Disambiguating Visual Motion Through Contextual Feedback Modulation

2004 ◽  
Vol 16 (10) ◽  
pp. 2041-2066 ◽  
Author(s):  
Pierre Bayerl ◽  
Heiko Neumann
Keyword(s):  
Time Course ◽  
Visual Motion ◽  
Activity Patterns ◽  
Image Features ◽  
Natural Image ◽  
Local Motion ◽  
Physiological Mechanisms ◽  
Feedback Processing ◽  
Aperture Problem ◽  
Gating Mechanism

Motion of an extended boundary can be measured locally by neurons only orthogonal to its orientation (aperture problem) while this ambiguity is resolved for localized image features, such as corners or nonocclusion junctions. The integration of local motion signals sampled along the outline of a moving form reveals the object velocity. We propose a new model of V1-MT feedforward and feedback processing in which localized V1 motion signals are integrated along the feedforward path by model MT cells. Top-down feedback from MT cells in turn emphasizes model V1 motion activities of matching velocity by excitatory modulation and thus realizes an attentional gating mechanism. The model dynamics implement a guided filling-in process to disambiguate motion signals through biased on-center, off-surround competition. Our model makes predictions concerning the time course of cells in area MT and V1 and the disambiguation process of activity patterns in these areas and serves as a means to link physiological mechanisms with perceptual behavior. We further demonstrate that our model also successfully processes natural image sequences.

Area MT Neurons Respond to Visual Motion Distant From Their Receptive Fields

2005 ◽  
Vol 94 (6) ◽  
pp. 4156-4167 ◽  
Author(s):  
Daniel Zaksas ◽  
Tatiana Pasternak
Keyword(s):  
Time Course ◽  
Visual Motion ◽  
Cognitive Task ◽  
Receptive Fields ◽  
Direction Selectivity ◽  
Task Demands ◽  
Visual Signals ◽  
Area Mt ◽  
Mt Neurons ◽  
Stimulus Offset

Neurons in cortical area MT have localized receptive fields (RF) representing the contralateral hemifield and play an important role in processing visual motion. We recorded the activity of these neurons during a behavioral task in which two monkeys were required to discriminate and remember visual motion presented in the ipsilateral hemifield. During the task, the monkeys viewed two stimuli, sample and test, separated by a brief delay and reported whether they contained motion in the same or in opposite directions. Fifty to 70% of MT neurons were activated by the motion stimuli presented in the ipsilateral hemifield at locations far removed from their classical receptive fields. These responses were in the form of excitation or suppression and were delayed relative to conventional MT responses. Both excitatory and suppressive responses were direction selective, but the nature and the time course of their directionality differed from the conventional excitatory responses recorded with stimuli in the RF. Direction selectivity of the excitatory remote response was transient and early, whereas the suppressive response developed later and persisted after stimulus offset. The presence or absence of these unusual responses on error trials, as well as their magnitude, was affected by the behavioral significance of stimuli used in the task. We hypothesize that these responses represent top-down signals from brain region(s) accessing information about stimuli in the entire visual field and about the behavioral state of the animal. The recruitment of neurons in the opposite hemisphere during processing of behaviorally relevant visual signals reveals a mechanism by which sensory processing can be affected by cognitive task demands.

scholarly journals An Effective feature set in Quality Estimation of Natural Scene Statistics Images

2019 ◽  
Vol 9 (2) ◽  
pp. 2881-2888
Keyword(s):  
Image Quality Assessment ◽  
Image Features ◽  
Quality Score ◽  
Natural Image ◽  
Natural Scene ◽  
Natural Scene Statistics ◽  
Quality Estimation ◽  
Objective Quality ◽  
Quality Value

Quality estimation in images is an area which demands high attention of researchers. Many recent algorithms in Image quality assessment relies on the computation of definite values from the image or comparison with the original pristine image. Here, we propose the extraction of a set of specific features from image and processing is done on these extracted features to obtain the objective quality score. The detailed inspection of behaviour of this set of highly specific image features extracted through less complex mathematical procedure from a collection good quality and low quality set of Natural Scene Statistics images available in LIVE dataset is elaborated in this work. Our studies and results are compared with the subjective opinion value and is proven to be accurate. The obtained results are demonstrated using statistical and graphical manner for promptness in understanding the nature of quality of the image. Thus the proposed feature set is proven to be complete in assessing the quantitative quality value of any Natural image.

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.

