diff --git a/index.html b/index.html
index 56c8f346..ecadba25 100644
--- a/index.html
+++ b/index.html
@@ -49,6 +49,8 @@
 		<script src="sketches/color_gradient.js"></script>
 		<script src="sketches/whites.js"></script>
 		<script src="sketches/watercolor.js"></script>
+		<script src="sketches/reverse_spoke.js"></script>
+		<script src="sketches/checker.js"></script>
 		<script src="sketches/poggendorff.js"></script>
 		<script src="lib/js/head.min.js"></script>
 		<script src="js/reveal.js"></script>
diff --git a/npm-debug.log.3884792172 b/npm-debug.log.3884792172
new file mode 100644
index 00000000..e69de29b
diff --git a/sketches/checker.js b/sketches/checker.js
new file mode 100644
index 00000000..22cdde90
--- /dev/null
+++ b/sketches/checker.js
@@ -0,0 +1,119 @@
+//Author: Alvaro Rodriguez
+//March 7th 2017
+
+//Implementado desde 0
+var c = 0;
+
+var sketch8 = function( p ){
+	var n = 10;
+	p.setup = function(){
+		var myCanvas = p.createCanvas(400, 400);
+		p.background(192,255,255);
+	};
+
+	p.draw = function(){
+	
+	//Draw matriz (green squares)
+	p.background(192,255,255);
+  	var n = 10;
+  	for(var j = 0;  j < 10; j++){
+    	for(var i = 0; i < 10; i++){
+      	p.fill(0,255,0);
+      	p.noStroke();
+    	if(j %2 == 0 && i % 2 == 0)
+    		p.rect(i*40,j*40,40,40);
+    	else if(j % 2 != 0 && i %2 !=0)
+      		p.rect(i*40,j*40,40,40);
+    	}
+    }
+	 
+	if(!p.mouseIsPressed){
+		var k;
+		var c = 1;
+
+		for(var i = n-1; i >=1; i--){
+		    k = i;
+		    for(var j = 1; j <= n-i; j++){
+		      if(i == 9 || i == 8 || i == 6 || i == 3 || i == 1){
+		        p.fill(255,255,255);
+		          p.noStroke();
+
+			      p.triangle((k*40),(j*40)-9,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5,(j*40)-4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)+4.5,(j*40)-4.5);
+		          
+		          p.triangle((k*40),(j*40)+9,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)+4.5,(k*40)+4.5,(j*40)+4.5);
+		          
+		          p.fill(0);
+		          p.triangle((k*40)-9,(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5);
+		          
+		          p.triangle((k*40)+9,(j*40),(k*40)+4.5,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)+4.5,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5);
+		      }
+		      else{
+		         p.fill(0);
+		          p.noStroke();
+		          p.triangle((k*40),(j*40)-9,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5,(j*40)-4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)+4.5,(j*40)-4.5);
+		          
+		          p.triangle((k*40),(j*40)+9,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)+4.5,(k*40)+4.5,(j*40)+4.5);
+		          
+		          p.fill(255,255,255);
+		          p.triangle((k*40)-9,(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)-4.5,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5);
+		          
+		          p.triangle((k*40)+9,(j*40),(k*40)+4.5,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5);
+		          p.triangle((k*40),(j*40),(k*40)+4.5,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5); 
+		      }
+		      k++;
+		      c++;
+		    }
+	    }
+
+	    for(var i = 2; i <= n-1; i++){
+			k = i;
+		    for(var j = 1; j <= n-i; j++){
+		     if(i == 2 || i == 4 || i == 7 || i == 9){
+		       p.fill(255,255,255);
+		          p.noStroke();
+		          p.triangle((j*40),(k*40)-9,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5,(k*40)-4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)+4.5,(k*40)-4.5);
