Reward Value Is More Important Than Physical Saliency During Bumblebee Visual Search For Multiple Rewarding Targets

Nityananda, Vivek; Chıttka, Lars · 2020 · OpenAlex-citations

DOI: 10.1101/2020.10.01.322172

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Summary

This study investigates how bumblebees prioritize visual search targets when multiple rewarding flowers are present, specifically examining the interplay between physical saliency (color contrast against the background) and reward value (sucrose concentration). While previous research has established that bees can distinguish single targets from distractors, less is known about how they allocate attention between multiple familiar, rewarding options in complex environments. The authors aimed to determine whether bottom-up processes (saliency) or top-down processes (reward history) dominate bee visual search, drawing parallels to human visual attention studies where reward value can override physical salience. The researchers conducted three experiments using individually tagged bumblebees trained to recognize two distinct rewarding flower types amidst distractors. In Experiment 1, bees chose between high-saliency and low-saliency flowers offering equal rewards. In Experiment 2, bees chose between high-reward (50% sucrose) and low-reward (30% sucrose) flowers with similar saliency. Experiment 3 combined these factors, pitting high-reward, low-saliency flowers against low-reward, high-saliency flowers. Bees were trained sequentially on two discrimination tasks and then tested without reinforcement to measure choice proportions, search times, and attention (inspection time). Video tracking analyzed bee positions to quantify attention metrics, while generalized linear models assessed the impact of saliency, reward, and training order. The results demonstrated that bees effectively ignored distractors and preferred both more salient and higher-rewarding targets when other factors were equal. Crucially, in Experiment 3, bees chose high-reward, low-saliency flowers as frequently as low-reward, high-saliency flowers, indicating that reward value can compensate for lower physical salience. Furthermore, bees exhibited faster search times and longer inspection durations for high-reward targets, suggesting heightened attention. A significant effect of training order was also observed: bees were more likely to choose targets encountered in the most recent training session, regardless of reward or saliency. This recency effect persisted even when controlling for training duration, highlighting the role of search history in visual attention. These findings suggest that bumblebee visual search is influenced by a combination of physical saliency, reward value, and recent experience. The ability of reward value to attract attention despite low saliency parallels findings in human cognition, implying that reward-based attention mechanisms may be evolutionarily conserved across species. This study advances the understanding of animal foraging behavior by demonstrating that bees do not rely solely on bottom-up visual cues but integrate top-down reward expectations and search history to optimize foraging efficiency in complex floral environments.

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• visual search