Overlapping two Stimuli - 1 ms Stimuli still visible / Does it run with 60 Hz?

#1

Hello,

I am trying out Superlab and I want to show a 2nd Stimuli for 13 ms while a main Stimuli is shown for 2000ms. In addition, I want to randomise when exactly the 2nd Stimuli overlaps Stimuli 1. After Stimuli 2 was shown for one frame, I want Stimuli 1 to return for its remaining duration. Is that possible with Superlab? How?

My second question refers to subliminal stimuli. I created an event / stimuli (picture) that is displayed for 1 out of 60 frames. I set the time limit under the input tab to 1 ms. Anyway, it is still possible to see the picture in most cases (80-90% of the time). Any ideas how to handle it? I used fraps to measure the fps and it seems that Superlab does not really “play” the experiment with 60 frames per second (60 Hz is set in display options). Any ideas how to fix that? I tried multiple computers, notebooks and displays / projectors.

Thank you,

Angelica

#2

For your main stimulus, how many are there? Are they coming from a word list, or a list of pictures? Or is it always one stimulus being presented? If you can answer the same questions about the interrupter stimulus that would be helpful.

Also, what type of participant responses are required? Is there no response and the participant just watches, or do they need to press a key (or keys) during the first showing of the main stimulus? Is there responses during the remainder of the main stimulus or after the interruption?

In regards to your second question, in the SuperLab 4.5 Manual, Chapter 5 explains why you can typically never show a stimulus for less than about 17 ms. The manual states:

To determine the minimum exposure of a stimulus in milliseconds, divide 1000 by the refresh rate. For example, if your monitor and video card’s refresh rate is 60 Hz, then each cycle is 1000 divided by 60, or 16.67 ms.

This means that typically every stimulus is visible, however depending on the word, picture, or number, you would not necessarily have time to recognize it. If you have an experiment where a stimulus seems to linger more than 20 ms and you cannot determine why, we can look over the experiment settings.

#3

[QUOTE=MonikaT;6571]For your main stimulus, how many are there? Are they coming from a word list, or a list of pictures? Or is it always one stimulus being presented? If you can answer the same questions about the interrupter stimulus that would be helpful.
[/QUOTE]

They come from a word list. They are simple one digit numbers. The Idea is to pop up a picture file for 1 frame while the number is shown. It would also be possible to interrupt the stimulus from the word list, show the picture and continue to the stimulus from the word list.

No response is require. I use superlab only to show stimuli to subjects before I do a pen & paper task.

[QUOTE=MonikaT;6571]
In regards to your second question, in the SuperLab 4.5 Manual, Chapter 5 explains why you can typically never show a stimulus for less than about 17 ms. The manual states:

To determine the minimum exposure of a stimulus in milliseconds, divide 1000 by the refresh rate. For example, if your monitor and video card’s refresh rate is 60 Hz, then each cycle is 1000 divided by 60, or 16.67 ms.

This means that typically every stimulus is visible, however depending on the word, picture, or number, you would not necessarily have time to recognize it. If you have an experiment where a stimulus seems to linger more than 20 ms and you cannot determine why, we can look over the experiment settings.[/QUOTE]

Well I tried out displays with 75hz and 85hz refresh rates. The one frame picture is still visible for the eye.

#4

Due to your experiment not requiring a participant response, we can build your experiment with ease. A demo is attached.

The feature that makes it easy is within the Trial Editor, under the Options tab. This feature can extend the duration of each trial to some preset length. (In your case, something around two seconds.)

However, due to this technique, this particular demo experiment will not collect any participant input from the time of the interruption until the beginning of the following trial. If you had wanted to collect a participants response, this would require a different method.

Please open the attached demo and read the notes we added just below each trial name and event name. The notes that are shown when you open the Trial Editor and Event Editor.

words_with_interruptions.sl5 (5.35 KB)