Vaesen re: Kelp and Greco

Here in Erkenntnis.

Hass on the Muller-Lyer II

Further, the fact that I have to construct my fully determinate figure, implies the correctness of Merleau-Ponty's different, better interpretation of the Muller-Lyer illusion: that perceptual indeterminacy is ontologically basic, that things such as ambiguity, illusions, and mirages, are fundamental aspects of the perceptual synergy out ofwhich our so-called "objective" constructions are built."
Lawrence Hass. Merleau-Ponty's Philosophy (p. 38-9). Kindle Edition. 

So, here are three claims Hass makes above:
1) I have to construct the fully determinate figure.
2) Perceptual indeterminacy is ontologically basic.
3) Things such as ambiguity, illusions, and mirages are fundamental aspects of the perceptual synergy out of which our so-called "objective" constructions are built.

I  don't see how 1) implies 2) or 3).  Of course, there is the obvious missing premise one could supply, "If I have to construct the fully determinate figure, then perceptual indeterminacy is ontologically basic."  But, I don't see why this conditional is plausible.

I'm not even sure I understand 3).  It's at least plausible to me that ambiguity, illusions and mirages are fundamental aspects of the perceptual synergy.  But, I'm not quite getting the part about our so-called "objective" constructions being built out of what?  Ambiguities, illusions, mirages?  The perceptual synergy?

Loughlin reviews Rowlands' New Science of the Mind

Here in Phenomenology and the Cognitive Sciences.