Average Direction Of Motion Research Articles

Implicit Neurofeedback Training of Feature-Based Attention Promotes Biased Sensory Processing during Integrative Decision-Making.

Complex perceptual decisions, in which information must be integrated across multiple sources of evidence, are ubiquitous but are not well understood. Such decisions rely on sensory processing of each individual source of evidence, and are therefore vulnerable to bias if sensory processing resources are disproportionately allocated among visual inputs. To investigate this, we developed an implicit neurofeedback protocol embedded within a complex decision-making task to bias sensory processing in favor of one source of evidence over another. Human participants of both sexes (N = 30) were asked to report the average motion direction across two fields of oriented moving bars. Bars of different orientations flickered at different frequencies, thus inducing steady-state visual evoked potentials. Unbeknownst to participants, neurofeedback was implemented to implicitly reward attention to a specific "trained" orientation (rather than any particular motion direction). As attentional selectivity for this orientation increased, the motion coherence of both fields of bars increased, making the task easier without altering the relative reliability of the two sources of evidence. Critically, these neurofeedback trials were alternated with "test" trials in which motion coherence was not contingent on attentional selectivity, allowing us to assess the training efficacy. The protocol successfully biased sensory processing, resulting in earlier and stronger encoding of the trained evidence source. In turn, this evidence was weighted more heavily in behavioral and neural representations of the integrated average, although the two sources of evidence were always matched in reliability. These results demonstrate how biases in sensory processing can impact integrative decision-making processes.SIGNIFICANCE STATEMENT Many everyday decisions require active integration of different sources of sensory information, such as deciding when it is safe to cross a road, yet little is known about how the brain prioritizes sensory sources in the service of adaptive behavior, or whether such decisions can be altered through learning. Here we addressed these questions using a novel behavioral protocol that provided observers with real-time feedback of their own brain activity patterns in which sensory processing was implicitly biased toward a subset of the available information. We show that, while such biases are a normal and adaptive mechanism for humans to process complex visual information, they can also contribute to suboptimal decision-making.

Stimulus Reliability Automatically Biases Temporal Integration of Discrete Perceptual Targets in the Human Brain.

Many decisions, from crossing a busy street to choosing a profession, require integration of discrete sensory events. Previous studies have shown that integrative decision-making favors more reliable stimuli, mimicking statistically optimal integration. It remains unclear, however, whether reliability biases operate even when they lead to suboptimal performance. To address this issue, we asked human observers to reproduce the average motion direction of two suprathreshold coherent motion signals presented successively and with varying levels of reliability, while simultaneously recording whole-brain activity using electroencephalography. By definition, the averaging task should engender equal weighting of the two component motion signals, but instead we found robust behavioral biases in participants' average decisions that favored the more reliable stimulus. Using population-tuning modeling of brain activity we characterized tuning to the average motion direction. In keeping with the behavioral biases, the neural tuning profiles also exhibited reliability biases. A control experiment revealed that observers were able to reproduce motion directions of low and high reliability with equal precision, suggesting that unbiased integration in this task was not only theoretically optimal but demonstrably possible. Our findings reveal that temporal integration of discrete sensory events in the brain is automatically and suboptimally weighted according to stimulus reliability.SIGNIFICANCE STATEMENT Many everyday decisions require integration of several sources of information. To safely cross a busy road, for example, one must consider the movement of vehicles with different speeds and trajectories. Previous research has shown that individual stimuli are weighted according to their reliability. Whereas reliability biases typically yield performance that closely mimics statistically optimal integration, it remains unknown whether such biases arise even when they lead to suboptimal performance. Here we combined a novel integrative decision-making task with concurrent brain recording and modeling to address this question. While unbiased decisions were optimal in the task, observers nevertheless exhibited robust reliability biases in both behavior and brain activity, suggesting that reliability-weighted integration is automatic and dissociable from statistically optimal integration.

Vicsek model of self-propelled particles with hybrid noise

In self-propelled particle models, the interactions are generally subject to some type of noise, which is introduced either during or after the interactions between the particles. Here, self-propelled particles are subject to two different types of noise. If the orientation between them is less than a certain rate [Formula: see text], a vectorial noise is introduced in each particle–particle interaction, otherwise, an angular noise is introduced in the average direction of motion, already calculated, of neighboring particles. We vary the rate [Formula: see text] over a wide range ([Formula: see text]) and study the change in the nature of the phase transition. The product-moment correlation coefficient between the order parameter and the hybrid noise, is calculated. We found that in the combination of the two types of noise, the critical noise decreases with increasing the parameter [Formula: see text], and by analysis of the Binder cumulant we estimate the value of [Formula: see text] as from which begins to appear the effects of the vectorial noise on the phase transition.

