Visual processing and collective motion-related decision-making in desert locusts

Abstract

Collectively moving groups of animals rely on the decision-making of locally interacting individuals in order to maintain swarm cohesion. However, the complex and noisy visual environment poses a major challenge to the extraction and processing of relevant information. We addressed this challenge by studying swarming-related decision-making in desert locust last-instar nymphs. Controlled visual stimuli, in the form of random dot kinematograms, were presented to tethered locust nymphs in a trackball set-up, while monitoring movement trajectory and walking parameters. In a complementary set of experiments, the neurophysiological basis of the observed behavioural responses was explored. Our results suggest that locusts use filtering and discrimination upon encountering multiple stimuli simultaneously. Specifically, we show that locusts are sensitive to differences in speed at the individual conspecific level, and to movement coherence at the group level, and may use these to filter out non-relevant stimuli. The locusts also discriminate and assign different weights to different stimuli, with an observed interactive effect of stimulus size, relative abundance and motion direction. Our findings provide insights into the cognitive abilities of locusts in the domain of decision-making and visual-based collective motion, and support locusts as a model for investigating sensory-motor integration and motion-related decision-making in the intricate swarm environment.

Pausing to swarm: locust intermittent motion is instrumental for swarming-related visual processing

“…Our recent report [24] provided initial insight into the cognitive abilities of locusts in the domain of decisionmaking and visual-based collective motion, supporting the use of locusts as a model for investigating sensory-motor integration and motion-related decision-making within the intricate swarm environment. In addition to the challenges noted by Bleichman et al [24], Krongauz et al [25] has recently discussed some other issues pertaining to swarming-related visual processing: namely, the problem of visual occlusions (see also [26]), as well as the basic challenges of assessing a locust neighbours' headings and speeds. The latter are of course further complicated by the subject locust's own motion relative to the environment as well as to its neighbours.…”

The relative contribution of acoustic signals versus movement cues in group coordination and collective decision-making

“…For example, both vertebrates and non-vertebrates decrease in their ability to discriminate between numerical differences as the number of individuals involved in a collective behaviour increases (Weber's Law). One notable factor in most invertebrate and bacterial systems is that they rarely use acoustic cues or signals, and instead use very local modes of communication-such as cell-to-cell signalling in bacteria [139], pheromones in ants [140] or physical cues in locusts [141,142]. The reasons for this-sensory limitations-are likely similar to why similar local cues are used in large groups of vertebrates, like starlings [19] and fish [143].…”

Vision-Based Collective Motion: A Locust-Inspired Reductionist Model

“…It is not known whether locust visual perception mechanisms are able to recognize peers. Experiments reported in [56] show that an individual locust responds by walking when exposed to visual images composed of randomly-moving dots that are projected via computer screens to both eyes. As the dots are positioned randomly and do not mimic the shape or the colors of locust nymphs, these results seem to indicate that the motion is triggered in the individual sans a dedicated peer recognition mechanism.…”

“…For example, locusts have a pair of visually-sensitive neurons that encode looming stimuli and cause the locust to produce escape behaviors [46]. The visual stimuli directly affect the behavior of the individual without passing through object recognition mechanisms [56].…”