Image-matching during ant navigation occurs through saccade-like body turns controlled by learned visual features

Abstract

Visual memories of landmarks play a major role in guiding the habitual foraging routes of ants and bees, but how these memories engage visuo-motor control systems during guidance is poorly understood. We approach this problem through a study of image matching, a navigational strategy in which insects reach a familiar place by moving so that their current retinal image transforms to match a memorized snapshot of the scene viewed from that place. Analysis of how navigating wood ants correct their course when close to a goal reveals a significant part of the mechanism underlying this transformation. Ants followed a short route to an inconspicuous feeder positioned at a fixed distance from a vertical luminance edge. They responded to an unexpected jump of the edge by turning to face the new feeder position specified by the edge. Importantly, the initial speed of the turn increased linearly with the turn's amplitude. This correlation implies that the ants' turns are driven initially by their prior calculation of the angular difference between the current retinal position of the edge and its desired position in their memorized view. Similar turns keep ants to their path during unperturbed routes. The neural circuitry mediating image-matching is thus concerned not only with the storage of views, but also with making exact comparisons between the retinal positions of a visual feature in a memorized view and of the same feature in the current retinal image.view-based-homing | snapshot | memory-retrieval | insect

Looking and homing: how displaced ants decide where to go

“…The results of our comparatively coarse analysis of gaze directions in M. croslandi ants cannot be easily reconciled with the findings by Lent et al [24] that wood ants perform very targeted and pre-calculated saccadic body rotations to minimize the angular difference between the retinal position of a salient edge that defines the location of a target feeder and the position of that edge in the memorized view. First, our ants tend to make many saccades into the same direction before reversing scanning direction (figures 3 and 7c), and thus do not appear to align individual features in the panorama with a memorized view.…”

Scene perception and the visual control of travel direction in navigating wood ants

“…The jump induces a transient increase in the frequency of SLTs (figure 4b). SLTs evoked this way have similar properties to spontaneous SLTs [41] and are delayed until ants reach the point of a zig or zag in which they normally face the goal (figure 4c). This delay makes it possible to show that the ant's direction of travel, as given by its mean body orientation over a complete zigzag cycle, is linked more tightly to the performance of SLTs than to the jump of the visual pattern [33].…”

“…The initial segment of the route can be sustained without much need for further SLTs. In contrast, the ants in the experiment of figure 2 were trained over a 1.2 m route to approach a feeder that lay very close to a black rectangle on an LCD screen and inset 15 cm from one edge [41]. Ants tended to take a straight path and generated SLTs almost to the feeder, indicating that they are guided actively over the whole of this route.…”

“…The ant's speed of rotation at the start of an SLT is related linearly to the size of the turn needed to face the goal (the goal angle in figure 1). This relationship (figure 2d) indicates that before turning ants compute the approximate size of the SLT, although the precision of the pre-computed turn may well be improved by visual feedback during its execution [41]. These saccades resemble those of male hoverflies tracking a potential mate [42], but with a major difference.…”

A desert ant's memory of recent visual experience and the control of route guidance

“…By rotating so as to align the current retinal view with retinotopic visual memories acquired on previous trips, an individual will automatically travel in the habitual directions from points along a route [8][9][10][11][12][13][14][15]. This widely used mechanism can be termed 'alignment image-matching' [11,16].…”