Both visual area V1 and the medial temporal (MT) region of the human brain are involved in motion perception. V1 is thought to process “local motion,” such as the movement of a bird flying across a relatively small part of space, while MT is thought to process “global motion,” such as the movement of a flock of birds flying across the sky. However, recent studies using fMRI to measure human brain activity have identified signals in V1 that appear to be global motion signals, although it is unclear whether these are related to global motion processing or some other process. In two experiments, a series of stimulus manipulations were conducted to determine the extent to which these signals in V1 reflect global motion. Although initial results have so far proven inconclusive, they highlight discrepancies between previous results, suggesting that V1 motion signals may be more interesting than researchers have assumed.

Both visual area V1 and the medial temporal (MT) region of the human brain play a role in motion perception. V1 is thought to process "local motion," such as the movement of a single bird flying across a relatively small part of space, while MT is thought to process "global motion," such as the movement of an entire flock of birds flying across the sky. However, recent studies using fMRI to measure human brain activity have identified signals in V1 that appear to be global motion signals, although it is unclear whether these are related to global motion processing or stem from some other process. In two experiments, a series of stimulus manipulations were conducted to determine the extent to which these signals in V1 really reflect global motion. Although initial results have so far proven inconclusive, they highlight discrepancies between previous results, suggesting that these motion signals in V1 may be more interesting than researchers have assumed.

The ability to correctly determine the position of objects in space is fundamental to any visual system. For an animal to successfully engage with a dynamic and complex spatial environment it must be able to encode not only the identity of the objects in a visual scene, but also where those objects are. In the human visual system, multiple regions are organized in topographic maps, where locations on cortex have direct correspondence with locations in the visual field. In principle, the position of an object could simply be encoded by the location of the neural activity in one or more of these cortical maps. The task turns out not to be so simple, however, because motion signals can cause the perceived position of stationary objects to deviate from their actual position in the world. A wide variety of these illusory motion-induced position shifts have been demonstrated over the years, beginning with a demonstration by Fröhlich (1923) that the starting position of a moving object appears to be shifted along its trajectory. The goal of this thesis is to investigate the stage in visual processing at which the interaction between motion and position encoding takes place, as well as the implications of this interaction for position encoding in general. To do this, we combined a version of the motion-induced position shift known as the flash grab effect (Anstis & Cavanagh, 2012; Anstis & Cavanagh, in press), with a bistable stimulus in which global motion percepts deviate from local motion signals measured at the moving edge. Specifically, we used psychophysics and functional neuroimaging (fMRI) to (a) measure the influence of local and global motion on motion-induced position shifts, (b) investigate the effects of local and global motion on position over time, and (c) identify regions in visual cortex that are responsible for coding perceived rather than physical position. Our psychophysical results demonstrate that both local and global motion influence motion-induce position shifts. This suggests that motion signals arising at both early and late stages in visual processing make independent contributions to these effects. Surprisingly, our fMRI data show that primary visual cortex encodes shifts in perceived position. Taken together, these studies present strong evidence for a multi-stage model of the interaction between motion and perceived position, and suggest that perceived position is encoded as early as primary visual cortex.

Motion processing is an essential piece of the complex brain machinery that allows us to reconstruct the 3D layout of objects in the environment, to break camouflage, to perform scene segmentation, to estimate the ego movement, and to control our action. Although motion perception and its neural basis have been a topic of intensive research and modeling the last two decades, recent experimental evidences have stressed the dynamical aspects of motion integration and segmentation. This book presents the most recent approaches that have changed our view of biological motion processing. These new experimental evidences call for new models emphasizing the collective dynamics of large population of neurons rather than the properties of separate individual filters. Chapters will stress how the dynamics of motion processing can be used as a general approach to understand the brain dynamics itself.

The neurosciences have experienced tremendous and wonderful progress in many areas, and the spectrum encompassing the neurosciences is expansive. Suffice it to mention a few classical fields: electrophysiology, genetics, physics, computer sciences, and more recently, social and marketing neurosciences. Of course, this large growth resulted in the production of many books. Perhaps the visual system and the visual cortex were in the vanguard because most animals do not produce their own light and offer thus the invaluable advantage of allowing investigators to conduct experiments in full control of the stimulus. In addition, the fascinating evolution of scientific techniques, the immense productivity of recent research, and the ensuing literature make it virtually impossible to publish in a single volume all worthwhile work accomplished throughout the scientific world. The days when a single individual, as Diderot, could undertake the production of an encyclopedia are gone forever. Indeed most approaches to studying the nervous system are valid and neuroscientists produce an almost astronomical number of interesting data accompanied by extremely worthy hypotheses which in turn generate new ventures in search of brain functions. Yet, it is fully justified to make an encore and to publish a book dedicated to visual cortex and beyond. Many reasons validate a book assembling chapters written by active researchers. Each has the opportunity to bind together data and explore original ideas whose fate will not fall into the hands of uncompromising reviewers of traditional journals. This book focuses on the cerebral cortex with a large emphasis on vision. Yet it offers the reader diverse approaches employed to investigate the brain, for instance, computer simulation, cellular responses, or rivalry between various targets and goal directed actions. This volume thus covers a large spectrum of research even though it is impossible to include all topics in the extremely diverse field of neurosciences.

The brain's ability to detect movement within the retinal image is crucial not only for determining the trajectories of moving objects, but also for identifying and interpreting image motion resulting from eye and head movements. This book summarizes our knowledge of how information about image motion is encoded in the brain. Key Features * Valuable reference source for those involved in the rapidly expanding area of motion perception * Strong emphasis on integration of physiological, computation, and psychophysical approaches * Topics include: * Principles of local motion detection * Inputs to local motion detectors * Integration of motion signals * Higher-order interpretation of motion * Motion detection and eye movements