___________________________________________________________________________________________________________________ Stop Signal Task (SST) ___________________________________________________________________________________________________________________ Script Author: David Nitz (firstname.lastname@example.org) for Millisecond Software, LLC last updated: 03-01-2022 by K. Borchert (email@example.com) for Millisecond Software, LLC Script Copyright © 03-01-2022 Millisecond Software Millisecond Software thanks Dr. Sylvain Iceta for sharing his French translations! Any errors in the French translations are due to updates to the instructions made by Millisecond Software. ___________________________________________________________________________________________________________________ BACKGROUND INFO ___________________________________________________________________________________________________________________ This script implements the 'Stop Signal Task' as described in: Verbruggen, F., Logan, G. D., & Stevens, M. A. (2008). STOP-IT: Windows executable software for the stop-signal paradigm. Behavior Research Methods, 40(2), 479-483. Additional References: Logan, G. D. (1994). On the ability to inhibit thought and action: A user’s guide to the stop signal paradigm. In D. Dagenbach & T. H. Carr, Inhibitory processes in attention, memory, and language (pp. 189-239). San Diego: Academic Press ___________________________________________________________________________________________________________________ TASK DESCRIPTION ___________________________________________________________________________________________________________________ After looking at a fixation circle, participants are presented an arrow withing this circle that either points right or left. The task is to press the left response key if the arrow points to the left and press the right response key if the arrow points to the right UNLESS a signal beep is played AFTER the presentation of the arrow. In this case the response should be stopped before execution. The delay between presentation of arrow and signal beep (starting at 250ms) is adjusted up or down (by 50ms) depending on performance. The delay gets longer if the previous signal stop was successful (up to 1150ms) and it gets smaller if the previous signal stop was not successful (down to 50ms). The stimlus onset asynchrony between the start of each trial (onset of fixation circles) is 2000ms. Participants can respond up until the next trial starts. ___________________________________________________________________________________________________________________ DURATION ___________________________________________________________________________________________________________________ the default set-up of the script takes appr. 12 minutes to complete ___________________________________________________________________________________________________________________ DATA FILE INFORMATION ___________________________________________________________________________________________________________________ The default data stored in the data files are: (1) Raw data file: 'stopsignalTask_french_raw*.iqdat' (a separate file for each participant) build: The specific Inquisit version used (the 'build') that was run computer.platform: the platform the script was run on (win/mac/ios/android) date, time: date and time script was run subject, group: with the current subject/groupnumber session: with the current session id blockcode, blocknum: the name and number of the current block (built-in Inquisit variable) blocknumber: Number of Test Blocks (custom variable) expressions.blocknumber_adj: adjusted number of test blocks trialcode, trialnum: the name and number of the currently recorded trial (built-in Inquisit variable) Note: trialnum is a built-in Inquisit variable; it counts all trials run; even those that do not store data to the data file such as feedback trials. Thus, trialnum may not reflect the number of main trials run per block. trialnumber: Number of trials run in a block (custom variable) trialnumber_adj: adjusted Number of trials run in a block (does not count the first one) stimulus: 1 = left arrow, 2 = right arrow signal: 1 = presence of an auditory signal, 0 otherwise ACC: 0 = incorrect; 2 = correct response: key pressed by subject (scancode of response button pressed; 32 = D; 37 = K) responseCategory: 1 = left; 2 = right; 0 = no response rt: reaction time in ms (0 = no response) ns_ntotal : total number of ns trials ss_ntotal: total number of ss trials ssd: ssd for the current trial p_rs: probability of reacting in ss trials => p(response|signal) ssd: mean stop signal delays (in ms) in ss trials ssrt: estimation of the covert stop signal reaction time in ms (SSRT) (the time required to stop the initiated go-process) => the slower the SSRT the more difficult to stop the go-process => the faster the SSRT the easier to stop the go-process (measure of inhibition ability) sr_rt: mean reaction time (in ms) in ss trials in ms ns_rt: mean reaction time (in ms) in correct ns trials, across blocks => 'choice reaction time' ns_hit : percentage of mean number of hits in ns trials miss: percentage of mean number of misses in ns trials z_score: z-score of p(response|signal) with expected mean = n*p; standard deviation = sqrt(n*p*q); with n= number of stop signal trials; p = parameters.p; q = 1-p p_value: p-value that corresponds to the calculated z-value NOTE: z-score and corresponding p-value indicate whether a participant inhibited significantly more or less than 50% of the time (see parameters.p) (Verbruggen et al: for participants who inhibited significantly more or less than 50% of the time the subtraction method to calculate SSRT (see SSRT) cannot be used) (2) Summary data file: 'stopsignaltask_french_summary*.iqdat' (a separate file for each participant) inquisit.version: Inquisit version run computer.platform: the platform the script was run on (win/mac/ios/android) startdate: date script was run starttime: time script was started subjectid: assigned subject id number groupid: assigned group id number sessionid: assigned session id number elapsedtime: time it took to run script (in ms); measured from onset to offset of script completed: 0 = script was not completed (prematurely aborted); 1 = script was completed (all conditions run) p_rs: probability of reacting in ss trials => p(response|signal) ssd: mean stop signal delays (in ms) in ss trials ssrt: estimation of the covert stop signal reaction time in ms (SSRT) (the time required to stop the initiated go-process) => the slower the SSRT the more difficult to stop the go-process => the faster the SSRT the easier to stop the go-process (measure of inhibition ability) sr_rt: mean reaction time in ss trials in ms ns_rt: mean reaction time in correct ns trials, across blocks => 'choice reaction time' ns_hit : percentage of mean number of hits in ns trials miss: percentage of mean number of misses in ns trials z_score: z-score of p(response|signal) with expected mean = n*p; standard deviation = sqrt(n*p*q) p_value: p-value that corresponds to the calculated z-value NOTE: z-score and corresponding p-value indicate whether a participant inhibited significantly more or less than 50% of the time (see parameters.p) (Verbruggen et al: for participants who inhibited significantly more or less than 50% of the time the subtraction method to calculate SSRT (see SSRT) cannot be used) ___________________________________________________________________________________________________________________ EXPERIMENTAL SET-UP ___________________________________________________________________________________________________________________ * tests Stop Signal Delays between: 50ms (min) - 1150ms (max) with adjustment steps = 50ms * The initial Stop Signal Delay is set to 250ms * The total trialduration of each signal and no signal trial is 2000ms (= SOA between onsets of fixation stims) * half the arrows in each trialtype point left, the other right 1 Practice Block: 32 trials (8 signal trials : 24 no signal trials = 1:3) 3 Test Blocks: 64 trials each (16 signal trials : 48 no signal trials = 1:3) ___________________________________________________________________________________________________________________ INSTRUCTIONS ___________________________________________________________________________________________________________________ see section Editable Stimuli ___________________________________________________________________________________________________________________ EDITABLE CODE ___________________________________________________________________________________________________________________ check below for (relatively) easily editable parameters, stimuli, instructions etc. Keep in mind that you can use this script as a template and therefore always "mess" with the entire code to further customize your experiment. The parameters you can change are: Adjustable Task Parameters: - resetpracticessd Boolean switch to determine whether SSD should be reset to start value (parameters.ssd_start) after practice block. Default is 'false'. - leftkey Keyboard scan code for the left response key. Default is "D" - rightkey Keyboard scan code for the right response key. Default is "K" - minssd Minimum allowable Stop Signal Delay (SSD). Default is '50'. Given that a '0' delay does not make sense, this value should usually be set to match parameters.adjustment. - maxssd Maximum allowable Stop Signal Delay (SSD). Default is '1150'. Given the default trial/stimulus timing '/ stimulustimes = [0=fixation; 250=stim; 1500=erasestim]', this value should be chosen such that 'maxssd + stopsignalduration <= 1250'. Otherwise the Stop Signal would occur *after* the given trial has already terminated, which, of course, would not make any sense. - adjustment Amount in ms by which SSD should be in- or decreased depending on successful or unsuccessful response inhibition. Default is '50'. - ssd_start Initial Stop Signal Delay (SSD) in ms. Default is '250'. - pretrialpause Duration of pretrialpause in ms. Default is '500'. - trialduration Total duration for a given trial in ms. Default is '2000'. - waitbetweenblocks Wait period between blocks in seconds. Default is '10'. - p Target response inhibition probability. Default is '0.5'. Do *not* change this value unless you are very familiar with the Stop Signal paradigm.