Aardvark employees would get the questions from beta test users and route them to users who were online and would have the answer to the question. This was done to test out the concept before the company spent the time and money to build it, said Damon Horowitz, co-founder of Aardvark, who spoke at Startup Lessons Learned, a conference in San Francisco on Friday.

“If people like this in super crappy form, then this is worth building, because they’ll like it even more,” Horowitz said of their initial idea.

At the same time it was testing a “fake” product powered by humans, the company started building the automated product to replace humans. While it used humans “behind the curtain,” it gained the benefit of learning from all the questions, including how to route the questions and the entire process with users.

This is a really good idea, as I’ve argued before on this blog and in a chapter for developers of mobile health interventions. What better way to (a) learn about how people will use and experience your service and (b) get training data for your machine learning system than to have humans-in-the-loop run the service?

My friend Chris Streeter wondered whether this was all done by Aardvark employees or whether workers on Amazon Mechanical Turk may have also been involved, especially in identifying the expertise of the early users of the service so that the employees could route the questions to the right place. I think this highlights how different parts of a service can draw on human and non-human intelligence in a variety of ways — via a micro-labor market, using skilled employees who will gain hands-on experience with customers, etc.

I also wonder what UIs the humans-in-the-loop used to accomplish this. It’d be great to get a peak. I’d expect that these were certainly rough around the edges, as was the Aardvark customer-facing UI.

Aardvark does a good job of being a quite sociable agent (e.g., when using it via instant messaging) that also gets out of the way of the human–human interaction between question askers and answers. I wonder how the language used by humans to coordinate and hand-off questions may have played into creating a positive para-social interaction with vark.

“Supertaskers did a phenomenal job of performing several different tasks at once,” Watson says. “We’d all like to think we could do the same, but the odds are overwhelmingly against it.” (Wired News & Science News)

The researchers, Watson and Strayer, argue that they have good evidence for the existence of this individual variation. One can find many media reports of this “discovery” of “supertaskers” (e.g., Psychology Today). I do not think this conclusion is well justified.

First, let’s consider the methods used in this research. 100 college students each completed driving tasks and an auditory task on a mobile phone — separately and in combination — over a single 1.5 hour session. The auditory task is designed to measure differences in executive attention by requiring participants do hold past items in memory while completing math tasks. The researchers identified “supertaskers” as those participants who met the following “stringent” requirements: they were both (a) in the top 25% of participants in performance in the single-task portions and (b) and not different in their dual-task performance on at least three of the four measures by more than the standard error. Since two of the four measures are associated with each of the two tasks (driving: brake reaction time, following distance; mobile phone task: memory performance, math performance), this requires that ‘’supertaskers” do as well on both measures of either the driving or mobile phone task and one measure of the other task.

There may be many issues with the validity of the inference in this work. I want to focus on one in particular: the inference from the observation of differences between participants’ performance in a single 1.5 hour session to the conclusion that there are stable, “trait” differences among participants, such that some are “supertaskers”. This conclusion is simply not justified. To illustrate this, let’s consider how the methods of this study differ from those usually (and reasonably) used by psychologists to reach such conclusions.

Psychologists often study individual differences using the following approach. First, identify some plausible trait of individuals. Second, construct a questionnaire or other (perhaps behavioral) test that measures that trait. Third, demonstrate that this test has high reliability — that is, that the differences between people are much larger than the differences between the same person taking the test at different times. Fourth, then use this test to measure the trait and see if it predicts differences in some experiment. A key point here is that in order to conclude that the test measures a stable individual difference (i.e., a trait) researchers need to establish high test-retest reliability; otherwise, the test might just be measuring differences in temporary mood.

Returning to Watson and Strayer’s research, it is easy to see the problem: we have no idea whether the variation observed should be attributed to stable individual differences (i.e., being a “supertasker”) or to unstable differences. That is, if we brought those same “supertasker” participants back into the lab and they did another session, would they still exhibit the same lack of performance difference between the single- and dual-task conditions? This research gives us no reason that expect that they would.

Watson and Strayer do some additional analysis with the aim of ruling out their observations being a fluke. One might think this addresses my criticism, but it does not. They

performed a Monte Carlo simulation in which randomly selected single-dual task pairs of variables from the existing data set were obtained for each of the 4 dependent measures and then subjected to the same algorithm that was used to classify the supertaskers.

