A Neuromorphic Recurrent Model for Figure-Ground Segregation of Coherent Motion

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 84-84
Author(s):  
W H A Beaudot
Keyword(s):  
Temporal Integration ◽  
Receptive Fields ◽  
Optimal Solution ◽  
Coherent Motion ◽  
Motion Processing ◽  
Global Motion ◽  
Local Motion ◽  
Aperture Problem ◽  
Visual Inputs ◽  
Spatial Convergence

A neuromorphic model of the retino-cortical motion processing stream is proposed which incorporates both feedforward and feedback mechanisms. The feedforward stream consists of motion integration from the retina to the MT area. Retinal spatiotemporal filtering provides X-like and Y-like visual inputs with band-pass characteristics to the V1 area (Beaudot, 1996 Perception25 Supplement, 30 – 31). V1 direction-selective cells respond to local motion resulting from nonlinear interactions between retinal inputs. MT direction-selective cells respond to global motion resulting from spatial convergence and temporal integration of V1 signals. This feedforward stream provides a fine representation of local motion in V1 and a coarse representation of global motion in MT. However, it is unable to deal with the aperture problem. Solving this problem requires the adjunction of local constraints related to both smoothness and discontinuity of coherent motion, as well as some minimisation techniques to obtain the optimal solution. We propose a plausible neural substrate for this computation by incorporating excitatory intracortical feedbacks in V1 and their modulation by reciprocal connections from MT. The underlying enhancement or depression of V1 responses according to the strength of MT responses reflects changes in the spatiotemporal properties of the V1 receptive fields. This mechanism induces a dynamic competition between local and global motion representations in V1. On convergence of these dynamics, responses of V1 direction-selective cells provide a fine representation of ‘true’ motion, thus solving the aperture problem and allowing a figure - ground segregation based on coherent motion. The model is compatible with recent anatomical, physiological, and psychophysical evidence [Bullier et al, 1996 Journal de Physiologie (Paris)90 217 – 220].

Improving motion detection via anodal transcranial direct current stimulation

2020 ◽  
Vol 38 (5) ◽  
pp. 395-405
Author(s):  
Luca Battaglini ◽  
Federica Mena ◽  
Clara Casco
Keyword(s):  
Direct Current ◽  
Signal To Noise Ratio ◽  
Individual Performance ◽  
Coherent Motion ◽  
Motion Processing ◽  
Global Motion ◽  
Local Motion ◽  
Processing Efficiency ◽  
Temporal Area ◽  
Direct Current Stimulation

Background: To study motion perception, a stimulus consisting of a field of small, moving dots is often used. Generally, some of the dots coherently move in the same direction (signal) while the rest move randomly (noise). A percept of global coherent motion (CM) results when many different local motion signals are combined. CM computation is a complex process that requires the integrity of the middle-temporal area (MT/V5) and there is evidence that increasing the number of dots presented in the stimulus makes such computation more efficient. Objective: In this study, we explored whether anodal direct current stimulation (tDCS) over MT/V5 would increase individual performance in a CM task at a low signal-to-noise ratio (SNR, i.e. low percentage of coherent dots) and with a target consisting of a large number of moving dots (high dot numerosity, e.g. >250 dots) with respect to low dot numerosity (<60 dots), indicating that tDCS favour the integration of local motion signal into a single global percept (global motion). Method: Participants were asked to perform a CM detection task (two-interval forced-choice, 2IFC) while they received anodal, cathodal, or sham stimulation on three different days. Results: Our findings showed no effect of cathodal tDCS with respect to the sham condition. Instead, anodal tDCS improves performance, but mostly when dot numerosity is high (>400 dots) to promote efficient global motion processing. Conclusions: The present study suggests that tDCS may be used under appropriate stimulus conditions (low SNR and high dot numerosity) to boost the global motion processing efficiency, and may be useful to empower clinical protocols to treat visual deficits.

scholarly journals S-cone signals invisible to the motion system can improve motion extraction via grouping by color

