Predicting User Performance and Errors by Marc Halbrügge

Author:Marc Halbrügge
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Design

A three-factor within-subjects design as applied, the factors being goal relevance (device- versus task-orientation), task necessity (non-obligatory vs. obligatory), and secondary task difficulty (none versus onset to onset stimulus intervals 5 s, 4 s, 3 s). User tasks were grouped into four blocks of eleven to twelve individual tasks. Each participant was randomly assigned to one of eight pre-selected block sequences so that block position and block succession were counterbalanced across participants as well. The secondary WMU task was always introduced after the completion of the first block and its sequential demand was gradually increased from 5 s stimulus interval in the second to 3 s in the fourth and last block. Each interval was split into equally long stimulus and blank phases.

Procedure

Every block started with comparatively easy recipe search tasks, e.g., “search for German main dishes and select lamb chops”.9 Users would then have to change the search attributes, e.g., “change the dish from appetizer to dessert and select baked apples”. The second half of each block was made of more complex tasks that were spread over more screens of the interface and/or needed memorizing more items. The participants either had to create ingredients lists for a given number of servings, or had to make shopping lists using a subset of the ingredients list, e.g., without salt and flour. All instructions were read to the participants by the experimenter. Every individual trial was closed by a simple question the participants had to answer to keep them focused on the kitchen setting, e.g., “how long does the preparation take?” During each instruction phase the complete screen was blanked (see Fig. 6.12).

Fig. 6.12Sequence of screens within a single trial in the dual task condition

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