Thirty people in the room,
and the migration plan
in twelve slides.
You had worked hard on them.
Every point was there,
written out in full,
so nobody could miss it.
Then you talked through them,
line by line,
so nobody could miss it twice.
Afterwards
the questions came in.
Every one of them
was answered on a slide.
Nobody had been rude.
They had been looking.
They just had not taken it in.
Here is what the room was doing.
People read faster
than you speak.
So they read the slide
while you were still on line two,
finished,
and then waited for you to catch up,
listening to words
they had already read.
Or they tried to do both.
Read one sentence
while hearing another,
in the same language,
with the same meaning,
at a different speed.
That is harder
than either alone.
People who study learning
have tested this.
Richard Mayer and his colleagues
compared a group
who saw a diagram with spoken explanation
against a group who got the same,
plus the words printed on the screen.
The group with the printed words
did worse
when asked to use what they had learned.
It is called
the redundancy effect.
The usual explanation
is that the eyes are already busy.
They have the diagram to look at.
Now they have text as well,
and they keep jumping between the two,
while the ears
carry the same words a third time.
It is not a law
for every case.
If there is no picture,
if the audience is working
in its second language,
or the room is noisy,
words on the screen
can help.
But a plan with a diagram in it,
read aloud to people
who could read it themselves,
costs attention
and returns none.
So split the jobs.
The slide carries the picture.
The shape of the migration,
the boxes that move,
a few words to label them.
Your voice
carries the sentences.
What happens first,
what could go wrong,
what you need from them.
And the full text,
every detail,
goes in a document
sent before or after,
where people can read it
at their own speed
without you talking over it.
If you catch yourself
reading a bullet aloud,
stop,
and say why it matters instead.
They can already read.
What they cannot do
is read your mind.
– Serguey Asael Shinder
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