Last week, we released a report with, among other findings, this major discovery: the median top retail website takes 7.25 seconds to load. This represents a 22% slowdown from the median load time of 5.94 seconds recorded just one year earlier.
If you’re new to the world of web performance, you need to know there’s a lot of talk about the importance of shaving not just seconds, but even milliseconds, off page load times. Case studies from companies ranging in size from small web shops to Walmart have found that faster pages correlate to improvements in page views, retention, conversions, revenue, and every other KPI you care about.
Today I want to talk about the “why” behind these findings.
Why exactly do we crave a faster online experience? Is this craving learned or acquired? And to what degree, if any, can it be overcome?
Slow pages cause “web stress”: increased agitation and poorer concentration
A 2010 study at Glasgow Caledonian University found that slowing down web pages during an online transaction led to increased agitation and poorer concentration in the study’s participants. The participants wore an EEG (electroencephalography) cap to monitor their brain wave activity. The experiment also used EOG (electrooculograph) technology to track eye movements and facial muscle movements. Participants completed tasks using either a 5Mb web connection, or a connection that had been artificially throttled to 2Mb.
Brain wave analysis from the experiment revealed that participants had to concentrate up to 50% harder when using badly performing websites. EOG technology and behavioral analysis of the subjects also revealed greater agitation and stress in these periods.
Why the stress? Blame it on our short-term memory.
Usability expert Jakob Nielsen states that human responses to poor load times is, in a large part, due to our poor short-term memory. Information stored in our short-term memory decays quickly, which is why we don’t perform as well when we have to wait, even for just a few seconds. And after 10 seconds? You can forget about it. Literally.
But why is this? This is where things get interesting.
At any given moment, there are three types of memory processing at work in your brain:
- Sensory memory
- Short-term memory
- Working memory
(There’s also long-term memory, but it doesn’t really come into play here.)
Sensory memory: Your occipital lobe (AKA “the memory store”) works in 100ms bursts.
Every time you see something, this visual information is taken in by photoreceptor cells in your eyes and then sent to the occipital lobe in your brain. This is called the “iconic memory”, which is just one of our three types of sensory memories. (The other two govern sound and touch.)
People have been studying how iconic memory works for almost 300 years. In one of the earliest studies, performed in 1740, a glowing coal was attached to a cart wheel and the wheel was rotated faster and faster until observers perceived an unbroken circle of light. The study concluded that the glowing coal had to perform a complete cycle in 100 milliseconds or less in order to achieve persistence of vision. After 100 milliseconds, the “memory store” runs out. This number has remained fairly consistent throughout the centuries.
Interestingly (and not coincidentally), 100 milliseconds is Google’s stated goal when it comes to page load times.
We have no control over how our sensory memory works.
Iconic memory, along with the other sensory memories, is primitive. We can’t consciously choose what information is stored in our iconic memory, and we can’t will it to last longer. If we could, we’d probably go crazy or accidentally walk in front of a bus. Some sensory memory does stick, of course, provided it’s used quickly and eventually consolidated into the long-term memory.
Short-term memory and working memory: Working together to keep you from walking in front of a bus.
If our sensory memory’s role is to provide comprehensive information on our entire sensory experience, it’s our short-term memory’s job to extract the relevant bits and throw them into the hopper of our working memory. Your short-term memory can store information for 10-15 seconds, at most, just enough time for your working memory to process, manipulate, and control that information.
The goal in getting page load times down to 100 millisecond is to keep information from falling through the cracks in our iconic memory, while also giving our short-term and working memory ample time to do all the parsing they need to do before they start losing information.
This is where we get into the idea of “flow”.
Flow: We’re hard-wired to perform tasks seamlessly.
Human beings have evolved to perform actions in beautiful, sequential flows. For hundreds of thousands of years, our day-to-day tasks — building a fire, hunting antelope, baking bread, milking a cow — have been a series of minute actions that flow more or less seamlessly into the next. This is hard-wired. It’s only in the past 40 or so years that we’ve imposed an entirely new way of processing information on our unsuspecting brains. And simply put: we aren’t wired to deal with the fits and starts of human-computer interaction.
I encourage you to follow the links in this post — and click on the infographic embedded in this post — for some fascinating additional reading on some of the science behind performance. And if you haven’t yet downloaded our free quarterly State of the Union for retail web performance, please do.
Download the report: State of the Union: Ecommerce Page Speed & Web Performance [Spring 2013]