Lo and behold, the OpenSesame documentation area is online at osdoc.cogsci.nl! The documentation area serves as a central point for everything that is related to OpenSesame, the graphical experiment builder. From tutorials and plug-ins to example experiments, it's all there. This is obviously a big improvement over my previous "system" of having documentation in the form of a bunch of loosely linked blog posts.

The documentation area is part of the preparation for the next version of OpenSesame, 0.24 "Cody Crick", which I hope to release in a month or so. I have tested it quite a bit and things are already working quite nicely. If you are interested in getting a sneak preview, you can find out how to get your hands on the development version through, yes, the documentation area!

Yesterday, the guys at the faculty techical department and I have been playing around with OpenSesame, trying to get a clear picture of how accurate the timing really is. We used a kind of modified buttonbox that simulates a button press when a light sensor is triggered. We attached the sensor to the screen and made an experiment that simply shows a white screen and waits for a button press. Since the sensor should, for all intents and purposes, respond instantaneously to the white display, we can use the "reaction times" as a measure of how accurate the timing is. Low reaction times are good and, even more importantly, a low variation is good.

I'm very pleased to say that the results look excellent, particularly when using the new "psycho" back-end (for now only available as an experimental GitHub code snapshot, but this will be part of 0.24), which uses PsychoPy to handle all display operations. On Windows XP, the reaction times are around 3ms and fairly constant. For Linux users it might be worth to note that, although the average reaction times are about the same (around 5ms), there is substantially more variation (I tested it on Ubuntu 10.04) (Update 1/6: I ran some more tests, and the problem was the compositing layer. With this turned off, the timing on Linux is excellent.) E-Prime users might be interested to know how this compares to E-Prime's performance. Well... there is no real difference. Using the same set-up …

Last week I was at the annual meeting of the Vision Sciences Society. One of the more exciting events of this conference was the illusion contest. And of the more exciting illusions of this contest was the one that you can see below, created by Mark Wexler. (The winner of the contest, incidentally, was the awesome illusion by Suchow and Alvarez that I described earlier.)

You will see a slowly (or at least not very quickly) clockwise rotating ring. You will also see intermittent counterclockwise rotations, which are brief and much faster.

So what's going on here? Basically, and as you might have guessed, the counterclockwise jumps are illusionary. The only thing that happens is that for a few frames the coloured squares out of which the ring is composed are completely randomized. Obviously, this randomized "noise" is not really rotating in any particular direction. And yet we perceive a fairly clear counterclockwise rotation.

This illusion bears some resemblance to the traditional motion after effect, in which prolonged exposure to a motion in one direction results in a small, but clear after effect of perceived motion in the opposite direction. But usually the illusory motion is much slower than the real motion that induces the after effect. In contrast, in Wexler's illusion the illusory motion is much faster than the motion that induced the effect.

It seems to be that the "noise" amplifies the motion after effect. Even if the line-segments were not randomized, you would still perceive a regular …

Update Jul 18 2011: SInce OpenSesame 0.24 has been released, the links below are no longer current.

It took some time, but we have finally created experimental Mac OS packages for OpenSesame (and when I say "we", I actually mean Daniel Schreij). It appears to work quite well, with the exception of two notable bugs (that have been discovered so far): The program crashes when running in window mode (fullscreen works fine) and you can't open Finder from the file pool.

There are two versions, for Mac OS Leopard (10.5) and Snow Leopard (10.6) respectively.

• Download OpenSesame 0.23 for Mac OS Leopard (10.5) (Outdated, 0.24 has been released)
  
• Download OpenSesame 0.23 for Mac OS Snow Leopard (10.6) (Outdated, 0.24 has been released)

Please note that these packages are still experimental and have not been as extensively tested as the Windows and Linux packages. If you find bugs or wish to provide feedback, please let us know!

What to expect for OpenSesame 0.24

On a semi-related note, development of the next version of OpenSesame (0,24 Cody Crick) is well under way. I want to further polish the user experience and fix all bugs that have come up. But far more exciting than these incremental changes is the fact that the "back-end" will be decoupled from the user interface. Right now, OpenSesame uses PyGame to handle all display, sound and input operations. PyGame is a fine and reliable back-end, but it …

“Of all the questions that may arise about eye movements, probably the least likely one is the simple question: Why?”

If I were to pass this question, from Walls' (1962) classic essay on the evolution of eye movements, on to you, what would you reply? Chances are that you would say that we make eye movements to look at things. That we use them to scan our surroundings. After all, if our eyes were fixed, it would be considerably more difficult to switch gaze from one object to the next. Head movements could do the job, of course, but not as effortlessly. But this post is about the evolutionary origins of eye movements, rather than the specifics of human vision. The relevant question is, therefore, whether other animals scan the environment in the same way that we do. And, to give a preview of what will follow, some do and some don't. Almost all sighted species make eye movements of some kind (or analogous head movements), but comparatively few actively look at objects the way that we do. They use their eyes to see, of course, and they may make an eye movement if something is completely outside of their field of view, but beyond this their direction of gaze says very little about what they are attending to. Assuming, of course, that they attend to specific objects at all. Therefore, eye movements must serve a function beyond scanning the environment.

The first eye movements

So what might this function …