The present commentary considers the question of what must be learned
in different types of motor skills, thereby limiting the question of w
hat should be adjusted in the APG model in order to explain successful
learning. It is concluded that an open loop model like the APG might
well be able to describe the learning pattern of motor skills in a sta
ble, predictable environment. Recent research on saccadic plasticity,
however, illustrates that motor skills performed in an unpredictable e
nvironment depend heavily on sensory (mostly visual) feedback.