Experimental Design

The study evaluated two main interface factors: "task presentation" and "display representation".

The task presentation alternatives concern the visual separation of the two clinical tasks and include three conditions:

1. 90 degree separation (90-D)
2. 0 degree separation (0-D)
3. Head-stabilization of the ECG object (HS).

The display representation alternatives concern the format of ECG information display and include two conditions:

1. Waveform
2. 3D.

All subjects performed the simultaneous ECG and BP tasks under all combinations of presentation and representation. The design is thus a 2x3 crossover factorial design. The order of trials is counterbalanced across subjects.

The protocol for each subject consists of these steps:

1. The subject read written instructions about the study and the simulated clinical tasks.
2. The subject watched a training video which showed the WF and 3D variants side-by-side through all the ten test rhythms
3. The subject performed a short trial run twice to insure understanding of the task instructions.
4. The subject performed six study runs corresponding to the six test conditions.

Each condition consists of a randomly created but consistently used (across subjects) series of heart rhythms built from eight rhythm primitives (two rhythms from the instruction set are never used). Each abnormal rhythm is shown 5 times for between 2-4 seconds each time. Between each repetition of an abnormal rhythm, a stretch of NSR is displayed to disambiguate responses when the user's responses lag behind. Each entire study run per condition thus presents the subject with 35 abnormal rhythm episodes to interpret, separated by 36 normal rhythm episodes, and lasts between 3-4 minutes. Concurrently, the subject sees on average about 40 abnormal BP events, depending on how rapidly they deal with deviations. Between conditions, the subjects are allowed to remove the head mounted display if they desire.

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