Today I learnt a couple interesting concepts called “stopping motor volume” and “sensory volume”:
The Northwestern researchers are the first to clearly quantify the stopping motor volume (the amount of space it takes for an animal — including one in a vehicle — to come to a complete stop) and sensory volume (the amount of space an animal senses around it) for any animal. They then explored the relationships between the two volumes, defining three modes in which an animal could find itself in relation to another object — collision (will collide every time), reactive (won’t collide if on your toes) or deliberative (have lots of space to think about it).
Why do these concepts matter?
“For example, a person driving during daylight typically is in deliberative mode — able to see objects far away with plenty of space to deliberate and form a response. That’s the ideal. But when the sun goes down, and the driver is relying on streetlamps and headlights to see, he or she is typically in reactive mode at best or collision mode at worst.”
And, of course it all started with a fish:
MacIver was inspired to think about these original concepts by the unusual animal he prefers to study: the black ghost knifefish, found in the murky waters of the Amazon River. The fish does not use a passive sensing system such as sight or hearing to hunt. Instead, the knifefish has an active sensing system: it generates a weak electric field all around its body, and sensors, also all around its body, register any perturbations. By fluttering a ribbon-like fin along the entire length of its body, the knifefish can swim both forward and backward to catch its prey, the water flea.
After developing their mathematical definitions of the volumes, the researchers applied them to the knifefish, using the plentiful data available on the animal. They coupled video analysis of prey capture behavior with computational modeling of the fish’s electrosensory capabilities and let the simulations run for several weeks in a computer cluster operated by the Chicago Biomedical Consortium.
MacIver and his team are the first to quantify and compare in any animal the three-dimensional volumes for movement and sensation. They showed that the knifefish is truly omnidirectional in moving and sensing and discovered that the two volumes (stopping motor and sensory) are roughly equal, with sensory volume just a little greater than stopping motor volume. This places the knifefish in the reactive mode, critical if the fish wants to eat, and not collide with, its prey.
The press release (linked to and quoted above) is based on a paper published in PLoS Biology, titled Omnidirectional Sensory and Motor Volumes in Electric Fish. Here is the abstract of the paper:
Active sensing organisms, such as bats, dolphins, and weakly electric fish, generate a 3-D space for active sensation by emitting self-generated energy into the environment. For a weakly electric fish, we demonstrate that the electrosensory space for prey detection has an unusual, omnidirectional shape. We compare this sensory volume with the animal’s motor volume—the volume swept out by the body over selected time intervals and over the time it takes to come to a stop from typical hunting velocities. We find that the motor volume has a similar omnidirectional shape, which can be attributed to the fish’s backward-swimming capabilities and body dynamics. We assessed the electrosensory space for prey detection by analyzing simulated changes in spiking activity of primary electrosensory afferents during empirically measured and synthetic prey capture trials. The animal’s motor volume was reconstructed from video recordings of body motion during prey capture behavior. Our results suggest that in weakly electric fish, there is a close connection between the shape of the sensory and motor volumes. We consider three general spatial relationships between 3-D sensory and motor volumes in active and passive-sensing animals, and we examine hypotheses about these relationships in the context of the volumes we quantify for weakly electric fish. We propose that the ratio of the sensory volume to the motor volume provides insight into behavioral control strategies across all animals.
And, here is the author summary:
Most animals, including humans, have sensory and motor capabilities that are biased in the forward direction. The black ghost knifefish, a nocturnal, weakly electric fish from the Amazon, is an interesting exception to this general rule. We demonstrate that these fish have sensing and motor capabilities that are omnidirectional. By combining video analysis of prey capture trajectories with computational modeling of the fish’s electrosensory capabilities, we were able to quantify and compare the 3-D volumes for sensation and movement. We found that the volume in which prey are detected is similar in size to the volume needed by the fish to stop. We suggest that this coupling may arise from constraints that the animal faces when using self-generated energy to probe its environment. This is similar to the way in which the angular coverage and range of an automobile’s headlights are designed to match certain motion characteristics of the vehicle, such as its typical cruising speed, turning angle, and stopping distance. We suggest that the degree of overlap between sensory and movement volumes can provide insight into the types of control strategies that are best suited for guiding behavior.
Link via Bora at A blog around the clock.