Moth study to aid robotics development

Sitting in a dark room watching a moth fly into a light might not be everyone’s idea of a good time, but it’s paying dividends for a University of Oxford researcher.

Tonya Muller, a PhD student in the university’s Department of Zoology, is studying the way hawk moths adjust their flight behaviour in response to wind gusts. A moth is tethered to a steel rod in a large white plastic orb, while a projector casts moving patterns of light onto the sphere’s surface. This illuminates the moth’s field of vision with oscillating stripes.

At regular intervals, Muller alters the direction, amplitude and frequency of the light stripes. The changing light patterns create altered visual environments for the moth, which aim to simulate real-world visual disruptions the moth experiences when exposed to wind gusts. As the patterns change, the moth adjusts its flight behaviour to maintain constant stability.

Though imperceptible to the human eye, the moth’s responses to the visual stimuli are detected by a force sensor attached to the steel rod and relayed to Muller’s computer. These recordings are helping Muller understand the moth’s visual-motor system and identify the mechanisms of visual feedback in insect flight control.

“Understanding vision-based flight control in insects has far-reaching uses in the fields of sensor development, signal processing and robotics,” said Muller, whose background is in mechanical engineering.

Vision is important for information gathering in insects and up to 50% of an insect’s brain can be composed of visual neurons. In fact, despite their small brain size, insects can solve extremely sophisticated orientation problems both rapidly and reliably. Yet their eyes are far less sophisticated than our own.

“Insects receive visual information through a relatively noisy, low-resolution sensor. But with this sensor they are able to process information at sufficient speeds to react and respond to unexpected disturbances,” Muller said. “This is extremely interesting from an engineering perspective because developing technologies that use simpler and fewer electrical sensors and perform equally well can reduce manufacturing costs and computational power.”

Insects also assess changes in their environment using information they receive from other sensory organs on their bodies (including antennae, airflow sensors and wing-load sensors). Studies have shown that insects pre-process and combine the information from these multiple sensory inputs prior to reaching the controller. Current robotic technologies, on the other hand, use serial processing systems in which multiple sensors deliver separate and distinct input to the controller. Robot sensors are also currently designed for a very narrow and predefined range of conditions.

These limitations impede the response time of today’s robots and restrict their ability to maintain or regain stability after unforeseen disturbances. For these reasons, discovering how the efficient parallel processing system seen in insects operates is an area of great interest for engineers developing sensory control systems in robotics.

“Insects might just be the perfect neural information processing model for improving sensory technologies and control systems in electronic applications such as robotics. Yet we are only just beginning to understand the basics of the mechanisms and pathways involved. We still don’t know how insects extract visual cues from their environment, which cues are the most important and how those cues are processed to achieve the fast and efficient flight stabilisation that we see.”

Preliminary results from Muller’s experiments suggest that hawk moths use the angular position and velocity of the projected stripes as a primary cue to stabilise their flight. While describing flight dynamics accurately is an important advancement in the field, it is only the first step towards identifying the mechanisms of the active control of visual feedback in insect flight.

“The next stage of this work will involve measuring the activity of the moths’ neurons in response to the visual stimuli presented,” Muller said. “These measurements will describe the electrophysiological pathways from the visual sensor to the flight dynamics in this species.”

In the future, Muller hopes to be able to use implanted electrodes to measure neural activity in the moths. “The ability to obtain this kind of data remotely from free-flying moths is the cutting edge of science in this field and a truly exciting prospect,” she said enthusiastically.