Drupal #states or conditions

Form alter

$form['my_field']['#states'] = array(
  'visible' => array(
    array(
      array(':input[name="field_other[und]"]' => array('value' => 'first')),
      'or',
      array(':input[name="field_other[und]"]' => array('value' => 'second')),
    ),
  ),
);