Visual Beacons Research Articles

The Wolf Spider Tigrosa helluo Uses Visual Associative and Beacon Landmarks During Water Maze Navigation Tasks

ABSTRACTWolf spiders can learn simple spatial navigation tasks. Previous studies have shown that the wolf spider Tigrosa helluo can use environmental edge features (reference frame landmarks) to learn the location of a dry target in flooded T‐mazes; however, the relative importance of different types or numbers of landmark cues to spatial learning remains unknown. We used a modified open arena water maze and recorded the ability of adult female T. helluo to find a target reward (a dark and dry cup) among cups that were identical to the target but flooded. We measured variation in spatial learning by measuring time to target with no landmark (control), with a beacon (a landmark that is part of the target), with an associative cue (a landmark associated with a specific navigational action), and with both a beacon and an associative cue (N = 92 subjects, n = 23 per landmark cue treatment). For each treatment, we tested females for five trials each on four consecutive days, with the last trial on the fourth day having an altered target location, totaling 19 training trials and one reversal trial (1840 trials). We found that spiders took significantly less time to find the target over subsequent trials within a day and learned more quickly when landmark cues were present, but we found no difference in the type or number of landmark features in the meantime to target entrance. After learning a target location, moving the landmark significantly increased the mean time to target entrance in the combined beacon and associative cue treatment relative to other treatments. Our results indicate that wolf spiders use visual beacons and associative cue landmarks alone or in combination and that performance improves across trials when landmarks are present and deteriorates more when multiple landmarks are moved.

Use of the sun compass by monocularly occluded homing pigeons in a food localisation task in an outdoor arena

Functional asymmetries of the avian visual system can be studied in monocularly occluded birds, as their hemispheres are largely independent. Right and left monocularly occluded homing pigeons and control birds under binocular view have been trained in a food localisation task in an octagonal outdoor arena provided with one coloured beacon on each wall. The three groups were tested after the removal of the visual beacons, so to assess their sun compass learning abilities. Pigeons using the left eye/right hemisphere system exhibited slower learning compared to the other monocular group. During the test in the arena void of visual beacons, the three groups of birds, regardless of their visual condition, were generally able to identify the training sector by exclusively relying on sun compass information. However, the directional choices of the pigeons with the left eye/right hemisphere in use were significantly affected by the removal of the beacons, while both control pigeons and birds with the right eye/left hemisphere in use displayed unaltered performances during the test. A subsample of pigeons of each group were re-trained in the octagonal arena with visual beacons present and tested after the removal of visual beacons after a 6 h fast clock-shift treatment. All birds displayed the expected deflection consistent to the sun compass use. While birds using either the left or the right visual systems were equally able to learn a sun compass-mediated spatial task, the left eye/right hemisphere visual system displayed an advantage in relying on visual beacons.

A mechanism for visual orientation may facilitate courtship in a fiddler crab

Some social signals are sexually selected both by female mating preferences and by male–male competition for mates. Studies of the behavioural mechanisms that mediate responses to these signals provide insight into how sexual selection operates. Courting male fiddler crabs, Uca terpsichores , sometimes build large sand structures called hoods at the openings to their burrows. Hoods attract females to males' burrows for mating because they elicit landmark orientation, a behaviour that is selected by predation. Males also orient visually to their own hoods when errors are introduced experimentally into their nonvisual mechanism for path integration. These errors occur naturally when males move far from their burrows to court females or fight neighbours. Here we explored whether courting males also use hoods as visual beacons to the location of their burrow. Crabs that rely on path integration to orient to their burrow keep their lateral axis closely aligned with the bearing home. We therefore measured and compared the distances males moved from their burrows and the maximum deviations between males' body axes and home bearings for males that did and did not build hoods, males that had their hood removed and males that had a hood added to their burrow. Males with hoods did not range further from their burrows than those without hoods, but they exhibited greater maximum deviations between their body axes and the bearings to their burrows. Hoods may facilitate courtship by allowing males to move more freely than when they rely on nonvisual path integration alone. • Courting male fiddler crabs build sand hoods that attract females for mating. • Males use their hood to find their burrow when their nonvisual path map fails. • Hoods also allow males to move more freely when courting females at a distance. • Multiple modes of sexual and natural selection favour this sexual signal.

