Time-Lapse Video Offers More Information in Less Time

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI August 1997 Column

DESIGNER'S TOOLBOX

Using time-lapse video compresses lengthy documentation, providing designers with quantitative data more quickly.

FDA's evaluation processes now include a consideration of human factors. Part of this focus is on product design procedures. Although FDA does not mandate specific procedures, it clearly wants evidence that the product design process incorporates due consideration of human factors. Addressing this key component for medical products requires study of relevant real-world tasks for which the product will be used.

Figure 1. Time-lapse video controller system.

Video documentation is essential for conducting observational research. For example, to develop a new surgical instrument, a designer should fully understand the relevant procedure by watching it, and it is helpful to see it more than once. This can be difficult if a surgical procedure lasts several hours. Video documentation enables the designer to review the procedure repeatedly within a convenient time schedule. Further, time-lapse video provides a solution for analyzing procedures that run several hours.

Time-lapse video entails taking samples rather than taping continuously. For example, a 1-second sample every 10 seconds drastically compresses the amount of video to review. When the tape is played back, the procedure unfolds like the old Disney films of blooming flowers.

One advantage of time-lapse video is that it usually requires only one videotape. Although this may seem like a small consideration, it allows the observer to set up a video camera without the need to change tapes frequently. Another advantage is that time-lapse video documentation enables designers to easily perform quantitative analyses. For example, each sample can be treated as a data point which the designer can use to determine the percentage of time in which the surgeon is using both hands or the percentage of time the surgeon's wrist is bent beyond a given number of degrees. Time-lapse video provides a manageable document that makes such data more accessible more quickly.

A time-lapse video system should contain a device that allows the designer to set both the length of the video sample and the frequency of the samples. For example, the system shown in the figure contains four pulse generators. Generator 1 creates a regular short pulse, which can be varied to alter the sample rate. This pulse stimulates generator 2, and a longer pulse, which trips a relay to turn the camera on. In the meantime, the second pulse stimulates generator 3, which can be varied to determine how long the camera will stay on. The end of the third pulse stimulates generator 4, which creates a pulse to turn the camera off. The camera remains off until generator 1 creates the next pulse to restart the cycle.

It is usually necessary to use trial and error to find the correct sample duration and sample rate for a given procedure. It is imperative to determine settings that compress the procedure to a manageable length without losing crucial pieces of information. One approach is to determine the length of the final summary video and to work back from that figure. Fifteen minutes seems to be a standard tolerance level for an average viewer. Typical settings might be a 1-second duration with four samples per minute. Such settings result in a final tape length of 4 minutes per hour of the original procedure.

A multiple-camera, split-screen system increases the amount of information, providing the designer with an additional view of a procedure. This can be particularly useful when evaluating the user's needs for a complex device or to allow the viewer to see the tasks when one camera is blocked. This advanced system also allows simultaneous close-ups and overview shots.

Stephen B. Wilcox is a partner in the Chicago-based firm Insight Product Development, and he runs Design Science, Insight's human factors and design research consulting group in Philadelphia.

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