter button. Our approach first detects and segments the salient subject. We track the scene motion over multiple frames and align the images in order to preserve desired sharpness and to produce aesthetically pleasing motion streaks. We capture an under-exposed burst and select the subset of input frames that will produce blur trails of controlled length, regardless of scene or camera motion velocity. We predict inter-frame motion and synthesize motion-blur to fill the temporal gaps between the input frames. Finally, we composite the blurred image with the sharp regular exposure to protect the sharpness of faces or areas of the scene that are barely moving, and produce a final high resolution and high dynamic range (HDR) photograph. Our system democratizes a capability previously reserved to professionals, and makes this creative style accessible to most casual photographers.

Recognizing and Recovering Ball Motion Based on Low-Frame-Rate Monocular Camera

Reconstructing sphere motion is an essential part of indoor screen-based ball sports. Current sphere recognition techniques require expensive high-precision equipment and complex field deployment, which limits the application of these techniques. This paper proposes a novel method for recognizing and recovering sphere motion based on a low-frame-rate monocular camera. The method captures ball motion streaks in input images, reconstructs trajectories in space, and then estimates ball speed. We evaluated the effectiveness of the streak detection method and obtained an F1-score of 0.97. We also compared the performance of the proposed trajectory reconstruction method with existing methods, and the proposed method outperformed the compared techniques.

The sources of peri-saccadic mislocalization: Evidence from the perception of intra-saccadic motion streaks

The sources of peri-saccadic mislocalization: Evidence from the perception of intra-saccadic motion streaks

Attractive effects of previous form information on heading estimation from optic flow occur at perceptual stage.

When moving in the environment, optic flow and form (e.g., motion streaks) information generally appear simultaneously. Previous studies have shown that observers can estimate their heading by integrating the simultaneously presented form and optic flow information. Recent work also found that the previously seen optic flow affected the current heading estimation. The current study conducted two experiments to explore whether and how the heading estimation from optic flow was affected by the previously seen form information. We found that the current heading estimates from optic flow were biased toward the location of the focus of expansion of the previously seen form stimulus, showing an attractive effect of the previous form. Additionally, the results revealed that the attractive effect of the previous form occurred at the perceptual stage rather than postperceptual stages (e.g., working memory). Our findings suggest that our visual system can integrate dynamic optic flow and static form information across the temporal domain to estimate our heading direction.

Intrasaccadic motion streaks jump-start gaze correction.

Rapid eye movements (saccades) incessantly shift objects across the retina. To establish object correspondence, the visual system is thought to match surface features of objects across saccades. Here, we show that an object's intrasaccadic retinal trace-a signal previously considered unavailable to visual processing-facilitates this match making. Human observers made saccades to a cued target in a circular stimulus array. Using high-speed visual projection, we swiftly rotated this array during the eyes' flight, displaying continuous intrasaccadic target motion. Observers' saccades landed between the target and a distractor, prompting secondary saccades. Independently of the availability of object features, which we controlled tightly, target motion increased the rate and reduced the latency of gaze-correcting saccades to the initial presaccadic target, in particular when the target's stimulus features incidentally gave rise to efficient motion streaks. These results suggest that intrasaccadic visual information informs the establishment of object correspondence and jump-starts gaze correction.

Pupillary response to real, illusory, and implied motion.

The perception of moving objects (real motion) is a critical function for interacting with a dynamic environment. Motion perception can be also induced by particular structural features of static images (illusory motion) or by photographic images of subjects in motion (implied motion, IM). Many cortical areas are involved in motion processing, particularly the medial temporal cortical area (MT), dedicated to the processing of real, illusory, and implied motion. Recently, there has been a growing interest in the influence of high-level visual processes on pupillary responses. However, just a few studies have measured the effect of motion processing on the pupil, and not always with consistent results. Here we systematically investigate the effects of real, illusory, and implied motion on the pupil diameter for the first time, by showing different types of stimuli (movies, illusions, and photos) with the same average luminance to the same observers. We find different pupillary responses depending on the nature of motion. Real motion elicits a larger pupillary dilation than IM, which in turn induces more dilation than control photos representing static subjects (No-IM). The pupil response is sensitive even to the strength of IM, as photos with enhanced IM (blur, motion streaks, speed lines) induce larger dilation than simple freezed IM (subjects captured in the instant they are moving). Also, the subject represented in the stimulus matters: human figures are interpreted as more dynamic and induce larger dilation than objects/animals. Interestingly, illusory motion induces much less dilation than all the other motion categories, despite being seen as moving. Overall, pupil responses depend on the individual perception of dynamicity, confirming that the pupil is modulated by the subjective interpretation of complex stimuli. We argue that the different pupillary responses to real, illusory, and implied motion reflect the top-down modulations of different cortical areas involved in their processing.

