How many objects are out there? In the same spirit of enthusi-
asm for infants' capacities, why not claim that they do arith-
metic? As it happens, they do. Or rather, some mechanisms in
their brains, as in ours, keep track of how many objects are
around. These mechanisms react to "impossible" changes—for
example, when two objects turn into one—and produce a reac-
tion of surprise. Show a six-month-old infant an object, put an
opaque screen in front of it. Then show them another object
and place it behind the screen. You then lift the screen and...
only one object is left. (Cognitive psychologists often use cheap
magic tricks like this in their experiments.) Infants find this [111]
extremely surprising, much more so than if the objects had
changed color or shape while they were hidden behind the
screen. So some part of their brains is keeping track of how
many objects were masked. Note that in an experiment like this
they have not yet seen the two objects together. So what sur-
prises them is not that something in the world has changed. It
is that something has changed in a way that is not expected.^16How do we know all this? Obviously, you do not ask a five-month-old
infant whether she finds it strange that 1 + 1 = 1. Experiments with
such young subjects rely on ingenious techniques that measure how
surprised and how attentive infants are, by tracking their gaze or
monitoring the intensity with which they suck a pacifier. When
infants watch repeated displays that conform to their expectations,
they quickly lose concentration and start looking around. If you
change what you show them in particular ways, you can get them to
focus again, which tells you that they noticed the change. Naturally,
you do not want to measure their reaction to a mere change, so you
change the stimuli in different ways and observe whether these differ-
ent changes produce the same effect or not. This gives you some indi-
cation about which changes are more attention-grabbing than others.
To sum up, then, a young mind is by no means a simple mind. Many
of the specialized capacities we find in adults are already present in
infants, in the form of particular expectations (e.g., that objects are
continuous), preferences (e.g., for differences between human faces as
opposed to those between giraffe faces) and ways of inferring (e.g., if
this thing moves of its own accord, try and identify its goal; if it moves
because someone pushed it, don't bother). These early capacities allow
the application of specific inference systems to specific domains of real-
THE KIND OF MIND ITTAKES