extract data from quiver plot

Hello,

I have a quiver plot called,

   hQ = quiver(x,y,U,V,.4,'k-');

The quiver plot is draw and how am i going to extract the velocity data from the figure at y = 0.5 ?

I tried using the get function,

a = get(hQ,'Vdata');

but this gives me all the Vdata. How can i improve the code to give me only the Vdata at y = 0.5 ?

Thank You