Motion Streak Neurons in the Mouse Visual Cortex

Motion streaks are smeared representation of fast-moving objects due to temporal integration. Here, we test for motion streak signals in mice with two-photon calcium imaging. For small dots moving at low speeds, neurons in primary visual cortex (V1) encode the component motion, with preferred direction along the axis perpendicular to their preferred orientation. At high speeds, V1 neurons prefer the direction along the axis parallel to their preferred orientation, as expected for encoding motion streaks. Whereas some V1 neurons (∼20%) display a switch of preferred motion axis with increasing speed, others (>40%) respond specifically to high speeds at the parallel axis. Motion streak neurons are also seen in higher visual lateromedial (LM), anterolateral (AL), and rostrolateral (RL) areas, but with higher transition speeds, and many still prefer the perpendicular axis even with fast motion. Our results thus indicate that diverse motion encoding exists in mouse visual cortex, with intriguing differences among visual areas.

Intra-saccadic motion streaks as cues to linking object locations across saccades.

When visual objects shift rapidly across the retina, they produce motion blur. Intra-saccadic visual signals, caused incessantly by our own saccades, are thought to be eliminated at early stages of visual processing. Here we investigate whether they are still available to the visual system and could—in principle—be used as cues for localizing objects as they change locations on the retina. Using a high-speed projection system, we developed a trans-saccadic identification task in which brief but continuous intra-saccadic object motion was key to successful performance. Observers made a saccade to a target stimulus that moved rapidly either up or down, strictly during the eye movement. Just as the target reached its final position, an identical distractor stimulus appeared on the opposite side, resulting in a display of two identical stimuli upon saccade landing. Observers had to identify the original target using the only available clue: the target's intra-saccadic movement. In an additional replay condition, we presented the observers’ own intra-saccadic retinal stimulus trajectories during fixation. Compared to the replay condition, task performance was impaired during saccades but recovered fully when a post-saccadic blank was introduced. Reverse regression analyses and confirmatory experiments showed that performance increased markedly when targets had long movement durations, low spatial frequencies, and orientations parallel to their retinal trajectory—features that promote intra-saccadic motion streaks. Although the potential functional role of intra-saccadic visual signals is still unclear, our results suggest that they could provide cues to tracking objects that rapidly change locations across saccades.

From retinal to world-centered perception of intra-saccadic motion streaks: Evidence for high-fidelity eye position information during saccades

From retinal to world-centered perception of intra-saccadic motion streaks: Evidence for high-fidelity eye position information during saccades

Temporal Integration of Motion Streaks in Migraine.

Migraine is associated with differences in visual perception, specifically, deficits in the perception of motion. Migraine groups commonly show poorer performance (higher thresholds) on global motion tasks compared to control groups. Successful performance on a global motion task depends on several factors, including integrating signals over time. A “motion streak” task was used to investigate specifically integration over time in migraine and control groups. The motion streak effect depends on the integration of a moving point over time to create the illusion of a line, or “streak”. There was evidence of a slower optimum speed for eliciting the motion streak effect in migraine compared to control groups, suggesting temporal integration is different in migraine. In addition, performance on the motion streak task showed a relationship with headache frequency.

All is not lost: Post-saccadic contributions to the perceptual omission of intra-saccadic streaks.

Saccades rapidly jerk the eye into new positions, yet we rarely experience the motion streaks imposed on the retinal image. Here we examined spatial and temporal properties of post-saccadic masking-one potential explanation of this perceptual omission. Observers judged the motion direction of a target stimulus, a Gaussian blob, that moved vertically upwards or downwards and then back to its initial position, just as observers made a saccade. We manipulated the onset and offset of the target and of distractors in various spatial relations to the target, and assessed their effect on performance and subjective confidence. Although the presence of the target after the saccade caused the strongest omission, the offset of spatially distant distractor stimuli upon saccade offset also impaired performance. The temporal properties of these two separate effects suggest that, in addition to masking, an independent effect of attentional distraction further accentuates perceptual omission of intra-saccadic motion streaks.

