Trigger system

What is a trigger?

  • is an electric signal of agreed size (and duration)
  • can be analog (volts) or digital (bits)
  • may communicate both timing information as well as event identity information
  • is our only means of recovering accurate timing information in an experiment
  • can greatly help the analysis and validation of your experimental data

Analog vs. digital triggers

  • 5 V analog signal
  • “all-at-once” potential change
  • 5 - 10 ms duration typically
  • one event per trigger channel
  • STI001 … STI016 in DACQ mimic analog trigger channels
  • one digital trigger channel may communicate many different events
    signal strength corresponds to the trigger value
    16 bits => 65536 values:
    000…001 == 1
    000…010 == 2
    000…011 == 3
    000…100 == 4
    STI101 in DACQ

Where do triggers come and go?

1. Stimulus control software
    ->Presentation, PsychoPy, Experiment Builder
2. Subject response devices
3. DACQ system
4. Auxiliary devices
    ->Eye-tracking, custom devices
5. Stimulus devices

Timing information and trigger-to-stimulus delays

  • MEG excels in temporally accurate mapping of brain activity
  • Don’t lose this benefit because of poorly planned triggering scheme or uncontrolled delays!
  • The delay from event-related trigger in DACQ to real event occurrence must be measured separately for each experimental setup    



Visual stimulation

  • FullHD, 60 (/120) Hz LED projector
  • Set Presentation / Settings / Video to “NVIDIA Quadro”
  • Presentation uses picture objects to control display
  • Stimulus timing (onset and duration) is based on the vertical refreshes of the display


  • a general object class
  • parameters: position, color, …
  • 2D & 3D
  • covers the whole display
  • consists of components like text, bitmaps, shapes
  • video also possible

Audio stimulation

  • Currently, two separate sound sources with stim-PC:
  • SoundBlaster ZxR sound card
  • Rotel amplifier via SPDIF / USB
  • choose these in Presentation / Settings / Audio
  • Three different output channels:
  • HiFi (thick sound tubes); connected to Rotel
  • LoFi thin sound tubes and panel speakers; connected to ZxR, choose with the balance audio box
  • bits-per-sample: resolution (quality) of the sound
  • number of channels: stereo
  • sampling frequency: 44100 Hz or 192000 Hz
  • mixer: use Presentation mixer; Exclusive mode often preferred


  • sound class
  • .wav -type files only
  • simultaneous sounds possible (“parallel”)
  • Auditory Stimulus Generation toolkit

Somatosensory stimulation

  • Controlled directly by trigger pulses
  • Constant-current electric stimulators ->current strength, pulse duration
  • Pneumatic devices ->“actuator” determines functionality
  • Trigger pulses can be generated in Presentation e.g. with the empty stimulus type nothing{} - or simply in DACQ

Input, output and response ports

  • I/O port settings: PCIe-6363
  • see Example_settings.exp for details on settings
  • code values: 256 - 8192 for trigger lines 9-14
    • lines 9 and 10 (codes 256 and 512) have been used for Elekta response pads
    • lines 11 - 14 (codes 1024, 2048, 4096, 8192) for CurDes (Please do not change these!)