Processing Fluency: The Missing Link in UX


Web performance has operated under a certain precept for some time: “Faster is Better.

We all know the “Three Second Rule” about the optimal window for page rendering (and the subsequent bounce when website loading takes too long), even though an analysis of the top ecommerce sites shows a considerable shortfall in the average page’s loading time, which we detailed in our most recent State of the Union Report.

Additionally, there’s been a conceptualization of websites in terms of them being like static paintings, with web designers being the artists. Maybe we should be looking at web designers as more of mini filmmakers, with their sites operating like “mini movies.” After all, the pages don’t tend to just “blip on” all at once. Instead, various elements pop up, move around, or come into focus, as in the case of progressive images.

So, is it all about the need for speed, or is there more to the equation when it comes to understanding the optimal level of user engagement when it comes to site rendering, and how does the “mini movie” concept impact user engagement?

Is there a missing link?

We decided to find out.

Employing The Latest Neuroscience Tools

We commissioned a neuroscience study with NeuroStrata, who we worked with last year to study progressive rendering. That research showed us what was possible with the available testing tools, and this time around we wanted to ask the question: “Is faster always better?”

First, we need to back up a bit.

Jacob Nielsen, a pioneer in usability studies, reported that the home pages of the most popular sites he studied took an average of 8 seconds to download, whereas the pages of the less popular sites took an average of 19 seconds to download. He therefore concludes that users will be annoyed or frustrated by pages that take any longer than about 10 seconds to load.

We’ve, of course, furthered that research, leading to the Three Second Rule. But moving beyond that somewhat simplistic point, requires digging in with a neuroscientific study. Just as we did in last year’s research, we utilized eye-tracking technology, paired with an EEG to see what was actually going on in the brains of site users.

We took three websites and presented them three ways:

  • Original: The original, unaltered rendering sequence.
  • Fast: The rendering sequence was changed to achieve the fastest load time without regard to how the page looked to the subjects while rendering.
  • Processing Fluency (PF): Here we surmised for the purposes of the study the intention of the page and then created a rendering sequence that focused on making the principal aspects salient and easy to process. We did this by looking at visual saliency models for the pages and then ‘determining a best rendering path’.

What we mean by “processing fluency” is that site rendering would unfold in an intuitive and expected way, related to task success, i.e., what the user came to the page to accomplish.

We deployed a combination of objective, non-articulated neuroscience methodologies and tools to measure user reactions at a deep non-conscious level. Our goal was to effectively evaluate emotions objectively, sensitively, and with meaningful granularity.

Test results were collated from a combination of tools which go further than trying to interpret facial micro-expressions:

  • Eye-tracking: An eye-tracker was mounted under a computer monitor. This monitored the gaze point and allowed for a visual “heat map” of where the eyes of users lingered the most on a given page.
  • Neuroimaging: An EEG (electroencephalography) system was used to measure brain responses, such as cognitive load, distraction, motivation and arousal.

The potential effects of rendering sequence were measured on both general responses to each web page, as well as to selected Areas of Interest (AOI). We were interested in testing whether initial emotional responses were predictive of later web page responses.

  • All 36 participants were asked to observe the loading of web pages on a computer monitor.
  • Three rendering sequence were tested: Fast, Original and Processing Fluent (PF).
  • During the trial, visual attention was measured with a stationary eye-tracker. Emotional and cognitive responses were recorded using EEG brain scanning (electroencephalogram).

What Did The Research Show?

We operated under the hypothesis that the page with the highest processing fluency will be more engaging than both other loading methods.

We want to understand whether a page that renders in a sequence that is in line with the subjects’ intentions and expectations will be more engaging than a page that renders in a sequence that is less-purposeful – even if that approach happens to be “faster.” We think the contextualization that occurs with an intentionally-structured loading sequence will create more engagement for the user.

This is related to the concept in psychology of “thin slicing,” which refers to making snap judgments based on small amounts of information, which could be considered “thin slices” of information. There’s a “first impression effect” in play, and these first impressions are often what stays with us.

So, was it speed that made the biggest first impression?

Indeed, as we hypothesized, the pages with the highest Processing Fluency were more engaging than pages accelerated opportunistically or those left unaltered.

These pages, when operated as successful “mini movies” in terms of how they rendered, scored better at the mental level than the other pages did when left to a default rendering sequence, or even when merely sped up.

The implication here is that rendering sequences must be tailored to the page. Faster is not always better in and of itself. It doesn’t affect emotional responses in any generalizable way – there’s no simple rule for affecting emotional responses through alterations of rendering sequence.

Visual complexity isn’t a driver, either. We didn’t find any significant relationship between visual complexity and emotional or cognitive responses.

The Bottom Line

The sequence in which a web page renders has a substantial effect on visitors’ emotional and cognitive response and at which order in which they will look at different items. At the same time, rendering sequence effects also depend on the context and design of websites as well as the speed of the page they are visiting. Some load types are optimal for certain websites, while they fail in other designs.

Remember: Rendering sequence – when tailored to the page’s context and paired with appropriate page optimization techniques – will offer the maximum amount of user engagement. This requires a web performance automation solution combined with human intelligence (including a clear understanding of the underlying principles) to determine the optimal rendering sequence for your web pages.

This is the missing part in the “faster is better” paradigm: It’s about the interplay between speed, context and rendering sequence.

You can read the full report here: Speed vs. Fluency in Website Loading: What Drives User Engagement?


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