Dear Perdiddle,
If you break down the separate uses of the visual system in putting, they are: 1. reading the surface to ascertain the break and pick a startline for the putt; 2. aligning or aiming the putter face at the target; 3. assessing distance of the putt for purpose of generating appropriate force or touch; and 4. using vision to help make a good stroke. If you have only one eye, the task above that suffers the most is the first, reading the surface. Interestingly, it is not assessing the distance of the putt or aiming the putter face or watching the stroke. All of these tasks can be done pretty much as effectively as a person with two good eyes.
The problem with reading the surface is that this is where "binocular disparity" and "stereopsis" help most in putting. Depth perception is very useful to perceiving subtle contours in the green at various distances from your position. But stereopsis and binocular rivalry are not absolutely essential, though, and you can work around lack of stereo vision to get as good a sense of depth and contour as possible. Just because you lack stereo vision does not necessarily mean you lack depth perception, but it does diminish depth perception. Depth perception is a lot more than stereoscopic vision alone.
There are so-called "monocular" cues to depth, such as an appreciation of apparent size of objects or figures in the scene versus what you know is the actual size. For example, the shape and appearance of the hole in a green appears different sizes depending on your distance from it, and yet you know that all holes on the greens are the same size -- one fist wide and deep. You also know that all grass blades on a recently mowed green are about the same actual size, and there is a gradient pattern of these blade specs as you look from near to far across a green surface, and the apparent size of the grass blades diminish in a regular way as distance increases over a flat and level surface, and diminish is other ways if the surface is tilted towards your face and eyes or away from your face and eyes. It is like holding a checkerboard at waist height and tilting it towards or away from your face and watching the changes in the apparent size of the checks pattern.
A non-visual set of cues comes from the body -- your sense of upright from the inner ear balance system, your sense of the body in space as registered in the pressure of the surface tilt against the soles of your feet, your sense of gravity affecting your limbs and posture on a tilted surface, and related body senses.
Another way to get more with less is to be very clear about the last 2-3 feet of every putt as the ball's path is defined into the hole by your consistent delivery speed of the ball to all holes. If you have a consistent tempo in your stroke, all balls arrive at all holes with approximately the same terminal velocity (revolutions of the ball per second at the front lip of the cup). This consistency lets you focus your IMAGINATION not your actual vision on the critical last few feet of the intended successful putt, and this gives you a very clear picture on the ground at the hole of how the ball will curve into the hole. With this clear picture, you can identify a clear target spot beside the hole (I say on the fall-line) that serves as both startline and distance / touch reference: putt the ball STRAIGHT AT and ONLY TO this target spot as if the green were flat and level without any break. This process gets you past the problem of "reading the putt" with depth perception and down to the final 2-3 feet where it really matters. The more experience you have with breaking putts, and the more you refer this experience into this final-section targeting process, the less your lack of stereo vision will hamper your reading of putts.
Aiming the putter face at a target from behind the ball is a lot easier than trying to aim the putter into a remembered total path of a visualized "read" from beside the ball. So a one-eyed golfer ought to work hard on orienting to the simple line between a ball and the chosen target in a connect-the-dots manner, and then use cues seen on the ball and on the ground near the ball when walking into the ball to place and aim the putter face thru the ball. If you get these references on the ball and ground down clearly from behind the ball, the aiming of the putter face does not require stereo vision to be performed accurately.
Vision for assessing distance is only one of many cues the brain relies upon for distance and especially for generating the appropriate touch. Fundamentally, stereo vision of an object allows some depth perception, but this is only one of a dozen or so ways the brain gauges distance. Ways that don't use stereopsis include comparing the apparent visual size of an object (e.g., the cup) to its actual size, the height of the eyes off the surface and the angle of regard of the eyes down to the surface at various distances, walking around a location while keeping constant vision of it, pacing off the distance, seeing the changes in the gradient of the apparent size of grass blades over distance, and other cues to distance. I teach a beside-the-ball technique of neck turn from ball to target that functions like the reostat on a light dimmer switch to correlate specific angles of neck turn with specific distances out from the ball, and then to correlate specific backstrokes with these neck angles. None of this really requires more than one-eyed vision so the golfer knows when to stop turning the neck targetward.
In my estimation, vision while making the stroke is more hurtful than helpful, so the lack of stereopsis is a blessing here. ust look at the ground behind the ball and keep the sight still here when making the stroke.
At bottom, the problem of the single-eye golfer is persisting in trying to read putts in the two-eyed manner, when the one-eyed manner is not that bad. You just need to know how to use the one-eyed system more specifically, so that you are actually looking for the right sort of cues -- cues that you will really get and can use instead of looking for two-eyed cues that you just won't get. The two-eyed cues aren't the be-all and end-all of perception, and emphasizing the one-eyed cues, the body cues, and the focused planning process ought to help.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
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