Mixed spatial and movement representations in the primate posterior parietal cortex

The posterior parietal cortex (PPC) of humans and non-human primates plays a key role in the sensory and motor transformations required to guide motor actions to objects of interest in the environment. Despite decades of research, the anatomical and functional organization of this region is still a matter of contention. It is generally accepted that specialized parietal subregions and their functional counterparts in the frontal cortex participate in distinct segregated networks related to eye, arm and hand movements. However, experimental evidence obtained primarily from single neuron recording studies in non-human primates has demonstrated a rich mixing of signals processed by parietal neurons, calling into question ideas for a strict functional specialization. Here, we present a brief account of this line of research together with the basic trends in the anatomical connectivity patterns of the parietal subregions. We review, the evidence related to the functional communication between subregions of the PPC and describe progress towards using parietal neuron activity in neuroprosthetic applications. Recent literature suggests a role for the PPC not as a constellation of specialized functional subdomains, but as a dynamic network of sensorimotor loci that combine multiple signals and work in concert to guide motor behavior

Perceiving virtual geographic slant: action influences perception

technical reportFour experiments varied the extent and nature of observer movement in a virtual environment to examine the influence of action on estimates of geographical slant. Previous slant studies demonstrated that people consciously overestimate hill slant but can still accurately guide an action toward the hill (Proffitt, Bhalla, Gossweiler & Midget, 1995). Related studies (Bhalla & Proffitt, 1999) suggest that one s potential to act may influence perception of slant and that distinct representations may independently inform perceptual and motoric responses. We found that in all conditions, perceptual judgments were overestimated and motoric adjustments were more accurate. The virtual environment allowed manipulation of the effort required to walk up simulated hills. Walking with the effort appropriate to the visual slant led to increased perceptual overestimation of slant compared to active walking with effort appropriate to level ground, while visually guided actions remained accurate

Ergonomics of the Operative Field in Paediatric Minimal Access Surgery

Imperial Users onl

Contemporary Robotics

This book book is a collection of 18 chapters written by internationally recognized experts and well-known professionals of the field. Chapters contribute to diverse facets of contemporary robotics and autonomous systems. The volume is organized in four thematic parts according to the main subjects, regarding the recent advances in the contemporary robotics. The first thematic topics of the book are devoted to the theoretical issues. This includes development of algorithms for automatic trajectory generation using redudancy resolution scheme, intelligent algorithms for robotic grasping, modelling approach for reactive mode handling of flexible manufacturing and design of an advanced controller for robot manipulators. The second part of the book deals with different aspects of robot calibration and sensing. This includes a geometric and treshold calibration of a multiple robotic line-vision system, robot-based inline 2D/3D quality monitoring using picture-giving and laser triangulation, and a study on prospective polymer composite materials for flexible tactile sensors. The third part addresses issues of mobile robots and multi-agent systems, including SLAM of mobile robots based on fusion of odometry and visual data, configuration of a localization system by a team of mobile robots, development of generic real-time motion controller for differential mobile robots, control of fuel cells of mobile robots, modelling of omni-directional wheeled-based robots, building of hunter- hybrid tracking environment, as well as design of a cooperative control in distributed population-based multi-agent approach. The fourth part presents recent approaches and results in humanoid and bioinspirative robotics. It deals with design of adaptive control of anthropomorphic biped gait, building of dynamic-based simulation for humanoid robot walking, building controller for perceptual motor control dynamics of humans and biomimetic approach to control mechatronic structure using smart materials

Temporal Analysis of Reference Frames in Parietal Cortex Area 5d during Reach Planning

The neural encoding of spatial and postural reference frames in posterior parietal cortex has traditionally been studied during fixed epochs, but the temporal evolution of these representations (or lack thereof) can provide insight into the underlying computations and functions of this region. Here we present single-unit data recorded from two rhesus macaques during a reach planning task. We found that area 5d coded the position of the hand relative to gaze before presentation of the reach target, but switched to coding the target location relative to hand position soon after target presentation. In the pretarget period the most relevant information for success in the task is the position of the hand relative to gaze; however, after target onset, the most task-relevant spatial relationship is the location of the target relative to the hand. The switch in coding suggests that population activity in area 5d may represent postural and spatial information in the reference frame that is most pertinent at each stage of the task. Moreover, although target−hand coding was dominant from soon after the reach target onset, this representation was not static but built in strength as movement onset approached, which we speculate could reflect a role for this region in building an accurate state estimate for the limb. We conclude that representations in area 5d are more flexible and dynamic than previously reported

An exploration of visuomotor and perceptual mechanisms in humans and rats.

