<p:selectOneButton onchange="getSelectedPeriod(this.value)" value="#{topRatingAuthorBackingBean.period}"
						styleClass="side-tab-buttons-group">
						<p:ajax update="sideTabBlockBody, sideTabBlockBodyEmpty" />
						<f:selectItems id="selectedPeriodItem" var="period"
							value="#{topRatingAuthorBackingBean.activePeriods}"
							itemLabel="#{period.name}" itemValue="#{period.name}"/>
					</p:selectOneButton>

<script type="text/javascript">
    					function getSelectedPeriod(selection) {
        					alert(selection);        					
  					 }
					</script>