That is, they broke apart the single-task and dual-task data for each participant and created new simulated participants by randomly sampling pairs single- and dual-task data. They found that on this analysis there would be only 1/15th of the observed ‘’supertaskers”. This is a good analysis to do. However, this just demonstrates that being labeled a “supertasker” is likely caused by the single- and dual-task data being generated by the same person in the same session. This stills leaves it quite open (and more plausible to me) that participants’ were in varying states for the session and this explains their (temporary) “supertasking”. It also allows that this greater frequency of “supertaskers” is due to participants who do well in whatever task they are given first being more likely to do well in subsequent tasks.

My aim in this post is to suggest some challenges that this kind of approach has to face. Part of my interest in this is that I’m quite sympathetic to identifying stable, observed differences in behavior and then “working backwards” to characterizing the traits that explain these downstream differences. This  exactly the approach that Maurits Kaptein and I are taking in our work on persuasion profiling: we observe how individuals respond to the use of different influence strategies and use this to (a) construct a “persuasion profile” for that individual and (b) characterize how much variation in the effects of these strategies there is in the population.

However, a critical step in this process is ruling out the alternative explanation that the observed differences are primarily due to differences in, e.g., mood, rather than stable individual differences. One way to do this is to observe the behavior in multiple sessions and multiple contexts. Another way to rule out this alternative explanation is if you observe a complex pattern of behavioral differences that previous work suggests could not be the result of temporary, unstable differences — or at least is more easily explained by previous theories about the relevant traits. That is, I’m enthusiastic about identifying stable, observed differences in behavior, but I don’t want to see researchers abandon the careful methods that have been used in the past to make the case for a new individual difference.

Watson, Strayer, and colleagues have apparently begun doing work that could be used to show the stability of the observed differences. The discussion section of their paper refers to some additional unpublished research in which they invited their “supertaskers” from this study and another study back into the lab and had them do some similar tasks measuring executive attention (but not driving) while in an fMRI machine. They report greater “coherence” in their performance in this second study and the previous study than control participants and better performance for “supertaskers” on dual-N-back tasks. But this is short of showing high test-retest reliability.

Since little is said about this work, I hesitate to conclude anything from it or criticize it. I’ve contacted the authors with the hope of learning more. My current sense is that Watson and Strayer’s entire case for “supertaskers” hinges on research of this kind.

References

One obvious way a model gets more complex is by adding predictors. There has recently been a good deal of attention on using the frequency of search terms to predict important goings-on — like flu trends. Sharad Goel et al. (blog post, paper) temper the excitement a bit by demonstrating that simple models using other, existing public data sets outperform the search data. In some cases (music popularity, in particular), adding the search data to the model improves predictions: the more complex combined model can “explain” some of the variance not handled by the more basic non-search-data models.

This echos one big takeaway from the Netflix Prize competition: committees win. The top competitors were all large teams formed from smaller teams and their models were tuned combinations of several models. That is, the strategy is, take a bunch of complex models and combine them.

One way of doing this is just taking a weighted average of the predictions of several simpler models. This works quite well when your measure of the value of your model is root mean squared error (RMSE), since RMSE is convex.

While often the larger model “explains” more of the variance, what “explains” means here is just that the R-squared is larger: less of the variance is error. More complex models can be difficult to understand, just like the phenomena they model. We will continue to need better tools to understand, visualize, and evaluate our models as their complexity increases. I think the committee metaphor will be an interesting and practical one to apply in the many cases where the best we can do is use a weighted average of several simpler, pretty good models.

It is helpful to start with a contrast between two kinds of cases.

Distributing attention towards a single goal

In the first, there is a single task or goal that involves dividing one’s attention, with the targets of attention somehow related, but of course somewhat independent. Patricia Greenfield used Pac-Man as an example: each of the ghosts must be attended to (in addition to Pac-Man himself), and each is moving independently, but each is related to the same larger goal.

Distributing attention among different goals

In the second kind of case, there are two completely unrelated tasks that divide attention, as in playing a game (e.g., solitaire) while also attending to a speech (e.g., in person, on TV). Anthony Wagner noted that in Greenfield’s listing of the benefits and costs of media multitasking, most of the listed benefits applied to the former case, while the costs she listed applied to the later. So keeping these different senses of multitasking straight is important.

