Human monitoring behavior in a multiple-instrument setting: independent sampling, sequential sampling or arrangement-dependent sampling

This study aims at contributing to the understanding of human monitoring behavior in multiple instrument settings. Eye movements were recorded so as to test whether sampling behavior is more consistent with traditional normative models (Senders, 1983) or with alternative approaches that emphasize heuristics and strategies rather than quantitative modelling. A core assumption of normative modelling concerns the premise that sampling one instrument is independent of the other instruments in an array. This assumption was tested in three experiments. In a first experiment, subjects monitored four independent continuous stochasts so as to detect critical situations. In a fast condition, two instruments were paired with two relatively fast changing instruments. In a slow condition, the two instruments were paired with two relatively slow changing instruments. Sampling one instrument appeared to be independent of the rates of change of the other instruments in the array. Furthermore, sampling was a function of the information generation rates of the individual instruments. This is in accordance with normative modelling. However, the spatial arrangement of the instruments on the display as well as the presence of a central fixation point strongly affected sampling behavior. In a second experiment, subjects monitored six instruments. In addition, there was no central fixation point. The results indicated again that a perceptual heuristic was used in that the spatial arrangement of the instruments on the display affected sampling behavior. Horizontal transitions occurred more often than would be predicted on the basis of independent sampling. Diagonal transitions occurred less often than would be predicted. Finally, a third experiment tested whether this preference for sampling by means of horizontal eye movements at the expense of diagonal eye movements would, under conflict situations, affect the mean sampling interval of specific instruments. In a four-instrument monitoring task, sampling intervals of two slow and two fast independent instruments were compared in different spatial arrangements. Sampling intervals strongly depended on the arrangement of the instruments on the display. Human monitoring seems to be biased by a tendency towards sampling by means of horizontal transitions at the cost of diagonal transitions. Under certain conditions, this tendency might make sampling intervals unrelated to the information generation rates of the individual instruments.