Performance load, chunking and usability in design.

Performance load refers to psychological cognitive and physical demand or load. It defines two areas cognitive and kinematic load. Cognitive is the mental processes of perception, memory judgement and reasoning.  Kinematic refers to the physical, for example the amount of physical effort in the process required. Load is referring to the weight that this process makes upon each individual.

I’m writing this blog for a university report and found the in class examples used unhelpful. Here’s some more dynamic examples of cognitive and kinematic load situations.

For cognitive load, consider a pilot and co-pilot who are flying a plane. Normally the cognitive load for these two people would be low, however consider the times where pilots cognitive load increases when operating under stress. A low cognitive load maybe something like running through a preflight task list, checking and communicating the procedure between pilot and co-pilot.

A higher level of load maybe approaching a landing in rain, with limited visibility,  being  thrown around by turbulance,  reliant only on cockpit instrumentation, and then a malfunction occurs, all whilst trying to communicate procedures.  A good indication of levels of stress is the ability of the crew to communicate to each other.

“For example, a pilots’s erroneous anticipation of a takeoff clearance resultedin the 1977 runway collision at Tenerife, Spain, which remains humanity’s worst aircraft accident”. (Bragg, 2006)
The human brain is much like a computer and “Following the analogy of cache memory in a computer, comprehension in human readers proceeds rapidly and efficiently if all of the elements involved in encoding, storage and immediate memory access operate effectively in phase”.(O’Rielly 1992) This creates a chunk of memory in an overall larger map of memory.
Chunking of information is something we aren’t really very good at but increase our stress levels and we do very badly at the encoding part. We can at times only process a finite number of different things at a time.  This number is believed to be about seven give plus or minus 2 depending on the individual. With inflight information, keeping track of the amount of information on hand is quite a task, but the worse conditions become the higher the performace load becomes. The way airlines have dealt with this is by chunking information into checklists, so that nothing get’s missed in the process, and it simply becomes a checking situation between pilot and co-pilot.
If we  were not aware of performance load and it’s effects, things like this can occur. Consider this recent case where a bus driver was found to have texted 11 times before having a crash. ”The driver sent six texts and received five texts, with the last text just before his pickup crashed into the back of a tractor truck, beginning a chain collision. The pickup was rear-ended by a school bus, which in turn was rammed by a second school bus” (CBS news 2011)

Unfortunately the driver in this case, increased his cognitive load, diverting his attention from the task at hand with tragic consequences.

An example for Kinematic load, I like to think of is the difference between manual and automatic cars.

What I am saying here is that reducing the physical steps increases the simplicity and load experienced.

For example normally driving there maybe little if any percieved difference between driving a manual or automatic vehicle, however add in a few stress factors like bad weather, slippery roads, a child screaming and what cognitive load we aren’t using by coordinating the shifting and selecting of gears may be better used focusing on where and what the car is about to hit.

How does all this apply to design? Well simply the easier you can make obtaining your information, in a well presented, logical, simple, way the easier the system is to use.

In websites usability is vitally important  “Usability primarily involves the interface—what elements appear onscreen and how efficient, intelligible, and intuitive they are…Research on the way people interact with computers has provided insight into how to define, develop, and enhance usability, which is significantly associated with five basic design elements: navigation, response time, content, interactivity, and responsiveness.” (Palmer 2002)

If information is presented efficiently it can be targeted towards our behaviours.  “Most owners of websites have them for a reason. There are target behaviours that they want us to engage in – quite often, even several target behaviours. An e-commerce site wants us to choose products and buy them. A non profit site wants us to loan money to help small business owners in different parts of the world…..Most behaviour isn’t conscious.”(Weinschenk 2009)

People don’t read, they scan! “One of the very few well documented facts about web usage is that people tend to spend very little time reading most webpages. Instead we scan (or skim) them looking for words or phrases that catch our eye.” (Krugg 2000) pg 22

In summary less is definately more, so make your design logical, simple and easy to follow. Don’t make people overthink or they won’t get the information when they need it.



Krugg, S.(2000). Don’t make me think too much. Indianapolis, Indiana, USA: New Riders Publishing.

Weinschenk, S.(2009). Neuro Web Design what makes them click?. Berkley, CA: New Riders Publishing


O’rielly, R. (1992). Chunking capacity in good and poor readers. Texas womens University, 0227089

Palmer, J. (2002). Designing for Web usability. Computer, Volume 35, Issue 7 ,p102-103, (2002). ISSN 0018-9162

Cortes, A. (2011).  A Theory of False Cognitive Expectancies in Airline Pilots.  Northcentral University,  349 2476

Bragg, R. (2006).  Runway Incursions. Bombardier Safety Standdown on Business Aviation Accident Prevention,Wichita, KS.


Bus crash information. (2012). Retreived May 10th, 2012, from

Chunking information. (2012). Retreived May 10th, 2012, from


Cockpit view. (2012). Retreived May 10th, 2012, from×400/transavia-b737-view-from-cockpit-on-final-for.jpg

Pilot picture. (2012). Retreived May 10th, 2012, from×307.jpg

VW gearbox. (2012). Retreived May 10th, 2012, from


4 thoughts on “Performance load, chunking and usability in design.

  1. Pingback: Alanna McKenzie

  2. Pingback: Learning Portfolio 3 (Week 11) – Questions | Alanna McKenzie

  3. Pingback: Performance Load – georgiafiorenzablog

  4. Pingback: Week 11 – Learning Portfolio III – matthewmullany

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