Electric fish may hold answers to better understanding of sensory abilities and movement

September 4, 2013 by Marlene Cimons
This image is of the electric ghost knifefish, Apteronotus albifrons, from South America. Credit: Photo courtesy of Per Erik Sviland

The weakly electric fish, so named because it generates a weak electric field, can do some very cool things. Using sensors located all over its body, for example, it can detect prey or predators that interrupt its surrounding electric field. This enables it to hunt in the dark, as well as to avoid being hunted by piranhas and other visually-guided fish that share its home.

It also has a unique propulsion system that allows it to swim backwards; in fact, the fish can switch from full speed ahead to full speed in reverse in a fifth of a second.

Like many things in nature, the weakly , found in South America and Africa, is inspiring scientists trying to answer fundamental questions, in this case about sensory abilities and movement, with the goal of better understanding and, ultimately, drawn from biology.

"The general question we are trying to understand is how the ability to sense the world is combined with the ability to move," says Malcolm MacIver, an associate professor of mechanical and at Northwestern University. "What is the relationship between the space you are able to sense, and your mechanical abilities?"

Using the fish as a , he is deciphering the relationship between the sensory volume, that is, the space in which the fish perceives things in its field, and the motor volume, the space in which it moves. He calls the field of study "infomechanics."

To explain the relationship, he suggests comparing two starkly different scenarios one might encounter while driving a car. On a clear sunny day, most people drive in "deliberative" mode, meaning the do not prompt any urgent responses to the circumstances or the driving environment. When encountering a dense fog, however, people typically switch to "reactive" mode—they slow down, for example, and become more alert to potential dangers on the road.

"When you're driving on a flat roadway on a sunny day, you can see a far distance ahead, and think about things, such as whether you're hungry or need to stop to use a restroom and want to get off an exit," he says. "In a fog, you don't have that luxury. The relationship between your sensory volume and where you are moving in your immediate future determines the kind of behavioral strategies you use."

How does this connect to the fish? "What the fish have allowed us to see is that most animals are in reactive mode, especially aquatic animals, because light doesn't travel very far in water, " he says. "Remember that our evolutionary ancestry started with animals in the water. My hypothesis is that something very important happened when we came up on land, as light can travel much farther in air than in water."

The weakly electric fish, a freshwater fish found in South America and Africa, has sensory receptors everywhere on its body, "which would be like us having eyeballs scattered across our body surface," he says. "The fish emits an electric field, and its sensors detect the field. So if something is out there, there is an interruption of the signal and the receptors pick up the distortion. It can do it in all directions."

The information researchers gain by studying the fish ultimately could have important applications, particularly in designing machines equipped with this so-called "electrosense," that is, the ability to maneuver and "sense" the world underwater with weak electric fields.

MacIver and his collaborators already have developed prototype robots that can move and "sense" in highly cluttered and dark underwater environments, and expect to see them in commercial use, including possibly by the US Navy, within the next few years.

"The underwater robots used during the Deepwater Horizon problem were held back by lack of maneuverability and sensor technology that could have helped them function well in turbid environments," he says, referring to the BP oil spill in 2010 in the Gulf of Mexico. "They were trying to operate in those huge plumes of oil mixed with water. You can't see in that. This technology has the potential to change all that."

MacIver also is working on a mechanical version of the fish's unique propulsion system.

"Most fish flap their fin, they wave the back portion of their body through the water, which propels them forward," he says. "Our fish doesn't swim that way. It keeps its body straight, and has a fin that goes almost of the full length of its body, down and along the belly. It ripples that fin, almost like a curtain in the wind. Using that, they are able to move in a highly acrobatic fashion."

Not only can it swim backwards, but "this fish can also move in all directions, including sideways and at an angle," he says. "It's like the helicopter of the water. If we had a device that could do this, we would have an aquatic helicopter."

They are working on it. "We have a bit further to go with the high maneuverability ," he says. "But we're getting there."

MacIver is conducting his research under a National Science Foundation (NSF) Faculty Early Career Development (CAREER) award, which he received in 2009 as part of NSF's American Recovery and Reinvestment Act. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education, and the integration of education and research within the context of the mission of their organization. NSF is funding his work with about $1.25 million over four years.

In 2009, he also received the Presidential Early Career Award for Scientists and Engineers (PECASE), which recognized his interdisciplinary work on the biomechanical and neural basis of intelligence, spanning robotics, biomechanics, neurobiology, philosophy and computation, as well as for his innovative science outreach efforts that include Hollywood science-fiction advisory efforts, interactive art installations and blogging for Discover magazine.

