1. Research Methods for HCI: Cognitive Modelling BCS HCI Tutorial 1 st September, 2008

2. Anna Cox, UCL Interaction Centre2 What is a cognitive model?  Specification of mental representations, operations and problem-solving strategies that occur during execution of computer-based tasks.  Can be: – General description of steps required to complete a task – Sophisticated computer simulation of users performing tasks with computers

3. Anna Cox, UCL Interaction Centre3 Why build cognitive models?  Help us develop a precise understanding of HCI  Sometimes enable us to make predictions about performance  Can be used early on in design as well as to evaluate existing designs

4. Anna Cox, UCL Interaction Centre4 Engineering models  Used to predict aspects of human performance before users are introduced to a system  Evaluate speed and number of operations required to perform different tasks

5. Anna Cox, UCL Interaction Centre5 Engineering models: GOMS  Goals  Operators  Methods  Selection rules

6. Anna Cox, UCL Interaction Centre6 Engineering models: KLM  Keystroke-level model – Restricted version of GOMS (no G or S!) – Predicts execution time to perform a task – All operators have specific execution time – Time to complete the task = sum of execution times of all the operators required to complete the task

7. Anna Cox, UCL Interaction Centre7 Cognitive Architectures  Sophisticated and complex programming environment within which psychological theory is represented  Can build models of a user completing a particular task within the architecture  The architecture constrains the way in which this can be done, thus ensuring that the model complies with existing psychological theory

8. Anna Cox, UCL Interaction Centre8 Cognitive Architectures: ACT-R  Theory of human cognition  Represents aspects of human memory, speech, vision, audition & motor systems  Built on top of LISP (so it helps if you’re familiar with that programming language)

9. Anna Cox, UCL Interaction Centre9 Peebles & Cheng (2003)  an experiment, eye movement study and cognitive modelling analysis to investigate the cognitive, perceptual and motor processes involved in a common graph reading task using two different types of Cartesian graph  Aim: to investigate how graph users’ ability to retrieve information can be affected by presenting the same information in slightly different types of the same class of diagram

10. Anna Cox, UCL Interaction Centre10 Experiment  participants presented with the value of a “given” variable and required use the graph to find the corresponding value of a “target” variable, – “when the value of oil is 2, what is the value of gas?”.

11. Anna Cox, UCL Interaction Centre11

12. Anna Cox, UCL Interaction Centre12 Results  The RT data showed that the graph used and the type of question asked both had a significant effect on the time it took for participants to retrieve the answer.

13. Anna Cox, UCL Interaction Centre13

14. Anna Cox, UCL Interaction Centre14 Eyetracking data  In 62.7% of all trials (irrespective of the graph used or question type being attempted), after having read the question at the start of a trial, participants redirected their visual attention to elements of the question at least once during the process of problem solving with the graph.

15. Anna Cox, UCL Interaction Centre15 Hypotheses about what could be going on a)Ps initially encode the three question elements but are unable to retain all of them in working memory or retrieve them when required due to the cognitive load involved in solving the problem, b)to reduce the load on working memory, participants break the problem into two sections, the first allowing them to reach the given location and the second to then proceed to the target location corresponding to the solution.

16. Anna Cox, UCL Interaction Centre16 What was going on?  During the process of model development it was found that on a significant proportion of trials the model was not able to retrieve question elements at the later stages of the trial because their activation had fallen below the retrieval threshold. (i.e. option a)  As a consequence new productions had to be added to allow the model to redirect attention to the question in order to re-encode the element and then return to solving the problem.  This was precisely the behaviour observed in the eye movement study.

17. Anna Cox, UCL Interaction Centre17 The numbered circles on the model screen shot indicate the sequence of fixations produced by the model