Update Jul 18 2011: SInce OpenSesame 0.24 has been released, the links below are no longer current.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• Download OpenSesame 0.23 for Mac OS Leopard (10.5) (Outdated, 0.24 has been released)
  
• Download OpenSesame 0.23 for Mac OS Snow Leopard (10.6) (Outdated, 0.24 has been released)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 …

There are only three types of eyes that are fundamentally different: simple eyes (like ours), apposition compound eyes (found in most insects) and superposition compound eyes (less common, but found in lobsters, for example). But hidden beyond this relative uniformity, there lies an enormous diversity. Every species is the product of evolution, and different environments place very different demands on the eyes. When you think of vision, you probably think of your own highly mobile, forward-facing eyes. But for most of the animal kingdom, vision is something very different.

A particularly striking example of specialized vision can be found in marine animals that live about 200 to 800 meters beneath the surface (Land, 2000; Land & Nilsson, 2002). A little bit of sunlight still penetrates to these depths. Sunlight obviously comes from above, so these midwater creatures live in an environment where everything below them is pretty much completely dark and everything above them is, during daytime at least, relatively light. This is a peculiar environment to live in and it has given rise to a peculiar type of vision.

Essentially, midwater animals have two pairs of eyes. One pair looks up at the surface, and one pair looks down into the dark deep. This is true for a wide variety of midwater species, regardless of what type of eyes they have, which in itself is a beautiful illustration of convergent evolution.

Some animals do not really have two distinct pairs of eyes, but rather a single pair with specialized optics …

“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.”

It's not hard to see why this famous quote from Darwin's “The Origin of Species” is a favorite among creationists, particularly when taken out of context. But actually, the story of the evolution of the eye is a wonderful illustration of the power of natural selection. And when told step-by-step it's not absurd at all.

Nowadays having eyes is nothing special, but it wasn't always like that. Although life has been around for billions of years, it was not until the Cambrian explosion, about half a billion years ago, that animals (that we would recognize as such) appeared. Before the Cambrian explosion, life consisted of simple cells and cell colonies, which, it's safe to assume, were blind. After, life was mostly still like that (it still is), but there were also complex animals, such as Trilobites, which were equipped with compound eyes, not unlike those of modern insects.

So what happened in between? There is no fossil evidence, but it's a good bet that the first “eye” was simply a light sensitive patch on the body of some lucky mutant (see (a) in the figure on the right). Of course, such a patch offers very little in terms of resolution and directionality …

The cogsci.nl software family has a new member! Mantra is a program for object tracking and has been designed specifically to be used in psychological experiments. For example, with Mantra you can track the hand of a participant while he/ she is performing some kind of experimental task. There are a number of example experiments available, showing how to use Mantra in combination with E-Prime and Python.

Although there are, of course, many object tracking systems available, the beauty of Mantra is that it doesn't require expensive dedicated hardware. You simply plug in a decent webcam and you are good to go!

You can find downloads and more information here!