Localization Of Objects In Space Research Articles

Unreferenced spatial localization under monocular and dichoptic viewing conditions

Knowledge of eye position in the brain is critical for localization of objects in space. To investigate the accuracy and precision of eye position feedback in an unreferenced environment, subjects with normal ocular alignment attempted to localize briefly presented targets during monocular and dichoptic viewing. In the task, subjects’ used a computer mouse to position a response disk at the remembered location of the target. Under dichoptic viewing (with red (right eye)–green (left eye) glasses), target and response disks were presented to the same or alternate eyes, leading to four conditions [green target–green response cue (LL), green–red (LR), red–green (RL), and red–red (RR)]. Time interval between target and response disks was varied and localization errors were the difference between the estimated and real positions of the target disk. Overall, the precision of spatial localization (variance across trials) became progressively worse with time. Under dichoptic viewing, localization errors were significantly greater for alternate-eye trials as compared to same-eye trials and were correlated to the average phoria of each subject. Our data suggests that during binocular dissociation, spatial localization may be achieved by combining a reliable versional efference copy signal with a proprioceptive signal that is unreliable perhaps because it is from the wrong eye or is too noisy.

Истина и обоснование для дедуктивных систем: базовые постулаты и аналитичность

The concept of analyticity plays an important role in establishing truths. Both in the traditional logic of terms and modern logic of predicates, similar approaches are used to reconstruct the idea of reliable substantiation. Kant used the categories of synthetic a priori, Frege relied on the features of terms (individual constants and functions) to formulate the conditions for the application of definitions. As a result, primary statements as the beginning for substantiation presuppose the existence and uniqueness of a defined subject (definite descriptions), similar to the localization of objects in space and time by Kant’s synthetic apriori judgments.

Towards a unified perspective of object shape and motion processing in human dorsal cortex.

Although object-related areas were discovered in human parietal cortex a decade ago, surprisingly little is known about the nature and purpose of these representations, and how they differ from those in the ventral processing stream. In this article, we review evidence for the unique contribution of object areas of dorsal cortex to three-dimensional (3-D) shape representation, the localization of objects in space, and in guiding reaching and grasping actions. We also highlight the role of dorsal cortex in form-motion interaction and spatiotemporal integration, possible functional relationships between 3-D shape and motion processing, and how these processes operate together in the service of supporting goal-directed actions with objects. Fundamental differences between the nature of object representations in the dorsal versus ventral processing streams are considered, with an emphasis on how and why dorsal cortex supports veridical (rather than invariant) representations of objects to guide goal-directed hand actions in dynamic visual environments.

Real-time MRI: recent advances using radial FLASH

Recent advances in real-time MRI result in high-quality images with acquisition times of only approximately 30 ms. The technique employs a fast low-angle shot sequence with proton density, T1 or T2/T1 contrast and radial data encoding for motion robustness. High temporal resolution is achieved by an up to 20-fold undersampling of the radial data. An iterative reconstruction algorithm estimates the image as the solution of a nonlinear inverse problem and ensures image fidelity by temporal regularization, which exploits the temporal continuity of successive frames during dynamic imaging. Preliminary real-time examinations at a field strength of 3T range from joint dynamics, speaking and swallowing to the 3D localization of objects in space. In particular, real-time MRI largely facilitates assessments of cardiovascular function and quantitative blood flow. Taken together, advanced real-time MRI methods allow for hitherto inaccessible studies, lead to more robust and shorter examinations, improve patient comf...

Intact memory for implicit contextual information in Korsakoff's amnesia

Implicit contextual learning is the ability to acquire contextual information from our surroundings without conscious awareness. Such contextual information facilitates the localization of objects in space. In a typical implicit contextual learning paradigm, subjects need to find a target among a number of distractors during visual search. Some of the configurations of stimuli are repeated during the experiment resulting in faster responses than for novel configurations, without subjects being aware of their repetition. Patients with Korsakoff's syndrome (KS) have been found to show devastating explicit spatial amnesia. Less is know about their implicit spatial memory abilities. The aim of the present research was to examine whether implicit contextual learning is intact in KS. Therefore, eighteen KS patients and twenty-two age-IQ- and education-matched controls performed the Implicit Contextual Learning task and a paradigm intended to assess explicit, spatial working memory, i.e. the Box task. Intact implicit contextual learning was observed in both the control group and the KS patients. In turn KS patients did have markedly lower explicit spatial working memory scores. The implicit learning effect was not related to the spatial working memory scores. Together these results clearly suggest that implicit and explicit spatial memory have a different neurocognitive basis.