Investigating the Effects of Motion Streaks on pQCT-Derived Leg Muscle Density and Its Association With Fractures

Lower peripheral quantitative computed tomography (pQCT)-derived leg muscle density has been associated with fragility fractures in postmenopausal women. Limb movement during image acquisition may result in motion streaks in muscle that could dilute this relationship. This cross-sectional study examined a subset of women from the Canadian Multicentre Osteoporosis Study. pQCT leg scans were qualitatively graded (1–5) for motion severity. Muscle and motion streak were segmented using semi-automated (watershed) and fully automated (threshold-based) methods, computing area, and density. Binary logistic regression evaluated odds ratios (ORs) for fragility or all-cause fractures related to each of these measures with covariate adjustment. Among the 223 women examined (mean age: 72.7 ± 7.1 years, body mass index: 26.30 ± 4.97 kg/m2), muscle density was significantly lower after removing motion (p < 0.001) for both methods. Motion streak areas segmented using the semi-automated method correlated better with visual motion grades (rho = 0.90, p < 0.01) compared to the fully automated method (rho = 0.65, p < 0.01). Although the analysis-reanalysis precision of motion streak area segmentation using the semi-automated method is above 5% error (6.44%), motion-corrected muscle density measures remained well within 2% analytical error. The effect of motion-correction on strengthening the association between muscle density and fragility fractures was significant when motion grade was ≥3 (p interaction <0.05). This observation was most dramatic for the semi-automated algorithm (OR: 1.62 [0.82,3.17] before to 2.19 [1.05,4.59] after correction). Although muscle density showed an overall association with all-cause fractures (OR: 1.49 [1.05,2.12]), the effect of motion-correction was again, most impactful within individuals with scans showing grade 3 or above motion. Correcting for motion in pQCT leg scans strengthened the relationship between muscle density and fragility fractures, particularly in scans with motion grades of 3 or above. Motion streaks are not confounders to the relationship between pQCT-derived leg muscle density and fractures, but may introduce heterogeneity in muscle density measurements, rendering associations with fractures to be weaker.

The interaction between orientation and motion signals in moving oriented Glass patterns.

Previous psychophysical evidence suggests that motion and orientation processing systems interact asymmetrically in the human visual system, with orientation information having a stronger influence on the perceived motion direction than vice versa. To investigate the mechanisms underlying this motion-form interaction we used moving and oriented Glass patterns (GPs), which consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented texture. In Experiment 1 we varied the angle between dipole orientation and motion direction (conflict angle). In separate sessions participants either judged the orientation or motion direction of the GP. In addition, the spatiotemporal characteristics of dipole motion were manipulated as a way to limit (Experiment 1) or favor (Experiment 2) the availability of orientation signals from motion (motion streaks). The results of Experiment 1 showed that apparent GP motion direction is attracted toward dipole orientation, and apparent GP orientation is repulsed from GP motion. The results of Experiment 2 showed stronger repulsion effects when judging the GP orientation, but stronger motion streaks from the GP motion can dominate over the signals provided by conflicting dipole orientation. These results are consistent with the proposal that two separate mechanisms contribute to our perception of stimuli which contain conflicting orientation and motion information: (i) perceived GP motion is mediated by spatial motion-direction sensors, in which signals from motion sensors are combined with excitatory input from orientation-tuned sensors tuned to orientations parallel to the axis of GP motion, (ii) perceived GP orientation is mediated by orientation-tuned sensors which mutually inhibit each other. The two mechanisms are revealed by the different effects of conflict angle and dipole lifetime on perceived orientation and motion direction.

The broad orientation dependence of the motion streak aftereffect reveals interactions between form and motion neurons.

The extended integration time of visual neurons can lead to the production of the neural equivalent of an orientation cue along the axis of motion in response to fast-moving objects. The dominant model argues that these motion streaks resolve the inherent directional uncertainty arising from the small size of receptive fields in V1, by combining spatial orientation with motion signals in V1. This model was tested in humans using visual aftereffects, in which adapting to a static grating causes the perceived direction of a subsequently presented motion stimulus to be tilted away from the adapting orientation. We found that a much broader range of orientations produced aftereffects than predicted by the current model, suggesting that these orientation cues influence motion perception at a later stage than V1. We also found that varying the spatial frequency of the adaptor changed the aftereffect from repulsive to attractive for motion-test but not form-test stimuli. Finally, manipulations of V1 excitability, using transcranial stimulation, reduced the aftereffect, suggesting that the orientation cue is dependent on V1. These results can be accounted for if the orientation information from the motion streak, gathered in V1, enters the motion system at a later stage of motion processing, most likely V5. A computational model of motion direction is presented incorporating gain modifications of broadly tuned motion-selective neurons by narrowly tuned orientation-selective cells in V1, which successfully accounts for the extant data. These results reinforce the suggestion that orientation places strong constraints on motion processing but in a previously undescribed manner.

