<s>
In	O
human-computer	O
interaction	O
,	O
low-key	B-General_Concept
feedback	I-General_Concept
is	O
a	O
type	O
of	O
output	B-General_Concept
that	O
takes	O
a	O
background	O
role	O
by	O
being	O
very	O
subtle	O
,	O
sometimes	O
nearly	O
imperceptible	O
.	O
</s>
<s>
Physical	O
machines	O
often	O
provide	O
rich	O
low-key	B-General_Concept
feedback	I-General_Concept
as	O
a	O
byproduct	O
of	O
their	O
design	O
.	O
</s>
<s>
In	O
computer	B-Application
software	I-Application
,	O
the	O
low-key	B-General_Concept
feedback	I-General_Concept
usually	O
needs	O
to	O
be	O
designed	O
in	O
.	O
</s>
<s>
The	O
benefit	O
of	O
low-key	B-General_Concept
feedback	I-General_Concept
is	O
that	O
it	O
can	O
provide	O
always	O
available	O
indication	O
without	O
cluttering	O
the	O
user	B-Application
interface	I-Application
with	O
explicit	O
indicators	O
such	O
as	O
text	O
labels	O
or	O
indicator	O
lights	O
.	O
</s>
<s>
The	O
downside	O
of	O
low-key	B-General_Concept
feedback	I-General_Concept
is	O
that	O
it	O
can	O
be	O
too	O
subtle	O
to	O
some	O
users	O
and	O
it	O
often	O
cannot	O
be	O
self-describing	O
to	O
beginners	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
dashboard	B-Protocol
lights	O
,	O
the	O
driver	O
also	O
perceives	O
the	O
sound	O
and	O
vibration	B-Algorithm
of	O
the	O
engine	O
.	O
</s>
<s>
An	O
abnormal	O
sound	O
or	O
vibration	B-Algorithm
alerts	O
the	O
driver	O
that	O
there	O
may	O
be	O
a	O
problem	O
,	O
while	O
a	O
typical	O
sound	O
or	O
vibration	B-Algorithm
assures	O
the	O
driver	O
that	O
everything	O
is	O
going	O
as	O
normal	O
.	O
</s>
<s>
Similarly	O
,	O
a	O
computer	B-Application
program	I-Application
that	O
has	O
two	O
modes	O
of	O
operation	O
might	O
employ	O
low-key	B-General_Concept
feedback	I-General_Concept
to	O
keep	O
the	O
user	O
informed	O
about	O
the	O
current	O
mode	O
.	O
</s>
<s>
A	O
web	B-Application
browser	I-Application
application	O
could	O
keep	O
track	O
of	O
the	O
pages	O
the	O
user	O
has	O
visited	O
and	O
alter	O
the	O
colors	O
of	O
links	O
that	O
point	O
to	O
pages	O
the	O
user	O
has	O
already	O
viewed	O
.	O
</s>
