Week 4

Physiological Issues

People like wearing sunglasses - lightweight, stylish, useful
People are used to wearing passive glasses at the theatre to see 3D movies - lightweight, useful
People do not like wearing heavy or unbalanced glasses
People do not like wearing helmets


Human eye has 2 types of photosensitive receptors: cones and rods



The cones are highly concentrated at the fovea and quickly taper off around the retina. For colour vision we have the greatest acuity at the fovea, or approximately at the center of out field of vision. Visual acuity drops off as we move away from the center of the field of view. However, we are very sensitive to motion on the periphery of our vision, so we can see movement even if we can't see what is moving.

The rods are highly concentrated 10-20 degrees around the fovea, but almost none are at the fovea itself - which is why if you are stargazing and want to see something dim you can not look directly at it.

There is also the optic nerve which is 10-20 degrees away from the fovea which connects your eye to your brain. This is the blind spot where there are no cones and no rods. We can not see anything at this point though we are so used to this that we do not notice it unless we try to see the blind spot.

Bill Sherman's diagram of the eye:

Seeing your blind spot - this image and others at http://serendip.brynmawr.edu/bb/blindspot1.html


The eye has a dynamic range of 7 orders of magnitude

Eye is sensitive to ratios of intensities not absolute magnitude. Brightness = Luminance^0.33. To make something appear n times brighter the luminance must be increased by n^3.


Most perceptual processes are driven by intensity not colour. Motion system is colour blind, depth perception is colour blind, object recognition is colour blind.

but uniquely coloured objects are easy to find

8 percent of men are color blind
1 percent of women are color blind
Are you colour blind? You can check on Wikipedia - http://en.wikipedia.org/wiki/Ishihara_color_test

Photoshop can be used to check images (View menu, Proof Setup, Color Blindness), as can the tool at http://colororacle.cartography.ch/ and couple good web sites to check your graphics are:  http://www.vischeck.com/vischeck/ and http://colorfilter.wickline.org/

Here is a nice set of on-line color tools:

Field of View

Each eye has approximately 150 degrees horizontal (60 degrees towards the nose and 90 degrees to the side) and 120 degrees vertically (50 degrees up and 80 degrees down)

Newer online gallery to see how much work your brain is doing

Visual Acuity

Below is an 'eye chart' showing the resolutions of various VR devices from the early 1990s when the CAVE was introduced. From left to right: 20/20 (6/6 in the metric world), CRT 20/40, HMD 20/425, BOOM 20/85, and CAVE 20/110 using the Snellen fraction (20/X where this viewer sees at 20 feet detail that the average person can see at x feet, 20/200 is legally blind)

Temporal Resolution

The real world doesn't flicker (aside from things like florescent lights). Some people can perceive flickering even at 60Hz (the image being refreshed 60 times per second) for a bright display with a large field of view but most people stop perceiving the flicker between 15Hz (for dark images) and 50Hz (for bright images).

Convergence and Accommodation for 3D scenes


In a 3D display environment the brain is getting two different cues about the virtual world. Some of these cues indicate this world is 3D (convergence and stereopsis). Some of these cues indicate that the world is flat (accomodation).

The eyes are focusing on the screen but they are converging depending on the position of the virtual objects which could be in front of, on, or behind the screen

Note that only 90-95% of the population can see in stereo

Simulator sickness

2 things are needed: a functioning vestibular system (canals in the inner ear) and a sense of motion

Symptoms: Nausea, eyestrain, blurred vision, difficulty concentrating, headache, drowsiness, fatigue

These symptoms can persist after the experience is finished.

Causes: still unknown but one common hypothesis is a mismatch between visual motion (what your eyes tell you) and the vestibular system (what your ears tell you)

Why would this cause us to become sick? Possibly an inherited trait - a mismatch between the eyes and ears might be caused by ingesting a poisonous substance so vomiting would be helpful in that case.

sense of motion is required
bright images are more likely to cause it than dark ones

wide field of view is more likely to cause it than narrow field of view

low resolution, low frame rate and high latency are also likely causes

Another hypothesis deals with the lack of a rest frame. When a user views images on a screen with an obvious border that border locates the user in the real world. Without that border the user loses his/her link to the real world and the affects of motion in the virtual world are more pronounced.

fighter pilots have 20 to 40 percent sickness rates in flight simulators - but experienced pilots get sick more often than novice pilots.

In a rotating field when walking forward, people tilt their heads and feel like they are rotating in the opposite direction.

This all affects the kinds of imagery you display and how it can move. Open fields are less likely to cause problems than walking through tight tunnels; tunnels are very aggressive  in terms of peripheral motion. This doesn't mean you should have any tunnels, but you should be careful how much time the users spend there.

For Thursday's Class

If your UIN ends in an odd number you should read this paper and produce a similar 1 page report to show on the wall and perhaps discuss.

Sizing up visualizations: effects of display size in focus+ context, overview+ detail, and zooming interfaces
Jakobsen, Hornbaek
Proceedings of the SIGCHI Conference on Human Factors in Computing Systems 2011

If your UIN ends in an even number you should read this paper
and produce a similar 1 page report to show on the wall and perhaps discuss.

Beyond visual acuity: the perceptual scalability of information visualizations for large displays
Yost, Haciahmetoglu, North
Proceedings of the SIGCHI Conference on Human Factors in Computing Systems 2007

Coming Next Week

Project 1 Review

Before the class on 10/8 please read

Enabling Multi-User Interaction in Large High-Resolution Distributed Environments
Jagodic, Renambot, Johnson, Leigh, Deshpande,
Future Generation Computer Systems, Elsevier, Vol. 27.7 (July 2011)

Again, you should produce a 1 page critique of the paper to put up on the wall Tuesday in class, and a subset of the students will be asked to talk more in depth about the paper.

last modified 9/20/13