AJAX :: Recover Parameter In Callback Function

I'm using ajax to call a webmethod from javascript. The call is successfully made to the webmethod but I'm not able to access the parameters I passed to the webmethod inside of the "OnSucceeded" callback method. I need access to those params because I need to perform more tasks on the client side when the webmethod returns. I'm assuming that the params are returned inside "usercontext", but the value of that param is "null" How can I have access to those params?

Here my sample code:

function OnSucceeded(result, usercontext , methodName)
{
alert( result + ' The value of usercontext is: ' + usercontext);
}
function OnFailed(error, userContext, methodName)
{
alert('Attempt to delete semantic attribute from page failed!');
}
function deleteSemanticAttribute()
{
var username = 'xxxxxx';
var password = 'yyyyyy'
PageMethods.GetMyData(username, password, OnSucceeded,OnFailed);
}
[WebMethod]
public static string GetMyData(string username, string password)
{
return "This is my test application!";
}