Images of illusory motion in primary visual cortex.
ABSTRACT Illusory motion can be generated by successively flashing a stationary visual stimulus in two spatial locations separated by several degrees of visual angle. In appropriate conditions, the apparent motion is indistinguishable from real motion: The observer experiences a luminous object traversing a continuous path from one stimulus location to the other through intervening positions where no physical stimuli exist. The phenomenon has been extensively investigated for nearly a century but little is known about its neurophysiological foundation. Here we present images of activations in the primary visual cortex in response to real and apparent motion. The images show that during apparent motion, a path connecting the cortical representations of the stimulus locations is filled in by activation. The activation along the path of apparent motion is similar to the activation found when a stimulus is presented in real motion between the two locations.
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ABSTRACT: A neural field model is presented that captures the essential non-linear characteristics of activity dynamics across several millimeters of visual cortex in response to local flashed and moving stimuli. We account for physiological data obtained by voltage-sensitive dye (VSD) imaging which reports mesoscopic population activity at high spatio-temporal resolution. Stimulation included a single flashed square, a single flashed bar, the line-motion paradigm--for which psychophysical studies showed that flashing a square briefly before a bar produces sensation of illusory motion within the bar--and moving squares controls. We consider a two-layer neural field (NF) model describing an excitatory and an inhibitory layer of neurons as a coupled system of non-linear integro-differential equations. Under the assumption that the aggregated activity of both layers is reflected by VSD imaging, our phenomenological model quantitatively accounts for the observed spatio-temporal activity patterns. Moreover, the model generalizes to novel similar stimuli as it matches activity evoked by moving squares of different speeds. Our results indicate that feedback from higher brain areas is not required to produce motion patterns in the case of the illusory line-motion paradigm. Physiological interpretation of the model suggests that a considerable fraction of the VSD signal may be due to inhibitory activity, supporting the notion that balanced intra-layer cortical interactions between inhibitory and excitatory populations play a major role in shaping dynamic stimulus representations in the early visual cortex.PLoS Computational Biology 01/2010; 6(9). · 4.87 Impact Factor
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ABSTRACT: Functional magnetic resonance imaging (fMRI) and neuron electrophysiology (neurophysiology) are two well-established ways to measure brain activity. Even though the spatial and temporal resolution of these techniques is very different, both measurements show a high level of consistency, i.e., for mapping feature preferences of cortical areas. There are, however, other striking differences between fMRI and neurophysiology, for example, fMRI has good accessibility to higher cognitive functions, a bias to measure synaptic activity, and a good sensitivity to detect feedback-related activity, all of which can shed a new light on the function of well-known brain areas like primary visual cortex, V1. Classically, it is believed that V1 cells are exhaustively characterized by their complex receptive field properties. Contrary to this view, however, fMRI shows that response properties in area V1 are spatially unstable, influenced by contextual information, and depend on internal states. This review will highlight some of the most striking new fMRI findings that show V1 is involved in higher cognitive functions. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 131–139, 2010International Journal of Imaging Systems and Technology 05/2010; 20(2):131 - 139. · 0.64 Impact Factor
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ABSTRACT: Experiments that test perceptual illusions and movement perception have relied predominantly on observing participant response to screen-based phenomena. There are a number of inherent problems to this experimental method as it involves flicker, ignores depth perception and bypasses the proprioceptive system, in short it is psychophysically distinct from dynam- ic real life (veridical) perception. Indeed there still is much disagreement regarding perception of apparent (screen-based) motion despite the fact that we view it in a myriad of ways on an everyday basis. With the aim of furthering our understand- ing and evaluation of veridical movement perception, the team sought to develop a replicable technique that included embod- ied, multi-sensory perception but eliminated the screen. They approached this by taking time-based techniques from anima- tion and converting them to the spatial;; grouping static objects according to Gestalt principles, to create sequential visual cues that, when lit with projected light, demand selective attention. ␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣ ␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣␣he name Diasynchronoscope comes from combining diachronic, (the study of a phenomenon as it changes through time) with synchronous and scope (view). In being so named, it evokes the early animation simulators such as the phenakistoscope and the zoetrope, regarded as direct ancestors of the project in acting both as art objects and experimental media. This paper documents the creation of this new, experimental medium in choreo- graphed time and discusses its potential as a novel tool for investigating aesthetics in movement.Computational Aesthetics in Graphics, Visualization, and Imaging; 05/2012