Neuropsychological, neurophysiological and psychophysical evidence support the notion of two separate and largely independent cortical visual systems: a dorsal system mediating visually guided action and a ventral system mediating object perception and recognition (Goodale & Milner, 1992). This thesis is divided into three parts that explore questions related to the two-visual-systems model, two in humans and one in rats. The first part explores whether dorsal representations are based on the veridical properties of the stimuli or whether they include information produced by filling-in mechanisms of cortical visual areas. All human experiments were carried out with the ELITE and SMART motion tracking systems. Kinematic analysis showed that grasping Kanizsa illusory squares and partly-occluded objects was as accurate as grasping luminance-defined targets and it is concluded that information about interpolated regions is available to the dorsal system for the calibration of the movement parameters. A Vernier acuity task confirmed that the perceptual localization of Kanizsa and luminance-defined contours is not equally accurate in the ventral visual system. The second part explores the effect of target dimensionality on grasping, focusing on the possibility that actions aimed at targets that contain two-dimensional information could be modulated by ventral visual mechanisms. The Diagonal Illusion (DI) was chosen to investigate this possibility because it is entirely the product of three- dimensional objects. The DI exerted an effect on both perception and action, although the latter was smaller, suggesting that the effects of illusions on action previously reported are not attributable to the presence of 2D information and, by implication, that 2D information in the target array does not elicit modulation by the ventral visual system. These conclusions were confirmed by a study that found similar kinematic profiles from grasps aimed at 3D, 2D and 2D-enhanced targets. Control studies ruled out potential confounding effects resulting from curvatures of the stimuli that could have acted as obstacles and from differences in haptic feedback. It is concluded that object-directed action is mediated by dorsal visual mechanisms, irrespective of target dimensionality. The third part seeks to find evidence of ventral visual processing in rats by measuring the perception of visual illusions and object recognition in this species. The aim is to establish whether rats could provide a suitable model to further investigate the dorsal and ventral visual systems. An automated apparatus with a touch-screen and computer generated stimuli was developed to train the animals. The results from the illusion studies are not conclusive as only one out of three groups of rats was able to solve a discrimination with Kanizsa illusory figures. The preliminary results from the object recognition studies are however clearer. Rats were able to use aspect ratio to solve a discrimination with stimuli that varied in size and location suggesting that size- and location-independent object recognition occurs in this species. Probe trials confirmed these results. It is concluded that rats may have visual processes comparable to those occurring in the ventral visual system of humans and primates

Role of visual information during stair locomotion

Vision provides relevant information for safe locomotion in a variety of environments. During stair locomotion visual information may be important to detect step boundaries, transitions between ground level and stairs, handrail location, and potential hazards. Although there is a large body of literature on the role of vision during locomotion there is relatively little focused on how visual information is used during stair walking. Stairs are related to a significant number of accidents in daily living, and many of these accidents are attributed to visual factors. Therefore, understanding the role of vision during stair walking could provide insight into the mechanisms involved in stair accidents. The purpose of this thesis was to investigate the properties of the visual input used to guide locomotion on stairs. Study 1 was design to describe the gaze patterns during stair locomotion with a specific focus on transitions and handrails. Study 2 investigated the effects of performing concurrent visual and non-visual tasks on walking performance and associated gaze behaviour during stair ascent. Study 3 explored the role of peripheral visual information during visual and non-visual dual tasking. Finally, Study 4 investigated the effects of restricting the lower peripheral visual field to walk on stairs. Studies relied on the measurement in health young adults of: gaze behaviour using an eye tracker, temporal characteristics of walking using foot switches, and reaction time and errors of dual task performance. Overall, the findings of these studies highlight the importance of the lower visual field in guiding stair locomotion and the specific importance for stair transitions. Moreover, foveal vision is not specifically critical to detecting handrails or steps. Results are interpreted in the light of the specialization of the dorsal ventral stream in processing peripheral visual field information. Findings of this thesis provide basic understanding on the role of vision for stair navigation with potential applications in stair-related accident prevention programs and stair design