Complications

But the conclusion should not be to think that this is a clear and stable distinction that slices multitasking phenomena in just the right way. Consider one ways of putting this distinction: the primary and secondary task can either be directed at the same goal or directed at different goals (or tasks). Let’s dig into this a bit more.²

Byron Reeves pointed out that sometimes “the IMing is about the game.” So we could distinguish whether the goal of the IMing is the same as the goal of the in-game task(s). But this making this kind of distinction requires identity conditions for goals or tasks that enable this distinction. As Ulrich Mayr commented, goals can be at many different levels, so in order to use goal identity as the criterion, one has to select a level in the hierarchy of goals.

Action identities and multitasking

We can think about this hierarchy of goals as the network of identities for an action that are connected with the “by” relation: one does one thing by doing (several) other things. If these goals are the goals of the person as they represent them, then this is the established approach taken by action identification theory (Vallacher & Wegner, 1987) — and this could be valuable lens for thinking about this. Action identification theory claims that people can report an action identity for what they are doing, and that this identity is the “prepotent identity”. This prepotent identity is generally the highest level identity under which the action is maintainable. This means that the prepotent identity is at least somewhat problematic if used to make this distinction between these two types of multitasking because then the distinction would be dependent on, e.g., how automatic or functionally transparent the behaviors involved are.

For example, if I am driving a car and everything is going well, I may represent the action as “seeing my friend Dave”. I may also represent my simultaneous, coordinating phone call with Dave under this same identity. But if driving becomes more difficult, then my prepotent identity will decrease in level in order to maintain the action. Then these two tasks would not share the prepotent action identity.

Prepotent action identities (i.e. the goal of the behavior as represented by the person in the moment) do not work to make this distinction for all uses. But I think that it actually does help makes some good distinctions about the experience of multitasking, especially if we examine change in action identities over time.

To return to case of media multitasking, consider the headline ticker on 24-hour news television. The headline ticker can be more or less related to what the talking heads are going on about. This could be evaluated as a semantic, topical relationship. But considered as a relationship of goals — and thus action identities — we can see that perhaps sometimes the goals coincide even when the content is quite different. For example, my goal may simply to be “get the latest news”, and I may be able to actually maintain this action — consuming both the headline ticker and the talking heads’ statements — under this high level identity. This is an importantly different case then if I don’t actually maintain the action at the level, but instead must descend to — and switch between — two (or more) lower level identities that are associated the two streams of content.

References

Vallacher, R. R., & Wegner, D. M. (1987). What do people think they’re doing? Action identification and human behavior. Psychological Review, 94(1), 3-15. 

1. The full name is the “Seminar on the impacts of media multitasking on children’s learning and development”.
2. As I was writing this, the topic re-emerged in the workshop discussion. I made some comments, but I think I may not have made myself clear to everyone. Hopefully this post is a bit of an improvement.

This name and description makes this sound quite like science fiction. In this post, I assimilate homuncular flexibility to the much more general phenomenon of distal attribution (Loomis, 1992; White, 1970). When I have a perceptual experience, I can just as well attribute that experience – and take it as being directed at or about – more proximal or distal phenomena. For example, I can attribute it to my sensory surface, or I can attribute it to a flower in the distance. White (1970) proposed that more distal attribution occurs when the afference (perception) is lawfully related to efference (action) on the proximal side of that distal entity. That is, if my action and perception are lawfully related on “my side” of that entity in the causal tree, then I will make attributions to that entity. Loomis (1992) adds the requirement that this lawful relationship be successfully modeled. This is close, but not quite right, for if I can make distal attributions even in the absence of an actual lawful relationship that I successfully model, my (perhaps inaccurate) modeling of a (perhaps non-existent) lawful relationship will do just fine.

Just as I attribute a sensory experience to a flower and not the air between me and the flower, so the blind man or the skilled hammer-user can attribute a sensory experience to the ground or the nail, rather than the handle of the cane or hammer. On consideration, I think we can see that these phenomena are very much what Lanier is talking about. When I learn to operate (and, not treated by Lanier, 2006, sense) my lobster-body, it is because I have modeled an efference–afference relationship, yielding a kind transparency. This is a quite familiar kind of experience. It might still be a quite dangerous or exciting idea, but its examples are ubiquitous, not restricted to virtual reality labs.

Lanier paraphrases biologist Jim Boyer as counting this capability as a kind of evolutionary artifact – a spandrel in the jargon of evolutionary theory. But I think a much better just-so evolutionary story can be given: it is this capability – to make distal attributions to the limits of the efference-afference relationships we successfully model – that makes us able to use tools so effectively. At an even more basic and general level, it is this capability that makes it possible for us to communicate meaningfully: our utterances have their meaning in the context of triangulating with other people such that the content of what we are saying is related to the common cause of both of our perceptual experiences (Davidson, 1984).

