Virtual Reality (Whisker mode)

Virtual Reality is a suite of technologies that is ideally suited to many kinds of psychology experiments. To the degree that a virtual environment takes over the signals from the natural environment, it can enable experiments that would be difficult or impossible to construct physically. And, equally interestingly, when virtual environments break down, we learn about how senses work in the natural world.

Most VR systems are designed for humans (who want to hog all the fun), but the same principles apply to non-human species, though the senses and motor mechanisms are different. Humans are highly visual and hand-oriented, so human VR is dominated by mimicking 3D visual worlds (coordinated with 3D audio cues) and hand tracking. Other animals use other senses and move differently.

I have seen “Virtual Reality” for insects who have totally different visual systems.  It is difficult to track the head and eyes of these small creatures, so the research tethered their heads, and digitally made the visual world move according to their muscle movements. (Kind of like a flight simulator for humans, no?)

A new paper by Nicholas J. Sofroniew and colleagues of the Howard Hughes Medical Institute describes a different sense mode entirely, “Natural Whisker-Guided Behavior by Head-Fixed Mice in Tactile Virtual Reality.”

The research team investigates how mice navigate in the dark, using their whiskers. In this case, the lights are out, and the sensory environment is a walled corridor. This is one the natural environments for mice, and they are very able to run in these passages.

The Virtual Reality system tethered the mouse’s head (a la flight simulator), and used a system of motorized paddles to present various “walls” to the vicinity of the head, where they could be sensed by the whiskers. In addition, the mouse was standing on a spherical treadmill, which lets the rodent run, and records exactly how it moves.

A quick web search indicates that the circular treadmill technique is widely used not only for mice, but for insects and crayfish among other species. There appear to be commercial products as well, and, of course, larger versions are used in human VR environments.

The work of the Hughes team is notable for the use of the “virtual walls”. They investigated the mice running in the dark, and measured the use of the whiskers. The latter was measured by infrared imagery, to analyze the bending of the whiskers when pressed by the ‘walls’.

With this apparatus, the researchers could simulate a large variety of “tunnels” by rapidly configuring the paddles to emulate what the mouse would “feel” running through a physical tunnel. E.g., a curved passage was represented by adjusting the angle of the paddle in time with the movement of the mouse on the treadmill, analogous to how visual VR adjusts the projection on the screen to match the virtual movement of the stationary human.

Cool!

The reported system was limited (the paddles were smooth, they only move certain directions), but even so, they could see that the mice navigated fairly naturally. They were able to conclude that “mice do not just compute their running angle based on an instantaneous measurement of wall position, but also take into account the velocity and acceleration of the wall.” I.e., mice normally sense their passages as they run through them.


 

  1. Nicholas J. Sofroniew, Jeremy D. Cohen, Albert K. Lee, and Karel Svoboda, Natural Whisker-Guided Behavior by Head-Fixed Mice in Tactile Virtual Reality. The Journal of Neuroscience, 34 (29):9537-9550, July 16, 2014 2014. http://www.jneurosci.org/content/34/29/9537.abstract

 

Thanks to Alan Craig for pointing me to this work.

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