Significance: Attention, observed in a wide variety of animals from insects to humans, involves selectively attending to behaviorally relevant stimuli while filtering out other stimuli. We designed a paradigm that allowed us to record brain activity in tethered, walking bees selecting virtual visual objects. We found that stimulus-specific brain activity increased when the bees controlled the position of the visual objects, and that activity decreased when bees were not in control. When bees were presented with competing objects, brain activity in the optic lobes preceded behavioral choices; this suggests that in animals with tiny brains, such as bees, attention-like processes are pushed far out into the sensory periphery. This trait is likely important for efficiently navigating complex visual environments.

Fine-tuned for image formation: We typically think of eyes as having one or more lenses for focusing incoming light onto a surface such as our retina. However, light can also be focused using arrays of mirrors, as is commonly done in telescopes. A biological example of this is the scallop, which can have up to 200 reflecting eyes that focus light onto two retinas. Palmer et al. find that spatial vision in the scallop is achieved through precise control of the size, shape, and packing density of the tiles of guanine that together make up an image-forming mirror at the back of each of the eyes. Science , this issue p. 1172

The quality of visual information that is available to an animal is limited by the size of its eyes. Differences in eye size can be observed even between closely related individuals, yet we understand little about how this affects vision. Insects are good models for exploring the effects of size on visual systems because many insect species exhibit size polymorphism. Previous work has been limited by difficulties in determining the 3D structure of eyes. We have developed a novel method based on x-ray microtomography to measure the 3D structure of insect eyes and to calculate predictions of their visual capabilities. We used our method to investigate visual allometry in the bumblebee Bombus terrestris and found that size affects specific aspects of vision, including binocular overlap, optical sensitivity, and dorsofrontal visual resolution. This reveals that differential scaling between eye areas provides flexibility that improves the visual capabilities of larger bumblebees.