The original iPod Shuffle had a clear proposition; a cheap, simple, and minimalist music player. Technically the first iPod to use flash memory and physically the smallest, it lacked any display, scroll wheel or playlist management features. The constant need to control, skip, manage, and navigate was replaced with a simpler and more relaxed lack of control. Instead, the device simply shuffled music at random or played tracks in order. The front of the device had a simple interface:

• Play/Pause
• Next Song/Fast Forward
• Previous Song/Fast Reverse
• Volume adjustment

On the back was a three-position switch to play music in order, or shuffled or to turn off the unit.

The second generation was just as simple as the first, but had more storage and less than half the size.

On 11 March, 2009 Apple released the third-generation Shuffle.

One of the key design decisions was to simply not have any buttons, apart from a button that switches between 'Off', 'Random' and 'Order'. All controls are now part of the earphones.

According to Apple:

The new iPod shuffle is amazingly small and even easier to use.

But is it easy to use?

Soon after the launch, forums, social media networks and blogs started to criticise the new Shuffle. Whilst some disliked being dependent on using Apple's earphones, others criticised the new interface. Physically, the control could be difficult to grab during sporting activities or for those with bigger hands, but more importantly, most of the functions are controlled via a central button that has no labels.

The lack of visual display raises a design challenge. Unfortunately, touch is a less accurate sensory mode than vision and typically slows users down. Apple could have designed an interface with elements that could have been recognised through tactile attributes such as feedback, resistance, size, weight, and/or texture. The father and grandfather of the current Shuffle are good examples of such a control. However, the solution was to include VoiceOver technology, a feature that speaks 14 languages and plays back track and playlist names. Although a minor issue, VoiceOver struggles with pronunciation. Perhaps in the future, additional language information will be included with each track.

One button, nine commands

Apple was once famous for the one-button mouse. Although historically some suggest that this decision was based on cost, it was often argued that one button is all you needed. The one button became a symbol of simplicity. In contrast, the new iPod Shuffle has a central button that accepts many user commands. In fact, this 'one button' handles 9 inputs:

1. click
2. click & hold
3. double-click & hold
4. triple-click & hold
5. triple-click and hold within 6 seconds
6. triple-click and hold after 6 seconds
7. click until a tone is played
8. click until you hear a name
9. click & hold until exit

There is no direct cognitive mapping between users' goals and the required actions. For example, why does 'double-click and hold' fast-forward a track, but 'triple-click' rewind? Moving to the next track is achieved by double-clicking. So how do you expect to move to the previous track? Did someone at the back just say "triple-click within 6 seconds of the track starting"? Correct.

 Poor learnability?

Ultimately, if the device is used frequently, many users will move from being novices to experts. However, if learnability is poor, some users will remain perpetually intermediate and potentially frustrated.

Learnability is inherent in interface features that allow novice users to understand how to use a device and how to attain optimal (level of) performance. Learnability is based on five main factors:

• Predictability: operation visibility - what elements of a user's knowledge from past interactions with this device can help to determine the outcomes of future interactions?
• Familiarity: guessability - to what extent can users' knowledge from other systems and real world objects could be applied to interactions with the device?
• Synthesisability: how does the interface help a user to asses the effect of past actions on the current state?
• Consistency: likeness in behaviour. In this context consistency is related to user inputs and the subsequent output responses.
• Generalisability: support for the user to extend their knowledge to other applications and devices.

In the case of the Shuffle, lack of visual display could slow down skills acquisition. The design is not based on familiar metaphors, and poor learnability may increase cognitive load. Many users will not be familiar with the Shuffle's interface, apart from iPhone users who use a similar earphone-based controller.

As a robust device consistency between actions and auditory feedback that arises as a consequence will be high and usage is likely to be frequent. Therefore, for many users learnability will eventually take place. It is possible that Apple plans to extend this interaction model to other devices. For those who mastered this control acquiring this skill will become generalisable and useful.

Does it matter?

So it might be difficult to learn. Arguably, it has beautiful industrial design, long battery life and impressive storage capacity. Apple could sell many of these fashion accessories to users who would simply click to play whilst sitting on the train, running, or going to the gym.

The best way to gain an in-depth insight would be to test the Shuffle with users. In the next few weeks we are planning to evaluate the Shuffle in one of Flow's experience laboratories and analyse its performance and user experience.

- Ofer Deshe, Principal User Experience Consultant

Thanks to Thibault Baradat-Bujoli for the original illustrations