Towards a Representation of AT Systems

1. Towards a Representation of AT Systems John Gilligan Dublin Institute of Technology Professor Peter Smith University of Sunderland

2. AT Systems • The classic definition of an AT system is that of the HAAT model of Cook and Hussey. Context

3. The HAAT model is an example of a PEO model

4. Representation Challenge • The Challenge is to represent all elements of the model, namely PERSON, ENVIRONMENT and OCCUPATION. • It is also imperative that the impact of ASSISTIVE TECHNOLOGY (AT) intervention be accommodated. • Let this discussion begin with (AT)

5. Assistive Technology • Assistive Technology is defined as: “Any product, instrument, equipment or technical system used by a disabled person, especially produced or generally available, preventing, compensating, relieving or neutralizing the impairment, disability or handicap”. ISO 9999:1998

6. AT and State Change • The central implication of this description of assistive technologies is that the technical aids bring about a state change. For example glasses bring about an improvement in what a user can see. Any description of the device must surely concern itself with this state change since this defines the enablement potential of the device.

7. A representation scheme to model AT systems must embody State Change. • The scheme chosen is Jensen’s Coloured Petri Nets (CPNS) • CPNS Represent State Change -hence their suitability for this task

8. Example Petri Net

9. What CPNS Represent • CPNS are directed graphs consisting of two kinds of nodes, places and transitions. • Transitions represent events, processes, activities, actions. • Places contain tokens which represent the states before and after the actions etc represented by the transitions.

10. How Petri Nets Work • Tokens move across Transitions effecting State change • This state change happens only if the guard is satisfied by the tokens at the input place • The change is determined by the output expression

11. Tokens, Guards, Expressions and Outcomes • Tokens represent components of the State. In our case, there will be tokens to represent Person, Environment and Intended Action and objects of the domain, at the very least. • Transition Guards represent conditions which must be satisfied if the event is to take place. • Outcome expressions describe the effects of the action • The expression defines the subset of tokens to move across to the out put place.

12. CPN Components G O P2 P1 E T1 Places P1, P2 Transition T1 Expression E Guard on T1 G Outcome of T1 O Elements of Petri Net

13. To Summarise • CPNS are Graphs with Place and Transition nodes • Activity is represented by Transitions. • Prerequisites to Activity performance are described in the Transition Guards. • The effects of the Activity are expressed in the Outcome expressions • The domain state Before and After the Activity are represente by tokens ate the Input and Output places.

14. This is Summarised in the following Diagram Transition Representing Action Input Expression Which defines the Subset of the Input State Currently in Focus Tokens Representing State Before Action Including Person Capacities And Environment Factors Tokens Representing State After Action P2 P1 T1 Guard Representing Barriers to Performance of Action Outcome Expression Which defines the Change which will take place as a result of Action Petri Net to Represent Action

15. Example In the following Diagram a CPN representing the activity of making tea is shown

16. Example of Activity Representation Activity Make Tea Input Expression Which defines the Subset of the Input State Currently in Focus Tokens Representing State Before Action Including Person Capacities And Environment Factors such as location of milk sugar tea, kettle Tokens Representing State After Action Including Person has A Cup of Tea,-and they are happier. P2 P1 T1 Guard Person must be able to - Lift Kettle Work buttons Open Milk carton etc Outcome Expression Which defines the Change which will take place as a result of Action Activity Making A Cup Of Tea

17. Another Example • The following CPN represents the activity of opening a drawer

18. Activity Open Drawer Agent Token John Action Token Pull1 Object Tokens Drawer1 and Handle1 Environment Token E1 Agent Token John Object Tokens’’’ Drawer1 and Handle1 Environment Token E1 P2 P1 T1 Guards Hand must fit handle Agent must be able to pull objects towards them etc Room must have sufficient light Outcome Expression Drawers position and status change Activity Opening Drawer1

19. Tasks and Subtasks • CPNs can represent the sub tasks of a task , the steps of an algorithm, the subroutines of a routine. For example consider.

20. Multi Step Petri Net

21. Note • Different instances of the same subtask occur across the net • For example We will lift the kettle and lift the sugar bowl at different times in the task • This is important later when discussing a link to the ICF

22. In Summary In order to model someone doing something in some environment, it is necessary to: • Represent features of the person and the factors that impact on their capacity and performance of the activity. • Characterise the activity in terms of its requirements on the person or barriers to its performance. • Represent the outcomes or changes that take place as a result of the activity being performed.

23. Advantages of Scheme • Intuitively seems to have all the elements required • Barriers to Activity Performance can be articulated through Transition Guard • Outcomes and Inputs are expressed as apart of same mechanism • Rich scheme founded in strong formal computer science

24. AT and State Change Revisited • State here refers to a snapshot of the world in which activity takes place. • There are two important states , the state before the activity happens and the state afterwards.