References

These human–technology relationships develop and endure over time and through radical changes in the situation. In particular, mobile phones are near-constant companions. They take on roles of both medium for communication with other people and independent interaction partner through dynamic physical, social, and cultural environments and tasks. The global phenomenon of mobile phone use highlights both that relationships with people and technologies are influenced by variable context and that these devices are, in some ways, a constant in amidst these everyday changes.

Situational variation and attribution

Situational variation is important for how people understand and interact with mobile technology. This variation is an input to the processes by which people disentangle the internal (personal or device) and external (situational) causes of an social entity’s behavior (Fiedler et al. 1999; Forsterling 1992; Kelley 1967), so this situational variation contributes to the traits and states attributed to human and technological entities. Furthermore, situational variation influences the relationship and interaction in other ways. For example, we have recently carried out an experiment providing evidence that this situational variation itself (rather than the characteristics of the situations) influences memory, creativity, and self-disclosure to a mobile service; in particular, people disclose more in places they have previously disclosed to the service, than in  new places (Sukumaran et al. 2009).

Not only does the situation vary, but mobile technologies are increasingly responsive to the environments they share with their human interactants. A system’s systematic and purposive responsiveness to the environment means means that explaining its behavior is about more than distinguishing internal and external causes: people explain behavior by attributing reasons to the entity, which may trivially either refer to internal or external causes. For example, contrast “Jack bought the house because it was secluded” (external) with “Jack bought the house because he wanted privacy” (internal) (Ross 1977, p. 176). Much research in the social cognition and attribution theory traditions of psychology has failed to address this richness of people’s everyday explanations of other ’s behavior (Malle 2004; McClure 2002), but contemporary, interdisciplinary work is elaborating on theories and methods from philosophy and developmental psychology to this end (e.g., the contributions to Malle et al. 2001).

These two developments — the increasing role of situational variation in human-technology relationships and a new appreciation of the richness of everyday explanations of behavior — are important to consider together in designing new research in human-computer interaction, psychology, and communication. Here are three suggestions about directions to pursue in light of this:

Design systems that provide constancy and support through radical situational changes in both the social and physical environment. For example, we have created a system that uses the voices of participants in an upcoming event as audio primes during transition periods (Sohn et al. 2009). This can help ease the transition from a long corporate meeting to a chat with fellow parents at a child’s soccer game.

Design experimental manipulations and measure based on features of folk psychology –  the implicit theory or capabilities by which we attribute, e.g., beliefs, thoughts, and desires (propositional attitudes) to others (Dennett 1987) — identified by philosophers. For example, attributions propositional attitudes (e.g., beliefs) to an entity have the linguistic feature that one cannot substitute different terms that refer to the same object while maintaining the truth or appropriateness of the statement. This opacity in attributions of propositional attitudes is the subject of a large literature (e.g., following Quine 1953), but this  has not been used as a lens for much empirical work, except for some developmental psychology  (e.g., Apperly and Robinson 2003). Human-computer interaction research should use this opacity (and other underused features of folk psychology) in studies of how people think about systems.

Connect work on mental models of systems (e.g., Kempton 1986; Norman 1988) to theories of social cognition and folk psychology. I think we can expect much larger overlap in the process involved than in the current research literature: people use folk psychology to understand, predict, and explain technological systems — not just other people.

References

With mTurk one can create a HIT that asks someone to rate some search results for a query, evaluate the credibility of a Wikipedia article, draw a sheep facing left, enter names for a provided color, annotate a photo of a person with pose information, or create a storyboard illustrating a new product idea. So Mechanical Turk can be used in many ways for basic research, building a training set for machine learning, or actually enabling a (perhaps prototype) service in use through a kind of Wizard-of-Oz approach. Additionally, I’ve used mTurk to code images captured by participants in a lab experiment (more on this in another post or article).

