DESCRIPTION The classic dictum in HCI, “know your users,” has broader implications than is generally realized. Users don’t exist in isolation. They live and work in contexts. They have roles, responsibilities, and tasks. All these elements—users themselves, their contexts, their responsibilities, and their goals—shape both the design possibilities and constraints of not only applications but also the rendering of any new interface paradigm.
APPLICATION TO NUI Working from our definition of the NUI, we can see that it means different things to different people in different ecological, social, and business contexts. A NUI that responds to in-air gestures would make no sense in a car. For most people, the evolved interface for automobiles requires one or two hands and one or two feet to drive. Thus many NUIs in autos employ voice input or rely on simple touchscreens not far away from the common sight lines. This simple example illustrates the interdependence of context, user capabilities, and task goals. Our discussion here is limited to the touch- and gesture-based NUIs offered on an increasing array of products. LESSONS FROM THE PAST NUIs that enable touch, gesture, and object recognition are well suited to contexts where users will walk up and use the system and where an interaction with the system is intended to be enjo,yable in and of itself. There are many walk up and use interfaces where the interaction is intended to be simply fun,ctional. Examples include parking meters, ATMs, and automated airport check-in systems. All of these are purely fun,ctional. The user is therefore a result and woe betide the overzealous designer who attempts to incorporate progressive difficulty or arcane mechanics into such a system. In contrast, the walk up and use NUI needs to be attractive in approach and engaging in use. That is in part because its use is often discretionary, and in many cases its sole goal is to provide engaging diversion while the user waits for something or someone. This engaged waiting state often serves a larger business strategy.
For example, for leisure and entertainment businesses, keeping the user amused is an important business goal. In other environments such as retail stores, the NUI provides a simple and intuitive interface of mutual interaction by two or more users. Thus a customer and salesperson can interact in a natural way much as they would across a desk. But in this case, the “desk” is enhanced by computer technology that allows both users to interact with the content on a equal basis.
In these environments there are different kinds of differentiation and numerous mechanisms to differentiate users when that is required in the interaction. There may also be contexts where user differentiation is not required or even desirable. l Differentiation by flexible role assignment. This is most readily demonstrated in game interfaces, which are common in leisure and entertainment environments. Here user roles are flexible at the beginning of the game and are often assigned by agreement or simple physical position. The system does not need to identify a specific person.
l Fixed role definition. Sales environments are typical examples. By definition there is a seller and a buyer. They interact across a table. While their task is tightly coupled, their interaction is fluid. The system may or may not need to identify a specific person or role. The buyer and the seller interact with the system in the same way. For those systems that provide information, individual identification is not needed. The further the system moves into the typical business transaction, the more requirement there is for personal identification. The system may need to identify the seller so that he or she can be credited for engaging the customer and making the sale. If the system is designed to complete the transaction, then in most cases the seller and the buyer (or more precisely the payee and the payment source) need to be individuated. l Personal identification. In this case, the unique user must be indentified at an early stage in the transaction because the nature of the transaction depends on knowing who the user is. A typical example is a loyalty card. Identification of the person cues the system to provide customized options based on who the user is. In some cases, the user may be identified not as an individual but as a member of a class of people, for example, people who bring in a circular or special offer coupon. They are unique only in being part of a class; high rollers are another example. l Identifying a user for the duration of the interaction. In this case, the user is uniquely identified in relation to the system, for example, this is the user on the “north” side of the system. This capability allows for role-differentiated interactions. For example, the person on the north side will be the goalie in a tabletop hockey game. l Differentiated roles. All the role differentiation we have discussed so far applies to end users. Any NUI system will also need to identify users in relation to roles with respect to the unit itself. These include end users, system managers, and support and maintenance staff. The system managers need access to tools and capabilities that are barred to end users.
DESIGN GUIDELINES The class into which users and their actions fall is determined by the type of identification used and in many cases the method of identification. Must l Don’t attempt to identify users if you don’t need to. Except in widely accepted contexts (for example, ATM systems), users prefer to remain anonymous. They are highly suspicious when asked to identify themselves for a system. l If users are asked to identify themselves, they must see a clear benefit and be assured that there will be no negative consequences to identifying themselves. For example, users readily accept the need to identify themselves when they make a purchase. However, they are reluctant to identify themselves to an automated system early in the shopping process. Should l When users are asked to identify themselves, the process should be easy, private, and secure. l For users with system management roles, user identification can use more traditional methods. Could l In some cases, mixing modalities of interaction may be the best way to approach the problem of identifying a specific person. For example, the interface may read a credit card that was supplied as the payment source and key into a database of customers indexed by that card number.
SUMMARY The challenge of identifying users in the NUI is made more complex by the following facts: l The system with the NUI is often in a public place. l The systems with NUIs are relatively novel and therefore don’t benefit from traditional social conventions. l For NUIs to use their native technology, for example, optical recognition, that technology needs to be sufficiently developed to read objects such as credit, ID cards or biometric elements.