Tutorial for Constructing Simulations in PDP - Computational Explorations in Cognitive Neuroscience - page 436

back in, as we have done with all of the projects for the
explorations in the topic. The following sections will
provide more useful applications of the script technol-
ogy.

Notice that this object is called Epoch_1 — all ob-
jects are created with sequentially increasing numbers
as a function of the number of other objects of that type
that have been created.

As before, do Structure/Move To Sub Gp for
this set of testing processes, calling the group Test ,
and then replace the _1 suffix with _Tst by doing
Structure/Change Name Suffix , Tst .
There are two parameters that are typically changed
on the epoch process to make it more appropriate for
testing rather than training.

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B.4 Creating a Testing Process

The set of processes that we created above is configured
for training the network. Although it is possible to mod-
ify these processes to make them suitable for testing the
network after it has been trained, it is usually a much
better idea just to create a new set of processes for each
different task you want to perform on the network (i.e.,
one for training, another for testing). We will go one
step further here and link in the testing process to the
training process, so that testing is performed automati-
cally during the course of training. This technique was
used in a number of the exercises.
To keep the different sets (hierarchies) of processes
organized, we will put each set into a different group .
Since this is commonly done, it has been automated.

The first is the order field, which should be
changed from PERMUTED to SEQUENTIAL .
The order of event presentation is usually permuted
(random, without replacement) so that there aren't any
unusual learning effects that arise from the events being
presented in the same order every time. During testing,
it is more useful to have the events in a predictable, se-
quential order.

The other parameter is the wt_update field, which
should be set to TEST instead of ON_LINE so that no
weight changes (learning) takes place during testing. Ok
this edit dialog.
You should see that the new processes are now vis-
ible in the project window. However, not everything
will necessarily fit in the window — in this case, press
the Maximize button, which automatically resizes the
project window to fit its contents. You may need to do
this as we go along when new statistics are created.
Now, we can get a control panel for this new testing
epoch process, and step through some testing events.

Edit the highest-level process in the hierarchy
(the Train_0 process in this case) (i.e., click with the
right mouse button on the Train_0 icon in the project
window, or do .processes/Edit/Train_0 in the
menu), and then do Structure/Move To Sub Gp in
the menu of the resulting edit dialog for Train_0 . It will
then prompt you for the name of the group, to which you
should enter Train , to indicate that this is the training
group of processes. As a further flourish, you can do
Structure/Change Name Suffix in the edit dialog,
and enter Trn — this will rename all the processes to
end in the more meaningful _Trn instead of _0 .
If you now do .processes/Edit , you will see
that all of the processes are now grouped together in the
Train subgroup.

, !

Select the Epoch_Tst icon in the project window,
and hit Ctrl Panel .Setthe step process in this con-
trol panel to be Trial_Tst instead of Epoch_Tst ,so
that when we hit the Step button, it will go one event
(trial) at a time. Then, hit ReInit and then the Step
button. You should see the first event presented to the
network. Continue to Step through the entire epoch.

Go ahead and Ok the edit dialog.
Now, let's create a testing process hierarchy. The typ-
ical way that testing is done is to present a single epoch
of events while measuring the network's responses to
these events. Thus, we will create an EpochProcess .

B.4.1 Monitoring Unit Activities

Let's imagine that we were interested in the hidden unit
activity patterns in response to these different events.
As we have seen in a number of the exercises, it is use-
ful to use a grid log to view activity patterns over time.

Do .processes/New/EpochProcess . When the
new object dialog comes up, press Ok with the right
mouse button, so that we can edit it.