Ling Li led the team to look through eyes made of stone

Ling Li, associate professor in the Department of Mechanical Engineering, has been awarded $1.05 million over three years to lead a team studying the visual abilities of a unique underwater creature with thousands of eyes.

Credits: Photo by Alex Parrish for Virginia Tech.

Ling Li, associate professor in the Department of Mechanical Engineering, has been awarded $1.05 million over three years to lead a team studying the visual abilities of a unique underwater creature with thousands of eyes.

The project reunited Li with a former collaborator, University of South Carolina Associate Professor Daniel Speiser. They also enlisted the expertise of an internationally recognized applied mathematician specializing in image processing, Daniel Baum of the Zuse Institute in Berlin.

What does the rocky eye see and what does it mean

The team’s research will focus on the chiton’s rocky eyes. This sea creature has a hard, pill-shaped outer shell with overlapping plates and a soft inner body. The shell is made of a calcium carbonate material called aragonite, one of the main ingredients in pearl formation. To view its surroundings, the chiton uses thousands of tiny stone eyes embedded in its shell’s armor plates, all formed from the same coarse material.

Speiser made early discoveries of the chiton’s optical system structure, formulating the idea of ​​the creature’s ability to see images. During Ph.D. Studying at the Massachusetts Institute of Technology and subsequent postdoctoral work at Harvard, Li joined forces with Speiser and collaborators to build on Speiser’s initial work and explore how the eye works. Together, they devised an experimental setup that allowed them to look directly through the lens of aragonite chitons, seeing a blurry but recognizable shape.

The aragonite eye is rigid and therefore unable to adjust its focus or gaze in the way the soft eye can in many creatures. While Speiser and Li’s early work demonstrated a working principle and structural basis suitable for a single stone eye, animals’ ability to process visual information extends beyond the individual eye. These rigid optical elements are interconnected by means of a complex network of microscopic channels that host photosensitive cells and a network of nerves, forming an integrated neural network. The animal gets visual feedback, but each eye doesn’t process that much data. Since one eye is about the width of a human hair, the vision of one-eyed chitons is far from high definition.

Still, chiton shells have hundreds to thousands of eyes. Do all the little pictures reunite in the chiton’s nervous system? Is he able to take the pieces and form the whole picture? Is the visual information obtained from the individual’s eye reassembled as a more high-definition image?

Answering new questions with new teams

Li and Speiser sought funding opportunities to explore this new question through their research. They received a grant from the Human Frontier Science program, a frontier basic research driver focused on living organisms. The program provides research funding to support innovative research into fundamental biological problems, particularly projects with new and interdisciplinary approaches that create international partnerships.

Li and Speiser’s project to uncover the working principle of a unique distributed chiton sensing system is of course new.

Li’s team at Virginia Tech has built a history of exploring unique material design strategies from nature, having studied ceramics inspired by sea urchins and starfish microlattices. Speiser has built a strong portfolio of projects in South Carolina in animal biology and physiology. The additional years of experience built up in their respective labs give them a deeper knowledge to draw and revisit their chiton questions.

Li and Speiser met Baum through a colleague and found that the German researcher’s background in image analysis and visualization of biological structures was a critical final piece of the puzzle of interpreting and reporting neural network data.

With support from the Human Frontier Science program, the team wanted to know how a simple marine mollusk processes visual feedback from thousands of eyes and how it brings together thousands of connected data points to make decisions about movement and perception of danger. Several different chiton species will be studied so the researchers can compare their results.

Li will use his expertise in biological materials and 3D material characterization to obtain high-resolution 3D data from the chiton sensor network. Baum’s team in Germany will then analyze Li’s dataset to create a digital model and formulate hypotheses about the function of the network. Speiser’s team would continue from there, testing his colleagues’ theories through animal behavior experiments. Li will reconsider that process, providing insight into how hard and soft materials work together. The team will also investigate how factors such as shell and eye regrowth after damage impact the resilience of this distributed sensing network.

Both Speiser and Baum really wanted to start this project because of its great potential.

“Learning more about the neural processing underlying vision in chitons is exciting, as is the opportunity to explore how chitons avoid compromising their protective systems by immersing the eye in them and how they reduce the metabolic costs incurred by networks that are widely distributed from hundreds to thousands. sensors,” Speiser said.

“This is an amazing project with two experts on biological materials and visual biological systems,” said Baum. “I’m really looking forward to getting started, adding my own expertise in image analysis and visualization to help explain the tunic’s interesting visual system.”

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