Eyes and Vision in Pool and Billiards
... various concepts and techniques for pool shot sighting and visual alignment.
Dr. Dave's answers to frequently-asked questions (FAQs),
mostly from the BD CCB and AZB discussion forums
maintained for the book: The Illustrated Principles of Pool and Billiards,
the DVD series: The Video Encyclopedia of Pool Shots (VEPS) and
The Video Encyclopedia of Pool Practice (VEPP), the Billiard University (BU),
and the monthly Billiards Digest "Illustrated Principles" instructional articless
--------------------------------------------------------------------------------
depth perception
dominant eye
eye pattern "best practices"
finding the center of the cue ball
quiet eyes
sighting
vision center
which ball to look at last
--------------------------------------------------------------------------------
depth perception
Is depth perception important in aiming?
Assuming you have already visualized the required impact line and ghost ball target (see NV 3.1 and NV 3.2), aligning the cue stick with the aiming line direction does not require depth perception. (In fact, the parallax created by binocular vision, even with a dominant eye, can make straight-line sighting difficult.) Now, some people might adjust their aim while in their stance based on their perception of the "angle of the shot," impact line, contact point, and/or ghost ball target. In that case, depth perception might be helpful.
A low stance helps one better align the cue with the desired aiming line, without requiring too much of a shift in eye (or head) motion between the CB contact point the aiming target, while fine tuning and verifying one's aim.
For more info, see dominant eye.
Interesting, the following research study showed no correlation between depth-perception ability (or other vision attributes) and pool-playing performance: "Perceptual-Motor Characteristics of Elite Performers in Aiming Sports" by Abernethy and Neal (1992).
from Qtec:
The difference between short and long bridge is that the EYES are further away from the QB when you play with a longer bridge. This means that when you focus on the QB or OB, you will see more of the shaft [ie. a longer line ] and therefore its easier to line up the cue on the line on the shot.
--------------------------------------------------------------------------------
dominant eye
Is one's dominant eye important in aiming?
This is debatable, and it might vary quite a bit from one person to the next. Now, head and eye position relative to the cue can be important in perceiving the desired tip contact point on the cue ball, especially if the cue tip is not close to the cue ball when lining up a shot. For illustrations and more information, see “Aim, Align, Sight - Part II: Visual Alignment” (BD, July, 2011).
3D visual perception, applied to aiming in pool, is a complicated topic that is certainly not fully understood. It is difficult to offer simple eye alignment advice (or a "formula") that will work for all people (e.g., always align your dominant eye over the cue or with the edge of the CB).
The most important advice on this issue is find the head position and sighting technique that helps create the most accurate cue tip contact point and aiming line (for a given individual). See the vision center resource page for drills and information on how to find the "vision center" head position. A person's "vision center" isn't necessarily related to which eye might be dominant or not. Regardless of where you place your head to aim and sight a shot, the most important thing is to be as consistent as possible (e.g., with a purposeful pre-shot routine), so the "sight picture" is always the same for the same type of shot.
Wikipedia has a good summaries and references dealing with dominant eye (including several methods for testing dominance) and related topics here:
ocular dominance
binocular vision
Here's a good article that makes an argument that eye dominance is not very important in pool: "Dominant Myth?" by Bob Fancher.
The following research study also showed no correlation between ocular dominance (or other vision attributes) and pool-playing performance: "Perceptual-Motor Characteristics of Elite Performers in Aiming Sports" by Abernethy and Neal (1992).
from RSB_FAQ:
For most people, one eye is much more dominant in seeing alignments than the other. Typically, right-handers are right-eyed, and vice versa. About 5% are "cross-dominant" (e.g., right-handed and left-eyed) and some are "ambi-ocular" (no dominant eye). To aim and sight well, it helps to locate your dominant eye directly over your cue. For cross-dominants, this may call for some adjustments in stance or neck/head angles. For ambi's, the stick will be under some spot between the eyes.
Here's how to test yourself: Hold your thumb up at arm's length, visually blocking some distant object (for example, a clock or a lamp). Don't focus on your thumb; focus on the distant object. You'll see a ghost of your thumb, since your dominant eye will be in line with both your thumb and the distant object, while your non-dominant eye will be seeing past your thumb, directly toward the distant object. With one eye seeing the thumb and the other not, you get a ghost. The ghost is centered on the distant object because your dominant eye is the one that tells you what's lined up with what.
So, when you close your non-dominant eye, the thumb becomes solid instead of ghostly, since the dominant eye is looking directly at the thumb. When you close your dominant eye, the thumb appears to jump to the side because the dominant eye (that was making the thumb line up with the distant object) is not in use.
Stroke into a mirror to see where your dominance spot is, relative to your shaft. It "should" be directly over the shaft. If it's not, but you're not having difficulty aiming or sinking balls, don't worry about it.
from henho:
... there is plenty of research on eye dominance in Medline or Pubmed, a couple of thousand articles to be exact....just one for example: A new interocular suppression technique for measuring sensory eye dominance.
Yang E, Blake R, McDonald JE.Invest Ophthalmol Vis Sci. 2009 Jul 23. PMID: 19628736
Each eye supplies information to the brain differently. The dominant eye is used to fixate on objects. If you look at a point, the fixation of the dominant eye will fall on the center of the point while the non-dominant eye will fall slightly off-center. By comparing the difference between the images supplied by each eye the brain is able calculate depth information in a scene. The degree to which any eye is dominant varies from person to person as well.
In scenarios where estimating depth is important, the functioning of both eyes in tandem is vital. I don't recommend skiing with an eyepatch any more than driving. However, in scenarios where determining a straight line between two points is needed, using the dominant eye confers an advantage over using both eyes. When shooting a gun, you want to align the sight of the gun with a target. If you kept both eyes open while sighting down the barrel of the gun, when you looked at the sight you would see two targets, and when you focused on the target you would see two sights. In this scenario, the depth information your brain is supplying you is not helpful in aligning the target and sight, and it is easier to sight with one eye.
Pool is an interesting scenario in that it requires good depth perception to estimate the line of sight, generally done while standing up, and in addition requires accurately lining up the cue ball with the contact point on the object ball. If you adopt a high stance and hold the cue under both eyes, you have the best depth judgment, which is needed to estimate the speed and direction of the hit. If you adopt a low stance and use your dominant eye, you have the best ability to line up the cueball and object ball. Most people go somewhere in between, where they can line up the balls while still having a general view of the table to guide the speed of their stroke.
This seems to come into play in the nature of various cue games. In three-cushion billiards players generally adopt a more erect stance that provides a good, continuous 3-d view of the table, allowing them to accurately predict the reaction of the balls. In snooker, the accuracy requirement that smaller balls present requires players to adopt a low stance sighting down the cue. In this game moreso than in billiards, players must first estimate what will happen on the shot and determine the line of sight, then remember the layout of the table when they are down on the shot since they don't have a good view of the balls.
from Billy_Bob:
Here is more reading about the dominant eye...
Ken Tewksbury, Master Instructor (See #6)...
http://www.tableskills.com/article-kt2.php
Robert Byrne: "If you are having trouble pocketing balls, it may be that you aren't bending over far enough and aiming the cue like a rifle with your dominant eye."
http://www.byrne.org/pool/tips/08-1998.html
Says Buddy Hall wrote good article on this: Billiards Digest in June 2001...
http://www.ez-shot-ghost-ball.com/dominant_eye.html
By Don 'The Master' Rose, BCA Advanced Instructor...
http://www.azbilliards.com/donrose/lesson4.html
