Holonomy algebras of pseudo-hyper-Kählerian manifolds of index 4

The holonomy algebra of a pseudo-hyper-Kählerian manifold of signature (4,4n+4) is a subalgebra of sp(1,n+1). Possible holonomy algebras of these manifolds are classified. Using this, a new proof of the classification of simply connected pseudo-hyper-Kählerian symmetric spaces of index 4 is obtained.