[visionegg] Re: Go loops

Dear Smriti,

It's a bit hard to follow what's going on without code, but it seems like you may be creating a new instance of Presentation on each trial, or at least slighly abusing the FlowControl system. (Well, my fault for foisting such a complex beast on the world!)

I have 2 alternative suggestions:

1) Drop the whole "go loop" (VisionEgg.FlowControl) thing and write your own loops. I find this more natural when running block trials requiring user responses such as your paradigm.

2) Instead of repeatedly calling Presentation.run_forever() (which is only meant to be called once), make each trial a single pass through the go() function (without entering between_go_loops). Then reset parameters in preparation for the next trial and call go() again to repeat.

This will require some changes to the controller code what you have already written. Here's an (untested) prototype which I just whipped up:

p = Presentation(blah,blah,blah)

def keydown(event):
   """handle responses from subject"""
   # get current time since go from Presentation instance
   t = p.time_sec_since_go # shorthand
   if t < 5.0:
       # too early, we don't care yet
       return
   if event.key == pygame.locals.K_q:
       print '"q" key pressed'
       p.parameters.go_duration = (0,'frames')

def every_frame_func(t=None):
"""gets called on every frame"""
if t > 10.0:
# subject took too long
print 'subject took too long, ending trial anyway'
p.parameters.go_duration = (0,'frames')
p.parameters.handle_event_callbacks = [(pygame.locals.KEYDOWN, keydown)]
p.add_controller(None, None, FunctionController(during_go_func=every_frame_func) )

for i in range(200): # do 200 trials:
   p.parameters.go_duration = ('forever',)
   # set other stimulus parameters here
   p.go()

Smriti Bhagat wrote:

Hi!
I have been using go loops with run forever and am experiencing trouble.

I want a stimulus to appear after some secs of the start of a trial, and I
want many trials repeated this way.
So typically I would have :
Start Trial -> n secs -> stimulus appears -> stimulus disappears ->
response  -> next trial.
Each trial runs for fixed length of time.

For this I am doing:
during_go_func : display stimulus
between_go_func : display another stimulus
                 and start another p.go()
p.run_forever()

This ensures that my experiment runs forever (until stopped) and each
trial is a fixed time go loop.
This works fine, except when I make the number of trials in an experiment
more than 260, when it says too many recursions.

I am looking for a cleaner way to do this.
Any ideas?

Thanks,
-Smriti.

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