In this case the horopter becomes a single-loop spiral passing through the fixation point and converging toward the vertical horopter at the top and bottom extremities and passing through the nodal point of the two eyes.
32.
The disparity of an object with different depth than the fixation point can alternatively be produced by presenting an image of the object to one eye and a laterally shifted version of the same image to the other eye.
33.
Certain persons with diplopia who cannot achieve fusion and yet do not suppress may display a certain type of spasm-like irregular movement of the eyes in the vicinity of the fixation point ( see : Horror fusionis ).
34.
Moreover, if one changes the fixation point along a given Vieth-M�ller circle such that the vergence value remains constant, one obtains an infinite family of such horopters, so long as the nodal point is not at the eye s rotation center.
35.
The geometric locus of horopteric points in this plane takes the form of the arc of a circle ( the "'Vieth-M�ller circle "') going from one nodal point to the other in space, passing through the fixation point.
36.
The second component is a line ( the "'Pr�vost Burckhardt line "') which is perpendicular to this arc, cutting it at the point midway between the two eyes ( which may, or may not, be the fixation point ).
37.
A major part of this research has involved the development and refinement of various implicit measures of attitude including the Implicit Association Test ( IAT ) to measure unconscious attitudes to things like carbon footprint, and eye tracking techniques to measure individual fixation points 25 times per second when consumers look at products, in order to measure core values.
