Chronos is a USB-based device offering solutions for many stages of your research. Such as – collecting responses, presenting sound, sending triggers and more.
Chronos features an onboard sound card, which eliminates delay issues in audio playback. Consumer sound cards often lack consistent audio timing. This can lead to differences between devices and cause delays in sound presentation.
Chronos also provides many digital inputs/outputs for external communication.
Connecting 2 devices
Connection between PRO devices and Chronos is established using a TTL wire. To be more specific, we use 1-bit TTL triggers to synchronize actions from 2 devices.
Let’s first cover the connection, and then we’ll give some practical examples.
Chronos AUX I/O Breakout Cable
With your Chronos device, you will receive an AUX I/O breakout cable. You get 2 digital outputs, but for 1-bit TTL triggers we only need one.
All PRO devices have 1-bit TTL input on the EEG cap. This cap input is in the form of a 2.5mm audio jack.
Tip of the audio jack is the Receiver line (Rx) and the ring is the Transmitter (Tx). We’ll connect OUT15 to Rx, and IN15 to Tx. In our setup, Chronos will be sending TTLs to the EEG cap.
Once you connect the 2 devices, you’ll need a PC to control them both. For Chronos you’ll use E-Prime software for communication. With PRO/PROX device you’ll need mbtStreamer.
Example no.1: send triggers when there’s a button response
In this example, Chronos will present a TTL trigger when:
- we present a stimulus in E-Prime (sound or image)
- a person responds to the stimulus using Chronos buttons
PROX device will then detect the trigger and include it in the EEG recording.
Connect Chronos to PC via USB and run E-Prime. Chronos add-on is available by default. Go to Experiment Object Properties window and add a Chronos device.
In Chronos properties, make sure to set Digital Output 15 (DO 15) to 1 at experiment start.
During the experiment, DO 15 can either be 1 (high) or 0 (low). So how does 1-bit TTL detection work with PROX device?
Our devices will only detect a drop in voltage from high to low. This means we need to ensure DO15 drops to 0 each time we want a TTL trigger.
Let’s say we’re presenting a sound to the participant using Chronos and a set of headphones. We give them the instruction to press the button after a certain sound. We’d like to send a TTL trigger for both stimulus and response.
In Stimulus properties window, we need to add Events which will trigger changes in DO15. First, we’ll add Stimulus.OnsetTime which represents the moment a stimulus is presented.
Then, add an Action that will happen with this Event. Select DigitalOutResetBit and type 15 in Custom: field.
Reset function will set DO15 bit to 0. Because of the “voltage drop” from 1 to 0, PROX device will detect it as a TTL trigger.
Now, we need to set DO15 to 1 again because we want to send a TTL trigger for the next action. We’ll use Stimulus.ActionTime as an Event to set DO15 to 1 – just select DigitalOutSetBit action.
ActionTime represents a timestamp at which the hardware’s driver returns control back to E-Prime. Period between OnsetTime and ActionTime is around 1 millisecond.
When the participant presses a Chronos button, we’ll add the DigitalOutResetBit action. A TTL trigger is then detected by PROX.
We added a short period of fixation, just to denote the beginning of a new trial. When we present the fixation cross, DO15 will be set to 1.
Check out our diagram to help understand how one trial works:
Record TTL with EEG
TTL triggers are recorded directly on PRO/PROX device memory. You can also visualize them alongside EEG in mbtStreamer software.
Example no.2: send triggers when audio is detected
In this example, we’ll present a word or question to the participant. Then, we expect an audible reaction from them (to say the word, phrase, sentence or give an answer).
Chronos will send a TTL trigger when:
- we present the phrase
- it detects a sound using a microphone. Also, we’ll record the detected sound.
Check out this representation of one experiment trial:
In Experiment Object Properties click on Sound in the list of devices. Change API field to Chronos – this means Chronos will handle audio in your experiment.
We want to start recording audio when our participant starts talking. So, in Chronos Device Properties, in Audio In tab, we’ll set StartMode to onset. You can set Onset Threshold for detecting sound changes to any percentage you’d like. This depends on how sensitive you want the mic to be.
StopMode indicates the end of audio recording, and this should be set to normal.
Since we want to record the participant’s response for 5 seconds, we’ll add a wait function after stimulus. We’ll set the waiting duration to 5s.
In Stimulus Properties, you’ll need to set Response Options i.e. buttons. Set value “6” that signifies the Chronos’ pseudo button. You won’t use any buttons, but for audio to be used as a trigger, this needs to be set.
While in this window, navigate to Task Events tab. We’ll add all the actions related to audio recording and sending TTL triggers. We also use DO15 in this example.