When creating HITs, a requester can specify a QuestionForm (QF) (e.g., via command line tools or an SDK) that is then presented to the worker by Amazon. This can include images, free text answers, multiple choice, etc. Additionally one can embed Flash or Java objects in it. But the easiest way of creating HITs is to use a QF and not create a Java or Flash application of one’s own. This is especially true for HITs that are handled well by the basic question form. The other option is to create an ExternalQuestion (EQ), which is hosted on one’s own server and is displayed in an iFrame. This provides greater freedom but requires additional development and it is you that must host the page (though you can do so through Amazon’s S3). QF HITs (without embeds) also offer a familiar interface to workers (though it is possible to create a more efficient, custom interface by, e.g., making all the targets larger). So when possible, it is often preferable to use a QF rather than an EQ.

For some of the uses of mTurk for powering a service, it can be important to minimize latency for specific HITs¹, including prioritizing particular new HITs over previously created HITs. For example, after some HIT has not been completed for a specific period after creation, it may still be important to complete it, but when it is completed may become less important. This can happen easily if the value of a HIT being completed has a sharp drop off after some time.

This should be done while maintaining high throughput; that is, you don’t want to reduce the rate at which your HITs are completed. When there are more HITs of the same type, workers can check a box to immediately start the next HIT of the same type when they submit the current one (see screenshot). Workers will often complete many HITs of the same type in a row. So throughput can drop substantially if any workers run out of HITs of the same type at any point: they may switch to another HIT type, or if they do your HITs once more appear, then there will be a delay. As we’ll see, these two requirements don’t seem to be well met by the platform — or at least certain uses of it.

Mechanical Turk does not provide a mechanism for prioritizing HITs of the same type, so without deleting all but particular high-priority HITs of that type, there is not a way to ensure that some particular HIT gets done before the rest. And deleting the other HITs would hurt throughput and increase latency for any new high-priority HITs added in the near future (since workers won’t simply start these once they finish their previous HITs).

EQ HITs allow one to avoid this problem. Unlike with QF HITs (without Flash and Java embeds), one does not have to specify the full content of the HIT in advance. When a worker accepts an EQ HIT, you can dynamically serve up the HIT you want to depending on changing priorities. But this means that you can’t take advantage of, e.g., the simplicity of creating and managing data from QF HITs. So though there are ways of coping, adding dynamic reprioritization to Mechanical Turk would be a boon for time-sensitive uses.

There are, of course, other factors that influence latency and throughput on mTurk when (EQ) HITs are reprioritized. Here are a few:

• HIT and sub-tasks duration. How long does it take for workers to complete a HIT, which may be composed of multiple sub-tasks? A worker cannot be assigned a new HIT until they complete (or reject) the previous one. This can be somewhat avoided by creating longer HITs that are subdivided into dynamically selected sub-tasks. This can be done with an EQ HIT or an embedded Flash or Java application in a QF HIT. But the sub-task duration is always a limiting factor, unless one is willing to force abortion of the current sub-task, replacing it will still in progress (with an EQ, Flash, or Java).
• Available workers. How many workers are logged into mTurk and completing task? How many are currently switching HIT types? This can vary with the time of day.
• Appeal of your HITs. How much do workers like your HITs — are they fun? How much do you pay for how much you ask? How many of their completed assignments do you approve?
• Reliability. How accurate or precise must your results be? How many workers do you need to complete a HIT before you have reliable results? Do other workers need to complete meta-HITs before the data can be used?

1. I use the term HIT somewhat loosely in this article. There are at least three uses that each differ in their identity conditions. (1) There are HITs considered as human intelligence tasks, and thus divided as we divide tasks; this means that a HIT in another sense can be composed of multiple HITs in this sense (tasks or sub-tasks). (2) There are HITs in Amazon’s technical sense of the term: a HIT is something that has the same HIT ID and therefore has the same specification. In QF HITs without embeds, this means all instances (assignments) of a HIT are the same in content; but in EQ HIT this is not necessarily true, since the content can be determined when assigned. (3) Finally, there is what Amazon calls assignments, specific instances of a HITs that are only completed once.

1. A general shift from examining non-discretionary use to discretionary use
2. How much easier it is to find (and not train) study participants unfamiliar with a system than experts (especially with a system that is only a prototype)
3. The push from practitioners in the direction, especially with the advent of the Web, where new users just show up at your site, often deep-linked

This focus sometimes comes in for criticism, especially when #2 is taken as a main cause of the choice.

On the other hand, some research threads in HCI continue to focus on expert use. As I’ve been reading a lot of research on both human performance modeling and situated & embodied approaches to HCI, it has been interesting to note that both instead have (comparatively) a much bigger focus on the performance and experience of expert and skilled use.