2009 ◽  
Vol 26 (2) ◽  
pp. 237-248 ◽  
Author(s):  
JASNA MARTINOVIC ◽  
GEORG MEYER ◽  
MATTHIAS M. MÜLLER ◽  
SOPHIE M. WUERGER
Keyword(s):  
Event Related Potentials ◽  
Event Related Potential ◽  
Coherent Motion ◽  
Behavioral Experiment ◽  
Motion Processing ◽  
Global Motion ◽  
Local Motion ◽  
Motion System ◽  
Motion Extraction ◽  
Related Potentials

AbstractThe purpose of this study was to test whether color–motion correlations carried by a pure color difference (S-cone component only) can be used to improve global motion extraction. We also examined the neural markers of color–motion correlation processing in event-related potentials. Color and motion information was dissociated using a two-colored random dot kinematogram, wherein coherent motion and motion noise differed from each other only in their S-cone component, with spatial and temporal parameters set so that global motion processing relied solely on a constant L-M component. Hence, when color and the local motion direction are correlated, more efficient segregation of coherent motion can only be brought about by the S-cone difference, and crucially, this S-cone component does not provide any effective input to a global motion mechanism but only changes the color appearance of the moving dots. The color contrasts (vector length in the S vs. L-M plane) of both the dots carrying coherent motion and the dots moving randomly were fixed at motion discrimination threshold to ensure equal effectiveness for motion extraction. In the behavioral experiment, participants were asked to discriminate between coherent and random motion, and d′ was determined for three different conditions: uncorrelated, uncued correlated, and cued correlated. In the electroencephalographic experiment, participants discriminated direction of motion for uncued correlated and cued correlated conditions. Color–motion correlations were found to improve performance. Cueing a specific color also modulated the N1 component of the event-related potential, with sources in visual area middle temporal. We conclude that S-cone signals “invisible” to the motion system can influence the analysis by direction-selective motion mechanisms through grouping of local motion signals by color. This grouping mechanism must precede motion processing and is likely to be under attentional control.

scholarly journals The direction after-effect is a global motion phenomenon

2019 ◽  
Vol 6 (3) ◽  
pp. 190114
Author(s):  
William Curran ◽  
Lee Beattie ◽  
Delfina Bilello ◽  
Laura A. Coulter ◽  
Jade A. Currie ◽  
...  
Keyword(s):  
Neural Mechanisms ◽  
Motion Processing ◽  
Global Motion ◽  
Local Motion ◽  
Motion Direction ◽  
Processing Level ◽  
True Motion ◽  
Pattern Motion ◽  
Moving Stimulus ◽  
After Effect

Prior experience influences visual perception. For example, extended viewing of a moving stimulus results in the misperception of a subsequent stimulus's motion direction—the direction after-effect (DAE). There has been an ongoing debate regarding the locus of the neural mechanisms underlying the DAE. We know the mechanisms are cortical, but there is uncertainty about where in the visual cortex they are located—at relatively early local motion processing stages, or at later global motion stages. We used a unikinetic plaid as an adapting stimulus, then measured the DAE experienced with a drifting random dot test stimulus. A unikinetic plaid comprises a static grating superimposed on a drifting grating of a different orientation. Observers cannot see the true motion direction of the moving component; instead they see pattern motion running parallel to the static component. The pattern motion of unikinetic plaids is encoded at the global processing level—specifically, in cortical areas MT and MST—and the local motion component is encoded earlier. We measured the direction after-effect as a function of the plaid's local and pattern motion directions. The DAE was induced by the plaid's pattern motion, but not by its component motion. This points to the neural mechanisms underlying the DAE being located at the global motion processing level, and no earlier than area MT.

scholarly journals The integration of local chromatic motion signals is sensitive to contrast polarity

2011 ◽  
Vol 28 (3) ◽  
pp. 239-246 ◽  
Author(s):  
SOPHIE M. WUERGER ◽  
ALEXA RUPPERTSBERG ◽  
STEPHANIE MALEK ◽  
MARCO BERTAMINI ◽  
JASNA MARTINOVIC
Keyword(s):  
Random Motion ◽  
Coherent Motion ◽  
Global Motion ◽  
Local Motion ◽  
Chromatic Contrast ◽  
Motion Direction ◽  
Contrast Polarity ◽  
Motion Integration ◽  
Integration Mechanisms ◽  
Contrast Thresholds

