Object Literal

Below I declared a basic object literal with 2 methods. The
"doSomething" method is call from the "useDoSomething" method but the
call is only sucessful if I use the "this" keyword or qualify the call
with "SomeObj".

Can someone describe why this is happening?

var SomeObj = {
doSomething : function()
{
return 'Did something'
},

useDoSomething : function()
{
//Doesn't work - doSomething() no defined.
return doSomething();
//Works
//return this.doSomething();
//Works
//return SomeObj.doSomething();
}
}

alert(SomeObj.doSomething());
alert(SomeObj.useDoSomething());