1. Limits in human information processing Dr Duncan Guest

2. Overview A brief review of various data indicating limits in human information processing Examples of where these limitations have implications for safety

3. Absolute identification Absolute identification is one of the most basic cognitive tasks. In the task, a participant is presented with a set of items that vary (typically equally spaced) along a single dimension. For example, pitch of a tone, intensity of a tone, length of a horizontal line, weight etc. As the number of items in a set is increased, performance deteriorates. Performance in=s measured in terms of bits of information. One bit of information is required to discriminate between 2 stimuli, 2 bits for 4 stimuli, 3 bits for 8 stimuli, 4 bits for 16 stimuli etc

4. Information transmitted from stimulus to response as a function of stimulus set size. The solid line is the maximum possible amount of information transmitted given perfect performance. Typical information transmission limits are about 2.5 (6 stimuli) for a variety of tasks including tone frequency and intensity, line length, angle of inclination, area of a square, hue and brightness (for a review see Stewart et al, 2005)

5. Braida and Durlach (1972) - information transmitted increases to an asymptote as the stimulus range increases The asymptotic limit in information transmission reached in absolute identification tasks indicates that severe limits of the cognitive system in terms of information processing and representation. Compare this to a computer? Do not ask a user to determine the level of a variable on the basis of a single sensory variable (e.g. colour, size, loudness).

6. A very simplistic account of memory Information not attended is lost (Lachter at al, 2004) Only information that is rehearsed enters LTM Sensory Information Sensory (iconic/echoic) memory Short term memory Long term memory At all stages of information processing we lose information – This needs to be understood when designing safety systems – What are the demands on attention at one particular time? – e.g. Multiple screens showing patient diagnostics in a hospital

7. Short term memory / Working memory Short term memory is what we use to complete various tasks – hence working memory Short term memory has a limited capacity Digit recall task STM capacity can be increased by chunking fbiciaibmitn = FBI CIA IBM ITN Only a limited amount of information chunks can be stored in short term memory –Cowan (2000) – STM can store 4 chunks of information –Miller (1956) – 7 items Implications for safety e.g. balance between amount of information that is presented and that which can actually be used

8. Implications of information processing limits on safety Working memory is resource limited. Performance is deteriorated when attempting two tasks concurrently that share the same limited resource. Dual task performance –Driving Kauranan & Summala (1999) – driving ability to stop is impaired as much when completing an auditory memory and addition task as it is to punching numbers into a keypad. Strayer & Johnston (2001) – drivers are as impaired at driving regardless of whether they were using a hand held device or a hands free device

9. Implications of information processing limits on safety Multiple object tracking

10. Implications of information processing limits on safety Dual task performance –Multiple object tracking Kunar et al (2008) – demonstrated that generating speech (e.g. having a conversation) impairs performance (response time and accuracy) in a multiple object tracking task. Telephone/radio conversation will therefore impair performance in all tasks requiring tracking of multiple objects (aviation/driving). Social factor – passengers may attend to the same task and modulate conversation according to the task difficulty, enabling attention to be fully switched to the driving task

11. Implications of information processing limits on safety Dual task performance –Aviation When a task performed concurrently with a visual flight task is auditory it should compete for fewer resources than a visual task improving performance. However, if the pilot turns to receive the auditory information it disrupts the flight task entirely (Helleberg & Wickens, 2000; Latorella, 1998) Understanding the social factors involved in communication (e.g. eye contact) is therefore important

12. Implications of information processing limits on safety IB

13. Implications of information processing limits on safety Visual attention –Inattentional Blindness – What we dont attend to, we are not aware of (Mack & Rock, 1992, Simons & Chabris, 1999) –Only 3-4 items can be attended simultaneously (Pylyshyn & Storm, 1988; Trick & Pylyshyn, 1994 ) Implications for –security (multiple screens), medicine (multiple diagnostics) –Tracking items (Alvarez & Franconeri, 2007) 8 items can be tracked if moving slowly Only 1 item can be tracked if it is fast moving Only 3-4 items can be tracked at any one time

14. Implications of information processing limits on safety Visual search –We are fast to find items that differ from all stimuli along some dimension – e.g. find the red vertical bar

16. Implications of information processing limits on safety Visual search –We are fast to find items that differ from all stimuli along some dimension –We are slow to find an object when its features are a conjunction of those of the distractors

18. Implications of information processing limits on safety Visual search –We are fast to find items that differ from all stimuli along some dimension –We are slow to find an object when its features are a conjunction of those of the distracting items –Search is also easier when the distracting items are highly similar and when the target item is less similar to the distractors (duncan & Humphreys, 1989) –Implications for design of interfaces – where do we want people to be attending?

19. Implications of information processing limits on safety Visual Search – X ray scanning (e.g. airport screening) Smith et al (2005) –Examined participants ability to search for items of a category in a visual search task. –Participants were trained to categorise stimuli from three categories (complex shapes - accuracy >75%) –They then had to complete a search task and had to indicate whether a member of Category A, B, C or no category member was present –This training and search task was modelled on the Transportation Security Administrations (TSA) current assessment and training procedures.

20. Implications of information processing limits on safety Performance was very poor There was a marked dependence on stimulus repetition. Stimuli were sampled from the same library during the task, then at several points the library was changed, impairing performance. Thus participants were unable to bring their category knowledge to bear on the task (even though they could still categorise the objects well in a post test)

21. Implications of information processing limits on safety This was replicated using more ecologically valid (although less controlled) stimuli

22. Implications of information processing limits on safety This was replicated using more ecologically valid (although less controlled) stimuli

23. Implications of information processing limits on safety Performance was equally as bad even when searching for items from 1, 2 or 3 targets. Performance deteriorated significantly when the number of items in the display was manipulated Performance deteriorated significantly when the within category similarity was decreased People cannot bring category knowledge to bear on this task. Perhaps they then use bottom up strategies of looking for particular shapes or features.

24. Implications of information processing limits on safety Implications for training methods using the Transportation Security Administrations (TSA) assessment and training procedures –use larger libraries to foster use of category level knowledge –routinely introduce new targets periodically BUT - If airport security staff do rely on familiarity to particular objects in the TSA library, then their performance on screening tasks will be inflated relative to the probability of picking up new dangerous items. Scanning xrays, particularly under time limited conditions is difficult. How well do we expect humans to be able to do it? Understanding the limitations of the cognitive system is vital in creating human-computer interfaces to improve safety.