Keynote for HTML5 Devconf Fall 2014. I discuss the psychological and physical response times of human beings as nodes on the Internet, and answer the title question.

1. Daniel Austin
GRIN Technologies, Inc.
“The Connected Life Company”
daniel.austin@grintech.net
V1.1

2. Getting Started With Web Performance
• Upcoming Title Change:
“The Definitive Guide to Web Performance”
• Pre-release available now
• First 4 Chapters online at OReilly.com
• Full release in Dec. 2014

3. Today’s Talk: Questions
Q: What Does Performance Mean?
Q: What Do ‘Fast’ and ‘Slow’ Mean?
Q: How Fast is Fast Enough?

4. The MPPC Model of Web Performance
T1 = Network Connection T2 = Server Duration T3 = Network Transport T4 = Client Processing

5. The User Time
Source: “The Economic Value of Rapid Response Time” Doherty & Thadani 1982, IBM Research

6. The Layer 8 Hypothesis
You are a Node on the Internet!
• The Internet Connects People,
Not Computers
• Humans are Machines that Turn
Data into Information

7. Hi, What’s Your Bandwidth?
Source: “The User Illusion” Tor Norretranders

8. Optical Transmission: MK1 Eyeball
• Human Visual Bandwidth ~ 8.75 MBPS
• Not a Simple Digital System!

9. The NeoCortical Visual Stack
Thus just ~100 ms after image photons impinge on the retina, a first wave of image-selective neuronal activity
is present throughout much of The Inferior Temporal lobe…
“How does the brain solve visual object recognition?” Dicarlo, et al Neuron. Feb 9, 2012; 73(3): 415–434

10. Grokking isn’t the Same as Seeing
• THuman = TP+TC+TM
• ~ 100ms to identify distinct objects
• ~ 150ms to respond
• => 250ms User ‘think time’
Perceptual
Processor
Cognitive
Processor
• 10x variability
Motor
Processor
TP ~ 100 ms [50-200ms]
TC ~ 70ms [30-100ms]
TM ~ 70ms [25-170ms]
Source: MIT/CSAIL

11. Cognitive Processing: Choice Response Times
• When faced with N
choices, users will take
O(log N) cycles to process
the data and respond.
(Hick-Hyman Law)
• This also means that users
can process additional
tasks in constant time

12. Fitt’s Law and the Web
• The motor processing time TM is related to the
size and apparent distance of the object on
the display and is limited by accuracy

13. Fitt’s Law and Mobile Devices
• Implications for RWD
• Size of UI objects on small screens limits accuracy
• May require qualitative redesign for human motor
limitations
• Wearables and small devices are near the point of
minimum usability for visual interaction
• Are recent increases in mobile phone sizes an
accommodation to Fitt’s Law?

14. Test Your Own Response Time
• Best Scores: ~100-200ms
• Try it yourself
http://www.humanbenchmark.com/tests/reactiontime

15. The Practice Effect
Can you optimize your own response time?
Yes, up to a point.
The Power Law of Practice indicates that
the time required to do a task the nth time
declines exponentially and then stabilizes.
Tn = T1*n-a with a ~ 0.2-0.6

16. Browsing Fast and Slow
Fast
THuman > TSystem
The system waits on the user
Slow
THuman < TSystem
The user waits on the system

17. Is 100ms ‘Fast Enough’?
• In most cases, THuman > 100ms
• But users are sensitive to changes ~ 30ms
• Client processing adds additional time
• User tasks often involve more than one response
step

18. It’s Fast Enough When…
…It Takes YOU Longer to Process the
Information…
…Than It Takes to Deliver It.

19. When It’s Fast Enough, Then What?
• Make it fast for everyone
• Then you can try adding more stuff to the page!
But not until then!
• Technologies are becoming available more quickly
than we can optimize them

20. Summing Up: How Fast is Fast Enough?
It’s Fast Enough When You are Waiting on Your Users,
Not Making Them Wait for You!
Human Mental Processing is Parameterized by ~100ms
Response Times
We Can’t Expect the Web to Achieve TV-level Response
Times
Ultimately, Performance Is About Respect.

21. Daniel Austin
GRIN Technologies, Inc.
“The Connected Life Company”
daniel.austin@grintech.net
V1.1
@daniel_b_austin
@GRINTechInc