Visual Acuity:
Can you imagine navigating in a world where you can't perceive its fine details? Or interpreting small visual signals when a "pixel" of your vision is the size of your thumb at arm's length? For many non-human animals these questions aren't hypotheticals, but instead reflect the reality of their reduced visual acuity.
Visual acuity (VA) is defined as an animal's ability to perceive static details and is one measurement of the fineness or coarseness of vision. As a sensory parameter visual acuity has a large impact on an animal because it 1) varies by up to 5 orders of magnitude between species and 2) is used in all sorts of behavioral tasks including predation, navigation, and signaling.
Students in the lab can study VA in a variety of ways including both physiological and behavioral projects. Currently one of the main lines of research is examining the visual acuity of band-winged grasshoppers including the local Carolina grasshopper. Previously, we have shown that VA in three species of band-winged grasshopper varies both with axis of view and is sexually dimorphic (females have ~25% sharper vision than males). However how this affects grasshopper behavior --- including their interpretation of numerous visual signals they produce --- is currently unknown.
Humans possess near elite Visual Acuity, with most animals having much coarser vision. Note the log scale on the y-axis with higher values indicating finer vision. Adapted from Caves, Brandley, and Johnsen (2018).
Visual Acuity in three species of band-winged grasshopper 1) varies by axis of view and 2) is sexually dimorphic in the finest axis of vision. Note that in insects VA is typically measured in degrees (rather than cycles per degree) so smaller values indicate finer vision.
A) Visual acuity perpendicular to the horizon is sexually dimorphic with females (darker shading) having finer vision. Additionally species differ significantly from one another. B) In contrast to A, visual acuity parallel to the horizon is both coarser and shows no significant sexual dimorphism. Error bars indicate 95% CI. Adapted from Duncan, Salazar, Garcia, and Brandley (in review).
Current Visual Acuity Related Projects:
1) How does the sexual dimorphism in VA within band-winged grasshoppers affect their ability to discern and interpret visual signals?
2) Do aspects of band-winged VA match their ability to escape from predators?
3) How much does VA vary within a species? (with Dr. Eleanor Caves)
In addition I'm always happy to support student-driven VA projects in other animals (especially those with compound eyes).
Relevant Papers:
* = undergraduate student
Caves, E.M., N.C. Brandley, and S Johnsen (2018). Visual acuity and the evolution of signals. Trends in Ecology & Evolution 33: 358-372
A. Duncan*, B. Salazar*, S. Garcia*, and N.C. Brandley (in review). A sexual dimorphism in the spatial vision of band-winged grasshoppers. preprint available here: https://www.biorxiv.org/content/10.1101/2020.09.18.303784v2