Rat anterior cingulate neurons responsive to rule or strategy changes are modulated by the hippocampal theta rhythm and sharp-wave ripples.

To better understand neural processing during adaptive learning of stimulus-response-reward contingencies, we recorded synchrony of neuronal activity in anterior cingulate cortex (ACC) and hippocampal rhythms in male rats acquiring and switching between spatial and visual discrimination tasks in a Y-maze. ACC population activity as well as single unit activity shifted shortly after task rule changes or just before the rats adopted different task strategies. Hippocampal theta oscillations (associated with memory encoding) modulated an elevated proportion of rule-change responsive neurons (70%), but other neurons that were correlated with strategy-change, strategy value and reward-rate were not.

How the Learning Path and the Very Structure of a Multifloored Environment Influence Human Spatial Memory.

Few studies have explored how humans memorize landmarks in complex multifloored buildings. They have observed that participants memorize an environment either by floors or by vertical columns, influenced by the learning path. However, the influence of the building's actual structure is not yet known.

Decision making under uncertainty: a quasimetric approach.

We propose a new approach for solving a class of discrete decision making problems under uncertainty with positive cost. This issue concerns multiple and diverse fields such as engineering, economics, artificial intelligence, cognitive science and many others. Basically, an agent has to choose a single or series of actions from a set of options, without knowing for sure their consequences.

How does horizontal and vertical navigation influence spatial memory of multifloored environments?

Although a number of studies have been devoted to 2-D navigation, relatively little is known about how the brain encodes and recalls navigation in complex multifloored environments. Previous studies have proposed that humans preferentially memorize buildings by a set of horizontal 2-D representations. Yet this might stem from the fact that environments were also explored by floors.

The probabilistic cell: implementation of a probabilistic inference by the biochemical mechanisms of phototransduction.

When we perceive the external world, our brain has to deal with the incompleteness and uncertainty associated with sensory inputs, memory and prior knowledge. In theoretical neuroscience probabilistic approaches have received a growing interest recently, as they account for the ability to reason with incomplete knowledge and to efficiently describe perceptive and behavioral tasks. How can the probability distributions that need to be estimated in these models be represented and processed in the brain, in particular at the single cell level? We consider the basic function carried out by photoreceptor cells which consists in detecting the presence or absence of light.

Interhemispheric synchrony in visual cortex and abnormal postnatal visual experience.

The question of whether neural synchrony may be preserved in adult mammalian visual cortex despite abnormal postnatal visual experience was investigated by combining anatomical and computational approaches. Single callosal axons in visual cortex of early monocularly deprived (MD) adult cats were labeled anterogradely with biocytin in vivo and reconstructed in 3D. Spike propagation was then orthodromically simulated within each of these axons with NEURON software.

Processing 3D form and 3D motion: respective contributions of attention-based and stimulus-driven activity.

This study aims at segregating the neural substrate for the 3D-form and 3D-motion attributes in structure-from-motion perception, and at disentangling the stimulus-driven and endogenous-attention-driven processing of these attributes. Attention and stimulus were manipulated independently: participants had to detect the transitions of one attribute--form, 3D motion or colour--while the visual stimulus underwent successive transitions of all attributes. We compared the BOLD activity related to form and 3D motion in three conditions: stimulus-driven processing (unattended transitions), endogenous attentional selection (task) or both stimulus-driven processing and attentional selection (attended transitions).

Stereoscopic depth perception in peripheral field and global processing of horizontal disparity gradient pattern.

This study investigates how the visual system detects a surface deviation from planar, induced by, crossed or uncrossed, horizontal disparities continuously increasing with eccentricity. Binocular disparities increased linearly and concentrically, between two given eccentricities. The thresholds of deformation detection were gathered using a method in which observers halted a dynamic stimulus.

A unified probabilistic model of the perception of three-dimensional structure from optic flow.

Human observers can perceive the three- dimensional (3-D) structure of their environment using various cues, an important one of which is optic flow. The motion of any point's projection on the retina depends both on the point's movement in space and on its distance from the eye. Therefore, retinal motion can be used to extract the 3-D structure of the environment and the shape of objects, in a process known as structure-from-motion (SFM).

Bayesian processing of vestibular information.

Complex self-motion stimulations in the dark can be powerfully disorienting and can create illusory motion percepts. In the absence of visual cues, the brain has to use angular and linear acceleration information provided by the vestibular canals and the otoliths, respectively. However, these sensors are inaccurate and ambiguous.

Measurement of the visual contribution to postural steadiness from the COP movement: methodology and reliability.

We studied the reliability of different measures of the visual contribution to postural steadiness by recording the postural sway during standing with eyes open (EO) or eyes closed (EC). The COP trajectory was recorded in 21 subjects aged 42-61 standing on a firm or foam support. The improvement of postural steadiness due to vision was measured with a higher reliability (i.

Postural stability in primary open angle glaucoma.