25. State Before • State Before reflects the status of the various components of the domain of activity prior to the execution of the action. • These components include Person, Environment including objects of the domain and Action descriptors which describe the aspects of the intended activity. • In CPNs State is represented by Tokens at the places of the net.

26. State Before Representation • State Before is represented by the tokens at the Input place • This is described in the following Diagram

27. Input Place State Before Action Environmental Tokens including Object Tokens Agent Tokens Representing Person Action Tokens Other Tokens

28. State Afterwards • State Afterwards reflects the status of the various components of the domain of activity after the execution of the action. • This is described by the tokens at the Output place • This is shown in the following Diagram

29. Output Place State After Action Environmental Tokens including Object Tokens Note some of these tokens are passed across the transition from input place to the output place after the action. Some are modified others not. The changes are described in the outcome expression of the transition Agent Tokens Representing Person Action Tokens Other Tokens

30. Moving from Input to Output Places • This happens across a Transition • Transitions represent two aspects of Activity through its guards and outcome expressions. • The structure of a Transition is shown in the following

31. Transition Guard which must be satisfied Expression of Outcome

32. Guards • In order for the activity to take place the guards on the transition must be satisfied. • In other words the guard describes potential barriers to the execution of the action.

33. Outcome expressions • The Outcome expression describes the effects of the action. • In other words what changes happen as a result of the activity

34. Putting all this Together By placing the input place to the left of the transition and the output place to the right we get a one transition CPN

35. Basic Structure of CPN unit Transition Outcome of Activity Guard which must be satisfied Output Place Input Place

36. To summarise this view of Action • Action Has three components • Parameters of the Intended Action such as Location, Duration etc • Guards of the Action • Outcomes of the Action • There is a Domain state before and after the action • This is summarised in the following

37. Intended Action Representation of Action State of the world before Action – State of the world After Action – Capacity Demands of Action and Object Outcomes of Action Person Capacities in The Context of that Action, Objects involved in the action and the environment in which the action is to take place before Action takes place Person and environment Capacities After Action Outcome expression Guard

38. Modelling AT systems • So far we have looked at using CPNs to model Activity. The next questions to answer is, how does AT impact on these models? • So what does AT do? • In terms of Activity, what contribution can AT make to the overall performance of the activity.

39. AT as Intervention • The roles different technologies play reflect to some degree, different intervention strategies which someone like an OT can make to increase occupational performance.

41. 1: Adapting the Task • When the Task method is altered the same task objects are used in the same environment but the method of performing the task is altered to make the task feasible given the persons circumstances. Examples of this kind of intervention, include one handed techniques (ref) for tasks normally requiring two hands e.g. one handed dressing or typing. • Mastering one handed methods require the capacity to learn and practice is a necessary component of this process.

42. Adapt the Task

43. CPN Structure for Task Adaptation • In the previous example we see that task adaptation is represented in the CPN simply as an alternative path between two places. • The idea is that if the guard isn’t satisfied on one path ,then it may be on this alternative path. • In this way the activity may be realised in another way

44. 2: Adapting the Environment • This intervention emphasizes selecting and implementing an environment that enables the person to perform with current skills and abilities (Dunn et al) • Examples of environmental adaptation include making changes to a home , to facilitate a wheelchair user perform every day activities. For example a bathroom could be adapted by the provision of a higher toilet to facilitate easier transfers, grab bars introduced for standing pivot transfers and recessed plumbing and drawers for easier access to the sink. (ref)

45. Environmental Change – Change Objects

46. CPN Structure for Environmental Adaptation • In the previous example we see that Environmental adaptation is represented in the CPN simply as an alternative path between two places. • The idea is that if the guard isn’t satisfied on one path ,then it may be on this alternative path. • In this way the activity may be realised in another way by changing the object involved. • There are also other structures which realise this

47. 3 Prevent Barriers to Task performance • Therapeutic interventions can prevent the occurrence or evolution of barriers to performance in context. • Family members could be trained in a hierarchy of assists, for example verbal cues, that can help maintain the remaining skills that a person with a progressive dementing illness still has.(Rogers et al 2000) • Technology can help prevent barriers resultant from discrepancies in task requirements and personal capacity. Consider a standard keyboard. • If someone with poor targeting abilities is repeatedly hitting two keys at once , then a key guard can prevent this difficulty by placing raised borders around each key button, which make it impossible to hit more than one key at a time.

48. The CPN For Barrier Prevention • This is complex which involves a discussion of how objects are represented and contextual capacities. • This will be postponed until after this.

49. 4 Restore or Establish Capacities • Improve the capacities of the agent through some intervention • This is really the classic exemplar of AT intervention.

50. Enhance Capacities