Maybe something like this would work:
% Clear the workspace and the screen
sca;
close all;
clear;
% Here we call some default settings for setting up Psychtoolbox
PsychDefaultSetup(2);
% Get the screen numbers
screens = Screen('Screens');
% Draw to the external screen if avaliable
screenNumber = max(screens);
% Define black and white
white = WhiteIndex(screenNumber);
black = BlackIndex(screenNumber);
% Open an on screen window
[window, windowRect] = PsychImaging('OpenWindow', screenNumber, black);
% Get the size of the on screen window
[screenXpixels, screenYpixels] = Screen('WindowSize', window);
% Query the frame duration
ifi = Screen('GetFlipInterval', window);
% Set up alpha-blending for smooth (anti-aliased) lines
Screen('BlendFunction', window, 'GL_SRC_ALPHA', 'GL_ONE_MINUS_SRC_ALPHA');
% Setup the text type for the window
Screen('TextFont', window, 'Ariel');
Screen('TextSize', window, 36);
% Get the centre coordinate of the window
[xCenter, yCenter] = RectCenter(windowRect);
% Here we load in an image from file. This one is a image of rabbits that
% is included with PTB
theImageLocation = [PsychtoolboxRoot 'PsychDemos' filesep...
'AlphaImageDemo' filesep 'IIT.jpg'];
theImage = imread(theImageLocation);
% Get the size of the image
ankit = size(theImage);
% Make the image into a texture
imageTexture = Screen('MakeTexture', window, theImage);
% Here we set the size of the arms of our fixation cross
fixCrossDimPix = 20;
% Now we set the coordinates (these are all relative to zero we will let
% the drawing routine center the cross in the center of our monitor for us)
xCoords = [-fixCrossDimPix fixCrossDimPix 0 0];
yCoords = [0 0 -fixCrossDimPix fixCrossDimPix];
allCoords = [xCoords; yCoords];
% Set the line width for our fixation cross
lineWidthPix = 4;
for i = 1:10
% Draw the image to the screen, unless otherwise specified PTB will draw
% the texture full size in the center of the screen. We first draw the
% image in its correct orientation.
Screen('DrawTexture', window, imageTexture, [], [], 0);
% Flip to the screen
Screen('Flip', window);
% % Wait for two seconds
WaitSecs(0.5); % 500 ms, as stated
% KbStrokeWait;
% Draw the fixation cross in white, set it to the center of our screen and
% set good quality antialiasing
Screen('DrawLines', window, allCoords,...
lineWidthPix, white, [xCenter yCenter], 2);
% Flip to the screen
Screen('Flip', window);
% Wait for a key press
WaitSecs (0.5); % 500 ms, as stated
% KbStrokeWait;
% Clear the screen
sca;
end