The orientation dependence of the motion streak aftereffect reveals interactions between form and motion neurons

The extended integration time of visual neurons leads to fast-moving objects producing the neural equivalent of an orientation cue along the axis of motion. The dominant model [Geisler, W.S. (1999). Motion streaks provide a spatial code for motion direction. Nature, 400(6739), 65–69] proposes that these ‘motion streaks’ resolve the inherent directional uncertainty arising from the small size of receptive fields in V1, by combining spatial orientation with motion signals in V1. This model was tested using visual aftereffects, where adapting to a static grating causes the perceived direction of a subsequently-presented fast motion stimulus to be repelled away from the adapting orientation. Using a similar adaptation method, we measured the angular dependence of this effect and found in each human observer that a much broader range of adapting orientations (mean of 38.82º instead of 21.72°) produced aftereffects than predicted by the current model of motion streaks. This suggests that motion streaks influence motion perception at a later stage than V1. We also found that varying the spatial frequency of the adaptor by approximately two octaves changed the aftereffect from repulsive to attractive for motion, but not form stimuli. Finally, manipulations of V1 excitability, using transcranial direct current stimulation, reduced the aftereffect, suggesting that the orientation cue is dependent upon V1. These results can be accounted for if the orientation information from the motion streak, gathered in V1, enters the motion system at a later stage of motion processing, most likely V5. A new computational model of motion direction is presented incorporating gain modifications of broadly-tuned motion-selective neurons, most likely in V5, by narrowly-tuned orientation-selective cells in V1, which successfully accounts for the data in the current study. These results stress that orientation places strong constraints on motion processing in a different way than the current models predict. Meeting abstract presented at VSS 2015

Temporal evolution of motion direction judgments

Existing models of perceptual decision-making for moving stimuli assume a continuous accumulation of sensory signals for a given direction of motion (Smith & Ratcliff, 2004). This predicts concurrent improvements in estimating motion axis (orientation of motion direction) and motion direction over time. Here, we present a novel finding that the visual system can extract motion axis orientation before detecting motion direction. Methods and results: To estimate the temporal evolution of motion direction judgments, we asked participants to adjust an on-screen arrow to indicate perceived direction of moving stimuli varying in duration (rigid texture motion; randomly chosen direction; 99% contrast, 11° radius, 5°/s speed; stimuli presented at 360Hz). As expected, participants’ responses were completely random for very brief stimulus motions (5ms) and distributed around the actual motion direction for long durations (>90ms). Interestingly, for intermediate durations (30-60ms), participants’ responses exhibited a clear bimodal distribution with equal peaks in the actual motion direction and in the opposite direction. These results indicate that participants extract motion axis information before having a sense of the actual motion direction. In a related experiment, we found that for certain brief stimulus durations, subjects were 100% correct at estimating motion axis while being at chance at perceiving motion direction. Next, we ran several experiments to rule out possible contributions of spatial signals (i.e., the well-known motion streaks). Finally, we explored the contrast and size dependency of this result (5-99% contrast; 1°-11° radius). The results reveled that rapid and early coding of motion axis was mainly associated with large, high-contrast moving stimuli, stimuli associated with center-surround suppression of motion signals (Tadin et al., 2003). Conclusion: We show the visual system can extract motion axis information considerably faster than motion direction information. The specificity to large, high-contrast motion stimuli offers new clues how center-surround suppression affects motion perception. Meeting abstract presented at VSS 2015

Broad tuning of motion streak aftereffect reveals reciprocal gain interactions between orientation and motion neurons

