DirectRT exposure presentation duration

[cthurgood]

Hi,

I am new to DirectRT but I have browsed through the discussion boards so hopefully what I’m about to ask hasn’t already been asked before.

I am doing a study for my PhD that involves subliminal exposure durations (ideally around 8-10ms – depending on the computer’s capabilities). I understand that the exposure duration of a stimulus is limited by the computer refresh rate. I have a laptop computer with an LCD screen that has a refresh rate of 60 Hz, but when I connected it to an external CRT monitor it was capable of a refresh rate of 100 Hz. I’m not too familiar with the concept of refresh rates but I assume that this means it takes 10 ms to write an image to this screen.

If I want to display images one after another (separated by a white background with black fixation cross) for 10 ms each, does this mean that the person will actually see the image for 10ms in its entire form – plus 10 ms either side in which the image is written on and off the screen? So in effect they are seeing the image in some form for about 30 ms? If this is the case would you recommend using some external device such as shutter goggles to act like a tachistoscope and ensure that the images are presented for the desired duration?

Thanks in advance for your help!