Thread Tools  
Junior Member
Join Date: Oct 2014
shobee is on a distinguished road Posts: 1
Lateralized presentations, Posted October 24th, 2014 #1
I am doing a matching to sample task, where two pictures appear above center as the "samples" and one picture appears below as a "target". Participant decides if the target matches either of the samples. I have 56 different pictures in events. Each picture repeats 4 times, but in different locations that I have already designated by pixels to the horizontal and vertical of center to be left and right visual field (lvf and rvf, respectively): For example, I have picture1 lvfsample, picture1 rvfsample, picture1 lvftarget, and picture1 rvftarget. This makes 224 events plus a Center X event. No help needed on that. Here's my difficulty: on a trial I want the center X to appear and remain for the duration of the trial (that is until the participant makes a response). After 3000 ms of X, I want the X to remain and three of the events (e.g., lvfsample, rvfsample, and lvf target) to flash simultaneously for a duration of just 200ms, after which just the central X remains, awaiting response from participant if they didn't respond during the 200ms picture presentations. The response is a simple key stroke (any key accepted). Once the participant responds, the next trial begins with the central X and so on. There will be about 800 trials in all (divided into blocks, no problem). I have already determined which three pictures appear per trial, so I need no help there.
Currently, I can make all three pictures plus the X appear in a flash simultaneously. The problem is that I can't make the X act independently of the three pictures. I'd also like the RT recording to begin at the onset of the three pictures, not the onset of the central X at the beginning of the trial. That way, participants can respond during their presentation or after their offset when it's just the central X. If that RT recording can't be set to coincide with picture onset, it's ok, as I'll just subtract 3000ms from the trial RTs to get an accurate number. So, the whole trial should last 3000ms+200ms+any additional RT. The big issues are:keeping the X on the whole trial, flashing pictures for 200ms after 3000ms of trial onset, keeping the trial on with the central X until participant makes a response.
Reply With Quote
Join Date: Aug 2006
Location: San Pedro, CA
Hisham is on a distinguished road Posts: 1,214
Posted October 27th, 2014 #2
I have attached an experiment that mimics what you are trying to do. Some notes:
  • For the events ‘lvfsample’ and ‘rvfsample’, the Erase screen before presenting stimulus checkbox is disabled, whereas the Keep stimulus invisible checkbox is enabled. This is so that these two visual items can appear with the next one at the same time. You can find these checkboxes by clicking on the Event Editor’s Stimulus tab, then Settings... button, then Presentation Options tab.
  • The event “words” resets the RT timer (see Event Editor’s Input tab). It also has feedback that prevents subsequent events in the trial from being presented if the participant responds.
  • After the three words are displayed, another event redisplays the X
  • I added a “Clear screen” event because otherwise the X was seemingly on the screen all the time. The “Clear screen” event provides a clue that a trial has ended and another one is about to start.
I hope this helps.
Attached Files
File Type: sl4 t_2032.sl4 (6.3 KB, 11 views)
Reply With Quote
Thread Tools
Posting Rules
Forum Jump:
© Copyright Cedrus Corporation, 1991-2014.
All times are GMT -7. The time now is 06:25 PM.