Hi there again!
Can I ask you for your advise?
I want to write an experiment with priming like this:
(80 milliseconds) Mask -> (12 milliseconds) Stimuli -> (80 milliseconds) Mask
I used "trialduration" to deteremine milliseconds for mask and stimuli as well. Need to say that after running it doesn't look like thing that I would like to have - an especially 12 milliseconds stimuli (I can see it without no additional effort). Do I have my milliseconds corect?
BTW.Is there's some way to randomise /hposition in picture element and then in MASK (shape element) get the exactly same value for /hposition?
--- A1 ---<picture picture_A1>/ items = ("XXX.jpg")/ hposition = 15/ vposition = 15/size = (20%, 20%)</picture><shape mascingA1>/ shape = rectangle/ size = (250, 250)/ color = black/ hposition = picture.picture_A1.hposition/ vposition = picture.picture_A1.vposition</shape>--- A2 ---<picture picture_A2>/ items = ("XXX.jpg")/ hposition = 80/ vposition = 80/size = (20%, 20%)</picture><shape mascingA2>/ shape = rectangle/ size = (250, 250)/ color = black/ hposition = picture.picture_A2.hposition/ vposition = picture.picture_A2.vposition</shape><shape blank>/ shape = rectangle/ size = (250, 250)/ color = blue</shape><shape blank2>/ shape = rectangle/ size = (250, 250)/ color = yellow</shape><shape blank3>/ shape = rectangle/ size = (250, 250)/ color = brown</shape><shape blank4>/ shape = rectangle/ size = (250, 250)/ color = black</shape>
--- A1 ---<trial blysk1>/ stimulusframes = [1=random(blank, blank2,blank3)]/ trialduration = 80/ correctresponse = (noresponse)</trial><trial mascA1>/ stimulusframes = [2=random(blank, blank2,blank3);6= mascingA1]/ correctresponse = (noresponse)/ trialduration = 80</trial><trial logoA1>/ stimulusframes = [1= picture_A1]/ correctresponse = (noresponse)/ trialduration = 12</trial><trial mascA1_2>/ stimulusframes = [2=random(blank, blank2,blank3);6= mascingA1]/ correctresponse = (noresponse)/ trialduration = 80</trial>--- A2 ---<trial mascA2>/ stimulusframes = [2=random(blank, blank2,blank3);6= mascingA2]/ correctresponse = (noresponse)/ trialduration = 80</trial><trial logoA2>/ stimulusframes = [1= picture_A2]/ correctresponse = (noresponse)/ trialduration = 12</trial><trial mascA2_2>/ stimulusframes = [2=random(blank, blank2,blank3);6= mascingA2]/ correctresponse = (noresponse)/ trialduration = 80</trial>
--- Blocks ---<block block_1A>/ screencolor = (255, 255, 255)/ trials = [1 = blysk1; 2= mascA1; 3=logoA1; 4=mascA1_2]</block><block block_2A>/ screencolor = (255, 255, 255)/ trials = [1 = blysk1; 2= mascA2; 3=logoA2; 4=mascA2_2]</block>
--- Experiment ---<expt>/ blocks = [1= random(block_1A, block_2A)]</expt
Kuba S: I want to write an experiment with priming like this: (80 milliseconds) Mask -> (12 milliseconds) Stimuli -> (80 milliseconds) Mask I used "trialduration" to deteremine milliseconds for mask and stimuli as well
I used "trialduration" to deteremine milliseconds for mask and stimuli as well
Well, first off, why in the world are you using the /trialduration attribute in order to achieve the desired stimulus durations and inter stimulus intervals (ISI). The starightforward way would be to use either the /stimulusframes or /stimulustimes attributes an have all your stims (forwardmask, prime, backwardmask) displayed by a single <trial> element:
<trial myprimingtrial>/ stimulustimes = [1=forwardmask; 81=prime; 93=backwardmask][...]</trial>
There is another problem, though, and that is why it is of *key importance* to get at least a basic understanding of how computer display technology works before trying to implement subliminal priming procedures. It may very well be, that you simply cannot achieve a prime display duration of 12ms in the real world. For a quick (but nevertheless informative) overview of how computers display stuff on screen, read (and understand!) this: http://www.psychopy.org/general/timing/millisecondPrecision.html#computer-monitors.
Note that whether you're using good, old cathode ray tube (CRT) monitors or modern liquid crystal (LCD) and thin-film-transistor (TFT) flatscreen displays can make a (huge) difference (see Plant & Turner, 2009). In general, flatscreen displays are currently considered unsuitable for subliminal priming procedures. There is a notable body of literature dealing with these issues, and I urge you to look into this *before* even thinking about doing any programming. For starters, here are a few references that come to mind (there is more, but I guess you know how to find literature on your own):
Plant, Hammond & Turner (Behavior Research Methods, 2004), Wiens et al. (Psychological Science, 2004), Plant & Turner (Behavior Research Methods, 2009), Elze & Tanner (Medical Physics, 2009).
Regards,
~Dave
"To understand recursion, you must first understand recursion." - Unknown Zen Master
Thanks for the above information. :-)
If I'm understanding this correctly, it suggests that we need to use CRT monitors instead of laptop screens (?), given the way that the image is presented on the screen, and the fact that LCDs take longer to display the image.
However, given that we have installed our versions of Inquisit on laptops, can we just hook our laptops up to a CRT monitor?
The next step, I suppose is figuring out the refresh rate of the CRT monitor. Assuming that it is 85 Hz, does this mean that each frame is presented for 11.7 ms (or is there some other info I need to know in order to calculate this)? Thus, if my script is as follows, does it mean that my subliminal prime will be presented for 23.4 ms??
<trial txneutralprime_nonwordtarget>
/ validresponse = ("e", "i")
/ correctresponse = ("e")
/ stimulusframes = [1=txforwardmask; 10=txneutralprime; 12=txbackwardmask; 13=txnonwordtarget]
</trial>
Thanks,
Leila
LSca15:If I'm understanding this correctly, it suggests that we need to use CRT monitors instead of laptop screens (?
Depends on the quality of your hardware. You'd need external equipment (oscilloscope, photo sensors) to measure the given monitors' properties and decide if they're suitable for subliminal stimulus display or not.
LSca15:However, given that we have installed our versions of Inquisit on laptops, can we just hook our laptops up to a CRT monitor?
If your laptops have suitable connectors for external displays (which would usually mean a VGA port in case of old CRT monitors), yes.
LSca15:The next step, I suppose is figuring out the refresh rate of the CRT monitor. Assuming that it is 85 Hz, does this mean that each frame is presented for 11.7 ms (or is there some other info I need to know in order to calculate this)?
1000(ms) / 85(Hz) = 11.76 ms
LSca15:Thus, if my script is as follows, does it mean that my subliminal prime will be presented for 23.4 ms??
It's presented for two frames (frames 10 and 11), thus approx. 2 x 11.76 ms = 23.52 ms (assuming suitable monitor performance).
OK, great, thanks!
So in terms of testing the quality of my hardware, I will need to evaluate the properties of the monitors --- sounds like I need to know more than just the refresh rate. I will start by looking at the references you suggested above, and will post anything else I find about which properties of monitors are important for subliminal stimuli presentation. Please let me know if any additional references come to mind!