Stop-Signal Task (SST) – PsyFlow Version

This task implements a Stop-Signal paradigm (SST) to assess inhibitory control mechanisms. Participants are asked to respond to left- or right-pointing arrows, but on some trials, they must inhibit their response when a red arrow appears. The task is built using the PsyFlow framework.

Task Overview

Participants are instructed to respond as quickly and accurately as possible to directional arrows by pressing the left or right arrow keys. Occasionally, a red arrow appears after a short delay, signaling participants to withhold their response.

The task uses an adaptive staircase procedure to dynamically adjust the stop-signal delay (SSD) to maintain approximately 50% successful inhibition on stop trials.

Task Flow

Step	Description
Instruction	A textbox (instruction_text) presents task instructions in Chinese. The participant presses the space bar to start.
Fixation	A fixation cross “+” is shown before each trial.
Go Trial	A white arrow points left or right. Participant should respond by pressing the matching arrow key.
Stop Trial	A red arrow appears after a delay (SSD); participant must inhibit their response.
Feedback	If no response is made on a go trial, a warning feedback is displayed.
Block Break	After each block, performance summaries are shown with options to rest.
Goodbye	A final thank-you screen and task termination.

Configuration Summary

All key settings are defined in config/config.yaml.

Subject Info (subinfo_fields)

Participants register with:

• Subject ID (three-digit number from 101–999)

• Session name

• Experimenter

• Gender (Male or Female)

Localized prompts are available via subinfo_mapping.

Window Settings (window)

• Resolution: 1920 × 1080

• Units: deg

• Fullscreen: True

• Monitor: testMonitor

• Background color: gray

Stimuli (stimuli)

Stimulus Name	Type	Description
fixation	text	Central fixation cross “+”
go_left, go_right	shape	White arrows indicating response direction
stop_left, stop_right	shape	Red arrows indicating stop signal
no_response_feedback	textbox	Feedback message for missed go responses
instruction_text	textbox	Pre-task instruction screen
block_break	textbox	Mid-task break screen
good_bye	textbox	Final thank-you screen
iti_stim	text	Blank screen during ITI

Timing (timing)

Phase	Duration
Fixation	0.5–0.8 seconds (randomized)
Go stimulus duration	1.0 second
No-response feedback	0.8 seconds
ITI	0.5–0.8 seconds (randomized)

Triggers (triggers)

The following event triggers are sent for synchronization (e.g., EEG, MEG):

Event	Code
Experiment start	98
Experiment end	99
Block start	100
Block end	101
Fixation onset	1
Go onset	10
Go response	11
Go miss	12
Pre-stop response	23
On-stop response	24
Post-stop response	25
No-response feedback onset	30

Adaptive Controller (controller)

The SST uses a staircase tracking algorithm to adjust stop-signal delay (SSD).

Parameter	Value
Initial SSD	0.25 seconds
Step Size	0.05 seconds
Minimum SSD	0.05 seconds
Maximum SSD	0.5 seconds
Target Success Rate	50% (1-up/1-down staircase method)

The staircase controller increases or decreases the SSD based on whether the participant successfully inhibits their response.

Running the Task

python main.py