How variation in head pitch could affect image matching algorithms for ant navigation

Abstract

Desert ants are a model system for animal navigation, using visual memory to follow long routes across both sparse and cluttered environments. Most accounts of this behaviour assume retinotopic image matching, e.g. recovering heading direction by finding a minimum in the image difference function as the viewpoint rotates. But most models neglect the potential image distortion that could result from unstable head motion. We report that for ants running across a short section of natural substrate, the head pitch varies substantially: by over 20 degrees with no load; and 60 degrees when carrying a large food item. There is no evidence of head stabilisation. Using a realistic simulation of the ant’s visual world, we demonstrate that this range of head pitch significantly degrades image matching. The effect of pitch variation can be ameliorated by a memory bank of densely sampled along a route so that an image sufficiently similar in pitch and location is available for comparison. However, with large pitch disturbance, inappropriate memories sampled at distant locations are often recalled and navigation along a route can be adversely affected. Ignoring images obtained at extreme pitches, or averaging images over several pitches, does not significantly improve performance.Electronic supplementary materialThe online version of this article (doi:10.1007/s00359-015-1005-8) contains supplementary material, which is available to authorized users.

Insect-Inspired Visual Navigation for Flying Robots

“…The idea of this was to see whether the effect of pitch changed with changing height. For this data set, the impact of pitch was detrimental to the route coverage as has been seen in [18] and did not vary with height, but at least in Location A, there remains some information for homing. We next tested whether images that were taken at a particular goal height, could be successfully used to home for a robot travelling at a different height (Fig.…”

Head roll stabilisation in the nocturnal bull ant Myrmecia pyriformis: Implications for visual navigation

“…Ardin et al (2015) have recently conducted a similar analysis on the effects of head pitch on navigational information. We find that at the location at which a reference image is taken, the orientation of that image can be recovered even if the current view is rotated up to 20 deg relative to the horizontal (left column, Fig.…”

“…Walking insects, however, face not only the predictable stride-cycle-dependent body oscillations but also unpredictable ground topography-dependent body rotations Egelhaaf, 2012, 2014). In the context of visual navigation, it is thus important to investigate to what extent pedestrian navigators, such as ants, are able to control head orientation around the roll and pitch axes while walking (Ardin et al, 2015 and literature review therein). Ants are assumed to memorise views of the nest environment during learning walks before they head out on their first foraging trip (e.g.…”

“…To make use of these memories for navigation, insects must be able to hold their visual system in defined orientations during acquisition and recall (e.g. Duelli, 1975;Weihmann and Blickhan, 2009;Ardin et al, 2015).…”

A champion of organismal biology

“…This approach will be a prerequisite for testing visual navigation algorithms under nearly 'reallife' conditions. The paper by Ardin et al (2015) addresses a so far neglected problem for navigation that relies on visual memories of the surroundings: the image distortions caused by variation in head pitch if ants run over uneven ground. Since there is no evidence for head stabilisation in Cataglyphis velox, homing performance may be drastically affected by such image distortions.…”