Hannah - How do I add a background image to my GUI or figure window? provides a good answer on how to add a background image to your figure. In your case, I suspect that you could do something like
box = 20;
i = 10;
x_range = pw_responses(i).x_range; %x range for which to plot background image
y_range = pw_responses(i).y_range; %y range for which to plot background image
im = pref_mat(y_range,x_range); %this plotted image is in the background_im.png file
hFig = figure(i);
hAxes = axes('Parent', hFig, 'units', 'normalized', 'position',[0 0 1 1]);
imagesc(im);
colormap(hsv);
set(hAxes, 'HandleVisibility', 'off', 'Visible','off');
for j = 1:441 %the following subplots are in the subplots.png file
y_vals = surr_cell_resp(j,:); %response curve
hSubPlot = subplot(box+1,box+1,j);
plot(x_vals,y_vals,'k')
set(hSubPlot, 'HandleVisibility', 'off', 'Visible','off', 'Color', 'none');
end
