4 x 4 Matrix on each visual field

I am trying to create an imaginary 4 by 4 matrix on each visual field. so that i can draw 12 cirlces on each side. can someone please help me to draw the matrix

clc;

clear all;

close all;

rng('shuffle');

Screen('Preference', 'SkipSyncTests', 1);

[window, window_size] = Screen('OpenWindow', 0, [255 255 255], [], 32,2);

x_middle = window_size(3)/2;

y_middle = window_size(4)/2;

cellsize = 160; % 160, 100, originally set to 150

stimsize = 52;

nrows = 4;

ncolumns = 8;

ncells = nrows*ncolumns;

% Building the grid

r = 1;

for i = 1:ncolumns

for j = 1: nrows

xCoord(r) = ((i-ncolumns)+1)*cellsize + x_middle;

yCoord(r) = ((j-nrows)+1)*cellsize + y_middle;

r=r+1;

end

end

maxjitter = (cellsize-stimsize);

for ii = 1:length(xCoord);

hold on

x_coordinate = xCoord(randperm(numel(xCoord),1))

y_coordinate = yCoord(randperm(numel(yCoord),1))

Screen('FillOval', window, [0 0 0], [x_coordinate y_coordinate x_coordinate y_coordinate]);

end

% Screen('FillOval', window, [0 0 0], [x_middle-160 y_middle-160 x_middle+160 y_middle+160]);

% Screen('FillOval', window, [0 0 0], [x_middle-320 y_middle-320 x_middle+320 y_middle+320]);

% Screen('FillOval', window, [0 0 0], [X Y X Y]);

Screen('Flip', window);

WaitSecs(3);

Screen('CloseAll');

Answer 1

[Deepak]

Hi @Migmar Tsering,

We can create a visual display with two 4x4 grids, one on each side of centre of the screen, representing the left and right visual fields, by using Psychtoolbox in MATLAB. We calculate the positions of these grids based on defined "cellsize" and "stimsize" parameters. Then, we randomly select 12 positions within each grid to draw circles using the "Screen('FillOval', ...)" function.

Below is the MATLAB code to achieve the same:

clc;
clear all;
close all;
rng('shuffle');
Screen('Preference', 'SkipSyncTests', 1);
[window, window_size] = Screen('OpenWindow', 0, [255 255 255], [], 32, 2);
x_middle = window_size(3) / 2;
y_middle = window_size(4) / 2;
cellsize = 160; % Size of each cell in the grid
stimsize = 52;  % Size of each stimulus (circle)
nrows = 4;
ncolumns = 4; % 4x4 grid per visual field
ncells = nrows * ncolumns;
num_circles_per_side = 12; % Total circles to draw on each side
% Building the grid for left and right visual fields
xOffset = -x_middle / 2; % Offset for left visual field
yOffset = 0;
% Preallocate coordinates
xCoord = zeros(1, ncells * 2);
yCoord = zeros(1, ncells * 2);
r = 1;
for side = [-1, 1] % -1 for left, 1 for right
    for i = 1:ncolumns
        for j = 1:nrows
            xCoord(r) = ((i - ncolumns / 2) * cellsize + x_middle + xOffset * side);
            yCoord(r) = ((j - nrows / 2) * cellsize + y_middle + yOffset);
            r = r + 1;
        end
    end
end
% Draw circles on each side
for side = 1:2 % 1 for left, 2 for right
    indices = (1:ncells) + (side - 1) * ncells;
    selected_indices = randperm(ncells, num_circles_per_side);
    
    for idx = selected_indices
        x = xCoord(indices(idx));
        y = yCoord(indices(idx));
        Screen('FillOval', window, [0 0 0], [x - stimsize / 2, y - stimsize / 2, x + stimsize / 2, y + stimsize / 2]);
    end
end
Screen('Flip', window);
WaitSecs(3);
Screen('CloseAll');

Please find attached the documentation of functions used for reference:

Screen: http://psychtoolbox.org/docs/Screen

randperm: www.mathworks.com/help/matlab/ref/randperm.html

zeros: www.mathworks.com/help/matlab/ref/zeros.html

I hope this helps in resolving the issue.