AbstractGlobal motion integration mechanisms can utilize signals defined by purely chromatic information. Is global motion integration sensitive to the polarity of such color signals? To answer this question, we employed isoluminant random dot kinematograms (RDKs) that contain a single chromatic contrast polarity or two different polarities. Single-polarity RDKs consisted of local motion signals with either a positive or a negative S or L–M component, while in the different-polarity RDKs, half the dots had a positive S or L–M component, and the other half had a negative S or L–M component. In all RDKs, the polarity and the motion direction of the local signals were uncorrelated. Observers discriminated between 50% coherent motion and random motion, and contrast thresholds were obtained for 81% correct responses. Contrast thresholds were obtained for three different dot densities (50, 100, and 200 dots). We report two main findings: (1) dependence on dot density is similar for both contrast polarities (+S vs. −S, +LM vs. −LM) but slightly steeper for S in comparison to LM and (2) thresholds for different-polarity RDKs are significantly higher than for single-polarity RDKs, which is inconsistent with a polarity-blind integration mechanism. We conclude that early motion integration mechanisms are sensitive to the polarity of the local motion signals and do not automatically integrate information across different polarities.

scholarly journals Population receptive field estimates for motion-defined stimuli

2018 ◽  
Author(s):  
Anna E. Hughes ◽  
John A. Greenwood ◽  
Nonie J. Finlayson ◽  
D. Samuel Schwarzkopf
Keyword(s):  
Receptive Field ◽  
Large Field ◽  
Motion Processing ◽  
Global Motion ◽  
Local Motion ◽  
Visual Hierarchy ◽  
Retinotopic Maps ◽  
Motion Condition ◽  
Early Visual Cortex ◽  
Kinetic Boundary

AbstractThe processing of motion changes throughout the visual hierarchy, from spatially restricted ‘local motion’ in early visual cortex to more complex large-field ‘global motion’ at later stages. Here we used functional magnetic resonance imaging (fMRI) to examine spatially selective responses in these areas related to the processing of random-dot stimuli defined by differences in motion. We used population receptive field (pRF) analyses to map retinotopic cortex using bar stimuli comprising coherently moving dots. In the first experiment, we used three separate background conditions: no background dots (dot-defined bar-only), dots moving coherently in the opposite direction to the bar (kinetic boundary) and dots moving incoherently in random directions (global motion). Clear retinotopic maps were obtained for the bar-only and kinetic-boundary conditions across visual areas V1-V3 and in higher dorsal areas. For the global-motion condition, retinotopic maps were much weaker in early areas and became clear only in higher areas, consistent with the emergence of global-motion processing throughout the visual hierarchy. However, in a second experiment we demonstrate that this pattern is not specific to motion-defined stimuli, with very similar results for a transparent-motion stimulus and a bar defined by a static low-level property (dot size) that should have driven responses particularly in V1. We further exclude explanations based on stimulus visibility by demonstrating that the observed differences in pRF properties do not follow the ability of observers to localise or attend to these bar elements. Rather, our findings indicate that dorsal extrastriate retinotopic maps may primarily be determined by the visibility of the neural responses to the bar relative to the background response (i.e. neural signal-to-noise ratios) and suggests that claims about stimulus selectivity from pRF experiments must be interpreted with caution.

scholarly journals Center-surround interactions underlie bipolar cell motion sensing in the mouse retina

2021 ◽  
Author(s):  
Sarah Strauss ◽  
Maria M Korympidou ◽  
Yanli Ran ◽  
Katrin Franke ◽  
Timm Schubert ◽  
...  
Keyword(s):  
Bipolar Cell ◽  
Ganglion Cells ◽  
Receptive Fields ◽  
Amacrine Cells ◽  
Bipolar Cells ◽  
Mouse Retina ◽  
Motion Processing ◽  
Local Motion ◽  
Motion Sensing ◽  
Motion Sensitivity

Motion is a critical aspect of vision. We studied the representation of motion in mouse retinal bipolar cells and found, surprisingly, that some bipolar cells possess motion-sensing capabilities that rely on their center-surround receptive fields. Using a glutamate sensor, we directly observed motion-sensitive bipolar cell synaptic output, which was strongest for local motion and dependent on the motion's origin. We characterized bipolar cell receptive fields and found that there are motion and non-motion sensitive bipolar cell types, the majority being motion sensitive. Next, we used these bipolar cell receptive fields along with connectomics to design biophysical models of downstream cells. The models and experiments demonstrated that bipolar cells pass motion-sensitive excitation to starburst amacrine cells through direction-specific signals mediated by bipolar cells' center-surround receptive field structure. As bipolar cells provide excitation to most amacrine and ganglion cells, their motion sensitivity may contribute to motion processing throughout the visual system.

