We tend to talk very glibly about scanning a list of results from a search without for one moment considering what this action involves. The speed at which the results can be scanned and appreciated in terms of their potential relevance varies from searcher to searcher. Anything that inhibits this scanning speed is likely to have an impact on the level of satisfaction with the search application. This scanning speed is also known as perceptual speed.

It is important not to confuse perceptual speed with readability. Perceptual speed relates to the ability of the searcher to make out words and other information elements so that they can home in on potentially relevant items.  Readability is about the comprehension of those elements in the process of extracting information and knowledge. When you walk in the departure area of a major airport looking for your flight amongst 30 others you do not start at the top and read each one in turn until you come to your flight. You just scan the destination column until you come to a shape that looks a lot like Paris and then check the time and departure gate. How quickly you can do this is a function of perceptual speed. 

Perceptual speed factors come to the fore in the case of federated, multi-lingual, cross-lingual and aggregated search when the user interface may be presenting results from different applications in different formats. This is a particular feature of a recent paper by Arguello and Choi.

Defining ‘perceptual speed’

We need to take account of the impact of perceptual speed and learning in the context of information retrieval. This issue has been on the research agenda since the 1970s. This early work, its implications and the setting of an agenda for research was the subject of a paper presented to the SIGIR Conference in 1994 by Bryce Allen at the University of Illinois. Perceptual speed is a cognitive ability defined as the speed in comparing figures or symbols, scanning to find figures or symbols, or carrying out other very simple tasks involving visual perception. Allen had shown in some work on CD-ROM search that this ability influences performance of untrained users who search information retrieval systems. He also suggested that people who score higher on standard tests of perceptual speed perform higher quality searches (as measured by standard precision and recall ratios) than those who score lower on the tests.

Measuring personal perceptual speed

This brings us to a key issue in the consideration of perceptual speed, namely the challenges of measuring perceptual speed. This issue is discussed in detail in a paper by Olivia Foulds, Leif Azzopardi and Martin Halvey (all at the University of Strathclyde) that they presented (virtually) at the CHIIR 20 conference in 2020. The title of the paper was Reflecting upon Perceptual Speed Tests in Information Retrieval: Limitations, Challenges, and Recommendations. This link is to an open access version from the University of Strathclyde. It includes a very comprehensive bibliography. When you note that this bibliography extends to 45 research papers you will conclude that this is a complex but very important topic.

The abstract to the paper is an excellent summary of the current position

“Prior studies using PS [Perceptual Speed] tests have demonstrated that PS affects multiple factors in Information Retrieval (IR), such as a user’s search performance, interaction with the system, time spent completing tasks, and subjective impression of their workload. With greater knowledge of PS, systems could be designed that accommodate users with low PS to improve their overall search experience. However, in this perspectives paper, we analyse how PS tests have been used in IR, and identify multiple uncertainties regarding PS content, administration, analysis, and reporting of findings. Consequently, we aim to stir discussion between IR researchers by drawing awareness to these issues. As a result, we further discuss challenges involved in advancing how future PS tests are used in IR. Finally, we propose recommendations that have the potential for enhancing the reliability and validity of current PS tests.”

The implications of perceptual speed capabilities are not just about the design of the results themselves but also about the amount of visual clutter that the search user is presented with, typically a stack of filters on the left of the screen and various other options presented on the right of the screen. In another recent paper Olivia Foulds and Dawn Wood on the implications for tactical warfare situations

“Our results found that clutter of any kind causes negative effects on a user’s search performance and subjective feelings. This suggests that regardless of the content, if it visually has to be processed, performance degrades. This reaffirms work that demonstrated how peripherally viewed distracting objects can overload cognition even without direct gaze, leading to a bottleneck that impairs object perception.”

It would be very useful to have a reliable perceptual speed test but until we do it remains important to be aware of the implications of perceptual speed and to be aware of them when conducting usability tests. It could be that the outcomes of these tests are being biased because the test subjects have widely differing capabilities of perceptual speed that neither they nor the test moderators are aware of.

Perceptual speed, working memory and inhibitory attention

The situation is further complicated by the fact that being able to use search interfaces effectively is not just function of perceptual speed but also of working memory and of inhibitory attention control. Inhibitory attention refers to someone’s ability to ignore (or inhibit attention to) stimuli that are not relevant to the task at hand. These issues are discussed in detail in papers by Adele Diamond and by Jamie Arguello and Bogeum Choi. I would also recommend a Master’s thesis [45pp download] by Lauren Turpin entitled Vertical Search Behavior and Preference of Users with Different Visual Memory and Perceptual Speed Abilities, which she undertook under the supervision of Jamie Arguello.

Perceptual speed and stopping distance

There is always time pressure on a search, and the idea that a user works through each item in turn, assesses its relevance and then moves on to the next item is not realistic. As a result, another factor to take into account is the extent to which perceptual speed has an impact on stopping distance. This is the number of results examined before the user either runs out of time or decides that the results are now starting to show significantly lower levels of relevance so there is no point in continuing. For users who find the process of scanning slow or difficult they may decide to abandon reviewing the results through what might be regarded as cognitive tiredness. This highlights the benefits of taking a cognitive rather than mechanistic approach to optimising search performance. 

 The implications for search user interface design

The wider issue about these challenges is that so much of information retrieval and enterprise search development is focused on the matching of a query to an index and nominally presenting the most relevant documents as far towards the top of a results list as possible. That is of course a very valid and important objective but assumes a degree of optimum cognitive performance and subject knowledge that is arguably unreal and certainly highly variable. This also brings into play the issue about the extent to which a search user with some degree of dyslexia (it is a spectrum cognitive disorder) will have a slower perceptual speed, compounding their difficulties in using search applications. When you also take into account recent research on the difficulties that users experience in interpreting documents you will understand why I recommend that specifying search functionality should start with a consideration of how the results are going to be displayed in the user interface.

Martin White