Introduction to the PDP Simulation Environment - Computational Explorations in Cognitive Neuroscience - page 421

Viewing weights and other values associated with
connections is also possible, but it requires one extra
step. Buttons associated with connection variables are
at the top of the list of variables, and begin with either
an r. (for receiving connection values) or an s. (for
sending connection values). For example, to view the
weights coming into a particular unit, you would select
the r.wt button. Then, however, you must also se-
lect the unit for which you wish to view the weights —
this is done using the View tool instead of the normal
Select one, as indicated by the buttons at the upper
left-hand side of the window. You can only view the
weights for one unit at a time, since the weight values
are displayed over the other unit squares in the display.
After selecting a connection variable, simply click with
the left mouse button any unit in the display, and this
will show the connection values on the corresponding
units that are on the other side of connection. Thus,
somewhat confusingly, when you select to view the re-
ceiving weights, the units that are lit up in the display
are the sending units, since these are the ones that the
selected unit receives from. Note that if you want to se-
lect an object for editing within the netview window, you
must ensure that the Select , not View , tool is active.
It is also possible to view multiple variables at the
same time, by using an extended selection procedure.
Select the first variable to view as before with the left
mouse button. To view an additional variable, simply
select it with the middle mouse button (or hold down
the shift key while pressing the left mouse button). The
units will now be split, showing both variables in each
unit. Any number of additional variables may be se-
lected (though it is typically quite difficult to actually
interpret such displays).

A.7 Specs

The details of the specs for the Leabra algorithm are
presented in appendix C. You will not need to use the
actual spec objects themselves for any of the provided
simulations, but they will be essential should you try
to develop a model on your own. The tutorial in ap-
pendix B provides more details on how to use these
specs when building a network.

A.8 Networks and NetViews

A network consists of Layer objects containing Unit
objects, which are connected with Connection objects.
One possibly confusing aspect of the network is the
Projection object, which specifies connectivity on a
layer-to-layer basis (e.g., the projection specifies that
the hidden layer receives from the input layer). It is the
responsibility of the Projection object to actually create
all the individual connections between units in the re-
spective layers. The patterns of connectivity are deter-
minedbythe ProjectionSpec , which is the spec object
associated with the Projection.
There are also Spec objects associated with Layers,
Units, and Connections. These are where you should
look for all the controlling parameters for the network.

A.8.1 NetView

The NetView displays a graphical representation of
the network, showing the individual units as colored
squares organized within layers, with projections rep-
resented by arrows. The units in the display obtain
their color as a function of the currently selected vari-
able (other modes of display are available through the
Disp Md menu on the right-hand side of the window).
The available variables are represented by buttons ar-
ranged in the lower left hand side of the display. Note
that there may be more buttons than space to display
them, in which case the scroll bar may be used to view
them all. Clicking with the left mouse button on one of
these variables will select it for display over the units in
the network. In this way, one can alternately view all of
the important state variables associated with the units.

A.9 Environments and EnviroViews

The EnviroView provides a display of the environment
object, showing the events listed in buttons down the
left hand side of the display. When one of these event
buttons is clicked, the pattern values for that event are
displayed over on the right. Multiple such events can
be selected by using the middle button, or shift and left-
click. To turn a selected event off, also use middle but-
ton or shift and left-click.