N_SAMPLES = 50;
DELTA = -3:1:3;
N_DELTA = length(DELTA);
SCREEN_SIZE = get(0,'ScreenSize');
WIN_SIZE = round(SCREEN_SIZE * 0.5);
LINE_LEN = WIN_SIZE(4)/10;
LINE_GAP = LINE_LEN/4;
LINE_Y = [WIN_SIZE(4)/2-LINE_LEN WIN_SIZE(4)/2-LINE_GAP;  WIN_SIZE(4)/2+LINE_GAP WIN_SIZE(4)/2+LINE_LEN];
LINE_WIDTH = 5;
FIG_N = 1;



figure(FIG_N);clf;
set(FIG_N,'Position',SCREEN_SIZE);


L = zeros(1,N_DELTA);
R = L;

for t=1:N_SAMPLES,
    figure(FIG_N); clf;
    pause(0.5);
    hold on;
    for i=1:2,
        if i==1, j=ceil(N_DELTA*rand(1,1)); delta = DELTA(j); d(t) = delta; else delta=0; end;
        plot(WIN_SIZE(3)/2+delta*[1 1], LINE_Y(i,:),'k','LineWidth',LINE_WIDTH);
    end;
    axis([WIN_SIZE(1) WIN_SIZE(1)+WIN_SIZE(3) WIN_SIZE(2) WIN_SIZE(2)+WIN_SIZE(4)]);
    axis off;
    drawnow;
    pause(0.5);
    ANS_GIVEN = 0;
    while(~ANS_GIVEN),
        percept = input('','s');
        if percept == 'l',
            L(j) = L(j)+1;
            ANS_GIVEN=1;
        elseif percept == 'r',
            R(j) = R(j)+1;
            ANS_GIVEN = 1;
        end;
    end;
        
end;

figure(2); clf
TOT = R+L;
plot(DELTA,R./TOT,'g','LineWidth',2); hold on;
plot(DELTA,L./TOT,'r','LineWidth',2); hold off;