Custom Sort for Lastname, Firstname

I am trying to implement a custom sort, and it is not working. I am a noob to datatables and have taken over a system where they were used extensively. I followed some tutorials and built a custom sort. Looking for a little help as to why the custom sort I put in is not being called.

The mDataProp patient_name comes through like this "Doe, John" some are blank "". I want to split the patient name on the , and then sort on the last name. Currently it sorts on the first name after the "," by default. So "Rose, Axl" orders before "Michaels, Brett"... when what I want is "Michaels, Brett" followed by "Rose, Axl".

one other problem I have is the bVisisble: false not working with the bSaveState: true... using Chrome v 33. But that's a discussion for another day unless someone has an answer right away.

var activityTable;
   	
        $(function() {
    	
    jQuery.fn.dataTableExt.oSort['full_name-asc']  = function(x,y) {
    	    var last_name_x = x.split(",")[0];
    	    var last_name_y = y.split(",")[0];
    	    
    	    return ((last_name_x < last_name_y) ? -1 : ((last_name_x > last_name_y) ?  1 : 0));
    	};
    	 
    	jQuery.fn.dataTableExt.oSort['full_name-desc'] = function(x,y) {
    	    var last_name_x = x.split(",")[0];
    	    var last_name_y = y.split(",")[0];
    	    
    	    return ((last_name_x < last_name_y) ?  1 : ((last_name_x > last_name_y) ? -1 : 0));
    	};

        activityTable = $('#activity_table').dataTable( {
            "bStateSave": false,
            "iCookieDuration": 86400,
            "sPaginationType": "full_numbers",
            "bServerSide": true,
            "sAjaxSource": "/activity/listajax/id/<?php echo isset ( $id ) ? "$id/" : "null/"; ?>patient_id/<?php echo isset ( $patient_id ) ? "$patient_id/" : "0/"; ?>client_id/<?php echo isset ( $client_id ) ? "$client_id/" : "0/"; ?><?php echo isset ( $popup ) && $popup ? "popup/1/" : "" ?>",
            "bJQueryUI": true,
            "bProcessing": true,
            "iDisplayLength": 50,
            "aaSorting": [[ 0, "desc" ]],
            "fnPreDrawCallback": function(){
                $(".dataTables_processing").html('<?php echo Controller::ajax_loading (); ?>');
            },
            "fnInitComplete": function(oSettings, json) {

            },
            "fnServerData": function ( sSource, aoData, fnCallback ) {
                $.getJSON( sSource, aoData, function (json) {
                    if (json.error != undefined) {
                        window.location = "/login/";
                    } else {
                        fnCallback(json);
                    }
                } );
            },
            "aoColumns": [
                {"mDataProp": "date"},
                {"mDataProp": "organization_name"},
                {"sType": "full_name", "mDataProp": "patient_name"},
                {"mDataProp": "lastname","bVisible" : false},
                {"mDataProp": "mr_number"},
                {"mDataProp": "contact_type"},
                {"mDataProp": "user_name"},
                {"mDataProp": "is_submitted"},
                {"mDataProp": "buttons", "bSortable" : false, "bSearchable": false}
            ]
        });
        activityTable.fnSetFilteringDelay(500);
        $("#extend_search").change(function(){
            if($(this).attr('checked')) {
                val = 1;
            } else {
                val = 0;
            }
            var today = new Date();
            var expire = new Date();
            expire.setTime(today.getTime()+720000);
            document.cookie = "search_activity="+val+";expires="+expire.toGMTString()+";path=/";
            activityTable.fnReloadAjax();
        });
    });