Exercice to judge the distance between two point. Why it's so hard?

Hi there, as i had troubles with shape réplication, i decided to practice something simpler in appareance but who gave me hell as well.

My goal is to put two point or marks on a piece of cardboard, i then try to draw to marks that are exactly the same distance apart, i then check using my cardboard, i have been doing it for a week, but my ability to see mistakes do not improve, im often shocked by how much i am unaccurate.

Any idea on how to get this skill?

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Hi Sow, you seem to be making this much harder than it needs to be! It’s worth sticking to the early shape replication exercises and procedures described exactly in LoD, as you’ll have more chance of success with them than simply trying to reproduce an arbitrary measurement by eye, and you’re not really learning or practising anything practical by doing so.

So with the shape replications if you keep your reference very close and in alignment with your drawing as in the picture below, the bounding boxes (or vertical/horizontal guides) act as a fixed basis of comparison. This should give you the best and easiest route to achieve accurate reproductions at this stage.
Practice Practice Practice!

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Thanks man, will stick to instruction then.

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Yes in a sight size manner, i use the cardboard to check that my guess is correct.

Greetings Sow and all (and a Happy New Year as it is 1/1/2021 at the time of this posting!)

The subjective visual space perceived by humans does not reflect a simple transformation of objective physical space; rather, perceived space has an idiosyncratic, non-veridical relationship with the real world. Regardless of some of the claims to the contrary that have arisen within the different theories regarding the nature of visual perception—we have been aware of this for some time. In the 18th century, the Irish philosopher George Berkeley provided some insight into this physical and perceptual disparity. In his “Essay Towards a New Theory of Vision,” Berkeley pointed out that the judgment of distance, for
example, cannot be derived directly from the geometrical information in the retinal image. Thus, a given line in the retinal image could have been generated by the edge of a physically small object nearby, or equally well by an edge associated with a larger object farther away.

In other words, our judgements regarding distance, like just about all others aspects of perception, is a contextually derived conclusion that we have likely found useful in the past.

As seen in this image—we cannot be sure about the length, position and distance of a stimuli without additional contextual clues as many different stimuli can produce the same response.

As seen in this example from from Neuroscient Dale Purves (purveslab.net), we can observe variation in apparent line length as a function of orientation. A) The horizontal line in this figure looks shorter than the vertical or oblique lines, despite the fact that all the lines are identical in length. B) Quantitative assessment of the apparent length of a line reported by subjects as a function of its orientation in the retinal image (orientation is expressed as the angle between the line and the horizontal axis). The maximum length seen by observers occurs when the line is oriented approximately 30° from vertical, at which point it appears about 10-15% longer than the minimum length seen when the orientation of the stimulus is horizontal. The data shown here is an average of psychophysical results reported in the literature (After Howe and Purves, 2002).

Specifically, as seen in Sow’s original post, the apparent distance between a pair of dots varies systematically with the orientation of an imaginary line between them (as Wundt first showed in 1862), and a perfect square or circle appears to be slightly elongated along its vertical axis. Indeed, numerous observers have pointed out that measurements made with rulers or protractors of a variety of simple visual stimuli are often at odds with the perceptions they elicit.

It is also very important to remember that while the claim continues to propagate—the truth is—no, practicing observational representationalism (representational drawing/painting from observation) does not make you see “more accurately.”

What certain types of practice in the realm of observational representationalism CAN develop is the establishment and reinforcement of specific visuomotor responses to specific types of visual information that are conducive to representational efforts. These associations can be strengthened in a number of ways—including something as simple as reserving measurements for mark evaluation instead of mark establishment.

So in simple terms—be aware of the biases that tend to occur when navigating the chasm between the physical world and our perceptions–and work (deliberately practice) to reinforce new or modified associations between specific observation and resulting visually guided responses.

Hope that heps!

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