Multimodal interactions in insect navigation

Animals travelling through the world receive input from multiple sensory modalities that could be important for the guidance of their journeys. Given the availability of a rich array of cues, from idiothetic information to input from sky compasses and visual information through to olfactory and other cues (e.g. gustatory, magnetic, anemotactic or thermal) it is no surprise to see multimodality in most aspects of navigation. In this review, we present the current knowledge of multimodal cue use during orientation and navigation in insects. Multimodal cue use is adapted to a species’ sensory ecology and shapes navigation behaviour both during the learning of environmental cues and when performing complex foraging journeys. The simultaneous use of multiple cues is beneficial because it provides redundant navigational information, and in general, multimodality increases robustness, accuracy and overall foraging success. We use examples from sensorimotor behaviours in mosquitoes and flies as well as from large scale navigation in ants, bees and insects that migrate seasonally over large distances, asking at each stage how multiple cues are combined behaviourally and what insects gain from using different modalities

Internet use and its relation to mental and physical health among older adults

This exploratory study examined relations between frequency of Internet use among adults 65 and older and perceptions of social support and personal control. Additionally, standard multiple regression procedures were employed to assess the usefulness of frequency of Internet use, perceived social support, and perceived control as predictors of mental and physical health. Results were that frequency of Internet use was uncorrelated with perceptions of social support and personal control and was not predictive of mental or physical health. Perceived social support and perceived control emerged as predictors of mental and physical health. Recommendations for future research that refines measurement of Internet use and that examines the relation of Internet use to the mental and physical health of older adults are provided

A decentralised neural model explaining optimal integration of navigational strategies in insects

Insect navigation arises from the coordinated action of concurrent guidance systems but the neural mechanisms through which each functions, and are then coordinated, remains unknown. We propose that insects require distinct strategies to retrace familiar routes (route-following) and directly return from novel to familiar terrain (homing) using different aspects of frequency encoded views that are processed in different neural pathways. We also demonstrate how the Central Complex and Mushroom Bodies regions of the insect brain may work in tandem to coordinate the directional output of different guidance cues through a contextually switched ring-attractor inspired by neural recordings. The resultant unified model of insect navigation reproduces behavioural data from a series of cue conflict experiments in realistic animal environments and offers testable hypotheses of where and how insects process visual cues, utilise the different information that they provide and coordinate their outputs to achieve the adaptive behaviours observed in the wild

Visual homing in field crickets and desert ants: a comparative behavioural and modelling study

Visually guided navigation represents a long standing goal in robotics. Insights may be drawn from various insect species for which visual information has been shown sufficient for navigation in complex environments, however the generality of visual homing abilities across insect species remains unclear. Furthermore variousmodels have been proposed as strategies employed by navigating insects yet comparative studies across models and species are lacking. This work addresses these questions in two insect species not previously studied: the field cricket Gryllus bimaculatus for which almost no navigational data is available; and the European desert ant Cataglyphis velox, a relation of the African desert ant Cataglyphis bicolor which has become a model species for insect navigation studies. The ability of crickets to return to a hidden target using surrounding visual cues was tested using an analogue of the Morris water-maze, a standard paradigm for spatial memory testing in rodents. Crickets learned to re-locate the hidden target using the provided visual cues, with the best performance recorded when a natural image was provided as stimulus rather than clearly identifiable landmarks. The role of vision in navigation was also observed for desert ants within their natural habitat. Foraging ants formed individual, idiosyncratic, visually guided routes through their cluttered surroundings as has been reported in other ant species inhabiting similar environments. In the absence of other cues ants recalled their route even when displaced along their path indicating that ants recall previously visited places rather than a sequence of manoeuvres. Image databases were collected within the environments experienced by the insects using custompanoramic cameras that approximated the insect eye viewof the world. Six biologically plausible visual homing models were implemented and their performance assessed across experimental conditions. The models were first assessed on their ability to replicate the relative performance across the various visual surrounds in which crickets were tested. That is, best performance was sought with the natural scene, followed by blank walls and then the distinct landmarks. Only two models were able to reproduce the pattern of results observed in crickets: pixel-wise image difference with RunDown and the centre of mass average landmark vector. The efficacy of models was then assessed across locations in the ant habitat. A 3D world was generated from the captured images providing noise free and high spatial resolution images asmodel input. Best performancewas found for optic flow and image difference based models. However in many locations the centre of mass average landmark vector failed to provide reliable guidance. This work shows that two previously unstudied insect species can navigate using surrounding visual cues alone. Moreover six biologically plausible models of visual navigation were assessed in the same environments as the insects and only an image difference based model succeeded in all experimental conditions

