Callback for changed ActiveRecord attributes?

I am aware of ActiveRecord::Dirty and the related methods, but I don't see a means by which I can subscribe to an attribute changed event. Something like:

class Person < ActiveRecord::Base
  def attribute_changed(attribute_name, old_value, new_value)
  end

  #or

  attribute_changed do |attribute_name, old_value, new_value|
  end
end

Is there a Rails standard or plugin for this? I feel that it must be there somewhere and I'm just missing it.