How to present two versions of instruction text at random?

Hi!

I'm trying to implement a function in my script (for running the Stroop task), that randomly presents either Instruction Text 1 or 2. The script contains 8 pseudorandom sequences for presentation of the words 'purple' and 'orange' in either the colour 'purple' or 'orange'. The 8 sequences stand for 8 runs of scanning. After each sequence (which contains 182 events) I want to present either Instruction Text 1 or 2 to change response mapping (we use a button box). Ideally, the script should present Instruction text 1 for all odd-numbered sequences & Instr.text 2 for all even-numbered sequences.

I already tried some things like mod, repmat, isodd & the following:

respmapping= seq(1:8); if respmapping==seq{2}||seq{4}||s eq{6}||seq{8} InstructText2; else InstructText1;

( error message on this: ??? Undefined function or method 'eq' for input arguments of type 'cell'. Error in ==> StroopScript at 244 if respmapping==seq{2}||seq{4}||seq{6}||seq{8} )

Nothing worked so far since most arguments are for arrays of scalars or cells. It's probably easy, but I got stuck. Could anyone help me?

Here a bit more of my (very long) script:

InstructText1 = ['Press LEFT for COLOUR. Press RIGHT for WORD.\n\n'... 'The task will begin when you press a button.\n\n\n'... 'Name colour or word as fast and\n\n'... 'accurate as possible.']; Screen('TextSize', expWin, 30);

InstructText2 = ['Press RIGHT for COLOUR. Press LEFT for WORD.\n\n'... 'The task will begin when you press a button.\n\n\n'... 'Name colour or word as fast and\n\n'... 'accurate as possible.']; Screen('TextSize', expWin, 30);

for Session=1:nSessions

    %make random sequence for aud/vis cues
    %cuemodality=zeros(size(seq{Session});
    ntrials=sum(seq{Session}>0);
    tempcuemodalities=[repmat({'vis'},1,ntrials/2), repmat({'aud'},1,ntrials/2)];
    tempcuemodalities=tempcuemodalities(randperm(length(tempcuemodalities)));
    cuemodalities=repmat({'null'},1,nEvents);
    cuemodalities(seq{Session}>0)=tempcuemodalities;

    respmapping= seq(1:8);
    if respmapping==seq{2}||seq{4}||seq{6}||seq{8}
        InstructText2;
    else
         InstructText1;
    end
  %Screen('TextSize', expWin, 24);
            %DrawFormattedText(expWin, 'Take a short break', 'center', 'center');
            %Screen('Flip', expWin);
    Screen('TextSize', expWin, 30);      
    Screen('Flip', expWin);
    DrawFormattedText(expWin, InstructText1, 'center', 'center');
    [temp inst_onset]=Screen('Flip', expWin);
    KbWait([], 3);
    Screen('Flip', expWin);
    DrawFormattedText(expWin, InstructText2, 'center', 'center');
    [temp inst_onset]=Screen('Flip', expWin);
    KbWait([], 3);

    % draw fixation cross
    Screen('DrawTexture', expWin, fixcross);
    Screen('Flip', expWin);

Thanks!

Answer 1

[Sean de Wolski]

Just looking at your error message:

error message on this: ??? Undefined function or method 'eq' for input arguments of type 'cell'.

Which of your cells is a cell array of cells? Apparently one of them is, so even when you extract the first cell level, you retrieve a cell. This would worry me that something wierd was going on if it is not your intention.

Answer 2

[Christiane]

@ Sean de Wolski: seq is my cell array of cells I guess. Don't know why matlab calls the variable 'eq' though.

[Sean de Wolski]

eq is the MATLAB function equals and is what is called when you use == to test equality.

Answer 3

[Matt Tearle]

I see several problems. Is seq a cell array of strings or a cell array of cells (or something else)? Either way,

respmapping = seq(1:8);

creates a cell array that's equivalent to the first 8 elements of seq. That is, respmapping is also a cell array. Hence

respmapping ==

is never going to work (regardless of the right-hand side).

Also, you can't do

x == y || z

you have to do

x == y || x == z

I'm also not sure what

InstructText2;

is supposed to do. It looks like InstructText2 is a string variable. In which case, this would just display it to the screen, except the semicolon suppresses the display. So it does nothing.

Finally, if seq is a cell array of strings, use strcmp instead of ==. But the fundamental issue is what you're trying to compare the strings to. I really don't understand what

respmapping= seq(1:8);

is supposed to do.