Event Related Potentials (ERPs)

About Event Related Potentials (ERPs)

An event-related potential (ERP) is the measured brain response that is the direct result of a specific sense|sensory, cognition|cognitive, or motor system|motor event.<ref name="Luck">Template:Cite book</ref>

Presentation Software

There are several software that can set-up an experiment which presents some stimulus (audio, images, video, etc.) to a subject in order to elicit ERPs in the EEG signal. It is very important that the recorded EEG data is synchronized with those stimulus in order to detect the ERPs when analyzing the data. The NIC software provides the basic infrastructure to receive those markers from this kind of software every time a stimuli is presented. Please refer to the Interacting_with_NIC section for the details on how NIC handles the reception of the markers.

In the following section we detail how some of the most relevant presentation software can be configured to send markers to NIC.

Presentation

The Presentation software allows to connect to a remote application by using sockets in the PCL program section of an experiment scenario. This socket can be used to send markers to NIC every time a stimuli is presented. The following example shows how to proceed in order to send markers to NIC.

scenario = "Sending triggers to NIC";

begin;

text { caption = "Hello world!"; font_size = 24; } hello;

picture {
   text hello;
   x = 0; y = 100;
} hello_pic;

trial {
   picture hello_pic;
   time = 0;
} hello_trial;

begin_pcl;

bool isConnected = false;
# socket creation
socket s = new socket();

hello.set_caption( "Connecting to trigger server..." );
hello.redraw();
hello_trial.set_duration( 1000 );
hello_trial.present();

# Connect to the NIC server. The example assumes that NIC runs
# on the same computer as Presentation. Change "localhost" by the IP or
# computer's name where NIC is running. The NIC server runs on port 1234.
# The time-out at 5 secs (5000 ms) can be changed according to your needs.
# 8 bits for the codification and no ecryption.
isConnected = s.open( "localhost", 1234, 5000, socket::ANSI , socket::UNENCRYPTED );
if isConnected == true
then
	hello_trial.set_duration( 3000 );
	loop
		int i = 1
	until
		i > 50
	begin
		hello.set_caption( "Sending trigger # " + string( i ) );
		hello.redraw();
		# The NIC server process a trigger whenever it receives 
		# a string with the following format:
		# <TRIGGER>xxx</TRIGGER>
		# where xxx is any number different from zero.
		s.send("<TRIGGER>" + string( i ) + "</TRIGGER>");
		hello_trial.present();
	
		i = i + 1
   end
else
	hello.set_caption( "Time out connecting to the server" );
	hello.redraw();
	hello_trial.present();
end

TCP/IP configuration settings in the Presentation software

Presentation extension manager

LSL data port properties

The line

isConnected = s.open( "localhost", 1234, 5000, socket::ANSI , socket::UNENCRYPTED );

can be simplified to the following in case the parameters are set in "Settings->Advanced->TCP/IP Defaults".

isConnected = s.open();

An alternative way of synchronizing the presented stimulus by the Presentation software and NIC is by means of the Lab Streaming Layer (LSL) protocol. To get use of this functionality you need to install the LSL Presentation Extension in you Presentation software through the Presentation extension manager.

Once the extension is registered, it can be selected as a data port in Presentation's port settings. Information about the stream outlet name, ID, and connection status can be found in the data port properties window reachable through the "Properties" button that appears when the data port is selected within Presentation's port settings. The Connection Settings property allows users to choose whether the LSL stream outlet should be automatically opened whenever when Presentation starts, or whether it must be manually opened after Presentation is launched. All events that are logged in the Presentation logfile will also be sent out as LSL markers.

Please refer to the Interacting_with_NIC section for the details on how to configure NIC to handle the reception of the markers from the LSL.