Afficher texte si case 1 coché

<script type="text/javascript">
function verifie_form(arg)      
{
if(arg==1)           
{                
document.getElementById('radio1').style.visibility='visible';           
}           else           {
document.getElementById('radio1').style.visibility='hidden';           
}      
} 
</script>

<form action="page.php" method="post">
      <p><label><input type="radio" name="b" value="1" onclick="verifie_form(1)" />Radio 1</label></p>      
	  <p><label><input type="radio" name="b" value="2" onclick="verifie_form(2)"  checked="checked"/>Radio 2</label></p>      
	  <p><label><input type="radio" name="b" value="3" onclick="verifie_form(3)" />Radio 3</label></p>      
	  <p><label><input type="radio" name="b" value="4" onclick="verifie_form(4)" />Radio 4</label></p>      
	  <p><label><input type="radio" name="b" value="5" onclick="verifie_form(5)" />Radio 5</label></p>      
	  <p id="radio1">Texte 1 qui apparaît</p> 
</form>