Interface - Designing Games - page 231

HOMOGENOUS REDUNDANCY is repeating the same message multiple
times in the same way.
Sometimes we can do this sneakily so that players don't notice. For
example, we place the same audio log in five different places, but once the
player listens to one of them, we have the others silently disappear.
In other cases, we don't have a way of knowing whether the player ac-
tually got the message. For example, the player will hear a message played
over loudspeakers, but there's no guarantee that he listened to it. In these
cases, we might just have to repeat it. But simple repetition can be grating,
so it's often better to use diverse redundancy .
DIVERSE REDUNDANCY is communicating the same information multiple
times in different ways.
In a shooter, we might have the companion character yell at you to
jump out the window (dialogue), have the character visually wave toward
the window (animation), place a visually highlighted path of wooden
planks leading to the window (level visuals), and place an on-screen ob-
jective marker instructing the player to jump out the window (HUD).
Quadruple redundancy means that the message will probably get through,
even in a high-pressure situation.
Other times, it is appropriate to only show secondary and tertiary
messages when the primary message has failed. This is called passive
redundancy .
PASSIVE REDUNDANCY is the use of secondary messages only when the
primary message fails.
In the window-jumping example, if the companion character had a
second or third line of dialogue that they use only if the player doesn't
jump through the window fast enough, they would be using passive re-
dundancy. The danger with this is that it is often hard to tell if the player
missed the first message, or if he is deliberately ignoring it. If the player is
deliberately ignoring the first message, passive redundant messages can
be irritating.