A Visual Global Positioning System for Unmanned Aerial Vehicles Used in Photogrammetric Applications

The combination of photogrammetric aerial and terrestrial recording methods can provide new opportunities for photogrammetric applications. A UAV (Unmanned Aerial Vehicle), in our case a helicopter system, can cover both the aerial and quasi-terrestrial image acquisition methods. A UAV can be equipped with an on-board high resolution camera and a priori knowledge of the operating area where to perform photogrammetric tasks. In this general scenario our paper proposes vision-based techniques for localizing a UAV. Only natural landmarks provided by a feature tracking algorithm will be considered, without the help of visual beacons or landmarks with known positions. The novel idea is to perform global localization, position tracking and localization failure recovery (kidnapping) based only on visual matching between current view and available georeferenced satellite images. The matching is based on SIFT features and the system estimates the position of the UAV and its altitude on the base of the reference image. The vision system replaces the GPS signal combining position information from visual odometry and georeferenced imagery. Georeferenced satellite or aerial images must be available on-board beforehand or downloaded during the flight. The growing availability of high resolution satellite images (e.g., provided by Google Earth or other local information sources) makes this topic very interesting and timely. Experiments with both synthetic (i.e., taken from satellites or datasets and pre elaborated) and real world images have been performed to test the accuracy and the robustness of our method. Results show sufficient performance if compared with common GPS systems and give a good performance also in the altitude estimation, even if in this last case there are only preliminary results.

Vision-Based Odometry and SLAM for Medium and High Altitude Flying UAVs

This paper proposes vision-based techniques for localizing an unmanned aerial vehicle (UAV) by means of an on-board camera. Only natural landmarks provided by a feature tracking algorithm will be considered, without the help of visual beacons or landmarks with known positions. First, it is described a monocular visual odometer which could be used as a backup system when the accuracy of GPS is reduced to critical levels. Homography-based techniques are used to compute the UAV relative translation and rotation by means of the images gathered by an onboard camera. The analysis of the problem takes into account the stochastic nature of the estimation and practical implementation issues. The visual odometer is then integrated into a simultaneous localization and mapping (SLAM) scheme in order to reduce the impact of cumulative errors in odometry-based position estimation approaches. Novel prediction and landmark initialization for SLAM in UAVs are presented. The paper is supported by an extensive experimental work where the proposed algorithms have been tested and validated using real UAVs.

Computer Vision-based Navigation and Predefined Track Following Control of a Small Robotic Airship

For small robotic airships, it is required that the airship should be capable of following a predefined track. In this paper, computer vision-based navigation and optimal fuzzy control strategies for the robotic airship are proposed. Firstly, visual navigation based on natural landmarks of the environment is introduced. For example, when the airship is flying over a city, buildings can be used as visual beacons whose geometrical properties are known from the digital map or a geographical information system (GIS). Then a geometrical methodology is adopted to extract information about the orientation and position of the airship. In order to keep the airship on a predefined track, a fuzzy flight control system is designed, which uses those data as its input. And genetic algorithms (GAs), a general-purpose global optimization method, are utilized to optimize the membership functions of the fuzzy controller. Finally, the navigation and control strategies are validated.

Level sets and stable manifold approximations for perceptually driven non-holonomically constrained navigation

This paper addresses problems of robot navigation in the presence of non-holonomic motion constraints arising from kinematics as well as holonomic constraints arising from perception. We consider the theoretical problem of visually registering a unicycle with respect to camera images of a known, persistent landmark. We propose a general hybrid procedure that adapts to this constrained motion setting the standard feedback controller arising from a navigation function in the fully actuated case. The algorithm switches back and forth between moving down and across the associated gradient field toward the stable manifold it induces in the constrained dynamics. Guaranteed to avoid obstacles in all cases, after the introduction of some technical (and not easily verified) additional assumptions, the algorithm can be readily shown to converge to an arbitrarily small neighborhood of the goal. We then introduce a more realistic, 'relaxed' version of the algorithm that appears to result in asymptotic convergence to the goal. Illustrative simulations are provided for two different perceptual models appropriate to environments with visual beacons.

Route finding by rats in an open arena

Rats were repeatedly exposed to an open arena containing two depletable food sources in a discrete-trials procedure. Their movement patterns were recorded and compared to adaptive foraging tactics such as minimizing distance or energy expenditure, thigmotaxis, and trail following. They were also compared to the predictions of the associative route-finder model of Reid and Staddon [Reid, A.K., Staddon, J.E.R., 1998. A dynamic route finder for the cognitive map. Psychol. Rev. 105 (3), 585-601]. We manipulated the presence/absence of food, goal cups, and a wooden runway to determine the influence of local and distal stimuli (visual, olfactory, and tactile) on movement patterns. Increased experience in the arena produced decreases in travel distance and time to the food sources. Local and distal stimuli influenced movement patterns in ways compatible with visual beacons and trail following. The route-finder model accurately predicted movement patterns except those that were influenced by local and distal stimuli. These results show how certain stimuli influence movement and provide a guide for the incorporation of local and distal stimuli in a future version of the dynamic route-finder model.