Background: This study evaluated the visual contribution to postural steadiness in primary open angle glaucoma (POAG), in correlation with the mean deviation (MD) measured through conventional perimetry, and with the Advanced Glaucoma Intervention Study (AGIS) score, which quantifies the extent of losses in the visual field.

Methods: In 35 POAG patients and 21 age-matched normal subjects, the sway of the centre of pressure of the feet, on a firm or foam support, was recorded. The subjects stood on a force-plate with eyes closed, or with one or two eyes open.

Perception and reproduction of force direction in the horizontal plane.

In this study, we evaluated the capacity of human beings to perceive and reproduce forces applied to the hand. We tested for perceptive distortions and/or privileged directions in the performance of these two tasks. Subjects resisted a reference force applied by a joystick in a given direction, with instructions to keep the hand at a constant position.

Perception of plane orientation from self-generated and passively observed optic flow.

We investigated the perception of three-dimensional plane orientation--focusing on the perception of tilt--from optic flow generated by the observer's active movement around a simulated stationary object, and compared the performance to that of an immobile observer receiving a replay of the same optic flow. We found that perception of plane orientation is more precise in the active than in the immobile case. In particular, in the case of the immobile observer, the presence of shear in optic flow drastically diminishes the precision of tilt perception, whereas in the active observer, this decrease in performance is greatly reduced.

Visuovestibular perception of self-motion modeled as a dynamic optimization process.

This article describes a computational model for the sensory perception of self-motion, considered as a compromise between sensory information and physical coherence constraints. This compromise is realized by a dynamic optimization process minimizing a set of cost functions. Measure constraints are expressed as quadratic errors between motion estimates and corresponding sensory signals, using internal models of sensor transfer functions.

Contribution of extraretinal signals to the scaling of object distance during self-motion.

We investigated the role of extraretinal information in the perception of absolute distance. In a computer-simulated environment, monocular observers judged the distance of objects positioned at different locations in depth while performing frontoparallel movements of the head. The objects were spheres covered with random dots subtending three different visual angles.

Absolute distance perception during in-depth head movement: calibrating optic flow with extra-retinal information.

We investigated the ability of monocular human observer to scale absolute distance during sagittal head motion in the presence of pure optic flow information. Subjects were presented at eye-level computer-generated spheres (covered with randomly distributed dots) placed at several distances. We compared the condition of self-motion (SM) versus object-motion (OM) using equivalent optic flow field.

Visual perception of planar orientation: dominance of static depth cues over motion cues.

We measured the ability to report the tilt (direction of maximal slope) of a plane under monocular viewing conditions, from static depth cues (square grid patterns) and motion parallax (small rotations of the plane about a frontoparallel axis). These two cues were presented separately, or simultaneously. In the latter case they specified tilts that were either collinear (coherent case) or orthogonal (conflict case).

Role of lateral acceleration in curve driving: driver model and experiments on a real vehicle and a driving simulator.

Experimental studies show that automobile drivers adjust their speed in curves so that maximum vehicle lateral accelerations decrease at high speeds. This pattern of lateral accelerations is described by a new driver model, assuming drivers control a variable safety margin of perceived lateral acceleration according to their anticipated steering deviations. Compared with a minimum time-to-lane-crossing (H.

The stationarity hypothesis: an allocentric criterion in visual perception.

Having long considered that extraretinal information plays little or no role in spatial vision, the study of structure from motion (SfM) has confounded a moving observer perceiving a stationary object with a non-moving observer perceiving a rigid object undergoing equal and opposite motion. However, recently it has been shown that extraretinal information does play an important role in the extraction of structure from motion by enhancing motion cues for objects that are stationary in an allocentric, world-fixed reference frame (Nature 409 (2001) 85). Here, we test whether stationarity per se is a criterion in SfM by pitting it against rigidity.

Lines and dots: characteristics of the motion integration process.

Local motion detectors can only provide the velocity component perpendicular to a moving line that crosses their receptive field, leading to an ambiguity known as the "aperture problem". This problem is solved exactly for rigid objects translating in the screen plane via the intersection of constraints (IOC). In natural scenes, however, object motions are not restricted to fronto-parallel translations, and several objects with distinct motions may be present in the visual space.

Self-motion and the perception of stationary objects.

One of the ways that we perceive shape is through seeing motion. Visual motion may be actively generated (for example, in locomotion), or passively observed. In the study of the perception of three-dimensional structure from motion, the non-moving, passive observer in an environment of moving rigid objects has been used as a substitute for an active observer moving in an environment of stationary objects; this 'rigidity hypothesis' has played a central role in computational and experimental studies of structure from motion.

Analysis of pointing errors reveals properties of data representations and coordinate transformations within the central nervous system.

The execution of a simple pointing task invokes a chain of processing that includes visual acquisition of the target, coordination of multimodal proprioceptive signals, and ultimately the generation of a motor command that will drive the finger to the desired target location. These processes in the sensorimotor chain can be described in terms of internal representations of the target or limb positions and coordinate transformations between different internal reference frames. In this article we first describe how different types of error analysis can be used to identify properties of the internal representations and coordinate transformations within the central nervous system.