Mislocalization of Flashed and Stationary Visual Stimuli after Adaptation of Reactive and Scanning Saccades

When we look around and register the location of visual objects, our oculomotor system continuously prepares targets for saccadic eye movements. The preparation of saccade targets may be directly involved in the perception of object location because modification of saccade amplitude by saccade adaptation leads to a distortion of the visual localization of briefly flashed spatial probes. Here, we investigated effects of adaptation on the localization of continuously visible objects. We compared adaptation-induced mislocalization of probes that were present for 20 ms during the saccade preparation period and of probes that were present for >1 s before saccade initiation. We studied the mislocalization of these probes for two different saccade types, reactive saccades to a suddenly appearing target and scanning saccades in the self-paced viewing of a stationary scene. Adaptation of reactive saccades induced mislocalization of flashed probes. Adaptation of scanning saccades induced in addition also mislocalization of stationary objects. The mislocalization occurred in the absence of visual landmarks and must therefore originate from the change in saccade motor parameters. After adaptation of one type of saccade, the saccade amplitude change and the mislocalization transferred only weakly to the other saccade type. Mislocalization of flashed and stationary probes thus followed the selectivity of saccade adaptation. Since the generation and adaptation of reactive and scanning saccades are known to involve partially different brain mechanisms, our results suggest that visual localization of objects in space is linked to saccade targeting at multiple sites in the brain.

Gaze direction effects in the primary visual cortex are eccentricity-dependent

Event Abstract Back to Event Gaze direction effects in the primary visual cortex are eccentricity-dependent Simona Celebrini1*, Jean-Baptiste Durand1 and Yves Trotter1 1 Université de Toulouse, CerCo, UPS CNRS, UMR5549, France By integrating visual and eye position signals, V1 neurons with central receptive fields participate in the neuronal mechanisms underlying the localization of objects in space. Because of anatomical and functional differences in their cortical representations and the presence of vertical disparity in eccentric receptive fields, the foveal and peripheral visual fields might not be equally involved in this localization process. To evaluate their respective contributions, we compared the effects of similar gaze direction changes on responses of neurons located in the central and peripheral representations of V1. Single and multi unit recordings were made in dorsal and calcarine V1 on awake behaving monkeys performing a visual fixation task at different gaze eccentricities. Although we did not find a higher frequency of gain effects, we report larger gain values and a higher sensitivity to gaze direction in peripheral V1. We also report a clear influence of the receptive field egocentric eccentricity; peripheral V1 cells present a higher signal-to-noise ratio when responding to objects located in the straight-ahead position in space. This result suggests that egocentric information could be present at the level of single neurons in V1. Furthermore, we propose that eye position information implicated in visual gains, is mainly carried by extra retinal signal of sensory motor origin. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Oral Presentation Topic: Sensory systems Citation: Celebrini S, Durand J and Trotter Y (2009). Gaze direction effects in the primary visual cortex are eccentricity-dependent. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.116 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Nov 2009; Published Online: 23 Nov 2009. * Correspondence: Simona Celebrini, Université de Toulouse, CerCo, UPS CNRS, UMR5549, Toulouse, France, simona@cerco.ups-tlse.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Simona Celebrini Jean-Baptiste Durand Yves Trotter Google Simona Celebrini Jean-Baptiste Durand Yves Trotter Google Scholar Simona Celebrini Jean-Baptiste Durand Yves Trotter PubMed Simona Celebrini Jean-Baptiste Durand Yves Trotter Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Motor space structures perceptual space: Evidence from human saccadic adaptation

