Stroop2 Specs
Basic Task: This is identical to Stroop1 except as noted.
Practice should be the same. The task, the basic design, and the trialtypes are the same. File Structure is the same. There are again two blocktypes but they are slightly different. They are:
Blocktype Interval
from one trial to the next
1 Just like the Fixed 1.5 seconds in Stroop1
2 Subject responds to some tones before they get the colored word
In blocktype 2, have a 1.5 second break before the first tone. The subject hears a tone, then responds; 200 msec after they respond, play another randomly chosen tone and so on (for details on the number of tones to play, see below). The tones should be 250 hz or 800 hz in pitch, and randomly choose which to present. After the last tone, wait 200 msec before presenting the colored word. The subject never knows when the tones will stop and the colored word will begin.
Before blocktype2 blocks, say “Please prepare to respond to tones during this block. Rest your fingers on the response keys please.”
There should be 12 blocks each composed of 30 trials per block rather than 20. The blocks should alternate between blocktype 1 and blocktype 2. The subject’s order condition (1 or 2) should determine which blocktype they start with in block 1.
Instructions to include in file:
Thank you for participating in our experiment. In this study, you will be seeing colored words or letter strings on the screen. Your task is to name the color of the “ink” in which the word is printed as quickly as possible. If you see XXXX you would say “red!”. Sometimes the word will be confusing, e.g., Green. You should also say “red!” to this. We are interested in both speed and accuracy. Try to respond as quickly and as accurately as you can. You will do 12 blocks of trials, each lasting just a few minutes.
Next page:
In some blocks of trials, we would like you to respond to a few tones before you see the colored word. If you hear a high tone (press to hear sample tone), press S. If you hear a low tone (press to hear sample tone), press X. The keys are labeled. During blocks when there will be tones, please rest the index and middle fingers of your left hand on the two keys.
You will never know exactly how many tones will be presented; occasionally there may be quite a few. Please try to keep your eye on the box where the words will appear while the tones are sounding. The blocks don’t last more than a few minutes. If you have any questions, please ask the experimenter now. Thanks again for participating.
Determining the Number of Tones
I’d like to use a discrete exponential distribution with a mean 3, which has the advantage of a fixed hazard function (even if it’s played 100 tones, the chance of the next tone being the last is just the same as it was for the first tone). Here is some pseudocode to compute this (I’m using goto just because I’m not certain of what VB syntax offers in the way of do-while stuff):
NumTones = 1
Label1
If Rand > .666 then goto Label2
NumTones = NumTones + 1
Goto Label1
Label2
Naturally I assume here that Rand is a uniformly distributed random variable in the range [0..1] taking a new value each time it is called.