Contents

display an image in cogent with dimensions in visual angle

Elliot Freeman 02/07

scrDimH = 100;              %% horizontal screen dimension (mm)
scrDimV = 75;              %% vertical screen dimension (mm)
viewDist = 570;                 %% viewing distance (mm)
window = 0;
bg = [.5, .5, .5];
stimRGB = [1 0 0];

calculate screen dimensions in degrees

scrDegH = visang(viewDist, [], scrDimH); % horizontal screen dimension in degrees
scrDegV = visang(viewDist, [], scrDimV); % vertical screen dimension in degrees

Error using ==> evalin
Undefined command/function 'visang'.

make stimulus array

imSize = 50;                           % image size: n X n
lamda = 5;                             % wavelength (number of pixels per cycle)
theta = 0;                             % grating orientation
sigma = 5;                             % gaussian standard deviation in pixels
phase = 0.25;                            % phase (0 -> 1)
trim = .005;                           % trim off edges of gaussian with values < trim

start up cogent

config_display(window);
config_keyboard;
start_cogent

set screen coordinates to visual angle

this command rescales the display coordinates left to right edges now go from -scrDegH/2 to scrDegH/2 lower and upper edges now go from -scrDegV/2 to scrDegV/2 Zero is always at the centre.

cgscale(scrDegH);

make grid of points

make coordinates for a regular grid

nItemsPerRow = 5;                                   % how many elements per row
pos = linspace(-scrDegV, scrDegV, nItemsPerRow) /2;  % 2dimensional grid of position
pos = pos * .8;                                     % scale a bit to stop falling off edge of screen
[gridX gridY] = meshgrid(pos);                      % make grid
npos = length(pos) .^2;                             % total number of elements
cgellipse(gridX, gridY, ones(npos,1), ones(npos,1), 'f'); % put up ellipses
cgflip(bg(1), bg(2), bg(3));                        % show it
waitkeydown(inf)

make a radial pattern of gabors

[theta radius] = cart2pol(gridX, gridY);            % find orientation and radius from centre for each position
theta = ((-theta / (pi*2)) * 360);                  % convert from radians to degrees of orientation
theta = theta + 90;                                 % add 90: radial pattern; add 0: circular pattern

load image into sprite

for i = 1:npos
    % make gabors varying in orientation
    im = gaborFn(imSize, lamda, sigma, theta(i), phase);  % gabor function
    im = (im + 1) / 2;            % convert values -1:1 to 0:1

    % transpose and split into 3 colour channels
    im = im';
    imRGB = [im(:) im(:) im(:)];     % reassemble into 3-column array
    cgloadarray(i, imSize, imSize, imRGB);
end

put stimulus up on display in different locations

if cgdrawsprite has no width/height arguments (or they are 0,0) the image is displayed unscaled i.e. all pixels are normal size

for i = 1: npos

    cgdrawsprite(i, gridX(i), gridY(i));            % put stimulus in successive grid positions
end
cgflip(bg(1), bg(2), bg(3));        % show it
waitkeydown(inf)

same display with eccentricity scaling

if cgdrawsprite has width/height arguments, the image dimensions are in visual angle

for i = 1:npos
    % put stimulus in successive grid positions with different sizes
    cgdrawsprite(i, gridX(i), gridY(i), radius(i)/2, radius(i)/2);
end
cgflip(bg(1), bg(2), bg(3));        % show it

all done

waitkeydown(inf)
cgshut;

Published with MATLAB® 7.1