Event Abstract Back to Event Broad tuning of motion streak aftereffect reveals reciprocal gain interactions between orientation and motion neurons Matthew Tang1*, J. Edwin Dickinson1, Troy Visser1 and David Badcock1 1 The University of Western Australia, Psychology, Australia The extended integration time of neurons leads to fast-moving objects producing neural orientation cues along the axis of motion. The current model [Geisler, W.S. (1999). Motion streaks provide a spatial code for motion direction. Nature, 400(6739), 65-69] argues that these orientation cues resolve direction ambiguity arising from the aperture problem, where the small size of receptive fields of neurons in V1 leads to direction uncertainty for contours that extend beyond their borders, by combining spatial orientation and motion signals in V1. We provide a comprehensive test of this model using a visual aftereffect, where adapting to a static grating causes the perceived direction of a subsequently-presented motion stimuli to be tilted away from the adapting orientation. Critically, a much broader range of orientations produced aftereffects than predicted by the current model, suggesting that orientation cues enter the motion system later in the processing sequence. Following this, we found that varying the spatial frequency of the adaptor changed the aftereffect from repulsive in perceived orientation to attractive for motion but not form stimuli. This is inconsistent with Geisler's model as the orientation selective neurons in V1 are spatial-frequency selective and provides evidence that motion streaks enter at V5, as this area integrates across spatial frequencies. We lastly manipulated V1 excitability using transcranial direct current stimulation that reduced the aftereffect, suggesting that the orientation cue is dependent upon V1. We provide a new computational model that accurately predicts our results in which motion streaks are detected by orientation-selective V1 neurons that exert gain onto motion-selective V5 neurons. Our model provides a new mechanism for form and motion interactions, leading to a number of unique predictions. Additionally, the differential spatial frequency effect is a new finding and has implications for models of motion processing. Keywords: Computational modelling, tDCS, Tilt aftereffect, motion streaks, form-motion interactions Conference: XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014. Presentation Type: Poster Topic: Sensation and Perception Citation: Tang M, Dickinson J, Visser T and Badcock D (2015). Broad tuning of motion streak aftereffect reveals reciprocal gain interactions between orientation and motion neurons. Conference Abstract: XII International Conference on Cognitive Neuroscience (ICON-XII). doi: 10.3389/conf.fnhum.2015.217.00348 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2015; Published Online: 24 Apr 2015. * Correspondence: Mr. Matthew Tang, The University of Western Australia, Psychology, Crawley, Australia, matthew.tang@uwa.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Matthew Tang J. Edwin Dickinson Troy Visser David Badcock Google Matthew Tang J. Edwin Dickinson Troy Visser David Badcock Google Scholar Matthew Tang J. Edwin Dickinson Troy Visser David Badcock PubMed Matthew Tang J. Edwin Dickinson Troy Visser David Badcock Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Temporal summation of global form signals in dynamic Glass patterns

The ability to perceive complex objects in the environment requires that the visual system integrate local form information into global shapes. Glass patterns (GPs) are stimuli that are commonly used to study this integration process. GPs consist of randomly positioned dot-pairs oriented in a coherent way to create a global form. When multiple GPs are presented sequentially, observers report a percept of illusory coherent motion and have lower detection thresholds relative to a single presentation GPs. The percept of illusory motion has been attributed to the visual system interpreting the dot-pairs in GPs as motion streaks. However, it remains unclear why dynamic GPs are detected at lower thresholds than static GPs. Two main differences exist between static and dynamic GPs: (a) dynamic GPs contain multiple presentations of global form signals compared to a single presentation in static GPs and (b) dynamic GPs have a greater temporal frequency than static GPs. Here we investigated which of these two factors contributed to the heightened sensitivities for dynamic GPs. We systematically varied the number of unique GPs and the rate at which each unique frame is presented (i.e., temporal frequency). The results show that, within the range of temporal frequency used, the primary influence on detection thresholds was the number of unique frames. These results suggest that the improved detection sensitivities can be driven by a mechanism of temporal summation of global form.

Unified representation of motion and motion streak patterns in a model of cortical form-motion interaction

Problem. Direction selective neurons in visual cortex (V1) encode spatio-temporal movements of visual patterns. It has been suggested that motion directions are also spatially encoded in the form channel as oriented motion streaks (Burr, Curr. Biol., 2000), while only fast motions lead to motion streak patterns (Apthorp et al., Proc. Roy. Soc. London B, 2013). Geisler (Nature, 1999) proposed that motion streaks aid determining visual motion direction estimation while their awareness is suppressed in normal vision conditions (Wallis & Arnold, Curr. Biol., 2009). The underlying neural mechanisms of such form-motion interaction are, however, still unknown. Method. We propose a neural model that acquires data from an event-based vision sensor that responds to temporal changes in the input intensity. Model area V1 uses spatio-temporal filters to detect visual motion and forwards activations to be integrated in model area MT. Orientation-selective contrast cells in model areas V1 and V2 spatially integrate recent visual events and respond to oriented structures parallel to movement direction when sufficiently fast motion is presented. Form cells' responses temporally cease already for slow motions. Results and Conclusion. We probed the model with dark/light random dot patterns moving at different directions and speeds, replicating experimental settings. For higher speeds oriented contrast-sensitive cells are co-activated along an orientation parallel to the motion direction, viz., signaling motion streaks or speedlines. For slow motions no such responses occur. Adaptation effects confirm experimental findings from psychophysics. The model suggests that motion streaks occur in the form channel as a direct consequence of fast coherent motions along single directions without the need to assume separate motion channel representations. The model makes predictions concerning the strength of the streak patterns and sheds new light upon mechanisms of computing motion from form. Meeting abstract presented at VSS 2014