Apple’s “Parallax” eye candy in the default iOS 7 settings stuff-up is giving untold grief to people who have vestibulo-ocular-reflex (VOR) and other balance disorders: This article explains the effect, the underlying optical and physiological principles… And most importantly, how to fix it.
Apple started to put “eye candy” into their operating systems all the way back in 1998 with Mac OS9 in the original G3 iMac; and this CPU cycle-stealing, performance-sapping and battery draining tradition was turbocharged in Mac OS X and then into iOS with all sorts of “special effects” such as the transition vortex and the new “parallax” effect, which among other things makes the icons “float” above the wallpaper on the home screen, appearing to shift a little bit as you move the phone around. Although some people find this “cool,” in fact not only do many people find this annoying, but this also immediately triggered an avalanche of complaints of seasickness and vertigo, not only among with people who have vestibular problems, but also among the general public, as evidenced by this Tweet from actress Mia Farrow:
What basically happens is that the vestibulo-ocular reflex (VOR) ensures best vision during head motion by moving the eyes contrary to the head to stabilize the line of sight in space. For people who have VOR, nystagmus, and other balance disorders, iOS 7′s Parallax eye candy has been triggering vertigo and/or causing other discomforts such as seasickness-like nausea, as Mia Farrow reported… An Epic iPhone #FAIL
The VOR has three main components:
- The peripheral sensory apparatus (a set of motion sensors: the semicircular canals, SCCs, and the otolith organs);
- A central processing mechanism;
- The motor output (the eye muscles).
The SCCs sense angular acceleration to detect head rotation; the otolith organs sense linear acceleration to detect both head translation and the position of the head relative to gravity. The SCCs are arranged in a push-pull configuration with two coplanar canals on each side (like the left and right horizontal canals) working together. During angular head movements, if one part is excited the other is inhibited and vice versa. While the head is at rest, the primary vestibular afferents have a tonic discharge which is exactly balanced between corresponding canals. During rotation, the head velocity corresponds to the difference in the firing rate between SCC pairs. Knowledge of the geometrical arrangement of the SCCs within the head and of the functional properties of the otolith organs allows to localize and interpret certain patterns of nystagmus and ocular misalignment.
Parallax basics and its’ application in iOS 7:
This is a classic example of parallax (although this is fake parallax). You can create another example of parallax yourself. Hold you thumb out straight in front of your face at arms length. Now close one eye and find an object in the distance to line your thumb up with. Ready? Now switch the eye that was closed. Notice anything? Your thumb will no longer be lined up with that distant object any more. Also, note that different objects will have different angular shifts depending on their distance from the observation location. Here is a diagram showing how a person’s two eyes see the thumb at different angles:
But is parallax useful? Yes: Parallax has been used since the 1920′s in cameras to determine distance to the subject and pass this on to the focusing mechanism, originally with side-mounted rangefinders: When the two images in the viewfinder align, then the lens will focus at that distance:
Parallax can also be used to find the distance to some of the closer stars. As the Earth moves from one side of the Sun to the other during a 6 month time interval, our observation location has shifted by twice our orbital radius of 93 million miles. This shift is small compared to the distance to the stars, starting at 48 light years, so it’s a difficult task. However, with precision instruments, it is successfully employed for nearer stars.
For more on how parallax is implemented via the tilt sensors, please see the Bootnotes.
Disabling parallax in iOS 7:
You can reduce the amount of motion, turn off Parallax and limit the animations of other apps and icon badges by going to Settings → General → Accessibility → Reduce Motion. Additionally you can also try to Increase Contrast and enable Bold Text to see if that helps to reduce the amount of motion you encounter in iOS 7.
The old axiom of design engineering applies to Apple for this stuff-up: Just because you can, doesn’t mean you should.
Rhett Allain has a good explanation of iOS 7 faux parallax in Parallax and the iOS 7 Wallpaper in Wired Science Blogs, from which we are excerpting, with edited images:
Distance to the Wallpaper:
For the iPhone, this is just a little tiny bit different than parallax. Normally, you have a known change in observation distance and then use the apparent change in angular position to find the distance to that object. In this case, the observation location (your face) doesn’t move. Instead, the phone tilts. However, this is exactly the same as if the phone was stationary and your head moved. A stationary phone makes for a simpler diagram.
We really don’t even need the top triangle in this case: We can measure the change in viewing angle and we can also measure the background shift s1. If we assume the distance s1 is close to the same distance as the arc-length, then the following approximate constituitive relationships would hold →
The greater the background shift, the further away it is from the front icons. How is this different from parallax in astronomy? In that case, you would measure the change in angular position and use the arc-length to find the observation distance. So, it’s mostly the same.
But how do we determine the value of s1? That is fairly simple: We just measure it with a ruler and some screen shots. Here are two screen views at different angles:
Notice the shift in the red lines in the background (I took a picture of lines just so that this would be easier to see). If we use a real life ruler, the distance from the top red line to the bottom one is 4.4 cm. We can use this scale to measure the shift in one of the red lines. This measurement could be accomplished with a drawing program and converting pixels to cm or you could load this image into Tracker Video Analysis. For this case, we get a background shift of 0.31 cm.
What about the change in viewing angle? Well, it turns out that the compass app in iOS 7 has a built in angle measurement. Yes, it’s on the “second” page of the app when you swipe the compass to the left. Now, it’s not perfect but we tried to hold the phone steady to switch apps. Here’s what we get:
For the other angle, we get a tilt of 46°. Let’s just call this an angle change of 90°. Now we can put my values in to get the distance from the background to the icons. Remember that we need the angle in units of radians instead of degrees, where 1 radian = 360 ∕ 2π ≈ 57.288°
That’s not too far back, and that’s a good thing, because we made another assumption that we didn’t disclose. we assumed that the measurements on the background were the actual distances and not the apparent distances. Just image in the background was 1 meter behind the icons. If this were the case, our measurements wouldn’t really tell you the distance the background shifted — It would give the apparent shift. With a distance of just 0.197 cm, the difference between apparent and actual lengths is small enough to ignore.
- The Vestibulo-Ocular Reflex: Kinematic Model by Olivier Coenen, The Computational Neurobiology Laboratory, Salk Institute
- Vestibulo-ocular reflex by Michael Fetter, Department of Neurology, SRH Clinic Karlsbad-Langensteinbach, Karlsbad, Germany
- Nystagmus definition in the MedLinePlus medical encyclopedia.
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