The COGENT 'Modal Model' Model

Because this is a short tutorial, and since we are concentrating on producing a simple cognitive model rather than a complete experimental program, we start the tutorial with a model in which we already have a developed experimental environment, which presents the stimuli, collects responses and graphs results. This "stub" model should be installed on your machine. Use the explorer to find "Tutorial_initial.cog". Click on the file to open it. You should see a screen like this:

This is the main box-arrow diagram of the model. It comprises three Compound boxes, linked by arrows. The box labelled "Experimenter" presents stimuli and collects responses, and uses the "Graph Package" to display a graphical representation of the serial position curve (as shown already above). You can find the graph display by double-clicking on the "Graph Package" box, which will open a new window which looks like this:

The graph display itself is opened by double-clicking the box at the bottom of the diagram labelled "Graph Display". When you open it, you need to click on the "Current Contents (Image)" tab to view the graph.

Of course there is no graph yet, since there is no data. You should by now be able to see that each box in a box-arrow diagram represents an object, and when you open it, you have a variety of different views available -- the exact range of views depends on the object type. Objects that contain other objects, which they display as a box-arrow diagram, are known as Compounds and are represented with a rectangle. Round-ended boxes are Buffers, of which there is a range of types. For example, the graph display is an Analogue Buffer, which is specialised for holding and displaying graphical information.

Finally in this section, we can introduce the Subject box and its relation to the Experimenter. Return to the main box-arrow diagram, and double-click on the Compound labelled "Subject". This as its name suggests, is going to contain our model of the human subject in the free-recall task. But since this model isn't built yet, it contains only a stub, looking something like this:

The hexagonal box labelled "Input/Output" is a Process, and it will handle all interaction with the Experimenter. Double-click on it to open it, then switch to the "Messages" tab, which will initially display a blank screen.

Now notice the row of buttons marked in red on the toolbar at the top of the window, like this:    

This is the run toolbar, and it is displayed in the window of every open box. It provides access to the instructions most commonly used when running a model. (More advanced instructions are available from the "Run" menu.) The buttons' functions are as follows:

ButtonAction PerformedEquivalent Menu Item
Initialise execution model Run->Initialise->Session
Stop Execution Run->Stop
Step Through Predefined Number of Cycles Run->Step
Execute one trial Run->Run Trial
Execute one block of trials Run->Run Block

The first thing to do is click on the "Initialise execution model" button, to initialise the model. Then click the "Execute one trial" button; you should see signs of activity, and messages should accumulate in the open window. These messages are being sent by the Experimenter -- in this model the Experimenter sends a message of the form word(Word) to the Subject on each successive cycle. When the Experimenter has sent 25 words to the Subject, it sends a final recall message, like this:

The model will ultimately need to be able to respond appropriately to these messages. The next section describes how to do this.