The 2007 International Congress of Neuroscience ran in Melbourne from the 12th to the 17th of July. It’s not every day that one of the world’s biggest neuro conferences is in your hometown! Yes, I only just got around to blogging it. Please forgive me if the details are a little fuzzy.
The first session I attended was a plenary by Prof. Mandyam Srinivasan, a neuroethologist who studies bee behaviour at ANU (and, more recently, at UQ). This was probably the best neuroscience lecture I had ever seen - I’d love to be able to give such charming presentations. Mandyam has amassed a substantial collection of high impact papers detailing the bee vision system, in particular, the concept of optic flow.
Because bee eyes are so close together, they don’t get much in the way of 3D information via parallax. However, they are able to infer distances by measuring how much of the world rushes by; the closer you are, the faster the surface appears to move. Think driving down a highway - trees by the road rush by, whilst hills in the distance remain static. This can be demonstrated by training bees to fly down a tunnel, with the striped walls attached to a sort of conveyor belt. By moving the walls at different speeds, you can mess with the bee’s flight down the narrow tunnel. Humans use these cues too, by the way.
He also talked about some work on decoding bee dances, extending research that earned Karl von Frisch the Nobel Prize in 1973. Srinivasan’s group has demonstrated that distances to food sources communicated by these dances are measured with respect to optic flow, such that the bees can be tricked into giving misleading dances if they travel down the tunnel with striped conveyor belt walls to get their food reward. It also seems that when bees traverse over low contrast terrain, such as calm open water, they perceive distances as being smaller (link to PLoS Biology paper).
This is shown in the photo above, in the path heading south west . The feeding station (white dots) was gradually moved away from the hive, over land, then water, then land again on the island.
Distance is communicated to other bees in the hive using a “waggle dance“. Briefly, the bee does a little loop, and then a zig-zag type motion (”waggle”), the duration of which is directly proportional to the distance to the food source (a sucrose solution). As shown above, the distance communicated is smaller when over low-contrast terrain, like open water. This is reflected in significance testing of curve fit slopes for each segment. This suggests that the bees are using optic flow to measure distance, as opposed to, say, energy consumption. An interesting tale lies in how one might conduct an experiment to test this alternate hypothesis, but I’ll save that one for another day.
The final talk of the visual motion processing symposium, given by Prof. Dario Floreano, director of the Laboratory of Intelligent Systems at École Polytechnique Fédérale de Lausanne in Zurich, also covered optic flow. It was quite different to the other talks, and certainly appealed to my inner engineer. Dario uses optic flow to get tiny autonomous flying robots (below) to navigate and avoid obstacles.
The planes fly in a room dubbed the holodeck, where different images, of varying contrast, can be projected onto the walls. Despite being sold as having heady military applications, Dario pointed out that this was mostly just for fun. My kind of project! That tiny 10 gram plane includes two cameras, two gyroscopes, an accelerometer, an anemometer, a bluetooth radio, and a microcontroller!
Finally, I invented the following award.
Award for Best Item of Exhibitor Swag
Not being a clinical conference, there weren’t any picnic baskets or trips to Tahiti on offer. There was, however, this…
It’s a reflective slap band thingy you put around your trouser leg to stop it getting caught in your bike chain! Get it? Neuroscientists are dorks who ride bikes with their pants tucked into their socks! I love it!