Critical exponents of a self-propelled particles system

The Vicsek model of self-propelled particles is an important tool in the study of the collective motion of live organisms. The model consists of particles that move with a constant velocity and adopt, in a region called the zone of repulsion, the average motion direction of their neighbors disturbed by an external noise. A second-order phase transition from a disordered state, with motion in random directions, to an ordered motion state was observed. In this work, we have estimated, using finite-size scaling arguments, the critical exponents β, γ and ν of the original Vicsek model as a function of parameters important to the model, such as the orientation radius size, density, and velocity modulus. Our results show that the critical exponents depend greatly on these parameters.

Study on the Phase Transition Behavior of Fishes Schooling System

The Vicsek’s model (VM) [T. Vicsek, et. al., Phys. Rev. Lett. 75, 1226 (1995)] is apopular approach to study nature of the phase transition of self-propelling system. In this model,the direction of motion of each particle depends on the average velocity of its neighboring particleswithin a circle of radius R. In this work, we consider a group of fishes as the particles, but weassumed that only the individuals of its neighbors within a circle sector with central angle ϕ (iscalled angle of view) and radius R, are taken into account the average direction of motion. Weused a similar model as the well known XY spin model on a square lattice of linear size L, theparticles can move freely on the plane (an off-lattice model). A phase diagram in the space (φ,ξc) has been established where φ = ϕ/2 2 [0, π] and ξc being the critical noise. We shown thatξc strongly depends on the view’s angle φ 0.5π, but slightly varies with φ < 0.5π. So, we canconclude that the schooling behavior of animal is only of the prey species, but not of the predator

Probing V5/MT excitability with transcranial magnetic stimulation following visual motion adaptation to random and coherent motion

The response to stimulating the visual cortex with transcranial magnetic stimulation (TMS) depends on its initial activation state, for example, visual motion adaptation biases perceived TMS-induced phosphene characteristics (e.g., color). We quantified this state dependence by assessing the probability of reporting a phosphene (P(λ) ) with "threshold" TMS (i.e., the TMS intensity producing P(λ) = 0.5 at baseline) following visual motion adaptation to a random dot motion display. Postadaptation, P(λ) was increased, and this effect was confined to the adapted neuronal population. We then adapted subjects using a population of moving dots of fixed average motion direction with standard deviations (SD) ranging from 1° to 128° (SD fixed for a given trial). P(λ) was significantly increased at all dot motion SDs except SD = 1°. Neuronal adaptation increases the susceptibility of the neuronal population to activation by threshold intensity TMS. Thus the process of neuronal adaption is not necessarily synonymous with a downmodulation of neuronal excitability.

Trajectory fluctuations accompanying the manipulation of spherical nanoparticles

We relate the frictional forces acting on spherical nanoparticles pushed by a scanning probe tip on a flat surface to the trajectories of the particles. Based on a simple collisional model, we predict that the average direction of motion of the nanoparticles is almost independent of the friction force, whereas the fluctuations of the particle directions are inversely proportional to friction. The model is applied to interpret the trajectory fluctuations and the apparent discontinuities observed when spherical gold particles are manipulated on a silicon-oxide surface by atomic force microscopy.

Hitting moving targets: a dissociation between the use of the target's speed and direction of motion.

Previous work has indicated that people do not use their judgment of a target's speed to determine where to hit it. Instead, they use their judgment of the target's changing position and an expected speed (based on the speed of previous targets). In the present study we investigate whether people also ignore the target's apparent direction of motion, and use the target's changing position and an expected direction of motion instead. Subjects hit targets that moved in slightly different directions across a screen. Sometimes the targets disappeared after 150 ms, long before the subjects could reach the screen. This prevented subjects from using the target's changing position to adjust their movements, making it possible to evaluate whether subjects were relying on the perceived or an expected (average) direction to guide their movements. The background moved perpendicular to the average direction of motion in some trials. This influences the target's perceived direction of motion while leaving its perceived position unaffected. When the background was stationary, subjects hit disappearing targets along their trajectory, just as they hit ones that remained visible. Moving the background affected the direction in which subjects started to move their hand, in accordance with the illusory change in direction of target motion. If the target disappeared, this resulted in a hit that was systematically off the target's trajectory. If the target remained visible, subjects corrected their initial error. Presumably they did so on the basis of information about the target's changing position, because if the target disappeared they did not correct the error. We conclude that people do use the target's perceived direction of motion to determine where to hit it. Thus the perceived direction of motion is treated differently than the perceived speed. This suggests that the motion of an object is not broken down into speed components in different directions, but that speed and direction are perceived and used separately.

