Comment form?

Hi,

I am wanting to add a few extra fields to my comments form. I have a found a few blog posts about using the comment_form_default_fields and I have added the following code to my functions.php

<?php 

add_filter('comment_form_default_fields','my_fields');
function my_fields($fields) {

    // New fields
    $fields['title'] = '<label>Title:</label><input type="text" name="title" value="'.(!empty($_POST['title']) ? $_POST['title'] : '').'" />';
    $fields['tracks'] = '<label>Tracks:</label><input type="text" name="tracks" value="'.(!empty($_POST['tracks']) ? $_POST['tracks'] : '').'" />';
    $fields['format'] = '<label>Format:</label><input type="text" name="format" value="'.(!empty($_POST['format']) ? $_POST['format'] : '').'" />';

    return $fields;
}
?>

Do I now need to do something else? The fields show up on the comments form on the website but when you post a comment the new fields dont get posted or come through to the back end for approval. Any help would be grealty appreciated.

Thanks