David, you may well have been down this route, but the following
little experiment I found quite interesting:
on mouseUp
put the millisecs into t0
show img "alex"
unlock screen
put the millisecs into t1
repeat
if the millisecs >= t1 + 30 then
hide img "alex"
unlock screen
put the millisecs into t2
exit repeat
end if
end repeat
put t1 - t0 && t2 - t0 && t2 - t1
end mouseUp
The 'unlock screen' meant that I always actually saw the image (I
believe it forces a screen refresh), and the repeat loop guarantees
(I think) that the image is visible for at least 30 ms.
The timing measurements were (on my 1.5Ghz G4 laptop):
t1 - t0 9 to 20
t2 - t0 45 to 60
t2 - t1 reliably 36 +- 1
No idea if this is helpful, but I thought I'd throw it in...
Best,
Mark
On 27 Apr 2007, at 13:10, David Glasgow wrote:
Thanks to all who previously chipped in on this topic. I have been
doing a bit of research, using the following script:
+++++++++++++++++++++
on mouseUp
-- scrollbars to fiddle with the various times
-- duration of the image of the person
get the thumbpos of scrollbar "milliseconds"
-- duration of the gap between picture and mask
put the thumbpos of scrollbar "gap" into tgap
-- this is the duration of the mask
put the thumbpos of scrollbar "show" into tshow
-- present a submarine style cross to focus attention
show group "targit"
wait 1000 milliseconds
hide group "targit"
put the milliseconds into tstart
show image "adf03"
wait it milliseconds
hide image "adf03"
put the milliseconds - tstart & return after field "actualtime"
wait tgap milliseconds
show grc "rectangle"
wait tshow milliseconds
hide grc "rectangle"
end mouseUp.
++++++++++++++++++++++
What happens is that a crosshair style target appears for 1 sec.
Then a picture of a person appears for 'it' milliseconds, then
there is a gap of tgap milliseconds, then a mask appears for tshow
milliseconds. The mask is a rect filled with a pattern. Its
purpose is a technical one, called backward masking (no, not like
on heavy metal records). If an image appears briefly followed by
the mask, the amount of conscious psychological processing
permitted by the person viewing it can be truncated. Images which
would be recognisable at a given display duration are rendered
invisible but still processed psychologically. Don't ask how, it
just works. (If your really want to know, take a look here -->
http://www.ac-psych.org/?id=3 )
You can above see that field 'actualtime' accumulates the duration
of the display of the picture of the person (plus the time taken to
do the timing) over successive runs. With the duration of the
person image set at 30 ms, (gap = 40 ms and mask = 160 ms), I
shouldn't be able to see the image of the person, at least not
conciously, but I can.
Now I expected to get variable effects in appearance, because I am
testing on a MacBook, so my guess is that the LCD just won't keep
up with these rapid display changes. What I was planning to do was
shift the test stack to a CRT box, and set the refresh rate to
100Hz (in fact I think it goes to 138Hz). In the literature, I can
see that images can be displayed for a single cycle at 60Hz, and
the effect can work). What surprised me on the MacBook is the
recorded variability of the durations, irrespective of the fact
that I can see the person when I shouldn't be able to. The mean
measured display time (set as above) is 38 ms, min 32 and max 50,
Standard Deviation = 4.46 (over 30 trials). I can slide the
scrollbar to such a short duration when I can't see the image of
the person, but of course I can't know whether this is because the
backward masking is working, or because the image really isn't
appearing!
One of the things which occurred to me is that I could adapt the
test script above to do a kind of calibration routine, so that the
milliseconds is set to fall in the middle of the distribution of
actual durations, so that some will be a little shorter than 30ms,
and others a little more.
I would welcome any thoughts or comments on what I am doing, and
suggestions for doing it better.
Best Wishes,
David Glasgow
Carlton Glasgow Partnership
http://www.i-psych.co.uk
_______________________________________________
use-revolution mailing list
[email protected]
Please visit this url to subscribe, unsubscribe and manage your
subscription preferences:
http://lists.runrev.com/mailman/listinfo/use-revolution
_______________________________________________
use-revolution mailing list
[email protected]
Please visit this url to subscribe, unsubscribe and manage your subscription
preferences:
http://lists.runrev.com/mailman/listinfo/use-revolution
