Task Model Tracing
1998 ACT-R Workshop
Derek Brock
J. Gregory Trafton
Jeremiah Jordan
Naval Research Laboratory
Washington, DC

HCI Problem:

Facilitating user interactions with an application - agenda

Aid user's situational understanding of the task

Identify and anticipate key task activities

Assist or perform non-trivial task actions

Recognize user preferences and strategies

HCI Problem: (cont.)

What sort of information is needed to facilitate user interactions with an application?

Organized, adaptable knowledge about:

The application and its task domain

The user's perspective


An applied cognitive modeling approach: ``task model tracing''

Develop a software backend that incorporates a ``task model'' (i.e., a cognitive model) of what an application should know about itself and the user

Keep pace with the user by ``tracing'' the user's task actions (i.e., matching user and application events against the task model)

Allow user to consult task model (i.e., make the task model interactive)

Knowledge issues - modeling the application task domain

Begin with a task analysis of the application

Task analysis implies a generic user model of how the task is performed (but sidesteps dynamic user modeling issues such as preferences, etc.)

Task analysis is transformed into a working model implemented within some architecture suitable for modeling cognitive activities (i.e., the task analysis is transformed into a ``runnable system'')

Knowledge issues - user modeling

Requires static and dynamic identification of task components that are key to the user's perspective such as:

Useful strategies, task objectives, other high-level features of task

Preferences, utility of previous actions, etc.

Level of skill, gaps in task knowledge

Requires maintaining an interaction history in a cognitively plausible way (as opposed to simple frequency counts, etc.)

Task model tracing testbed - major components

Application testbed - a probabalistic, relatively complex, planning and resource allocation task in a pseudo-military world written in Macintosh Common Lisp (sidesteps issue of interprocess communication)

Cognitive modeling environment - ACT-R (John Anderson, CMU)

Task model user interface

Task model tracing testbed - application testbed

Application task is to plan and execute a military land assault on a small number of geographical targets from a fixed base using a limited number of resources

Task model tracing testbed - application testbed (cont.)


``Light'' and ``heavy'' tanks (in short supply)

Strengths and weakness of the two types of tanks overlap to some degree, making it hard to know which may be best to use

Tanks must be ``outfitted'' with munitions and fuel which involves making tradeoffs

Task model tracing testbed - application testbed (cont.)

There are three possible targets, called ``destinations;'' each has its own characteristics (e.g., military strength, offensive capacity, distance from base, etc.)

Destinations are surrounded by a small number of geographic obstacles which may prevent a tank's reaching its target; at a minimum, obstacles increase a tank's fuel requirements

Task model tracing testbed - application testbed (cont.)

Tanks ``engage'' a destination when they arrive and may be defeated immediately; otherwise, a destination's strength is diminished by the tank's munitions strength

Several tanks are required to defeat a destination

Testbed allows various mission scenarios to be devised

Task model tracing testbed - cognitive modeling environment

ACT-R adaptive processing mechanisms are well suited to task model tracing user modeling goals

Task model tracing derives from the model tracing methodology used in ACT-based intelligent tutoring systems, the principal difference being the purpose for which it is employed (consultation and assistance vs. tutoring)

Task model tracing testbed - task model user interface

The application user interface is augmented with a dialog box named the ``task model interaction window'' (TMIW)

The TMIW is divided into two sections:
An area for reporting the current context of the task

An interactive area for displaying a selection of possible next actions the user may wish to take in the form of checkboxes (which function like a set of radio buttons)

Task model tracing testbed - task model user interface (cont.)

Two buttons allow the user to control the TMIW (i.e., interact with the task model):

The TMIW is consulted with the ``Assistance'' button

A selected next action is performed with the ``Do It'' button

Task model tracing system - outline

A task analysis of the application serves as the basis of an ACT-R task model:

Application-related declarative knowledge and rules are identified

Task actions which move the task forward are identified as ``contexts;'' those remaining are identified as ``aspects'' of contexts

Other ``meta-level'' concepts and rules necessary to describe the task in context and otherwise coordinate the task model are identified

Task model tracing system - outline (cont.)

The model's processing is factored into ``stages'' which discharge individual functions:

Bookkeeping (tracing the task model)

Context assessment

Reporting the current context

Anticipating and performing task actions

Task model tracing system - outline (cont.)

User interaction-related application events are serially communicated to the model and drive only its bookkeeping and context assessment stages

The user consults the task model in the task model interaction window (TMIW)

Task model tracing system - outline (cont.)

The TMIW displays a report summarizing the current context and an interactive list of possible next task actions on demand

Hence, the TMIW drives the task model's reporting and anticipation stages (including the performance of task actions)

The model ``performs'' task actions by making direct calls to application functions

Task model tracing - summary

Task modeling tracing...

Is an HCI effort to usefully facilitate user interactions with an application in the manner of an assistant (as opposed to a tutor).

Differs from model tracing principally in its intended purpose: the model is traced so the user may consult it

Seeks to utilize elements of ACT-R's approach to cognition as a means for achieving HCI user modeling goals (e.g., facilitating future interactions, etc.)

What's interesting about task model tracing?

Task analysis insights:

Context viewed as a discrete task performance step that tangibly moves the task forward

Categorization of other task actions as ``aspects'' of a particular context

Task analysis used to abstract meta-level, task-related concepts and rules (e.g., static, higher-level information about the task of interest from the user's perspective)

What's interesting about task model tracing? (cont.)

User interaction with an ``agent''

Task model satisfies definition of an agent (Russell & Norvig 1995) by ``perceiving'' and ``acting'' upon its environment

Consequently, task model tracing is a testbed for exploring dialogue-related issues associated with agents and intelligent user interfaces such as grounding, interruption, initiative, etc.

What's interesting about task model tracing? (cont.)

Cognitive issues

Can/does the option to consult a task model genuinely facilitate a user's task performance in and/or understanding of a non-deterministic domain?

What forms of assistance are beneficial or not?

What level of success can an ACT-R-based task model achieve in a dynamic (iterative) task environment in addressing difficult user modeling issues such as preference, strategic value, level of skill, etc.?

What's interesting about task model tracing? (cont.)

Cognitive modeling and model tracing

A cognitive model is being used to follow along as a user performs an HCI task that is not fundamentally algorithmic in nature

Task model tracing takes model tracing methodology beyond its intelligent tutoring origins into a different applied domain (i.e., intelligent user interfaces)

Through the use of processing ``stages,'' the modeling work proposes a structure for conceptually organizing and adding higher-level functions to the task model and relating them to its basic model tracing function

What's interesting about task model tracing? (cont.)

Interaction design and software engineering

Interaction with task model blurs standard application/user dialogue model

Future paradigm for application user interface programming (i.e., designing to accomodate requirements of intelligent user interface system)

Process and platform: layers vs. interapplication communication

Task model tracing - status of work

Several iterations of modeling; a subset of the task is implemented in the current model

Working examples of each of the immediate interactive goals for the TMIW

Earlier modeling work focused on some user modeling issues (choice of strategy and user preference)