MacIver uses three approaches in his work: mechanics and robotics for understanding the ways in which the body contributes to adaptive behavior; neurobiology for understanding the how sensory signals are processed for movement control; and computational modeling, for constructing supercomputer simulations of the body, nervous system, sensory signals and mechanical interactions with the world.

His collaborators include Kevin Lynch, a professor of mechanical engineering, Michael Peshkin, a professor of mechanical engineering, Neelesh Patankar, a professor of mechanical engineering, and David McLean, a professor of neurobiology, from Northwestern University; Julio Santos and James Solberg, of HDT Robotics, in Evanston, Ill.; George Lauder, a professor of zoology at the Museum of Comparative Zoology, Harvard University; Noah Cowan, a professor of mechanical engineering, and Eric Fortune, a professor of psychological and brain sciences at Johns Hopkins University.

MacIver also helped develop "Scale," a "singing electric fish" art installation that has appeared on exhibition in The Netherlands and in China. The multidisciplinary artwork was created by MacIver, visual artist Marlena Novak and composer and sound designer Jay Alan Yim, the latter two also from Northwestern. Twelve different species of electric fish from the Amazon River Basin comprise a "choir" whose sonified electrical fields provide the source tones for an immersive audiovisual experience.

"Every electric fish emits an electric field, and if you put it into a speaker, it's something you can hear," MacIver explains. "The fish aren't generating a sound, but if you dip the speaker leads into the water and amplify it, you can hear the audio equivalent of their electric field—an electric fish choir."

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1 / 5 (6) Sep 04, 2013
The weakly electric fish, a freshwater fish found in South America and Africa, has sensory receptors everywhere on its body, "which would be like us having eyeballs scattered across our body surface," he says. "The fish emits an electric field, and its sensors detect the field. So if something is out there, there is an interruption of the signal and the receptors pick up the distortion. It can do it in all directions."

Humans, along with other creatures, have these fields as well. But instead of the notion we have eyes all over our body, which is silly, our hair behaves as the antenna or receptors.
3.7 / 5 (3) Sep 04, 2013
So you can sense someone standing 10 feet behind you? You must be one hairy dude.
1 / 5 (5) Sep 04, 2013
So you can sense someone standing 10 feet behind you? You must be one hairy dude.

You've never experienced the feeling of someone staring, or more appropriately been caught staring at a woman's backside by someone who sensed being stared at? Here are some scientific papers on the matter of staring and being stared.

BTW, there may be some wisdom passed down by our ancestors in stories such as Sampson.
I've read about research the military supposedly performed in re Native American scouts who strangely lost their keen scouting abilities after their military haircuts.
Your hair stands up in the presence of strong EM fields because the hair is sensitive to these fields, antenna as mentioned above. This is why many animals act strangely around strong storms and earthquakes, they have the same sixth sense humans can have.
3.7 / 5 (3) Sep 06, 2013
Of course I've experienced the feeling of someone staring... only to turn around and find no one there. And then there have been the times when someone speaks directly behind me and I jump out of my skin because I had no idea they were there. You've fallen into the same trap as gambling addicts, always remembering the wins (randomly thinking someone is staring at you and finding they are) and forgetting the losses (randomly thinking someone is staring at you when no one is). Nice papers you found there, from prominent journals like "Journal of the Society for Psychical Research."
3.7 / 5 (3) Sep 06, 2013
There's no evidence the Native American scout story is true. But if it were true, one must question whether it was properly performed or interpreted. In many Native American cultures long hair is traditional. Its significance varies, representing things like strength, beauty, knowledge or "spirit," but it's not uncommonly reported that it is cut only only for significant reasons like mourning a death. Thus the scouts' decreased performance post-haircut was likely a psychological reaction, not a deprivation of some mythical sensory apparatus. If there's any truth to the stories at http://www.sott.n...air-Long , in which potential scouts were attacked in the middle of sleep, one can't help but wonder if the new recruits weren't sleeping well (stress of being drafted) at first but after they adjusted (and coincidentally finally got haircuts) they started sleeping better.
1 / 5 (2) Sep 06, 2013
I have to say the notion that we are covered with electrical atennae is just plain old brain dead. They are mechanoreceptors when short and sparse to make up for reduced pressure receptor density (touch sensitivity) across most of the skin. The incidental effect of detecting dry air through buildup of electrical potential is a passive effect that has no range, but rather stimulates the mechanoreceptors that detect hair deflection.

Long hair is less than useful for detecting squat unless it is rigid along its entire length like a whisker on a cat. Mechanoreception occurs at the hair root, so what doesn't cause deflection there is useless.

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