Collective behavior of interacting self-propelled particles

We discuss biologically inspired, inherently non-equilibrium models of self-propelled particles, in which the particles interact with their neighbors by choosing at each time step the local average direction of motion. We summarize some of the results of large-scale simulations and theoretical approaches about the effects of noise and dimensionality on the scaling behavior of such systems.

Collective motion of organisms in three dimensions

We study a model of flocking in order to describe the transitions during the collective motion of organisms (e.g., birds) in three dimensions. In this model the particles representing the organisms are self-propelled, i.e., they move with the same absolute velocity. In addition, the particles locally interact by choosing at each time step the average direction of motion of their neighbours and the effects of fluctuations are taken into account as well. We present the first results for large-scale flocking in the presence of noise in three dimensions. We show that depending on the control parameters both disordered and long-range ordered phases can be observed. The corresponding phase diagram has a number of features which are qualitatively different from those typical for the analogous equilibrium models.

Novel type of phase transition in a system of self-driven particles.

A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation ($\eta$) added. We present numerical evidence that this model results in a kinetic phase transition from no transport (zero average velocity, $| {\bf v}_a | =0$) to finite net transport through spontaneous symmetry breaking of the rotational symmetry. The transition is continuous since $| {\bf v}_a |$ is found to scale as $(\eta_c-\eta)^\beta$ with $\beta\simeq 0.45$.

Direct evidence for gravitational domination of the motion of gas within one light-week of the central object in NGC 4151 and the determination of the mass of the probable black hole

view Abstract Citations (131) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Direct Evidence for Gravitational Domination of the Motion of Gas within One Light-Week of the Central Object in NGC 4151 and the Determination of the Mass of the Probable Black Hole Gaskell, C. Martin Abstract A practical method is demonstrated for determining the average direction of motion of broad-line region gas in quasars. Analysis of the variability of the blue and red wings of the C IV λ1549 and Mg II λ2798 lines and the UV continuum in the low-luminosity quasar in NGC 4151 reveals that the red sides of both lines lead to blue sides in their variations. Outflow of the high-velocity gas (v > 5000 km s^-1^) emitting the C IV and Mg II lines is excluded at the 99.5% confidence level. The dominant motion of the gas is most likely to be inward, although totally random or chaotic motions are excluded only at the 93% level. It is suggested that the gravitational domination of the motion of the broad-line region clouds at small radii is a consequence of their high densities (N_e_>10^11^ cm^-3^). The demonstration that the broad-line region has its motions dominated by gravity (versus domination by a wind or radiation pressure) puts black hole accretion models onto an observational footing and permits the first simple kinematic determination of the mass of the black hole in a galactic nucleus. The mass is 5 x 10^7^ M_sun_ if the gas is indeed inflowing. Publication: The Astrophysical Journal Pub Date: February 1988 DOI: 10.1086/165986 Bibcode: 1988ApJ...325..114G Keywords: Black Holes (Astronomy); Galactic Nuclei; Gas Dynamics; Quasars; Seyfert Galaxies; Carbon; Cross Correlation; Error Analysis; Magnesium; Monte Carlo Method; Ultraviolet Spectra; Astrophysics; BLACK HOLES; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4151; GALAXIES: INTERNAL MOTIONS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; QUASARS full text sources ADS | data products SIMBAD (2) NED (2)

Rotational–translational models for interpretation of quasi-elastic light scattering spectra of motile bacteria

Quasi-elastic light scattering is a powerful tool for studying dynamic behavior of motile bacteria in liquid suspension. Previously we proposed an ellipsoidal structural model to account for the straight line motion of E. coli bacteria. We have in this article extended our structural model to include rotational motions superimposed on the translational motion of the center of mass. A general formulation is given by which the light scattering spectrum of any rotational-translational motion of a structured particle can be calculated. Specific calculations are carried out for three types of rotational motions, namely, planar wiggling motion, pure rotation, and helical rotation, around the average direction of motion. Further narrowing of the scattered field correlation function as compared with that of the straight line motion is observed in all three cases. We finally compare the helical rotation model with our previous experimental results for E. coli and find a substantial improvement over that of the straight line motion model.

The motions of peaks in ionospheric auroral absorption and auroral infrasonic waves

The average direction of motion of ‘peaks’ in ionospheric auroral absorption events changes with local time in a manner similar to that of the direction of propagation of auroral infrasonic bow waves (AIW) as observed in the auroral zone. A study of the morphology of motions of auroral absorption peaks can thus give information on the variation with local time of the motion of auroral arcs that generate AIW.