change comment labels

The following code works to change the reply title and submit button, but i cant seem to change the label for Name and Email…any ideas what i should specify here?

$comments_args = array(
        // change the title of send button
        'label_submit'=>'Post comment',
        'email' => '<p class="comment-form-email"><label for="email">' . _x( 'E-mail:', 'domainreference' ) . '</label> ' .( $req ? '<span class="required">*</span>' : '' ) .
    '<input id="email" name="email" type="text" value="' . esc_attr(  $commenter['comment_author_email'] ) .
    '" size="30"' . $aria_req . ' /></p>',
        // change the title of the reply section
        'title_reply'=>'Leave a reply',
          // redefine your own textarea (the comment body)
        'comment_field' => '<p class="comment-form-comment"><label for="comment">' . _x( 'Comment: *', 'noun' ) . '</label><br /><textarea style="height:100px;" id="comment" name="comment" aria-required="true"></textarea></p>',
);

comment_form($comments_args);