Recording eye tracking data with the TRACKPixx /Mini
This demo requires TRACKPixx Revision 16 or later. You can check for recent firmware updates at http://vpixx.com/whatsnew
In this demo we record the eye position data from the TRACKPixx Mini for 4 seconds, and then plot the result.
We capture images of the eye and display them on the screen to ensure the camera is positioned well. We then display a series of squares for the subject to fixate. Recording of eye movements starts when the “Enter” key is pressed, and continues for 4 seconds. On the TRACKPixx Mini, we read tracker data directly from the device using Datapixx('ReadTPxMiniData') and save it to an array.
TRACKPixx Mini data has the following format:
Timetag, Left Eye X, Left Eye Y, Left Pupil Diameter, Right Eye X, Right Eye Y, Right Pupil Diameter, Digital Input Values (24 bits), Left Blink Detection, Right Blink Detection, Digital Output Values (24 bits), Left Eye Fixation Flag, Right Eye Fixation Flag, Left Eye Saccade Flag, Right Eye Saccade Flag, Message code, Left Eye Raw X, Left Eye Raw Y, Right Eye Raw X, Right Eye Raw Y.
As a last step we generate 4 figures. The first 3 figures plot X and Y position over time for the left eye, the right eye, and both eyes. The last figure plots left and right pupil diameter over time. Data points where the X and Y positions equal 9000 are frames in which the eye position was lost (i.e., the participant blinked).
function TPxMiniRecordAndPlot()
%
% This demo will start the required things to start the TPx schedule to record data
% and it will show points for 4 secs and record raw or calibrated data.
% After the four seconds, the data will be plotted.
%
%
% Dec 22, 2017 dml written
Screen('Preference', 'SkipSyncTests', 1);
%% Step 1 -- Open the screen and show the eye.
%Ensure that the TPx/m has no open session before using it.
Datapixx('CloseTPxMini');
%'Initialize' opens a TPx/m session and determines the
%filter mode and screen margin to use for calibration. We
%recommend using filter mode 0 (no filtering).
%--> %It is mandatory to call 'Initialize' before using the
%TPx/m.
Datapixx('OpenTPxMini', 80);
%'GetEyeImageTPxMini' returns the image coming from the TPx/m
image = Datapixx('GetEyeImageTPxMini');
[windowPtr, windowRect]=PsychImaging('OpenWindow', 1 , 0);
KbName('UnifyKeyNames');
Screen('TextSize', windowPtr, 24);
i = 0;
% Display camera live stream.
while (1)
image = Datapixx('GetEyeImageTPxMini');
textureIndex=Screen('MakeTexture', windowPtr, image');
Screen('DrawTexture', windowPtr, textureIndex);
DrawFormattedText(windowPtr, 'Press Enter once the Eye are Focused', 'center', 700, 255);
Screen('Flip', windowPtr);
% Keypress goes to next step of demo
[pressed dummy keycode] = KbCheck;
if pressed
if keycode(KbName('escape'))
Screen('CloseAll');
Datapixx('CloseTPxMini');
return;
else
break;
end
end
end
WaitSecs(1);
%% Step 2 -- Show screen squares and record
cx = 1920/2;
cy = 1080/2;
dx = 400;
dy = 250;
xy = [cx+dx cy+dy; cx-dx cy+dy; cx-dx cy-dy; cx+dx cy-dy];
xy = [xy;xy]';
size = [30; 30; 30; 30; 10; 10; 10; 10]';
color = [255 255 255; 255 255 255; 255 255 255; 255 255 255; 0 0 0; 0 0 0; 0 0 0; 0 0 0]';
i = 0;
Screen('BlendFunction', windowPtr, 'GL_SRC_ALPHA', 'GL_ONE_MINUS_SRC_ALPHA');
recording = 0;
start_time = 0;
u = 1;
start_rec = 0;
start_time = GetSecs;
bufferData = zeros(120*20, 8);
bufferSecs = zeros(120*20, 1);
while (1)
time_now = GetSecs;
if (((time_now - start_time) > 1))% && ~recording)
i = i + 1;
%Screen('DrawDots', windowPtr, xy, size, color,[], 0);
Screen('DrawDots', windowPtr, [xy(:,mod(i,4)+1) xy(:,mod(i,4)+1)], [30;10]', [255 255 255; 0 0 0]', [], 0);
if ~recording
DrawFormattedText(windowPtr, 'Press enter when ready to record', 'center', 80, 255);
end
Screen('Flip', windowPtr);
start_time = time_now;
end
% Keypress goes to next step of demo
[pressed dummy keycode] = KbCheck;
if pressed
fprintf('Recording Data now');
if keycode(KbName('escape'))
Screen('CloseAll')
Datapixx('CloseTPxMini');
return;
else
recording = 1;
start_rec = GetSecs;
%break;
end
end
if (recording == 1)
%break;
[bufferData(u, :)] = Datapixx('ReadTPxMiniData');
u = u + 1;
curr_time = GetSecs;
if ((curr_time - start_rec) > 4)
finish_time = curr_time;
break;
end
end
end
WaitSecs(1.0);
%% Step 3 -- Analysis
DrawFormattedText(windowPtr, 'Analyzing Data...Please wait', 'center', 80, 255);
Screen('Flip', windowPtr);
fprintf('\nRecording lasted %f seconds\n I got %d frames (should have gotten: %d) \n', finish_time-start_rec, u-1, round((finish_time-start_rec)*120) );
% tt, leftx, lefty, leftpp, rightx, righty, rightpp, distance
bufferData = bufferData(1:(u-1),:);
figure;
hold on;
grid on;
title('Left Eye (Red: X, Blue: Y)');
xlabel('Timetags (seconds)');
ylabel('Gaze information (pixels)');
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,2), 'r')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,3), 'b')
figure;
hold on;
grid on;
title('Right Eye (Red: X, Blue: Y)');
xlabel('Timetags (seconds)');
ylabel('Gaze information (pixels)');
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,5), 'r')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,6), 'b')
figure;
hold on;
grid on;
title('Both Eyes (Red: Left X, Blue: Left Y, Black: Right X, Magenta: Right Y)');
xlabel('Timetags (seconds)');
ylabel('Gaze information (pixels)');
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,2), 'r')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,3), 'b')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,5), 'c')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,6), 'm')
figure;
hold on;
grid on;
title('Pupil over time (Red: Left, Blue: Right)');
xlabel('Timetags (seconds)');
ylabel('Pupil Size (pixels)');
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,4), 'r')
plot(bufferData(:,1)-bufferData(1,1), bufferData(:,7), 'b')
save bufferData
%% Close all!
Screen('CloseAll');
Datapixx('CloseTPxMini');
end