Shadlen's dots for OS9

1
I'm using Shadlen's dot code for OS9, and I was wondering if anyone
has used this code before. I am having dots move at different
directions and different times eg: 100%coherence at 90deg for 2 secs,
then 0% coherence at 90% for 2 secs. When I use 0% coherence or a very
low coherence, the dots seem to move extremely fast, even when the
speed is set to 0, the dots do not move, but they appear and disappear
very fast all over the screen creating the illusion of fast movement.
If the speed is semi-slow, the low coherence also makes the dots
appear to move very very fast because there are so many dots that just
appear and dissear quickly. Has anyone encountered anything like this?

Also, does anyone know of a way to control average dot lifetime? If I
run the dots for 10 seconds, many of the dots last the entire 10
seconds. Only a few last less than 5-7 seconds on a 10s scale.

Also, would this have been a lot easier with OSX? I could not get
something working on it, so I was forced to do it on a native OS9
machine. I also need to "split" the screen in two and have the dots
on both sides either A: the dots on the two side either move toward or
away from each other. or B: the dots on either side will change to two
different colors. Does the OSX have this functionality? Or will I have
to stick with the OS9 even though it will be a lot harder?



Thanks,
Gem Ventura
2
Hi Gem,

I have a new version of the Shadlen Dots for OS X that is
reasonably well tested -- and that solves many of the
problems you mention (e.g., control of dots lifetimes,
multiple apertures). It uses stenciling to create the
apertures, so it requires some changes to the psychtoolbox
source ... if others are interested, it would be great if
Allen could fold those changes into the standard release.
I'd be happy to make the code available.

I also have what is probably a newer version of the OS 9
dots than you have (it controls dot lifetime, for example)
that I'd be happy to send you, if you'd like it.

Josh

--- In psychtoolbox@yahoogroups.com, "gem_ventura" <gem.ventura@m...> wrote:
> I'm using Shadlen's dot code for OS9, and I was wondering if anyone
> has used this code before. I am having dots move at different
> directions and different times eg: 100%coherence at 90deg for 2 secs,
> then 0% coherence at 90% for 2 secs. When I use 0% coherence or a very
> low coherence, the dots seem to move extremely fast, even when the
> speed is set to 0, the dots do not move, but they appear and disappear
> very fast all over the screen creating the illusion of fast movement.
> If the speed is semi-slow, the low coherence also makes the dots
> appear to move very very fast because there are so many dots that just
> appear and dissear quickly. Has anyone encountered anything like this?
>
> Also, does anyone know of a way to control average dot lifetime? If I
> run the dots for 10 seconds, many of the dots last the entire 10
> seconds. Only a few last less than 5-7 seconds on a 10s scale.
>
> Also, would this have been a lot easier with OSX? I could not get
> something working on it, so I was forced to do it on a native OS9
> machine. I also need to "split" the screen in two and have the dots
> on both sides either A: the dots on the two side either move toward or
> away from each other. or B: the dots on either side will change to two
> different colors. Does the OSX have this functionality? Or will I have
> to stick with the OS9 even though it will be a lot harder?
>
>
>
> Thanks,
> Gem Ventura