Lecture 18 - Multitasking Flashcards
What are the limits to cognitive capacity?
Even when we do just ONE task there are limits to cognitive capacity
Limiting factors…
o working memory capacity (representational / storage capacity is limited)
o speed of processing (all processes take time)
o there are limits to the input any one process can handle (attention)
When do capacity limits become even more obvious?
When resources must be SHARED between TASKS
- have to get more than one task done in a certain time
- at least SOME tasks are time-critical (cannot wait) - so we must either try to do them simultaneously or switch back and forth
What are the main demands when multi-tasking
Competition for shared resources (dual-task interference)
When we try to switch between tasks (see following lectures)
o Task switching costs
o Retrospective memory (what’s left to be done)
o Prospective memory (monitoring triggers)
Executive control (planning, scheduling, prioritising, trouble-shooting)
SO: multitasking is not a single competence
executive control processes are critical
Main Example: Mobile Phones when Driving
- What do driving on the phone studies show?
Epidemiological studies show INCREASED ACCIDENTS (relative risk similar to driving at legal limit of alcohol)
Observational studies show: delayed braking at T-junction
Experimental studies show impaired breaking, detection of potential hazards, especially in young drivers
Studies: Driver in a simulator-follows pacer car in slow lane of motorway
- baseline v casual phone talk v alcohol conditions
Mobile Phone: slower reactions, more tail-end collisions, slower recovery
No sig diffs between talking on hand held and hands free
Main Example: What do further studies show about this effect (what scenarios increase/decrease)
Talking on hands-free mobile phone…
- reduced anticipatory glances to safety critical locations
(eg. parked lorry obscuring zebra crossing)
- reduced later recognition of memory of objects in driving environments
- increased probability of an unsafe lane change
Does talking to passengers have same effect? Crash risk data suggests NOT
- passengers are sensitive to driver’s load
- passengers help spot hazards
How is dual task interference measured in the lab?
ONLY TWO TASKS: designed for measurement and manipulation
Typically measures performance on
- A and B alone
- A and B combined
What are the possible sources of dual task interference?
- Competition for use of specialised domain-specific resources
o part of body (effectors, sense organs)
o brain “modules””: specific processes - Competition for use of general-purpose processing capacity
o Central Processor: with a limited capacity
o Pool of general-purpose processing resource? - Limited capacity of executive control mechanisms that set up and manage the flow of information through the system and/or sub-optimal control strategies
- Competition for Domain-Specific Resources
- Outline this competition
Two continuous speech inputs CANNOT simultaneously be understood or repeated - but both can be monitored (see attention lecture)
–> Performing a spatial tracking task interferes with use of visual imagery to remember stuff: both use visuo-spatial working memory
SO: where two different tasks use the same perceptual processes/response mechanisms: WE SHOULD EXPECT DUAL-TASK INTERFERENCE - TWO STREAMS CANNOT FULLY PROCESS AT THE SAME TIME
–> Unless information rate is low enough to switch the use of that resource between tasks
- Competition / General-Purpose Processor (Broadbent)
- Outline this theory
All inputs have to go through a central processor for an action to be performed - everything comes from all the senses
–> Assumed to be required for pattern recognition, access to memory, decision-making, action selection, awareness etc.
Outline a general-purpose resource pool (and its relation to task capacity)
General Purpose Resources Pool
–>Kahneman (1975) proposed a pool of general-purpose resources that is shared among concurrent tasks (like mental energy - including attention and effort)
The capacity of this general purpose resource might vary within and between people
Level of sustained attention
- diminishes with boredom or fatigue
- increases with time of day
Conditions of task sharing:
o If sum of capacity demands does not exceed available total = no interference
o Sum does exceed = interference
Increasing the difficulty of one task should reduce the capacity available for the other task
Example: A case of demanding tasks combined without interference (piano and novels)
University of Reading music students were tasked:
A - sight read Grade 2 or Grade 4 piano pieces
B - shadow prose from Austen novel (easier) or a text on Old Norse (harder)
Relatively little practice
Experiment: two sessions of dual task for each combination of easy and hard
FOUND: The rate of shadowing and number of shadowing errors were no different with and without concurrent sight reading
More shadowing errors for harder text
OVERALL:
- Shadowing performance not influenced by difficulty of music piece
- Sight-reading performance not influenced by difficulty of prose shadowed
Further Examples: Outline the research by Schaffer (1975) and North (1977)
Tasks combined without apparent interference:
–> Shaffer (1975): skilled visual copy-typing can be combined with shadowing of prose without interference
–> North (1977): continuous tracking + digit –> key task:
- identify digit with key press
- identify digit before the present one
- classify successive pair of digits
No effect of difficulty of digit task on tracking delays
Allport’s Claim: Outline the theory that we have no central general purpose processor?
Pairs of complex input-output translation tasks can be combined with little or no interference if they use NON-OVERLAPPING MODULES (different input codes/modalities/action systems/networks)
–> If there was something ‘central’ you really would EXPECT INTERFERENCE
BUT: even when tasks use completely different modules, some interference may arise due to coordination and control demands
- i.e as a consequence of the load on (specialised) executive processes
How does this relate back to the argument of driving and phones?
Do driving/navigation (a) and conversation (b) require different modules?
–> YES AND NO
o They use different input and output modalities BUT both require construction of a “mental model”
–> for driving; representation of route, goals, progress, road signs etc.
o The construction of the mental model for driving can be interfered with by a conversation that asks the driver to think about visuo-spatial arrangements
Outline the importance of PRACTICE
Tasks which CANNOT be combined without interference become EASIER to combine with practice
- eg. changing gear while driving
Spelke, Hirst, and Neisser (1976): after 85 hours of practice at reading stories at the same time as writing to dictation –> some participants showed little dual-task interference
–> because: practicing one task AUTOMATES IT: reduces the need for “executive control” - of the constituent process
–> practicing combining tasks develops optimal control strategies develops optimal control strategies for combining that particular task pair