Saccadic adaptation is the progressive correction of systematic saccade targeting errors. When a saccade to a particular target is adapted, saccades within a spatial window around the target, the adaptation field, are affected as a function of their distance from the adapted target. Furthermore, previous studies suggest that saccadic adaptation might modify the perceptual localization of objects in space. We investigated the localization of visual probes before and after saccadic adaptation, and examined whether the spatial layout of the observed mislocalizations was structurally similar to the saccadic adaptation field. We adapted a horizontal saccade directed towards a target 12° to the right. Thirty-eight saccades towards the right visual hemifield were then used to measure the adaptation field. The adaptation field was asymmetric: transfer of adaptation to saccades larger than the adapted saccade was greater than transfer to smaller saccades. Subjects judged the localization of 39 visual probes both within and outside the adaptation field. The perceived localization of a probe at a given position was proportional to the amount of transfer from the adapted saccade to the saccade towards that position. This similar effect of saccadic adaptation on both the action and perception representations of space suggests that the system providing saccade metrics also contributes to the metric used for the perception of space.

Fisiologia da visão binocular

A visão binocular de seres humanos resulta da superposição quase completa dos campos visuais de cada olho, o que suscita discriminação perceptual de localizações espaciais de objetos relativamente ao observador (localização egocêntrica) bem mais fina (estereopsia), mas isso ocorre em, apenas, uma faixa muito estreita (o horóptero). Aquém e além dela, acham-se presentes diplopia e confusão, sendo necessária supressão fisiológica (cortical) para evitá-las. Analisa-se a geometria do horóptero e suas implicações fisiológicas (o desvio de Hillebrand, a partição de Kundt, a área de Panum), assim como aspectos clínicos da visão binocular normal (percepção simultânea, fusão, visão estereoscópica) e de adaptações a seus estados afetados (supressão patológica, ambliopia, correspondência visual anômala).

Effects of Field of View on Judgments of Self-Location: Distortions in Distance Estimations Even When the Image Geometry Exactly Fits the Field of View

This research stems from the casual observation that the image of a television screen with 18° geometric ®eld of view (FOVg) as seen on a real television with 17° real FOV appears much “nearer” than the real television<Eth>as much as 98% closer. Does the image appear “nearer” because the distance to the real television is misjudged or is a mental model of a virtual subjective self-location created? Either way, all the projective mapping in the world, whether only in the z plane or in all x, y, and z planes, is irrelevant to explain this powerful perceptual or cognitive effect that the neglected variable of FOV has on self-location in virtual space. Accurate perception of the scene and precise self-location in virtual environments is the goal of accurate perspective geometries, scene computation, and helmet-mounted display (HMD) optics. Yet, as research has already clearly shown, accurate geometric projection is no guarantee of accurate perception: for instance, images viewed exactly at their proper projection points have repeatedly been seen at distorted distances or inaccurate directions. In addition to precise engineering, it is important to understand the psychology of selflocation, also called egocenters, to obtain an understanding of virtual space. A new theory, Cognitive Frame Theory, is proposed to deal with cognitive modi®cations of perception in a way that emphasizes the importance of self-location. Cognitive Frame Theory builds on the phenomenal geometry underlying self-location perceptions: the localization of objects in space requires a combination of perceived distance, perceived direction, and the perception of the position or motion of the self. A fundamentally novel component of the theory suggests that observers use their natural ®elds of view of 120° vertical by 180° horizontal as the primary standard for interpreting visual displays and their self-location in the space of those displays.

The Role of Ocular Muscle Proprioception in Visual Localization of Targets

The role of ocular muscle proprioception in the localization of visual targets has been investigated in normal humans by deviating one eye to create an experimental strabismus. The passively deviated eye was covered and the other eye viewed the target. With a hand-pointing task, targets were systematically mislocalized in the direction of the deviated nonviewing eye. A 4- to 6-degree error resulted when the nonviewing eye was offset 30 degrees from straight ahead. When the eye was deviated, the perceived "straight-ahead" was also displaced, by a similar amount, in the same direction. Since the efferent motor commands to the displaced and to the nondisplaced eyes are presumably identical by the law of equal innervation, the mislocalization of visual objects must be attributed to the change in proprioceptive information issued from the nonviewing, deviated eye. Thus proprioception contributes to the localization of objects in space.