Latitude Dependent Circadian Rhythms of Carabid Beetles

1986 ◽  
Vol 41 (9-10) ◽  
pp. 935-945
Author(s):  
Gisela Leyk ◽  
Wolfgang Martin
Keyword(s):  
Time Course ◽  
Activity Patterns ◽  
Carabid Beetles ◽  
Constant Darkness ◽  
Spectrum Estimation ◽  
Program System ◽  
Central European ◽  
Light Pulses ◽  
Different Types ◽  
Periodogram Analysis

Abstract Comparative studies of circadian activity rhythms were performed with three stocks of the species Pterostichus rhaeticus Heer (from Southern Europe, Central Europe, and the Subarctic) and with one Central European stock of the sibling species Pterostichus nigrita Paykull. The hehaviour was investigated in various LD conditions, constant conditions including LL with changes of the illumination intensity and constant darkness with light pulses. The data were analysed with the program system “Timesdia” containing various techniques like power spectrum estimation, periodogram analysis and complex demodulation. This allowed to reveal the time course of rhythms and to determine the number of phase jumps as a measure for precision. With the help of these methods, the activity patterns are classified in different types of behaviour: synchronization, temporarily synchronization, aperiodic behaviour, free run, temporarily free run, relative entrainment, and relative coordination. Besides graduated differences between the populations in south-to-north direction (e.g. in the tendency to rhythmic behaviour) the analysis revealed splitting of rhythms into two or even three components of different frequencies and transitions from rhythmic to aperiodic behaviour or vice versa after arbitrarily chosen light pulses in constant darkness. This behaviour cannot be explained by a system which is composed of one single limit cycle oscillator, but the results rather support a multi-oscillator model.

scholarly journals Occlusion and the solution to visual motion ambiguity: Looking beyond the aperture problem

10.1167/8.2.4 ◽  
2008 ◽  
Vol 8 (2) ◽  
pp. 4 ◽  
Author(s):  
Maarten J. van der Smagt ◽  
Gene R. Stoner
Keyword(s):  
Visual Motion ◽  
Aperture Problem

Local and Global Representations of Velocity: Transparency, Opponency, and Global Direction Perception

Perception ◽  
1997 ◽  
Vol 26 (8) ◽  
pp. 995-1010 ◽  
Author(s):  
Oliver Braddick
Keyword(s):  
Visual Motion ◽  
Multiple Scales ◽  
Human Subjects ◽  
Motion Processing ◽  
Spatial Integration ◽  
Local Motion ◽  
Directional Information ◽  
Object Based ◽  
Transparent Display ◽  
Winner Take All

Human subjects can perceive global motion or motions in displays containing diverse local motions, implying representation of velocity at multiple scales. The phenomena of flexible global direction judgments, and especially of motion transparency, also raise the issue of whether the representation of velocity at any one scale is single-valued or multi-valued. A new performance-based measure of transparency confirms that the visual system represents directional information for each component of a transparent display. However, results with the locally paired random-dot display introduced by Qian et al, show that representations of multiple velocities do not coexist at the finest spatial scale of motion analysis. Functionally distinct scales of motion processing may be associated with (i) local motion detectors which show a strong winner-take-all interaction; (ii) spatial integration of local signals to disambiguate velocity; (iii) selection of reliable velocity signals as proposed in the model of Nowlan and Sejnowski; (iv) object-based or surface-based representations that are not necessarily organised in a fixed spatial matrix. These possibilities are discussed in relation to the neurobiological organisation of the visual motion pathway.

scholarly journals Sodium channel gating currents in frog skeletal muscle.

1983 ◽  
Vol 82 (5) ◽  
pp. 679-701 ◽  
Author(s):  
D T Campbell
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Time Course ◽  
Channel Gating ◽  
Total Charge ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Gating Currents ◽  
Gating Mechanism ◽  
Charge Movements

Charge movements similar to those attributed to the sodium channel gating mechanism in nerve have been measured in frog skeletal muscle using the vaseline-gap voltage-clamp technique. The time course of gating currents elicited by moderate to strong depolarizations could be well fitted by the sum of two exponentials. The gating charge exhibits immobilization: at a holding potential of -90 mV the proportion of charge that returns after a depolarizing prepulse (OFF charge) decreases with the duration of the prepulse with a time course similar to inactivation of sodium currents measured in the same fiber at the same potential. OFF charge movements elicited by a return to more negative holding potentials of -120 or -150 mV show distinct fast and slow phases. At these holding potentials the total charge moved during both phases of the gating current is equal to the ON charge moved during the preceding prepulse. It is suggested that the slow component of OFF charge movement represents the slower return of charge "immobilized" during the prepulse. A slow mechanism of charge immobilization is also evident: the maximum charge moved for a strong depolarization is approximately doubled by changing the holding potential from -90 to -150 mV. Although they are larger in magnitude for a -150-mV holding potential, the gating currents elicited by steps to a given potential have similar kinetics whether the holding potential is -90 or -150 mV.

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