In the Phase I report we noted that automation does not refer to a single either-or entity. Rather, forms of automation can be considered to vary across a continuum of levels. The notion of levels of automation has been proposed by several authors (Billings, 1996a, 1996b; Parasuraman et al., 1990; Sheridan, 1980). In the Phase I report, we identified a 10-level scale, that can be thought of as representing low to high levels of automation (Table 1.1). In this report we expand on that scale in three important directions: (1) differentiating the automation of decision and action selection from the automation of information acquisition; (2) specifying an upper bound on automation of decision and action selection in terms of task complexity and risk; and (3) identifying a third dimension, related to the automation of action implementation.

First, in our view, the original scale best represents the range of automation for decision and action selection. A parallel scale, to be described, can be applied to the information automation. These scales reflect qualitative, relative levels of automation and are not intended to be dimensional, ordinal representations.

Acquisition of information can be considered a separate process from action selection. In both human and machine systems, there are (1) sensors that may vary in their sophistication and adaptability and (2) effectors (actuators) that have feedback control attached to do precise mechanical work according to plan. Eyes, radars, and information networks are examples of sensors, whereas hands and numerically controlled industrial robots are examples of effectors. We recognize that information acquisition and action selection can and do interact through feedback loops and iteration in both human and machine systems. Nevertheless, it is convenient to consider automation of information acquisition and action selection separately in human-machine systems.

Second, we suggest that specifications for the upper bounds on automation of decision and action selection are contingent on the level of task uncertainty. Finally, we propose a third scale that in this context is dichotomous, related to the automation of action implementation, applicable at the lower-levels of automation

TABLE I.1 Levels of Automation

Scale of Levels of Automation of Decision and Control Action



The computer decides everything and acts autonomously, ignoring the human.



informs the human only if it, the computer, decides to



informs the human only if asked, or



executes automatically, then necessarily informs the human, and



allows the human a restricted time to veto before automatic execution, or



executes that suggestion if the human approves, or



suggests one alternative, and



narrows the selection down to a few, or



The computer offers a complete set of decision/action alternatives, or



The computer offers no assistance: the human must take all decisions and actions.

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