Retinal curve implications
Perspective projections are mathematically precise but do have visual limitations. Very wide
angled sight line extensions will look quite distorted. To avoid this issue standard perspective
teaching is to keep your intended subject within a 60 degree cone
of projection and then
tweak the parts that do not appear right. Michelangelo wrote to restrict the drawing subject
to a 30 degree cone…..”distortions remain but are tolerable”.
If we project the 60 and 30 degree sight lines on to the area of a retina (1), we find the 60 degree
cone to be 7% of the entire visual field and a 30 degree cone comprises just 1.6%. This means
93.0 to 98.4% of a typical retinal field would fall into the range of known visual distortion for
perspective drawing.
How do humans convert potential distortion into functional data? Projecting sight lines onto the curved surface of the retina should reduce some of the distortions encountered in perspective drawing projections…..however, this curvature may create other issues to be
addressed.
It is important to understand that the eye does not see images. The eye is a visual data collection
device that sends electrical signals to the brain. The brain then creates image through conscious/subconscious processes…constantly comparing and editing data to build it’s best interpretation
of the environment around us. This process will generate distorted mental impressions when the
subject remains in the peripheral data fields of the retina and subject to our subconscious
filtering processes. Once we consciously ‘look’, we reorient our gaze to the acute area of vision
and it’s detailed data collection retinal field leading to an edit of our previous mental image.
Please note, our brains are constantly striving to minimize and correct perceptual errors however,
some images are resistant and may remain in a partially adjusted – hybridized state in our mental
map. An example of this would be the experience of 
Barbara’s tennis deck pergola. I conceived,
drew and built a model of the pergola…my expectation was well defined. However, after building
the actual piece…my experience was proportionally different. All dimensions measured as
proposed but, the structure was somehow narrower than expected…and the roof pitch appeared
steeper. Following is an explanation for this deviation – a curvature created issue.
The projected data becomes unequally compressed due to it’s location in the peripheral retinal
field. With an eye level at 5′ 5″ the ground plane interrupts the pergola from occupying the lower (2)
quarter of the retinal field, leaving the image
in a three sided compression – one increment on
each side and one for height (3). This 2:1 horizontal to vertical shift (4) fits my pergola experience
and a projection tool that recreates this shift has been developed both for illustration here and
as a design tool on future projects.
(1) – individual retinal fields vary – our calculation was based on a 132 degree field found in a medical
illustration. Some individuals have retinal fields approaching 180 degrees.
(2) – Technically because the light rays invert behind the eye lens the ground plane would project
to the upper retinal field. The correcting of this inverted data, upper/lower and left/right, are
examples of some of the subconscious data processing constantly occurring in order to generate
our mental image.
(3) – Compression is due to the curved surface of the retina intercepting a sight line sooner than
a flat plane and it’s circumference length being shorter than the flat plane intercept distance.
(4) – 2:1 ratio will vary depending on the data points location on the retinal curve. Perceived
visual compression will exponentially increase with each degree of rotation from our central
vision axis.
Lens altered light trajectories
Priority is given to our acute vision function, a rather small 5 degree cone of vision (1). The lens
is manipulated to focus this function alone and all other acuity fields are secondary but
affected. As we move about and selectively scan items in our environment the lens is continuously
adjusted causing light projecting from these secondary fields to fluctuate across the peripheral
retinal fields.
How does the brain process this fluctuating peripheral data to construct a coherent background?
If the brain uses geometric projections we should experience distortions in our mental background
image due to the altering of these light trajectories…with wider trajectories experiencing ever
greater levels of distortion with each degree of rotation from the central vision axis.
Binocular vision and head, eye and body movement should increase the amount of data available
for comparison, allowing the brain to construct a ‘cleanest mental map’ of congruent information.
Efficiency is important and impactful. Areas of critical information will be pursued in the acute
vision field…while non-critical spatial inaccuracies in our peripheral fields may go unconfirmed
for energy / time considerations. (2).
These persistent non-critical spatial inaccuracies can flavor our perception of a space and insight
into their presence / contribution should assist designers in more closely achieving the intended
visual experience in their work.
(1) – A 5 degree cone projects to only 0.02% of a 132 degree retinal field, meaning 99.98% of the
retina is receiving altered light trajectories.
(2) – Moving objects will be tracked in the peripheral fields but, static objects are not.