Tilt Illusion

 

 

 

What to see

 

Two striped disks ro­tate slowly over a bi­par­tite blue back­ground grat­ing. This is just the eye catcher…

 

What to do

 

Grab the hor­i­zon­tal slider and move it such that the grat­ings on the two disks are aligned (collinear). Then do one of two things:
• click the ± but­ton. That in­verts the back­ground grat­ing di­rec­tion, now they are no longer aligned
  or
• click the “hide” but­ton. When the back­ground grat­ing dis­ap­pears, again the disks are no longer aligned, and you can read the mis­align­ment angle in the box at the left.

 

The demon­stra­tion is set up to allow quan­ti­ta­tive mea­sure­ments on the strength of the il­lu­sion de­pend­ing on the angle dis­par­ity of the back­ground grat­ings.

 

Comments

 

This is now gen­er­ally known as the “tilt il­lu­sion” and was first de­scribed by Gib­son (1937). Blake­more and col­leagues de­vel­oped an ex­plana­tory hy­poth­e­sis that the tilt il­lu­sion is caused by lat­eral in­hi­bi­tion be­tween cor­ti­cal ori­en­ta­tion de­tec­tors. A more re­cent sug­ges­tion by Schwartz traces the ef­fect to op­ti­mized pro­cess­ing of nat­ural image sta­tis­tics (which doesn't con­tra­dict the in­hi­bi­tion ex­pla­na­tion, but puts it into a Bayesian con­text). Rather than fur­ther para­phrase, I point to the ex­cel­lent Wikipedia entry on this sub­ject.

 

Sources

 

Blake­more C, Car­pen­ter RHS, George­son MA (1970) Lat­eral in­hi­bi­tion be­tween ori­en­ta­tion de­tec­tors in the human vi­sual sys­tem. Na­ture 228:37–39

Gib­son JJ (1937) Adap­ta­tion, af­ter-ef­fect, and con­trast in the per­cep­tion of tilted lines. II. Si­mul­ta­ne­ous con­trast and the areal re­stric­tion of the af­ter-ef­fect. J Exp Psy­chol:553–569

Wikipedia: Vi­sual tilt ef­fects

 

 

Created: 2012-05-07

Last update: 2013-10-04