3 ms·

> permits up to 250ms latency for touch screen response. That is ridiculously high. It practically guarantees people will think it's not working and tap again

> permits up to 250ms latency for touch screen response. That is ridiculously high. It practically guarantees people will think it's not working and tap again You're saying people evaluate and react to checkbox feedback faster than 4 times/sec? I'm not a UX person so this claim seems laughable. I might believe twice that as beyond reasonable, but there is no way the average person waits less than a quarter of a second before assuming their input failed and duplicate the effort. One can hardly even observe and process that quickly - even when paying attention.

the__alchemist 2y ago
250ms is significant in this context, and is a longer period than you evidently think.
- vsuperpower2021 2y ago
  The user is either a web developer or has some neurological disorder that dulls his ability to react. There's no other explanation for not knowing how long 250 ms is.
mrob 2y ago
Your actions are pipelined. The waiting happens in parallel with doing the next action. The 250ms delay causes a timeout exception and flushes the pipeline.
danielvf 2y ago
Imagine you have a system that ignores taps a substantial percentage of the time (either because it required more precise finger placement, or because that's life). Also most successful taps complete quickly, with only some having 250ms latency. Combine these two and most of time when nothing has happened after 250ms, it's because the tap failed to register and a new tap attempt is needed. There's been plenty of research for decades showing that 250ms response time in UX is a noticeable slowdown.
- maicro 2y ago
  I had a similar comment so I'll just add-on here - jitter definitely is a huge issue. If an interface is _consistently_ slow you know to slow down, space out actions and wait for visual confirmations; if an interface is generally responsive, though, you can get into a "rhythm" of actions which, which can lead to chaos and confusion as you try to figure out both the new state of the system, and what actions you need to take to get back on track.
  - QuercusMax 2y ago
    This is exactly what triggered the Therac-25 radiation therapy defect: the UI was very slow to update, but experienced users knew what order to hit the buttons to go through the screens quickly. Except that there was a bug where if you go too quickly, some of the software safety interlocks didn't work right, and they had removed the hardware safeties in the update from Therac-20.
- NoMoreNicksLeft 2y ago
  What's the latest research show for a reasonable latency for something like this, anyone know?
  - shepherdjerred 2y ago
    https://www.semanticscholar.org/paper/How-Much-Faster-is-Fast-Enough%3A-User-Perception-of-Deber-Jota/cd4c54600245f906667d469b02ed551350ee64ff https://www.semanticscholar.org/paper/How-Much-Faster-is-Fas...
    - NoMoreNicksLeft 2y ago
      Wow. I can believe it needs to be sub-250ms, but some of that is a little ridiculous. 60ms? Maybe I'm just old and my fast-twitch game's weak...
kurthr 2y ago
As someone with long industry experience, I share your disbelief. I'd need to see the Fitts tests results for 250ms max delay (<150ms median?) on button state, as long press is also a thing. On touch/trackpads typical double tap rate is 4-5Hz and maximum tap rate is about 10-15Hz, achievable by relatively few. It's notable that you're dealing with a touchscreen here and not a mouse (people are faster at that). Most premium Android phones in 2016 were 120-30ms motion-photon response time (low to midrange probably hit 250), while iPhones were ~80ms. Haptics add another ~30ms delay. There have been massive improvements since 2016, as it has been a competitive metric, but even with >120Hz screens sub 60ms max true latency is uncommon. As (actually my long term memory of) the MS video shows faster refresh and lower latency greatly improve smoothness and are useful for moving objects, especially scrolling (though tearing is a real issue). The problem is much more pronounced in VR/MR as eye tracking of diagonal motion is VERY discriminating. That's why they shoot for >240Hz refresh rates. Over 1kHz there doesn't seem to be a lot of improvement (2ms latency) due to a combination of cone/rod/neural filtering. If you want a very generic worst case latency calculation based on the touch acquisition rate and display refresh rate assuming no position calculation delay it is: Latency = 2/Ftouch + 2/Fdispl = 2/16Hz + 2/16Hz = 250ms
- mrob 2y ago
  Comparing latency with maximum tap rate is the same kind of fallacy as comparing it with reaction time.
  - kurthr 2y ago
    "It practically guarantees people will think it's not working and tap again" Please provide a link to your data and analysis. Seriously, I hope you don't work for a major touchscreen supplier. A good UI can deal with relatively high latency input, a bad UI can make any latency unusable. Finger motion before/after contact and rapid high force contact bounces are common problems. Many high performance interfaces "gracefully" degrade report latency to similar levels under high interference conditions.
    - mrob 2y ago
dialup_sounds 2y ago
250ms definitely noticable, even when touch typing a continuous input, not just a single tap: https://input-delay.glitch.me/ https://input-delay.glitch.me/
deleted 2y ago
[deleted]

the__alchemist 2y ago

250ms is significant in this context, and is a longer period than you evidently think.

