Developmental Crowding and the Perceptive Field

With the havoc wreaked by COVID you may have missed publication of this article in PLOS ONE last year, as did I: Development of global visual processing: From the retina to the perceptive field. The corresponding author is Uri Polat, who is affiliated with The School of Optometry and Vision Science and The Mina & Everard Goodman Faculty of Life Sciences, of Bar Ilan University in Ramat-Gan, Israel. If the name Uri Polat is familiar to you it may be because he co-authored a seminal paper with Dennis Levi in 1996 that was the first nail in the coffin of the concept that amblyopia can’t be improved after age 7. In 2013 I blogged about the clinical appreciation of developmental crowding, and how that relates to young children with delays in reading acquisition as well as for patients with amblyopia who function as if they have a learning disability.

I like Polat’s use of the term “perceptive field” in this new PLOS ONE article. Although optometry students learn about receptive fields in the visual cortex, Polat and colleagues coin the term perceptive field which has a more developmental ring to it regarding retinal development. In the abstract they write: “Our data suggest that the developmental processes at the retina and visual cortex occur in the same age range. Thus, in parallel to maturation of the PF, which enables reduction in crowding, foveal development contributes to increasing contrast sensitivity.”

The age range where there is typically a big crossover point is around age 6. Clinicians are familiar with this in terms of when children are better able to keep place on the whole line when reading a Snellen Chart rather than requiring pointing or the isolating of letters. It is why developmental saccade tests like the King-Devick and DEM have norms beginning at age 6. Understanding and appreciating crowding serves as the basis for why children’s books have larger print and liberal spacing until age 6, and then each year thereafter progress toward smaller print with tighter spacing, in essence becoming relatively more crowded.

Helping children who lag in retinal and/or cortical development is done through many types of sheets or workbooks that progress from larger font and spacing toward smaller font and spacing. This is the sequence followed in Michigan Letter Tracking (Ann Arbor Series) workbooks, and more recently in a variety of Petrosyan workbooks available through Bernell, or computerized through Anteo. Versions of this are customizable in other computerized programs such as Binovi and Neuro Visual Trainer, and an auto-pacing function built into the ambiNet program. Downloadable Hart Chart Decoding sheets are fun for this as well, zooming the size in or out, as well as Dr. Sarah Lane’s downloadable worksheets.

Although all VT practices deal with “retained crowding” at some level, less common is a parallel approach to training contrast sensitivity.

Doing this with letters likely transfers to reading performance, while doing this with Gabor patches is becoming popular with computerized programs that enhance dynamic visual skills as required for night driving and sports vision. With all of these approaches, using Polat’s terminology, we can say that we are training the perceptive field.

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