Sky segmentation with ultraviolet images can be used for navigation

Stone, Thomas; Mangan, Michael; Ardin, Paul; Webb, Barbara

doi:10.15607/rss.2014.x.047

Cited by 44 publications

(39 citation statements)

References 24 publications

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“…It has recently been reported that UV contrast is highly effective for sky segmentation and the resulting binary panoramic skyline images can support effective navigation in ants [29,30]. The night-active M. vindex may be forced to slow down their UV receptors not only to ensure sufficient skyline contrast for landmark guidance [28], but also to obtain reliable compass information from the dim pattern of polarized skylight in the evening twilight [24].…”

Section: Discussion (A) Three Spectrally Distinct Photoreceptors In Antsmentioning

confidence: 99%

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Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

et al. 2015

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Ants are thought to be special among Hymenopterans in having only dichromatic colour vision based on two spectrally distinct photoreceptors. Many ants are highly visual animals, however, and use vision extensively for navigation. We show here that two congeneric day-and night-active Australian ants have three spectrally distinct photoreceptor types, potentially supporting trichromatic colour vision. Electroretinogram recordings show the presence of three spectral sensitivities with peaks (l max ) at 370, 450 and 550 nm in the night-active Myrmecia vindex and peaks at 370, 470 and 510 nm in the day-active Myrmecia croslandi. Intracellular electrophysiology on individual photoreceptors confirmed that the night-active M. vindex has three spectral sensitivities with peaks (l max ) at 370, 430 and 550 nm. A large number of the intracellular recordings in the night-active M. vindex show unusually broad-band spectral sensitivities, suggesting that photoreceptors may be coupled. Spectral measurements at different temporal frequencies revealed that the ultraviolet receptors are comparatively slow. We discuss the adaptive significance and the probability of trichromacy in Myrmecia ants in the context of dim light vision and visual navigation.

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Section: Discussion (A) Three Spectrally Distinct Photoreceptors In Antsmentioning

confidence: 99%

“…UV images are highly effective for sky/horizon segmentation and the horizon contour can be used to support effective navigation [29]. It has also been argued that the ant visual system is well suited for the extraction of skyline contour information based on the presence of a UV-green opponent channel [30].…”

Section: Introductionmentioning

confidence: 99%

Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

et al. 2015

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“…As shown by [20], local UV-only separation can be used to extract the skyline from panoramic images in real time in robot applications using similar computationally-inexpensive methods (e.g., watershed algorithm). They demonstrate that an agent can use this segmented skyline information to localize itself on a previously-driven track.…”

Section: Discussionmentioning

confidence: 99%

“…Local methods have been successfully used to extract the skyline using only the UV channel only on mobile robots [6,20]. However, in these studies, skyline extraction was mainly performed in suburban environments or in forests.…”

Section: Introductionmentioning

confidence: 99%

Spectral Skyline Separation: Extended Landmark Databases and Panoramic Imaging

Differt

Möller

2016

Sensors

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Evidence from behavioral experiments suggests that insects use the skyline as a cue for visual navigation. However, changes of lighting conditions, over hours, days or possibly seasons, significantly affect the appearance of the sky and ground objects. One possible solution to this problem is to extract the “skyline” by an illumination-invariant classification of the environment into two classes, ground objects and sky. In a previous study (Insect models of illumination-invariant skyline extraction from UV (ultraviolet) and green channels), we examined the idea of using two different color channels available for many insects (UV and green) to perform this segmentation. We found out that for suburban scenes in temperate zones, where the skyline is dominated by trees and artificial objects like houses, a “local” UV segmentation with adaptive thresholds applied to individual images leads to the most reliable classification. Furthermore, a “global” segmentation with fixed thresholds (trained on an image dataset recorded over several days) using UV-only information is only slightly worse compared to using both the UV and green channel. In this study, we address three issues: First, to enhance the limited range of environments covered by the dataset collected in the previous study, we gathered additional data samples of skylines consisting of minerals (stones, sand, earth) as ground objects. We could show that also for mineral-rich environments, UV-only segmentation achieves a quality comparable to multi-spectral (UV and green) segmentation. Second, we collected a wide variety of ground objects to examine their spectral characteristics under different lighting conditions. On the one hand, we found that the special case of diffusely-illuminated minerals increases the difficulty to reliably separate ground objects from the sky. On the other hand, the spectral characteristics of this collection of ground objects covers well with the data collected in the skyline databases, increasing, due to the increased variety of ground objects, the validity of our findings for novel environments. Third, we collected omnidirectional images, as often used for visual navigation tasks, of skylines using an UV-reflective hyperbolic mirror. We could show that “local” separation techniques can be adapted to the use of panoramic images by splitting the image into segments and finding individual thresholds for each segment. Contrarily, this is not possible for ‘global’ separation techniques.

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“…The green receptor in compound eyes, expressing another long-wavelength opsin AmLop1, is maximally sensitive at around 550 nm (Peitsch et al, 1992;Kevan et al, 2001). It has been suggested that UV-green contrast is highly effective for detecting the contrast between the sky and the terrestrial horizon line (Wilson, 1978;Möller, 2002;Kollmeier et al, 2006;Basten and Mallot, 2010;Stone et al, 2014) and the ocellar green receptor with a peak sensitivity shifted toward shorter wavelengths might contribute to sharpen this contrast by increasing its overlap with UV receptors. Some large ocellar interneurons (L-neurons) in honeybees have two spectral sensitivity peaks at 340 and at 500 nm, implying that these cells receive input from both types of photoreceptor (Milde, 1984).…”

Section: Two Spectrally Distinct Receptors In Ocellimentioning

confidence: 99%

Regional differences in the preferred e-vector orientation of honeybee ocellar photoreceptors

Ogawa

Ribi

Zeil

et al. 2017

Journal of Experimental Biology

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In addition to compound eyes, honeybees (Apis mellifera) possess three single-lens eyes called ocelli located on the top of the head. Ocelli are involved in head-attitude control and in some insects have been shown to provide celestial compass information. Anatomical and early electrophysiological studies have suggested that UV and blue-green photoreceptors in ocelli are polarization sensitive. However, their retinal distribution and receptor characteristics have not been documented. Here, we used intracellular electrophysiology to determine the relationship between the spectral and polarization sensitivity of the photoreceptors and their position within the visual field of the ocelli. We first determined a photoreceptor's spectral response through a series of monochromatic flashes (340-600 nm). We found UV and green receptors, with peak sensitivities at 360 and 500 nm, respectively. We subsequently measured polarization sensitivity at the photoreceptor's peak sensitivity wavelength by rotating a polarizer with monochromatic flashes. Polarization sensitivity (PS) values were significantly higher in UV receptors (3.8± 1.5, N=61) than in green receptors (2.1±0.6, N=60). Interestingly, most receptors with receptive fields below 35 deg elevation were sensitive to vertically polarized light while the receptors with visual fields above 35 deg were sensitive to a wide range of polarization angles. These results agree well with anatomical measurements showing differences in rhabdom orientations between dorsal and ventral retinae. We discuss the functional significance of the distribution of polarization sensitivities across the visual field of ocelli by highlighting the information the ocelli are able to extract from the bee's visual environment.

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Sky segmentation with ultraviolet images can be used for navigation

Cited by 44 publications

References 24 publications

Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

Spectral Skyline Separation: Extended Landmark Databases and Panoramic Imaging

Regional differences in the preferred e-vector orientation of honeybee ocellar photoreceptors

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