Mental Workload Methods

Transcription

1 Mental Workload Methods Introduction Mental Workload Methods Overview Categories of MW Assessment Techniques Subjective Workload Assessment Technique (SWAT) NASA TLX

2 Mental Workload Assessment Overview Design and evaluation of complex systems and procedures require mental workload(mwl) assessment It is required to evaluate the demand imposed on the people working with these systems As with physical ability, individuals have limited processing capacity and mental resources for performing various tasks Factors Affecting Mental Workload Task related factors Easy or difficult Competing tasks Constraints Individual specific Motivation to perform the task Strategies applied Mood and operator state Time scale (short such as air combat versus long such as a long haul flying) Fatigue Skills, training, practice, familiarity Input variables How the information presented is perceived by the operator Information processing variables Cognition Decision making Output variables Actions and execution of actions Image licensed under public domain, pixabay.com

3 Factors Affecting Mental Workload Categories of Mental Workload (MWL) Assessment Techniques Performance Measures Primary Task Measures (time taken, accuracy/errors, response time) Secondary Task Measures (subsidiary task and loading task paradigm) Psycho-Physiological Measures Heart Rate and Heart Rate Variability Pupil Diameter Visual Scanning / Eye Point of Gaze Eye Blink Activity (blink rate, blink duration, blink latency) Subjective Measures Rating Scale Mental Effort (RSME) Modified Cooper Harper Subjective Workload Assessment Technique (SWAT) NasaTLX

4 Subjective Workload Assessment Technique (SWAT) SWAT is a subjective workload measure that provides a three dimensional measure in terms of time load, mental effort and stress level of the operator Designed for the aviation industry to measure pilot mental workload, it can be used in other domains as well SWAT has the advantage of being one of the multi-dimensional measure whereas other MWL methods measure a single dimension of workload only like heart rate, reaction time, etc. SWAT Rating Scales I. Time Load 1. Often have spare time. Interruptions or overlap among activities occur infrequently or not at all. 2. Occasionally have spare time. Interruptions or overlap among activities occur infrequently. 3. Almost never have spare time. Interruptions or overlap among activities are very frequent, or occur all the time. II. Mental Effort Load 1. Very little conscious mental effort or concentration required. Activity is almost automatic, requiring little or no attention. 2. Moderate conscious mental effort or concentration required. Complexity of activity is moderately high due to uncertainty, unpredictability, or unfamiliarity. Considerable attention required. 3. Extensive mental effort and concentration are necessary. Very complex activity requiring total attention. III. Psychological Stress Load 1. Little confusion, risk, frustration, or anxiety exists and can be easily accommodated. 2. Moderate stress due to confusion, frustration, or anxiety noticeably adds to workload. Significant compensation is required to maintain adequate performance. 3. High to very intense stress due to confusion, frustration, or anxiety. High extreme determination and self-control required.

5 Subjective Workload Assessment Technique (SWAT) Procedure Define the tasks for analysis Select participants Scale development 27 combinations of the rating scale descriptors are presented in cards that are sorted by participants from lowest to highest workload An interval scale of workload from 1 to 100 is developed Event scoring For a particular task, the participant provides a 1-3 rating for each of the three workload dimensions Perform HTA on each of the tasks to understand them better Brief participants and conduct a pilot on a small task to familiarise the rating scale Perform the task The task is done by the participant and then the SWAT is administered SWAT score calculation Choose the scale value with the combination given by the participant This is then presented as individual workload scores for each dimension NASA TLX NASA TLX is a subjective workload rating technique The overall score is based on the weighted average of rating on 6 subscales NASA TLX is known to perform better than SWAT

6 NASA TLX Rating Sheet NASA TLX 15-pairwise comparisons

7 NASA TLX Workload Tally NASA TLX Additional Reading ppen_manual.pdf le.pdf

8 Summary Mental Workload measurement is important for assessing the use of complex systems and procedures There can be 3 types of measures for Mental Workload (MWL) Performance, Psycho-Physiological and Subjective SWAT uses card sorting and event scoring for measuring MWL NASA TLX uses a 6 subscale scale and weighted average for measuring MWL Reflection Question What other HF methods will you use prior to performing a mental workload assessment of scenario. Discuss what steps will be needed for a SWAT analysis