vsuperpower2021 2y ago
The user is either a web developer or has some neurological disorder that dulls his ability to react. There's no other explanation for not knowing how long 250 ms is.

mrob 2y ago

Your actions are pipelined. The waiting happens in parallel with doing the next action. The 250ms delay causes a timeout exception and flushes the pipeline.

danielvf 2y ago

Imagine you have a system that ignores taps a substantial percentage of the time (either because it required more precise finger placement, or because that's life). Also most successful taps complete quickly, with only some having 250ms latency. Combine these two and most of time when nothing has happened after 250ms, it's because the tap failed to register and a new tap attempt is needed. There's been plenty of research for decades showing that 250ms response time in UX is a noticeable slowdown.

maicro 2y ago
I had a similar comment so I'll just add-on here - jitter definitely is a huge issue. If an interface is _consistently_ slow you know to slow down, space out actions and wait for visual confirmations; if an interface is generally responsive, though, you can get into a "rhythm" of actions which, which can lead to chaos and confusion as you try to figure out both the new state of the system, and what actions you need to take to get back on track.
- QuercusMax 2y ago
  This is exactly what triggered the Therac-25 radiation therapy defect: the UI was very slow to update, but experienced users knew what order to hit the buttons to go through the screens quickly. Except that there was a bug where if you go too quickly, some of the software safety interlocks didn't work right, and they had removed the hardware safeties in the update from Therac-20.
NoMoreNicksLeft 2y ago
What's the latest research show for a reasonable latency for something like this, anyone know?
- shepherdjerred 2y ago
  https://www.semanticscholar.org/paper/How-Much-Faster-is-Fast-Enough%3A-User-Perception-of-Deber-Jota/cd4c54600245f906667d469b02ed551350ee64ff https://www.semanticscholar.org/paper/How-Much-Faster-is-Fas...
  - NoMoreNicksLeft 2y ago
    Wow. I can believe it needs to be sub-250ms, but some of that is a little ridiculous. 60ms? Maybe I'm just old and my fast-twitch game's weak...

kurthr 2y ago

As someone with long industry experience, I share your disbelief. I'd need to see the Fitts tests results for 250ms max delay (<150ms median?) on button state, as long press is also a thing. On touch/trackpads typical double tap rate is 4-5Hz and maximum tap rate is about 10-15Hz, achievable by relatively few. It's notable that you're dealing with a touchscreen here and not a mouse (people are faster at that). Most premium Android phones in 2016 were 120-30ms motion-photon response time (low to midrange probably hit 250), while iPhones were ~80ms. Haptics add another ~30ms delay. There have been massive improvements since 2016, as it has been a competitive metric, but even with >120Hz screens sub 60ms max true latency is uncommon. As (actually my long term memory of) the MS video shows faster refresh and lower latency greatly improve smoothness and are useful for moving objects, especially scrolling (though tearing is a real issue). The problem is much more pronounced in VR/MR as eye tracking of diagonal motion is VERY discriminating. That's why they shoot for >240Hz refresh rates. Over 1kHz there doesn't seem to be a lot of improvement (2ms latency) due to a combination of cone/rod/neural filtering. If you want a very generic worst case latency calculation based on the touch acquisition rate and display refresh rate assuming no position calculation delay it is: Latency = 2/Ftouch + 2/Fdispl = 2/16Hz + 2/16Hz = 250ms

mrob 2y ago
Comparing latency with maximum tap rate is the same kind of fallacy as comparing it with reaction time.
- kurthr 2y ago
  "It practically guarantees people will think it's not working and tap again" Please provide a link to your data and analysis. Seriously, I hope you don't work for a major touchscreen supplier. A good UI can deal with relatively high latency input, a bad UI can make any latency unusable. Finger motion before/after contact and rapid high force contact bounces are common problems. Many high performance interfaces "gracefully" degrade report latency to similar levels under high interference conditions.
  - mrob 2y ago

dialup_sounds 2y ago

250ms definitely noticable, even when touch typing a continuous input, not just a single tap: https://input-delay.glitch.me/ https://input-delay.glitch.me/

deleted 2y ago

[deleted]