+		          
+		          p.triangle((j*40),(k*40)+9,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)+4.5,(j*40)+4.5,(k*40)+4.5);
+		          
+		          p.fill(0);
+		          p.triangle((j*40)-9,(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5);
+		          
+		          p.triangle((j*40)+9,(k*40),(j*40)+4.5,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)+4.5,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5);
+		     }else{
+		       p.fill(0);
+		          p.noStroke();
+		          p.triangle((j*40),(k*40)-9,(j*40)-4.5,(k*40)-4.5,(j*40)+4.5,(k*40)-4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)+4.5,(k*40)-4.5);
+		          
+		          p.triangle((j*40),(k*40)+9,(j*40)-4.5,(k*40)+4.5,(j*40)+4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)+4.5,(j*40)+4.5,(k*40)+4.5);
+		          
+		          p.fill(255,255,255);
+		          p.triangle((j*40)-9,(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)-4.5,(k*40)-4.5,(j*40)-4.5,(k*40)+4.5);
+		          
+		          p.triangle((j*40)+9,(k*40),(j*40)+4.5,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5);
+		          p.triangle((j*40),(k*40),(j*40)+4.5,(k*40)-4.5,(j*40)+4.5,(k*40)+4.5);
+		     }           
+		      k++;
+		    }
+		  }
+	} 
+
+	  	
+	};
+
+}
+
+var myp5_8 = new p5(sketch8, 'checker_id');
\ No newline at end of file
diff --git a/sketches/reverse_spoke.js b/sketches/reverse_spoke.js
new file mode 100644
index 00000000..a03af1ac
--- /dev/null
+++ b/sketches/reverse_spoke.js
@@ -0,0 +1,58 @@
+//Author: Alvaro Rodriguez
+//March 4th 2017
+
+//Implementado desde 0
+var c = 0;
+var sketch6 = function( p ){
+	p.setup = function(){
+		var myCanvas = p.createCanvas(700, 400);
+		p.background(191,191,191);
+		p.frameRate(50);
+	};
+
+	p.draw = function(){
+	
+		p.stroke(0);
+
+		
+
+	 	p.ellipse(350,200, 350,350);
+	 	p.fill(0);
+		p.ellipse(350,200, 10,10);
+	  
+
+	  	var q = c;
+
+  		for(var i = 0; i <= 2*p.PI; i += p.QUARTER_PI/2){
+	        p.fill(q);
+	        p.stroke(127,127,127);
+	        p.strokeWeight(3);
+	        p.arc(350,200, 350, 350, i, i+p.QUARTER_PI/2, p.PIE);
+	        q+=15;
+	    //}
+	        q = q%255;
+  		}
+		 
+	  if(!p.mouseIsPressed){
+
+	  	p.ellipse(350,200, 350,350);
+	 	p.fill(0);
+		p.ellipse(350,200, 10,10);
+		p.noFill();
+
+		for(var i = 0; i <= 2*p.PI; i += p.QUARTER_PI/2){
+	        p.fill(c);
+	        p.stroke(127,127,127);
+	        p.strokeWeight(3);
+	        p.arc(350,200, 350, 350, i, i+p.QUARTER_PI/2, p.PIE);
+	        c+=15;
+	    //}
+	        c = c%255;
+  		}
+
+	  }
+	};
+
+}
+
+var myp5_6 = new p5(sketch6, 'reverse_spoke_illusion_id');
\ No newline at end of file
diff --git a/source.md b/source.md
index f5732d45..5b69d58c 100644
--- a/source.md
+++ b/source.md
@@ -645,6 +645,13 @@ V:
 
 ## Optical Illusions (others)
 
+<div id='reverse_spoke_illusion_id'></div>
+<a target="_blank" href="http://www.michaelbach.de/ot/mot-spokes/index.html">Reverse Spoke Illusion</a>
+
+V:
+
+## Optical Illusions (others)
+
 <figure>
     <img height='400' src='fig/Motion_illusion_in_star_arrangement.png'/>
     <figcaption>Movement illusions</figcaption>
@@ -664,8 +671,8 @@ V:
 ## Optical Illusions (others)
 
 <figure>
-    <img height='400' src='fig/checker.gif'/>
-    <figcaption>Checker</figcaption>
+    <div id='checker_id'></div>
+    <a target="_blank" href="http://www.anopticalillusion.com/2012/11/checkerboard-twisted-cord-illusion/">Checker</a>
 </figure>
 
 V: