A sigmoid curve

As shown in Figure 3

several sigmoid curves can be combined

to form a learning curve

A learning curve is a graphical representation

of the effect of learning

for a given period

It consists of a slow beginning, then an upward acceleration

continuing into a plateau

Generally

we think of the learning curve

as a simple upward curve

but it is actually more like peaks and valleys

Many of us hold the mistaken view

that learning consists of

a steady upward progression only

However

deep learning often takes place

in the valley called a "slump"

For example

learning too many English words

may result in chaos or temporary turbulence

but the ability to remember more words

will improve through this process

The deeper the valley is, the more we can learn

Thus

a sigmoid curve is not only a mathematical symbol