Sky segmentation with ultraviolet images can be used for navigation

Inspired by ant navigation, we explore a method for sky segmentation using ultraviolet (UV) light. A standard camera is adapted to allow collection of outdoor images containing light in the visible range, in UV only and in green only. Automatic segmentation of the sky region using UV only is significantly more accurate and far more consistent than visible wavelengths over a wide range of locations, times and weather conditions, and can be accomplished with a very low complexity algorithm. We apply this method to obtain compact binary (sky vs non-sky) images from panoramic UV images taken along a 2km route in an urban environment. Using either sequence SLAM or a visual compass on these images produces reliable localisation and orientation on a subsequent traversal of the route under different weather conditions

Place recognition with event-based cameras and a neural implementation of SeqSLAM

Event-based cameras (Figure 1) offer much potential to the fields of robotics and computer vision, in part due to their large dynamic range and extremely high “frame rates”. These attributes make them, at least in theory, particularly suitable for enabling tasks like navigation and mapping on high speed robotic platforms under challenging lighting conditions, a task which has been particularly challenging for traditional algorithms and camera sensors. Before these tasks become feasible however, progress must be made towards adapting and innovating current RGB-camera-based algorithms to work with eventbased cameras. In this paper we present ongoing research investigating two distinct approaches to incorporating event-based cameras for robotic navigation: 1. The investigation of suitable place recognition / loop closure techniques, and 2. The development of efficient neural implementations of place recognition techniques that enable the possibility of place recognition using event-based cameras at very high frame rates using neuromorphic computing hardware. Figure 1: The first commercial event camera: (a) DVS128; (b) a stream of events (upward and downward spikes: positive and negative events); (c) image-like visualisation of accumulated events within a time interval (white and black: positive and negative events). From (H. Kim, 2014)]

Lianas have a greater competitive effect than trees of similar biomass on tropical canopy trees

Lianas (woody vines) reduce growth and survival of host trees in both temperate and tropical forests; however, the relative strength of liana‐tree competition in comparison to tree‐tree competition remains unexplored. When controlling for biomass, lianas may have greater competitive effects than trees because the unique morphology of lianas allows them to reach the forest canopy at relatively small stem diameters and deploy a substantial crown above their host. We tested the hypothesis that lianas have a greater negative effect on canopy trees than do trees of similar biomass with a liana‐ and tree sapling‐cutting experiment in a seasonal tropical moist forest in Panama. The response of canopy trees to the cutting treatments was characterized as the change in their daily water use by measuring their sap velocity before and after cutting. We compared the responses of canopy trees around which a similar biomass of either lianas or tree saplings had been cut to control trees with no cutting. Liana cutting increased canopy‐tree sap velocity by ∼8% from before to after cutting relative to control trees during the dry season. In contrast, canopy‐tree sap velocity did not respond to tree cutting, probably because trees with biomass similar to lianas were confined to the forest understory. We observed a similar pattern of sap velocity changes during the wet season, but treatment differences were not significant. Our results demonstrate that release from liana competition, but not tree competition, resulted in increased water transport in canopy trees, and suggests that relative to their biomass, lianas have greater competitive effects on canopy tree performance than do competing trees

Unique Competitive Effects of Lianas and Trees in a Tropical Forest Understory

Lianas are an important component of tropical forests, contributing up to 25 % of the woody stems and 35 % of woody species diversity. Lianas invest less in structural support but more in leaves compared to trees of similar biomass. These physiological and morphological differences suggest that lianas may interact with neighboring plants in ways that are different from similarly sized trees. However, the vast majority of past liana competition studies have failed to identify the unique competitive effects of lianas by controlling for the amount of biomass removed. We assessed liana competition in the forest understory over the course of 3 years by removing liana biomass and an equal amount of tree biomass in 40 plots at 10 sites in a secondary tropical moist forest in central Panama. We found that growth of understory trees and lianas, as well as planted seedlings, was limited due to competitive effects from both lianas and trees, though the competitive impacts varied by species, season, and size of neighbors. The removal of trees resulted in greater survival of planted seedlings compared to the removal of lianas, apparently related to a greater release from competition for light. In contrast, lianas had a species-specific negative effect on drought-tolerant Dipteryx oleifera seedlings during the dry season, potentially due to competition for water. We conclude that, at local scales, lianas and trees have unique and differential effects on understory dynamics, with lianas potentially competing more strongly during the dry season, and trees competing more strongly for light