Sorry about that. Please give this replacement a try:
function SSI_CustomGraphicalCheckbox(GraphicalCheckboxObj, InputObj, blnCheck)
{
if (blnCheck && /^Q16_a_/.test(InputObj.name))
{
document.getElementById('Q16_b_1').checked = false;
document.getElementById('Q16_b_1_graphical').className = 'graphical_select radiobox';
}
}