THE ROUGH GUIDE TO PSYCHOLOGYpicture we have today is more complete. An abundance of psychology
and cognitive neuroscience research over the last decade suggests that
the stereotypical teenager is coping not only with a hormonal surge, but
also with a still-maturing brain.
Much of the evidence has come from brain imaging. While teenagers
are beginning to look like adults on the outside, scans have shown that
the brain continues to change in profound ways right through adoles-
cence and into early adulthood. In particular, there’s a major pruning
back of excess grey matter during this time, combined with an increase
in the “myelination” of brain cells, providing the fatty insulation that
improves communication speed between neurons. Crucially, these
patterns of maturation aren’t uniform. Rather, regions involved in motor
control and perception mature first, while regions at the front and side
of the brain involved in weighing risks and rewards, self-control and
thinking about other people’s points of view tend to mature later on.
These brain differences between teenagers and adults have observ-
able behavioural consequences. In 2004, for instance, Beatriz Luna and
her colleagues in the Laboratory of Neurocognitive Development at the
University of Pittsburgh tested nearly 250 people aged between eight
and thirty years on a range of eye-movement tasks and found a series of
performance differences between teens and adults. The tasks involved
looking at an on-screen target as quickly as possible; ignoring the impulse
to look at a target, looking instead in the other direction; and remem-
bering target positions – these were tests of processing speed, inhibitory
control and working memory (see Chapter 4), respectively. The researchers
found that processing speed only reached mature adult performance at
age fifteen, inhibitory control at age fourteen, while working memory
didn’t reach adult performance until age nineteen.
These performance measures may seem rather removed from real life.
More recent research shows an important social skill – perspective-taking
ability – also continues to develop right into late adolescence. Iroise
Dumontheil at UCL and her colleagues tested children, adults, younger
and older teens on a tricky computerized task that required them to move
objects, such as balls and toys, housed on a set of shelves (see opposite).
Crucially, the instructions came from a “director” who was located on the
other side of the shelves and who could only see into those cubby holes
that had no back to them. This meant that when he issued an instruction,
such as “move the small rabbit up”, and there was more than one rabbit
on the shelves, the participants had to consider which cubby holes the
director could and couldn’t see, so as to disambiguate the command.