The claim that sound-meaning correlations can be nonarbitrary gained a lot of attention recently in 2016, after of the work of Blasi et al. 
"By analyzing word lists covering nearly two-thirds of the world’s languages, we demonstrate that a considerable proportion of 100 basic vocabulary items carry strong associations with specific kinds of human speech sounds, occurring persistently across continents and linguistic lineages (linguistic families or isolates)."  \cite{Blasi_2016}
More recently Cuskley et. al. examined the literature on the "kiki-bouba effect" and observed that most accounts pointed to the mapping between acoustic or articulatory properties of sound and shape. According to them, previous studies failed in consider that, for the literate subject, the influence of the shapes of the graphemes could function as an underlying matching mechanism.  It is possible that as the traditional alphabets evolved, the congruent shapes were biased against incongruent ones.
"We compare traditional accounts of direct audio or articulatory-visual mapping with an account in which the effect is heavily influenced by matching between the shapes of graphemes and the abstract shape targets. The results of our two studies suggest that the dominant mechanism underlying the effect for literate subjects is matching based on aligning letter curvature and shape roundedness (i.e. non-words with curved letters are matched to round shapes). We show that letter curvature is strong enough to significantly influence word–shape associations even in auditory tasks, where written word forms are never presented to participants." \cite{Cuskley_2015}
Even with so much evidence that supports some kind of motivated sound-shape mapping, many important questions remain. What is the basis for cross-modal matching: entire words, segments, the transition between segments or phonological features? What is the dominant iconic ground for the mappings? How is the cross-modal mapping achieved? What is the role of the Vision, Proprioception, Haptic senses and literacy in mapping sounds to meaning? Besides that, what does it mean? What are the implications for linguistics, semiotics, neurolinguistics, psychology, literacy, dyslexia and speech disorders? 
To answer those questions goes way beyond the objective of this paper. Our goal is to demonstrate how uniskript alphabets incorporate many of the sound-shape correspondences strongly supported by research. The literature indicates, for instance, that front and closed vowels are associated with the concept of "smallness", while open and back vowels are associated with the concept of "largeness". The front closed vowel in uniskript is represented by a smaller shape, while open vowels are represented using bigger shapes. The number of lines used mirrors the association between the sounds and conceptual size. The curve in the back vowels also makes them look bigger than the front vowels. The "fullness" associated with bilabial sounds in Blasi et al \cite{Blasi2016} is represented in uniskript by using ellipses for p, b, and m.
Additionally, anterior high vowels are usually associated with the concept of "sharp", or "spiky", while back vowels are associated with the concepts of "roundness" and "smoothness". Front and back vowels are differentiated in uniskript by the use of straight angles versus curved lines, matching the concepts or "sharp" and "smooth" respectively.
For the literate subject, the printed page is perceived as a metaphor for the physical space around them. In the western world, where the directionality of writing is from left to right, the left side of the printed shape is perceived as its "front", while the right side of a printed shape is perceived as its "back". Based on this perception, uniskript represents the backward movement of the tongue in the articulation of the back vowels by placing the curve at the right side of the glyph.

General Applications

By combining featural-shape indexicality and sound-shape congruency, uniskript alphabets provide transparent and intuitive writing systems, which can be applied in a variety of different contexts. 
According to Shukla \cite{Shukla2016},  the possibility of  "inventing novel teaching methods" which would take advantage of the Kiki-Bouba effect to reinforce the cross-modal integration of abstract concepts could significantly improve education:
Complex concepts typically take time to be thoroughly encoded and espoused by students. Shortening the time invested in learning while reducing the rate at which conceptual learning is blurred/forgotten would subsequently raise the standard of education for all types of people in all types of settings. \cite{shukla}
Literacy methods could also take advantage of those cross-modal bias to make learning how to read easier \cite{Yee}. Different versions of uniskript alphabets have been used in the last ten years as a tool to develop meta phonemic awareness and to teach the alphabetic principle to pre-literate children. ELA teachers report that kindergarten and first-grade children in the Navajo Reservation exposed to uniskript phonics from 2017-2018 tested better on the Arizona Standards Reading Foundations for ELA compared to children in the previous years who were not exposed to it \cite{Polido2018}
First-grade students of Kapuna School in the Gulf Province in Papua New Guinea received uniskript classes. The teacher reports that:
"After 5 weeks I had most of them starting to blend and write words for stories. I left them at that point, but Rosa continued giving them practice, and by September when I checked them again they could write one sentence stories in both Koriki Uniskript and English. This is a far faster acquisition of literacy than the Kapuna Year Two class described above - half a year versus, one and a half years. I think they are probably the most advanced first-year class in the province." \cite{petterson2014}
When used as a phonics method to teach literacy, uniskript instructors use specific manual gestures to accompany each one of the visual shapes. Each gesture is carefully designed to mimic both, the process of articulation in the mouth and the visual shape proposed for the phoneme.  The aim of the program, in this case,  is to explore cross-modal correspondences involving auditory, visual and haptic senses simultaneously, so students experience learning in a sensorial and intuitive way. To discuss the evidence on mouth-hand neurological mappings is beyond the scope of this working paper, but I want to shortly mention that research has shown connections between the mouth and manual movements. Vainio et al. \cite{Vainio_2018} propose that:
"the movements of the tongue body, operating mainly for vowel production, share the directional action planning processes with the hand movements. Conversely, the tongue articulators related to tongue tip and dorsum movements, operating mainly for consonant production, share the action planning processes with the precision and power grip, respectively."
Some of the manual gestures used to teach Uniskript English are illustrated in Figs. \ref{951476}\ref{599763} and \ref{430603} below: