Thomas Labhart

A mobile robot employing insect strategies for navigation

The ability to navigate in a complex environment is crucial for both animals and robots. Many animals use a combination of different strategies to return to significant locations in their environment. For example, the desert ant Cataglyphis is able to explore its desert habitat for hundreds of meters while foraging and return back to its nest precisely and on a straight line. The three main strategies that Cataglyphis is using to accomplish this task are path integration, visual piloting and systematic search. In this study, we use a synthetic methodology to gain additional insights into the navigation behavior of Cataglyphis. Inspired by the insect’s navigation system we have developed mechanisms for path integration and visual piloting that were successfully employed on the mobile robot Sahabot 2. On the one hand, the results obtained from these experiments provide support for the underlying biological models. On the other hand, by taking the parsimonious navigation strategies of insects as a guideline, computationally cheap navigation methods for mobile robots are derived from the insights gained in the experiments. ©2000 Elsevier Science B.V. All rights reserved.

Detectors for polarized skylight in insects: a survey of ommatidial specializations in the dorsal rim area of the compound eye

Apart from the sun, the polarization pattern of the sky offers insects a reference for visual compass orientation. Using behavioral experiments, it has been shown in a few insect species (field crickets, honey bees, desert ants, and house flies) that the detection of the oscillation plane of polarized skylight is mediated exclusively by a group of specialized ommatidia situated at the dorsal rim of the compound eye (dorsal rim area). The dorsal rim ommatidia of these species share a number physiological properties that make them especially suitable for polarization vision: each ommatidium contains two sets of homochromatic, strongly polarization‐sensitive photoreceptors with orthogonally‐arranged analyzer orientations. The physiological specialization of the dorsal rim area goes along with characteristic changes in ommatidial structure, providing actual anatomical hallmarks of polarized skylight detection, that are readily detectable in histological sections of compound eyes. The presence of anatomically specialized dorsal rim ommatidia in many other insect species belonging to a wide range of different orders indicates that polarized skylight detection is a common visual function in insects. However, fine‐structural disparities in the design of dorsal rim ommatidia of different insect groups indicate that polarization vision arose polyphyletically in the insects. Microsc. Res. Tech. 47:368–379, 1999.

Specialized photoreceptors at the dorsal rim of the honeybee's compound eye: Polarizational and angular sensitivity

Summary1.The spectral, polarizational and angular sensitivities of photoreceptor cells In the honeybee compound eye are examined by intracellular electrophysiological recordings. The specific aim of this paper is to compare the characteristics of receptor cells in the anatomically specialized dorsal rim area of the eye (containing non-twisted retinulae which are composed of 9 long receptor cells) with those of receptors in the remainder of the eye (containing twisted retinulae which are composed of 8 long cells and 1 short cell).2.The direction of the optical axis for each cell investigated was determined within a coordinate system of space that takes into consideration the head position of the flying bee. All the cells studied (except those in the frontal part of the eye) looked upwards in directions close to the zenith (Fig. 2).3.The UV-cells of the dorsal rim area exhibit high polarizational sensitivities (PS). The actual PS values depend on the amount of coupling between UV- and green-cells (Fig. 5a): UV-cells having relative green-sensitivities of >10% exhibit an average PS of 3.8; if the green-sensitivity is <10% it is 5.6 and rises to more than 10 for cells which either do not respond or hyperpolarize to green light. The overall average PS is 6.6. In marked contrast to this finding, most UV-cells in the remainder of the eye (in twisted retinulae) have PS <2.0 (Fig. 5b).4.Polarizational sensitivities of green-cells are only slightly higher in the dorsal rim area (PS =1.8) than in the other parts of the eye (PS=1.3) (Fig 5c, d).5.By measuring the direction of maximal sensitivity to the e-vector of linearly polarized light (Φmax), two populations of UV-receptors have been found in the dorsal rim area; theirΦmax values differ by 90° (Fig. 6).6.Angular sensitivity functions having unconventional shapes are measured in most receptors of the dorsal rim area. They show a relatively narrow peak in the center and a wide, flat brim in which the average sensitivity decreases from 8% at 7° off axis to 2% at 30° (Fig. 3b, d; 7). If UV-cells having this type of visual field are tested with off-axial (20–30°) stimuli, PS is still high andΦmax is the same as for on-axial stimulation. Thus, the UV-cells of the dorsal rim area are wide-field e-vector analyzers. Apparently, the wide visual fields are caused by corneal specializations in that part of the eye. Control experiments in other parts of the eye confirm the narrow visual fields as they have been described by former authors (Fig. 3a, c).7.The results are discussed in the light of recent behavioral and anatomical investigations on polarization vision. It is concluded that e-vector detection in the honeybee is performed mainly by the UV-receptors of the dorsal rim area.

An autonomous agent navigating with a polarized light compass

One of the fundamental abilities required in autonomous agents is homing. Natural agents—for instance, desert ants—solve the homing problem mainly by using path integration within an egocentric frame of reference. When employing such a mechanism, compass information for determining direction is necessary, and the precision of the compass will have a crucial effect on the precision of homing. For deriving compass information, certain insects use the pattern of polarized light in the sky that arises due to scattering of sunlight in the atmosphere (polarized light compass). The analysis of skylight polarization is mediated by specialized photoreceptors and neurons in the visual system. Inspired by the insects polarized light compass, we have constructed a polarization compass that was employed successfully on the mobile robot Sahabot. Three models for extracting compass information from the polarization pattern of the sky were tested. In this article, we describe the navigation system and report results of experiments performed with the Sahabot in one of the natural habitats of the desert ant Cataglyphis in North Africa.

Neural mechanisms in insect navigation: polarization compass and odometer.

Insect navigation relies on path integration, a procedure by which information about compass bearings pursued and distances travelled are combined to calculate position. Three neural levels of the polarization compass, which uses the polarization of skylight as a reference, have been analyzed in orthopteran insects. A group of dorsally directed, highly specialized ommatidia serve as polarization sensors. Polarization-opponent neurons in the optic lobe condition the polarization signal by removing unreliable and irrelevant components of the celestial stimulus. Neurons found in the central complex of the brain possibly represent elements of the compass output. The odometer for measuring travelling distances in honeybees relies on optic flow experienced during flight, whereas desert ants most probably use proprioreceptive cues.

The physiology of the cricket's compound eye with particular reference to the anatomically specialized dorsal rim area

Summary1.The spectral, angular and polarization sensitivities of photoreceptors in the crickets compound eye are measured by intracellular electrophysiology. The physiological characteristics of receptors in the anatomically specialized dorsal rim area (DRA) are compared with those of receptors in the adjacent dorsal area (DA) of the eye.2.The study of (1) the direction of the optical axis of each cell tested (with respect to natural head position; Fig. 2), (2) the retinal position of intracellularly stained cells and (3) the shapes of the visual fields (see below) suggests that the DRA contains blue-receptors only(λmax=435 nm), where-as the DA is composed of green-(λmax=510 nm) and UV-receptors (λmax ca. 340 nm) (Fig. 1).3.The visual fields of DA units exhibit the usual, narrow shapes with an average acceptance angle (Δρp) of 6°. In contrast, the visual fields of DRA receptors are much wider due to absence of screening pigment and corneal facets in this eye region: Δρ varies between 10° and 35°, but in many cells the angular sensitivity function is too broad to allow determination of Δρ (Figs. 3, 4).4.Polarization sensitivity (PS) in blue-cells (DRA) is much higher (

Photoreceptor design and optical properties affecting polarization sensitivity in ants and crickets

\overline {{\text{PS}}} = 8.3

Behavioural evidence for polarization vision in crickets

) than in green-cells (