A tangent map can be used on hair to change the angle of the diffuse and or the specular reflection on the surface of the normal. Basically allowing you to use a reflection or specular light as a reflection that doesn't actually line up with the normal of the surface. 

Normals maps are computed all at once in world space. Tangent maps are computed based on the normals direction of each polygon, in tangent space. 

If your hair doesn't look like it has lots of triangles in it, you probably don't need it in Poser.

It it looks like this  you need to use the tangent map.

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