Ajax.PeriodicalUpdater is not updating according to frequency

new Ajax.PeriodicalUpdater('message_field', "http://localhost:8888/lsl_application/php/update_message_field.php?"+param, { method: "GET", frequency: 2, decay: 1, onSuccess: onSuccess_forPeriodic, onFailure: function(xhrResponse){ alert("Failed to update!"+xhrResponse.statusText); } });