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.

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 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 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].

scholarly journals Representation of contralateral visual space in the human hippocampus

2020 ◽  
Author(s):  
Edward H Silson ◽  
Peter Zeidman ◽  
Tomas Knapen ◽  
Chris I Baker
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Receptive Field ◽  
Visual Information ◽  
Visual Space ◽  
Spatial Representations ◽  
Visual Hierarchy ◽  
Human Hippocampus ◽  
Human Connectome Project ◽  
Early Visual Cortex

AbstractThe initial encoding of visual information primarily from the contralateral visual field is a fundamental organizing principle of the primate visual system. Recently, the presence of such retinotopic sensitivity has been shown to extend well beyond early visual cortex to regions not historically considered retinotopically sensitive. In particular, human scene-selective regions in parahippocampal and medial parietal cortex exhibit prominent biases for the contralateral visual field. Here we used fMRI to test the hypothesis that the human hippocampus, which is thought to be anatomically connected with these scene-selective regions, would also exhibit a biased representation of contralateral visual space. First, population receptive field mapping with scene stimuli revealed strong biases for the contralateral visual field in bilateral hippocampus. Second, the distribution of retinotopic sensitivity suggested a more prominent representation in anterior medial portions of the hippocampus. Finally, the contralateral bias was confirmed in independent data taken from the Human Connectome Project initiative. The presence of contralateral biases in the hippocampus – a structure considered by many as the apex of the visual hierarchy - highlights the truly pervasive influence of retinotopy. Moreover, this finding has important implications for understanding how this information relates to the allocentric global spatial representations known to be encoded therein.Significance StatementRetinotopic encoding of visual information is an organizing principle of visual cortex. Recent work demonstrates this sensitivity in structures far beyond early visual cortex, including those anatomically connected to the hippocampus. Here, using population receptive field modelling in two independent sets of data we demonstrate a consistent bias for the contralateral visual field in bilateral hippocampus. Such a bias highlights the truly pervasive influence of retinotopy, with important implications for understanding how the presence of retinotopy relates to more allocentric spatial representations.

Effects of Vision Restoration Training on Early Visual Cortex in Patients With Cerebral Blindness Investigated With Functional Magnetic Resonance Imaging

2011 ◽  
Vol 105 (2) ◽  
pp. 872-882 ◽  
Author(s):  
M. Raemaekers ◽  
D. P. Bergsma ◽  
R. J. A. van Wezel ◽  
G. J. van der Wildt ◽  
A. V. van den Berg
Keyword(s):  
Magnetic Resonance Imaging ◽  
Visual Cortex ◽  
Magnetic Resonance ◽  
Visual Field ◽  
Receptive Field ◽  
Field Size ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Retinotopic Maps ◽  
Early Visual Cortex

Cerebral blindness is a loss of vision as a result of postchiasmatic damage to the visual pathways. Parts of the lost visual field can be restored through training. However, the neuronal mechanisms through which training effects occur are still unclear. We therefore assessed training-induced changes in brain function in eight patients with cerebral blindness. Visual fields were measured with perimetry and retinotopic maps were acquired with functional magnetic resonance imaging (fMRI) before and after vision restoration training. We assessed differences in hemodynamic responses between sessions that represented changes in amplitudes of neural responses and changes in receptive field locations and sizes. Perimetry results showed highly varied visual field recovery with shifts of the central visual field border ranging between 1 and 7°. fMRI results showed that, although retinotopic maps were mostly stable over sessions, there was a small shift of receptive field locations toward a higher eccentricity after training in addition to increases in receptive field sizes. In patients with bilateral brain activation, these effects were stronger in the affected than in the intact hemisphere. Changes in receptive field size and location could account for limited visual field recovery (±1°), although it could not account for the large increases in visual field size that were observed in some patients. Furthermore, the retinotopic maps strongly matched perimetry measurements before training. These results are taken to indicate that local visual field enlargements are caused by receptive field changes in early visual cortex, whereas large-scale improvement cannot be explained by this mechanism.

scholarly journals Global motion processing by populations of direction-selective retinal ganglion cells

2019 ◽  
Author(s):  
Jon Cafaro ◽  
Joel Zylberberg ◽  
Greg Field
Keyword(s):  
Ganglion Cells ◽  
Neural Population ◽  
Mouse Retina ◽  
Motion Processing ◽  
High Temporal Resolution ◽  
Retinal Ganglion ◽  
Global Motion ◽  
Local Motion ◽  
Motion Direction ◽  
Temporal Precision

AbstractSimple stimuli have been critical to understanding neural population codes in sensory systems. Yet it remains necessary to determine the extent to which this understanding generalizes to more complex conditions. To explore this problem, we measured how populations of direction-selective ganglion cells (DSGCs) from mouse retina respond to a global motion stimulus with its direction and speed changing dynamically. We then examined the encoding and decoding of motion direction in both individual and populations of DSGCs. Individual cells integrated global motion over ~200 ms, and responses were tuned to direction. However, responses were sparse and broadly tuned, which severely limited decoding performance from small DSGC populations. In contrast, larger populations compensated for response sparsity, enabling decoding with high temporal precision (<100 ms). At these timescales, correlated spiking was minimal and had little impact on decoding performance, unlike results obtained using simpler local motion stimuli decoded over longer timescales. We use these data to define different DSGC population decoding regimes that utilize or mitigate correlated spiking to achieve high spatial versus high temporal resolution.

Increased internal noise cannot account for motion coherence processing deficits in migraine

Cephalalgia ◽  
2011 ◽  
Vol 31 (11) ◽  
pp. 1199-1210 ◽  
Author(s):  
Kathryn E Webster ◽  
J Edwin Dickinson ◽  
Josephine Battista ◽  
Allison M McKendrick ◽  
David R Badcock
Keyword(s):  
Internal Noise ◽  
Motion Processing ◽  
Global Motion ◽  
Motion Direction ◽  
Significant Group ◽  
Motion Coherence ◽  
Significant Performance ◽  
Efficient Extraction ◽  
Processing Deficits ◽  
Spiral Angle

Aim: This study aimed to revisit previous findings of superior processing of motion direction in migraineurs with a more stringent direction discrimination task and to investigate whether increased internal noise can account for motion processing deficits in migraineurs. Methods: Groups of 13 migraineurs (4 with aura, 9 without aura) and 15 headache-free controls completed three psychophysical tasks: one detecting coherence in a motion stimulus, one discriminating the spiral angle in a glass pattern and another discriminating the spiral angle in a global-motion task. Internal noise estimates were obtained for all tasks using an N-pass method. Results: Consistent with previous research, migraineurs had higher motion coherence thresholds than controls. However, there were no significant performance differences on the spiral global-motion and global-form tasks. There was no significant group difference in internal noise estimates associated with any of the tasks. Conclusions: The results from this study suggest that variation in internal noise levels is not the mechanism driving motion coherence threshold differences in migraine. Rather, we argue that motion processing deficits may result from cortical changes leading to less efficient extraction of global-motion signals from noise.

scholarly journals Shared attentional resources for global and local motion processing

2007 ◽  
Vol 7 (10) ◽  
pp. 10 ◽  
Author(s):  
Paul F. Bulakowski ◽  
David W. Bressler ◽  
David Whitney
Keyword(s):  
Motion Processing ◽  
Local Motion ◽  
Attentional Resources ◽  
Global And Local
Sign in / Sign up

Export Citation Format

Share Document