Center-Surround Interactions in the Middle Temporal Visual Area of the Owl Monkey

2000 ◽  
Vol 84 (5) ◽  
pp. 2658-2669 ◽  
Author(s):  
Richard T. Born
Keyword(s):  
Visual Motion ◽  
Receptive Fields ◽  
Visual Area ◽  
Motion Processing ◽  
Wide Field ◽  
Local Motion ◽  
Middle Temporal ◽  
Visual Motion Processing ◽  
Owl Monkey ◽  
Motion Contrast

Microelectrode recording and 2-deoxyglucose (2dg) labeling were used to investigate center-surround interactions in the middle temporal visual area (MT) of the owl monkey. These techniques revealed columnar groups of neurons whose receptive fields had opposite types of center-surround interaction with respect to moving visual stimuli. In one type of column, neurons responded well to objects such as a single bar or spot but poorly to large textured stimuli such as random dots. This was often due to the fact that the receptive fields had antagonistic surrounds: surround motion in the same direction as that preferred by the center suppressed responses, thus rendering these neurons unresponsive to wide-field motion. In the second set of complementary, interdigitated columns, neuronal receptive fields had reinforcing surrounds and responded optimally to wide-field motion. This functional organization could not be accounted for by systematic differences in binocular disparity. Within both column types, neurons whose receptive fields exhibited center-surround interactions were found less frequently in the input layers compared with the other layers. Additional tests were done on single units to examine the nature of the center-surround interactions. The direction tuning of the surround was broader than that of the center, and the preferred direction, with respect to that of the center, tended to be either in the same or opposite direction and only rarely in orthogonal directions. Surround motion at various velocities modulated the overall responsiveness to centrally placed moving stimuli, but it did not produce shifts in the peaks of the center's tuning curves for either direction or speed. In layers 3B and 5 of the local motion processing columns, a number of neurons responded only to local motion contrast but did so over a region of the visual field that was much larger than the optimal stimulus size. The central feature of this receptive field type was the generalization of surround antagonism over retinotopic space—a property similar to other “complex” receptive fields described previously. The columnar organization of different types of center-surround interactions may reflect the initial segregation of visual motion information into wide-field and local motion contrast systems that serve complementary functions in visual motion processing. Such segregation appears to occur at later stages of the macaque motion processing stream, in the medial superior temporal area (MST), and has also been described in invertebrate visual systems where it appears to be involved in the important function of distinguishing background motion from object motion.

Spatial Integration in Coherent Motion Detection and in the Movement Aftereffect

Perception ◽  
1994 ◽  
Vol 23 (10) ◽  
pp. 1189-1195 ◽  
Author(s):  
Richard J A van Wezel ◽  
Frans A J Verstraten ◽  
R Eric Fredericksen ◽  
Wim A van de Grind
Keyword(s):  
Motion Detection ◽  
Detection System ◽  
Receptive Fields ◽  
Coherent Motion ◽  
Spatial Integration ◽  
Local Motion ◽  
Movement Aftereffect ◽  
Complex Interactions ◽  
New Information ◽  
Motion Detection System

Sensitivity characteristics and spatial integration properties of the motion-detection system are compared with those of the system responsible for the movement aftereffect (MAE), elicited by the same stimulus. This provides new information about the mechanisms involved in MAE generation. A screen was divided into a chequerboard where the squares were filled with random-pixel arrays moving in opposite directions. Changing the size of the squares produced drastic changes in the percept during the adaptation phase and in the MAE during the test phase. One striking new phenomenon that is described is ‘structure from MAE’. The results indicate that the receptive fields of units involved in eliciting the MAE are larger than the receptive-field sizes of units involved in detection and segregation of motion components in the stimulus. Furthermore, the results suggest that the receptive fields contributing to the MAE are involved in complex interactions in which different local motion directions are integrated in pattern-specific ways.

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