Referencing the text input from within jQuery autocomplete

Given the following code, how can I reference the input that has autocomplete bound to it from within the success() function in the $.ajax call? Neither $(this) or $e work.

$('.parent-input').autocomplete({
  source: function(request, response) {
    $.ajax({
      url: "/chunky/bacon",
      dataType: 'json',
      data: {
        product_id: $('#product-id').val(),
        term: request.term
      },
      success: function(data){
        var resultCount = data.length;
        // I NEED TO REFERENCE .parent-input HERE
        response( data );
      }
    });
  },
  minLength: 2,
  select: function(event, ui){
    addAssociatedProduct(ui.item.id, ui.item.value);
    $(this).val('');
    return false;
  }
});