Gaze Dependent Display

1
Hello,

I have a question concerning a Matlab code for a gaze dependent
display. I adapted some code which was in the forum, but mine does not
seem to work properly. The display just switches to another screen
after sometime. I pasted the code beneath. Could anyone help me with
this!
Thanks a lot.

Michael

function breaktrial = gazedependentdisplay(calltime, begintime,
endtime, xpos, ypos, reqFixTime, maxFCDur, fixTolerance)

global VSGET_eye_used;
global VSGET_ts;
global VSGET_mx;
global VSGET_my;

breaktrial = 0;

% verify fixation stability for a particular amount of time
% Eyelink('message', 'Check Fixation Start' );
% disp('Check Fixation Start');

[h]=crsGetScreenHeight();
fixTolerancePix=round(fixTolerance/100*h);
%movThresholdPix=round((par.stimRadius(trial)/100)*h/2);

tfcEnd=GetSecs+maxFCDur; %max time fixation check may take before we
enforce driftcorrection

errorp=Eyelink('CheckRecording');
if(errorp~=0)
error('Eyelink CheckRecording returned %d', errorp);
end

if Eyelink('NewFloatSampleAvailable') > 0
% get the sample in the form of an event structure
evt = Eyelink('NewestFloatSample');
if VSGET_eye_used ~= -1 % do we know which eye to use yet?
% if we do, get current gaze position from sample
x = evt.gx(VSGET_eye_used+1); % +1 as we're accessing MATLAB array
y = evt.gy(VSGET_eye_used+1);
% do we have valid data and is the pupil visible?
if x~=el.MISSING_DATA && y~=el.MISSING_DATA &&
evt.pa(VSGET_eye_used+1)>0
VSGET_mx=x;
VSGET_my=y;
end
end
end

d=sqrt((VSGET_mx-xpos)^2+(VSGET_my-ypos)^2);
if d<fixTolerancePix
if VSGET_ts<0
VSGET_ts=GetSecs;
elseif (GetSecs-VSGET_ts) > reqFixTime
fprintf('fixation point fixated long enough\n');
Eyelink('message', 'Check Fixation End' );
breaktrial = 1;
end
else
VSGET_ts=-1;
end

if GetSecs > tfcEnd
Eyelink('message', 'Enforcing driftcorrection: no accurate
fixation after %f secs', maxFCDur );
EyelinkDoDriftCorrection(el);
end
2
Michael,
Did you try out the gaze-dependent display example (and other examples)
in the eyelinktoolbox directory of the PTB? Does this work okay?
If so, maybe you can start from there.
Gr.
Frans


--- In psychtoolbox@yahoogroups.com, "michael.hegenloh" <mhegenloh@...> wrote:
>
> Hello,
>
> I have a question concerning a Matlab code for a gaze dependent
> display. I adapted some code which was in the forum, but mine does not
> seem to work properly. The display just switches to another screen
> after sometime. I pasted the code beneath. Could anyone help me with
> this!
> Thanks a lot.
>
> Michael
>
> function breaktrial = gazedependentdisplay(calltime, begintime,
> endtime, xpos, ypos, reqFixTime, maxFCDur, fixTolerance)
>
> global VSGET_eye_used;
> global VSGET_ts;
> global VSGET_mx;
> global VSGET_my;
>
> breaktrial = 0;
>
> % verify fixation stability for a particular amount of time
> % Eyelink('message', 'Check Fixation Start' );
> % disp('Check Fixation Start');
>
> [h]=crsGetScreenHeight();
> fixTolerancePix=round(fixTolerance/100*h);
> %movThresholdPix=round((par.stimRadius(trial)/100)*h/2);
>
> tfcEnd=GetSecs+maxFCDur; %max time fixation check may take before we
> enforce driftcorrection
>
> errorp=Eyelink('CheckRecording');
> if(errorp~=0)
> error('Eyelink CheckRecording returned %d', errorp);
> end
>
> if Eyelink('NewFloatSampleAvailable') > 0
> % get the sample in the form of an event structure
> evt = Eyelink('NewestFloatSample');
> if VSGET_eye_used ~= -1 % do we know which eye to use yet?
> % if we do, get current gaze position from sample
> x = evt.gx(VSGET_eye_used+1); % +1 as we're accessing MATLAB array
> y = evt.gy(VSGET_eye_used+1);
> % do we have valid data and is the pupil visible?
> if x~=el.MISSING_DATA && y~=el.MISSING_DATA &&
> evt.pa(VSGET_eye_used+1)>0
> VSGET_mx=x;
> VSGET_my=y;
> end
> end
> end
>
> d=sqrt((VSGET_mx-xpos)^2+(VSGET_my-ypos)^2);
> if d<fixTolerancePix
> if VSGET_ts<0
> VSGET_ts=GetSecs;
> elseif (GetSecs-VSGET_ts) > reqFixTime
> fprintf('fixation point fixated long enough\n');
> Eyelink('message', 'Check Fixation End' );
> breaktrial = 1;
> end
> else
> VSGET_ts=-1;
> end
>
> if GetSecs > tfcEnd
> Eyelink('message', 'Enforcing driftcorrection: no accurate
> fixation after %f secs', maxFCDur );
> EyelinkDoDriftCorrection(el);
> end
>