Richfaces combobox on selection changed event

Question

hello ! I have this code:

    <richfaces:comboBox value="#{ChoixContratBean.selectedFormule"} suggestionValues="#{ChoixContratBean.formules}">

<a4j:support event="onmouseover"action="#{ChoixContratBean.getDescriptionFormule}"
           reRender="reponse" />         </richfaces:comboBox>

I would like that when the user hovers with the mouse the different values in the combo, a new description of the product appears in :

<jsf:outputText id="reponse"  value="#{ChoixContratBean.descriptionFormuleSelected}" />

but no event is triggered when my mouse hovers the different values of the richfaces combo... instead, the event which is triggered is the simple mouseover on the combo itself. how to tell it it's the values in it to trigger the event from ??