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Elekta Response Pads & LabJack U3-LV

MATLAB Functions to use Elekta Response Pads with a LabJack U3-LV.

Before NAtA response pads were purchased, the Supplier-provided pads were used to recover participant responses. The code may still be useful when using a LabJack.

The Elekta Response Pads ("Bilateral Finger Response System") were attached, via BNC cables, to the Stimulus Interface #2 (STI102) trigger inputs In 15 (Left Pad) & In 16 (Right Pad) located in the Stimulus Cabinet.

Stimulus Interface #1 (STI101) is situated on the Control Room desk, and by default the two Interface boxes are operated in parallel.

In parallel operation the signals from Interface #2 are duplicated on Interface #1.

To record button presses on CHBH-ST-MEG-W02, Out 15 and Out 16 from Interface #1 were attached, via BNC cables to the LabJack U3-LV Interface Box inputs CIO0 (pin 9/bit 16) and CIO1 (pin 2/bit 17) respectively.

NOTE: Stimulus Interface #2 dipswitch orientation (in Stimulus Cabinet).
- Input Pull Up Resistor: ON
- Input Polarity: Raising Edge

The following MATLAB code was used to initialise the LabJack and record a response from the pads.

int_buttonInitalise.m

function lj = int_buttonInitalise()

%% Initalise Labjack
% Make the UD .NET assembly visible in MATLAB.
lj.ljasm = NET.addAssembly('LJUDDotNet');
lj.ljudObj = LabJack.LabJackUD.LJUD;

% Open the first found LabJack U3.
[lj.ljerror, lj.ljhandle] = lj.ljudObj.OpenLabJackS('LJ_dtU3', 'LJ_ctUSB', '0', true, 0);

% Start by using the pin_configuration_reset IOType so that all pin
% assignments are in the factory default condition.
lj.ljudObj.ePutS(lj.ljhandle, 'LJ_ioPIN_CONFIGURATION_RESET', 0, 0, 0);

% define voltage threshold for button press
lj.volt_thr = 0.1;

int_getResponse.m

function [resp,t] = int_getResponse(cfg)

% loop till broken from
while true

    % cycle through buttons
    for button = 1 : 2

        % get current state      
        [~,cs]  = cfg.lj.ljudObj.eDI(cfg.lj.ljhandle, button+15, 1); % check digital bit 16 (CIO0) and digital bit 17 (CIO1)

        % get time
        t       = GetSecs();

        % check if voltage exceeds threshold
        if cs < 1
            resp = button;
            WaitSecs(0.25); % wait to avoid press overlap
            return
        end
    end
end

Many thanks to Dr. Ben Griffiths for providing the code.