Visual effects with observe_field

<%= observe_field ‘search_form’,
:frequency => 0.5,
:update => ‘results’,
:url => { :controller => ‘users’, :action => ‘get_results’ },
:loading => “Element.show(‘indicator_gif_id’)”,
:complete => “Element.hide(‘indicator_gif_id’)”,
:with => “‘search_text=’ + value” %>

How do I add effects in this?]

Thanks