Grudin’s “Three Faces of Human-Computer Interaction” does a good job of explaining the human performance modeling (HPM) side of this. HPM owes a lot to human factors historically, and while The Psychology of Human-Computer Interaction successfully brought engineering-oriented cognitive psychology to the field, it was human factors, said Stuart Card, “that we were trying to improve” (Grudin 2005, p. 7). And the focus of human factors, which arose from maximizing productivity in industrial settings like factories, has been non-discretionary use. Fundamentally, it is hard for HPM to exist without a focus on expert use because many of the differences — and thus research contributions through new interaction techniques — can only be identified and are only important for use by experts or at least trained users. Grudin notes:

A leading modeler discouraged publication of a 1984 study of a repetitive task that showed people preferred a pleasant but slower interaction technique—a result significant for discretionary use, but not for modeling aimed at maximizing performance.

Situated action and embodied interaction approaches to HCI, which Harrison, Tatar, and Senger (2007) have called the “third paradigm of HCI”, are a bit different story. While HPM research, like a good amount in traditional cognitive science generally, contributes to science and design by assimilating people to information processors with actuators, situated and embodied interaction research borrows a fundamental concern of ethnomethodology, focusing on how people actively make behaviors intelligible by assimilating them to social and rational action.

There are at least three ways this motivates the study of skilled and expert users:

1. Along with this research topic comes a methodological concern for studying behavior in context with the people who really do it. For example, to study publishing systems and technology, the existing practices of people working in such a setting of interest are of critical importance.
2. These approaches emphasize the skills we all have and the value of drawing on them for design. For example, Dourish (2001) emphasizes the skills with which we all navigate the physical and social world as a resource for design. This is not unrelated to the first way.
3. These approaches, like and through their relationships to the participatory design movement, have a political, social, and ethical interest in empowering those who will be impacted by technology, especially when otherwise its design — and the decision to adopt it — would be out of their control. Non-discretionary use in institutions is the paradigm prompting situation for this.

I don’t have a broad conclusion to make. Rather, I just find it of note and interesting that these two very different threads in HCI research stand out from much other work as similar in this regard. Some of my current research is connecting these two threads, so expect more on their relationship.

References
Dourish, P. (2001). Where the Action Is: The Foundations of Embodied Interaction. MIT Press.
Grudin, J. (2005). Three Faces of Human-Computer Interaction. IEEE Ann. Hist. Comput. 27, 4 (Oct. 2005), 46-62.
Harrison, S., Tatar, D., and Senger, P. (2007). The Three Paradigms of HCI. Extended Abstracts CHI 2007.

Wizard of Oz techniques are well suited to prototyping mobile services, especially those using mobile messaging (SMS, MMS, voice messaging). When participants send a request, a wizard reads or listens to it and chooses the appropriate response, or just creates it on-the-fly. Since all user actions in mobile messaging are discrete messages and (depending on the application) the user can often tolerate a short delay, a few part-time wizards, such as you and a colleague, can manage a short field trial. As you’ll see, this can be used for purposes beyond many traditional uses of a Wizard of Oz.

Probing photo consumption needs with realistic motivations
One use for this technique in designing a mobile messaging service is a bit like a diary study. In designing an online and mobile photography service, we wanted to better understand what photos people wanted to view and what prompted these desires.¹ Instead of just making diary entries, participants actually made voice requests to the system for photos – and received a mobile message with photos fitting the request in return. We didn’t need to first build a robust system that could do this; a few of us served as wizards, listening to the request, doing a couple manual searches, and choosing which photos to return on demand. Though this can be done with a normal voice call, we used a mobile client application that also recorded contextual information not available via a normal voice call (e.g. location), so that participants could make context-aware requests as they saw fit (e.g. “I want too see photos of this park”)

In this case, we didn’t plan to (specifically) create a voice-based photo search system; instead, like a diary study, this technique served as a probe to understand what we should build. As a probe it provided realistic motivations for submitting requests, as the request would actually be fulfilled. This design research, in additional to other interviews and a usability study, informed our creation of Zurfer, a mobile application that supports exploring and conversing around personalized, location-aware channels of photos.
It is great if the Wizard of Oz prototype is quite similar to what you later build, but it can yield valuable insights even if not. Sometimes it is precisely these insights that can lead you to substantially change your design.

This study design can apply in designing many mobile services. As in our photos study, participants can be interviewed about the trigger for the requests (why did they want that media or information) and how satisfied they were with the (human-created) responses.²