Perceived Velocity in Dynamic Random-Dot Patterns is Influenced by Noise Type

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 303-303
Author(s):  
K A Owen ◽  
J E Raymond ◽  
P Thompson
Keyword(s):  
Random Walk ◽  
Random Noise ◽  
Coherent Motion ◽  
Local Motion ◽  
Noise Type ◽  
Isotropic Distribution ◽  
Random Position ◽  
Random Dot Patterns ◽  
Perceived Velocity ◽  
High Coherence

Local motion signals can be pooled to detect the direction of coherent motion in random-dot kinematograms (RDKs) having a high proportion of random noise. Noise type does not appear to affect direction discrimination in such displays (Scase et al, 1996 Vision Research36 2579 – 2586). We have observed that RDKs with low coherence yet an obvious global direction appear to move slower than similar RDKs with high coherence. Using judgements of relative speed between RDKs containing different proportions of noise in a 2AFC paradigm we have quantified this effect and sought to determine if the type of noise influences perceived velocity. Levels of coherence in all dot patterns were well above the thresholds for directional judgements. Dots were assigned as ‘Noise vs Signal’ randomly on each frame of the RDK. Noise dots were either of type ‘random position’ or of type ‘random walk’. Position noise dots were randomly repositioned within the area of the display on each frame and had an isotropic distribution of directions and variable speeds. Random-walk dots moved at the same speed on successive frames (their displacement matched to that of the signal dots) but in a randomly chosen direction. The two noise types yielded statistically different results. In RDKs containing random-walk noise, decreasing the coherence of the display (30% signal, 70% noise) reduced perceived velocity (on average to 0.75 of the actual velocity), while increasing the coherence of the display increased perceived velocity until at high coherence levels (80% signal, 20% noise) the perceived velocity approximated the veridical velocity (on average 0.96). The proportion of position noise in a display had no effect on perceived velocity. These basic results are discussed in relation to current models of motion detectors and velocity perception.

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.

A Computational Model of the Perceived Velocity of Moving Plaids

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 87-87
Author(s):  
I Lamouret ◽  
V Cornilleau-Pérès ◽  
J Droulez
Keyword(s):  
Optic Flow ◽  
Type Ii ◽  
Local Velocity ◽  
Local Motion ◽  
Aperture Problem ◽  
Tilted Line ◽  
Short Stimulus ◽  
Detection Mechanisms ◽  
Perceived Velocity ◽  
Gradient Models

Local motion detection mechanisms generally lead to one component of the optic flow becoming indeterminate. One way to solve this ‘aperture problem’ is to compute the optic flow which minimises some smoothing constraint. With iterative schemes the computed velocity array is suboptimal relative to the constraint until the process has converged. Under the original assumption that the iteration rate is sufficiently low to allow the perception of suboptimal flows at short stimulus durations, iterative gradient models give an accurate description of biases in the perception of tilted line velocity. We examine whether this approach can be applied to moving sinusoidal plaids. Our simulations are in agreement with a number of psychophysical results on both speed and direction perception. In particular we show that the effect of stimulus duration on the perceived direction of type II plaids [Yo and Wilson, 1992 Vision Research32(1)] can be accounted for without recourse to second-order mechanisms. The effects of contrast and component directions on the evolution rate of this bias are well reproduced. The model also successfully describes the effect of spatial frequency, and data obtained with gratings. These results suggest that iterative gradient schemes can model the dynamics of interactions between local velocity detectors, as revealed by psychophysical experiments with lines and plaids.

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.

LARGE DEVIATION ASYMPTOTICS FOR RANDOM-WALK TYPE PERTURBATIONS

2007 ◽  
Vol 07 (01) ◽  
pp. 75-89
Author(s):  
ZHIHUI YANG
Keyword(s):  
Random Walk ◽  
Random Walks ◽  
White Noise ◽  
Wiener Process ◽  
Stochastic Resonance ◽  
Large Deviation ◽  
Correction Term ◽  
Exit Problem ◽  
Wiener Processes ◽  
Noise Type

Symmetric random walks can be arranged to converge to a Wiener process in the area of normal deviation. However, random walks and Wiener processes have, in general, different asymptotics of the large deviation probabilities. The action functionals for random-walks and Wiener processes are compared in this paper. The correction term is calculated. Exit problem and stochastic resonance for random-walk-type perturbation are also considered and compared with the white-noise-type perturbation.

scholarly journals Seeing Global Motion in a Random Dot Image Sequence

i-Perception ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 204166952096110
Author(s):  
Chien-Chung Chen ◽  
Hiroshi Ashida ◽  
Xirui Yang ◽  
Pei-Yin Chen
Keyword(s):  
Random Walk ◽  
Image Sequence ◽  
Image Sequences ◽  
Spatial Context ◽  
Coherent Motion ◽  
Global Motion ◽  
Motion Direction ◽  
Motion Energy ◽  
Random Image ◽  
Perceived Motion

In a stimulus with multiple moving elements, an observer may perceive that the whole stimulus moves in unison if (a) one can associate an element in one frame with one in the next (correspondence) and (b) a sufficient proportion of correspondences signal a similar motion direction (coherence). We tested the necessity of these two conditions by asking the participants to rate the perceived intensity of linear, concentric, and radial motions for three types of stimuli: (a) random walk motion, in which the direction of each dot was randomly determined for each frame, (b) random image sequence, which was a set of uncorrelated random dot images presented in sequence, and (c) global motion, in which 35% of dots moved coherently. The participants perceived global motion not only in the global motion conditions but also in the random image sequences, though not in random walk motion. The type of perceived motion in the random image sequences depends on the spatial context of the stimuli. Thus, although there is neither a fixed correspondence across different frames nor a coherent motion direction, observers can still perceive global motion in the random image sequence. This result cannot be explained by motion energy or local aperture border effects.

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.

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].

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.

scholarly journals A random-dot kinematogram for web-based vision research

2017 ◽  
Author(s):  
Sivananda Rajananda ◽  
Hakwan Lau ◽  
Brian Odegaard
Keyword(s):  
Random Walk ◽  
Open Access ◽  
Vision Research ◽  
Web Browsers ◽  
Web Based ◽  
Online Platforms ◽  
Random Direction ◽  
Different Types ◽  
Random Position ◽  
Coherence Level

AbstractWeb-­based experiments using visual stimuli have become increasingly common in recent years, but many frequently-used stimuli in vision research have yet to be developed for online platforms. Here, we introduce the first open access random-dot kinematogram (RDK) for use in web browsers. This fully customizable RDK offers options to implement several different types of noise (random position, random walk, random direction) and parameters to control aperture shape, coherence level, the number of dots, and other features. We include links to commented JavaScript code for easy implementation in web-based experiments, as well as an example of how this stimulus can be integrated as a plugin with a JavaScript library for online studies (jsPsych).

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