The Antarium: A Reconstructed Visual Reality Device for Ant Navigation Research

Abstract

We constructed a large projection device (the Antarium) with 20,000 UV-Blue-Green LEDs that allows us to present tethered ants with views of their natural foraging environment. The ants walk on an air-cushioned trackball, their movements are registered and can be fed back to the visual panorama. Views are generated in a 3D model of the ants' environment so that they experience the changing visual world in the same way as they do when foraging naturally. The Antarium is a biscribed pentakis dodecahedron with 55 facets of identical isosceles triangles. The length of the base of the triangles is 368 mm resulting in a device that is roughly 1 m in diameter. Each triangle contains 361 blue/green LEDs and nine UV LEDs. The 55 triangles of the Antarium have 19,855 Green and Blue pixels and 495 UV pixels, covering 360° azimuth and elevation from -50° below the horizon to +90° above the horizon. The angular resolution is 1.5° for Green and Blue LEDs and 6.7° for UV LEDs, offering 65,536 intensity levels at a flicker frequency of more than 9,000 Hz and a framerate of 190 fps. Also, the direction and degree of polarisation of the UV LEDs can be adjusted through polarisers mounted on the axles of rotary actuators. We build 3D models of the natural foraging environment of ants using purely camera-based methods. We reconstruct panoramic scenes at any point within these models, by projecting panoramic images onto six virtual cameras which capture a cube-map of images to be projected by the LEDs of the Antarium. The Antarium is a unique instrument to investigate visual navigation in ants. In an open loop, it allows us to provide ants with familiar and unfamiliar views, with completely featureless visual scenes, or with scenes that are altered in spatial or spectral composition. In closed-loop, we can study the behavior of ants that are virtually displaced within their natural foraging environment. In the future, the Antarium can also be used to investigate the dynamics of navigational guidance and the neurophysiological basis of ant navigation in natural visual environments.

Keywords: LED arena; ants; reconstructed visual reality; virtual reality; visual navigation.

Figure 1

The Antarium. (A) Concept schematics of the biscribed pentakis dodecahedron with 55 facets of identical isosceles triangles carrying LEDs and control electronics and the trackball device. (B) Tethered ant on an air-cushioned trackball. The ants are free to rotate around the yaw axis, but its translational movements are registered by monitoring the rotations of the Styrofoam ball. (C) The tethered ant as seen by the Antarium camera. (D) The fully assembled Antarium. (E) The landscape panorama projected by the Antarium LEDs seen at 1.5° resolution, about twice the average resolution of ants.

Figure 2

The design of individual Antarium panels. (A) Photograph of one of the panels with LEDs seen as white rectangles. (B) Detail of the panel LED locations on the printed circuit board and the actuator axle location for polarizer disks. (C) Spectral sensitivities of Myrmecia ants compared with current LED emission spectra. Continuous lines: normalized spectral sensitivities of the nocturnal Myrmecia vindex recorded intracellularly (redrawn from Ogawa et al., 2015). Dotted lines: emission spectra of the LEDs used in the current version of the Antarium as per manufacturer specifications. (D) Schematic of how light polarization is achieved. (E) The data path of the Antarium.

Figure 3

The Antarium control electronics. (A) The distributor board and its major electronics. (B) The block diagram of the LED panel Field-Programmable Gate Array.

Figure 4

Proof of concept experiments. (A) Four panoramic views from the ants’ foraging habitat. Familiar is located on the ants’ foraging corridor, half-way toward their foraging tree; Nest is the view from the ants’ nest entrance; Unfamiliar if the view from a location about 5 m to the side of the foraging corridor and Unstructured is a synthetic view without landmark panorama. (B) Two examples (left and right) of ants responding to familiar scene rotations. Instances of rotations are marked by blue dots in the time course of path direction (top) panels and of speed (bottom panels). Fifteen seconds segments before (red) and after rotations (blue) are also marked on the intended paths of the ants (shown on the left) and on the time course of path direction (top panels). Paths are shown in the trackball coordinate system. (C) Same as (B), but in the presence of the unstructured scene. Note the difference in path direction oscillations in (B,C).

Figure 5

Proof of concept experiments. (A) The path (left), the time course of path direction (right-top), and time course of speed (right bottom) for an ant in the presence of the familiar view. Successive instances of scene rotation are marked by blue dots and numbered. Otherwise conventions as in Figure 4. (B) Top row: gaze (head, orange) and longitudinal body orientation (blue) over time from 15 s before and 15 s after rotation 2–4. Bottom row: head orientation relative to longitudinal body axis for the same segments. The vertical black line marks the moment of rotation.