Monday, February 09, 2009

Ergonomics for Interaction Designers: Part 3

The last of a 3 Part series. The fist two previously posted earlier ...

"Qualitative Observations Issues in Field Research

While interaction designers will typically lack special training in ergonomic assessment methods, most will have some degree of familiarity, if not significant experience with user-centered methods including contextual observation (aka ethnographic field research) and usability testing. All of these methods share objective observation as a common data gathering method, and really only vary in the particular variables or characteristics that are the subject of study. And while anthropometric data is intrinsically quantitative, qualitative observational research can be applied to identify ergonomic issues. With these factors in mind, I've developed a basic set of ergonomic observational criteria to use as guidelines when evaluating design fit. The guidelines are inspired by Stephen Pheasant's cardinal rules of anthropometrics, extended to qualitative field research.

Pheasant advised focusing on Reach, Clearance, Posture and Strength. I'll explain how these can be applied to a consumer electronics device, the InterAction Labs SQWEEZE Game Controller, pictured above. The SQWEEZE is an accessory to the Nintendo Wii - inserting a Wii controller into the SQWEEZE unit allows the user to apply push/pull forces for gaming - think of drawing a bow string to shoot an arrow, for example. While the SQWEEZE was well designed by ergonomics standards, it makes for a good example for explaining the four anthropometric characteristics:

o Reach typically refers to extending the arms and finger for effective control without over-extension. In the case of the airport Kiosk discussed in Parts 1 & 2 there's a clear potential for placing the touch screen at a height or distance that would be difficult for some people to access effectively. That type of reach is a non-issue for handheld devices like the SQWEEZE, but other types of reach can come into play. In the case of two-handed devices, the distance between the handles needs to be appropriately set to accommodate a comfortable grip. For the SQWEEZE, this distance actually varied between the push and pull positions as the handles flexed inward and outward respectively. Similarly, the diameter of the handles affects the user's ability to adequately wrap his or her fingers around them; a smaller-scale, but just as important, reach issue.
o While reach is about making sure things are not too far away, clearance is primarily focused on making sure things aren't too close together. In interaction design terms, we might think of this as literal "white space". There needs to be adequate room for the hands to move around the handles without bumping into anything, constraining usability or performance.
o We tend to think of posture as a full-body issue; standing upright or bending. But in fact posture, defined as deviation from a natural, comfortable position, can be examined at the level of a specific limb or limb-segment. In handheld controllers, wrist posture is frequently the factor of interest. A design that forces the joints into contorted, unconformable positions, particularly for extended periods, is an ergonomic failure.
o Strength was particularly important for the SQWEEZE as it's essentially a force transfer device. Testing with children indicated the device should not exceed 2.5lbs, but it also had to withstand up to 150lbs of crushing and pulling - the strength of a 90th percentile male. In more general terms, designs should avoid requiring significant exertion by the user, but need to have sufficient resistance to provide feedback and avoid accidental triggering, for example as on a mobile phone keypad.

I've just scratched the surface of these four key ergonomic factors, but I want to re-enforce a couple of critical issues to keep in mind. First, when we talk about an particular factor, it's important to consider it at multiple levels of scale. In the case of posture, we might look broadly at how someone approaches a kiosk from an overall body perspective, but then focus more narrowly on the deviation of the hands and fingers. Second, these factors are not independent of each other - in fact they are highly co-influential. For example, if there is limited visual access, then a user may change his or her body and limb postures to accommodate improved field-of-view, but in doing so, increase the extent of reach and reduce the effective transfer strength.

Last, but not least, I add a fifth factor which goes beyond the physical, to the perceptual and cognitive: Feedback. Feedback refers to the user's ability to receive input on the impact of their actions on the interface or system. For the SQWEEZE this can mean the tactile, visual and even audible mechanical feedback that corresponds with using the device. For a touch screen kiosk, there is the perceived resistance of the touch service, and the feedback from the software responses.

Putting all this together, a person conducting observational research can use these five factors as a checklist for identifying potential ergonomic problems in real-time, or post-hoc (e.g. with video review).

As a mnemonic aid, putting Feedback together with the other four ergonomic factors (Reach, Clearance, Posture and Strength), gives us FRCPS, or FoRCePS. This was actually created as a mental cue during surgical observations, thus the clinical abbreviations. I'm certainly open to more approachable re-combinations of the letters."    (Continued via DESIGNING *for humans)    [Usability Resources]

Observing Ergonomic Problems - Usability, User Interface Design

Observing Ergonomic Problems

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