Brian2828 wrote: > I'm working with a dataset for the Logan stop signal task (basically a > type of reaction time task with a random subset of trials requiring > that the particpant "stop" a prepotent response in the presence of an > auditory stop signal)and am having trouble writing script that will > analyze performance sequentially across trials. I want to know how > previous trials influence responses on the following trials. > > The data are organized in the data set below. I would like to take > the average of the React variable (reaction time)on trial N-1 where > trial N (trials where event = stop) and trial N-1 (event = Go). I > would then like to compare these reaction times to responses on trials > N + 1. > > Generally, I need to calculate an average of specific trials relative > to performance on previous trials. The location of stops are random. > Has anyone performed similar anaylses? Any suggestions/thoughts would > be greatly appreciated. > > Thanks, > Brian > > Subj Trial Cond Event React Key XX DUR > 1 14 O go 306 68 N/A 200 > 1 15 X go 432 65 N/A 200 > 1 16 X stop N/A 320 N/A 250 > 1 17 O go 393 68 N/A 250 > 1 18 O go 523 68 N/A 250 > 1 19 X go 420 65 N/A 250 > 1 20 O go 447 68 N/A 250 > 1 21 O go 528 68 N/A 250 > 1 22 X go 604 65 N/A 250 > 1 23 X go 525 65 N/A 250 > 1 24 X stop N/A 320 N/A 300 > 1 25 O go 343 68 N/A 300 > 1 26 O go 389 68 N/A 300 > 1 27 X go 403 65 N/A 300 > 1 28 X go 480 65 N/A 300 > 1 29 O stop N/A 320 N/A 350 > 1 30 O go 450 68 N/A 350 > 1 31 O go 421 68 N/A 350 > 1 32 X stop 390 65 N/A 300 > 1 33 O stop N/A 320 N/A 350 > 1 34 O go 437 68 N/A 350
You'll get more help with SPSS questions in the SPSS newsgroup (comp.soft-sys.stat.spss). You need to use the LAG function. LAG can only look at prior records in the file, so you'll need to sort in ascending order of trial for some things, in decending order for others. SOmething like this: * ----- Start of syntax --------- . * Create flags for Trials N-1, N, and N+1 . * Trial Type N-1 is a GO trial just before a STOP. sort cases by subj trial(d). if (event = 'go') and (lag(event)= 'stop') ttype = 1. exe. * Trial N follows Trial N-1. sort cases by subj trial. if lag(ttype) = 1 ttype = 2. exe. * Trial N+1 = GO after STOP . if (event = 'go') and (lag(event)= 'stop') ttype = 3. exe. value labels ttype 1 'N-1' 2 'N' 3 'N+1'. * ----- End of syntax --------- . This does not compute Trial Types for all of your cases--I wasn't sure what you want to do when you have two STOPs in a row, for example, or serveral GOs in a row. But it should get you started. Cheers, Bruce -- Bruce Weaver [EMAIL PROTECTED] www.angelfire.com/wv/bwhomedir/ . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
