The 11-month-old toddler Juli understood the concept of possession for the past months by pointing to some objects and identifying whose objects they belonged to.
For example, Juli pointed to the toothbrush and identified its possessor father, then pointed to another toothbrush and uttered mother, and pointed to her own toothbrush and either uttered Juli or me-me.
Eventually, she began to use ASL possessives. Before describing reversal errors in possessives, I need to explain about the pronoun acquisition and its reversal errors first.
In pronoun acquisition, reversal errors such as "I" for "you" and "you" for "me", is a classical phenomenon in hearing children. Hearing children often make reversal errors when using these pronouns at 20 months and complete the acquisition of personal pronouns at age two to three.
It may be easy to assume that the acquisition process would go faster or earlier due to the deictic and iconic nature of personal pronouns in sign language. But, it's not the case.
"The performance of deaf children matches that of hearing, both qualitatively and chronologically" (Rodda 1987, Petitto 1987), not putting the visual modality at an advantage.
Children acquiring sign langauge also tend to make the same pronoun reversals as do children acquiring spoken language.
Following Emmorey (2002) children who acquire ASL pronouns appear to go through three stages: 1) gestural (non-linguistic pointing to people and objects (beginning at about 9 months), which is the same age at which hearing children start using their first nonlinguistic pointing gestures;
2) pronoun reversal errors may occur and names may be used instead of pronouns (ages 1;6 to 2;0). Both speaking and signing children begin to use personal pronouns at the same age (around 18 months) and make the same kinds of errors. Petitto (1987) argues that children acquiring sign language do not recognize a pointing sign as a pronoun or a lexical sign until the age of about 18 months and then may regard it as a lexical sign and not personal pronoun with a shifting function.
3) the correct of use of personal pronouns (age 2;0 to 2;6).
This phenomenon of pronoun acquisition is a very exciting and important evidence that the brain is amodal. Regardless of iconicity (iconic or abstract) and modality (signed or spoken), the brain has its amodal timeline for language.
It all started when 13-month-old Juli found my glasses on the drawer and took them one morning. I caught her standing near the doorway, holding my glasses with a sheepish grin. I pointed to the glasses and told her "it's mine!"
Juli responded mine. I told no, ix-glasses mine. Juli again produced mine.
At a lunch, Juli pointed to the glasses and produced it. I replied mother, mine See the video. Juli leaned forward slightly and watched closely as if she was beginning to figure out that it was not a noun but something else (e.g. pronoun).
Later that same day, Juli picked up a photograph of herself (when she was baby) and pointed to herself few times as she walked around. It was not the first time. She had been pointing to herself whenever she saw a photograph of herself.
But interestingly, I had noticed lately that whenever she saw a photograph of herself, she pointed to herself. But, when it comes to her signed name. She usually would point to the photograph of herself rather than pointing to herself.
Then, when Juli was 15 months old (week 4), the earliest record of possessive pronoun that Juli used was as follows:
Grandma Z sat on the floor in the family room. She put Juli's artist cap on her head. Juli noticed and pointed at the cap. She produced mine++.
Juli reached for the cap and took it from Grandma Z's head and toddled away. Then she pointed at the toys all around them and produced mine.
Grandma Z was amused. She responded by teasing mine.
Later, she was about to leave for home. At the doorway, as Grandma Z was about to give Juli a goodbye kiss, Juli pointed at Grandma Z's car and produced mine. It could be what she meant it, or it could be a classical reversal error.
Now 23-month-old Juli used deictic pointing to people somehow constantly and correctly. Gestural pointing and linguistic pointing share the same form, but these processes are separate in the brain. It wasn't clear whether Juli used pointing as a non-linguistic gesture and/or a linguistic pronoun.
A possibility was that Juli transitioned from gestural to linguistic somehow smoothly (like the child in a study in Greek Sign Language). In the meanwhile, Juli used names instead of pronouns. In this way, classical reversal errors had been not easily detected.
I was kind of disappointed that I hadn't have a chance to observe this phenomenon. However, bingo! One day Juli revealed a classical reversal error, not in personal pronouns, but in possessive pronouns!
Something else interesting struck. Juli did not only produce a reversal error, though briefly, but she also quickly corrected herself by turning the palm orientation around.
For example, when I uttered yours, Juli initially produced yours but then quickly she turned her palm orientation which pointed toward herself without contacting with her torso. (See video)
Lately the phonological development began to build somehow more quickly and smoother in term of the movement and location primes. That is, whatever she perceived a new ASL word, she was able to produce it somehow adult-like on the fly.
For example, starting to play a YouTube video on television took almost forever. I told Juli that it was so slow. Juli produced slow with the movement being forward. I repeated it and she made the correct movement (backward instead of forward).
The following referential words and phrases that Juli used this week: father bye-bye, mother bye-bye (good night to parents at bedtime), drive firefighter(truck) (her excuse/reason to get out of the closed safety gate away from bedtime), grandfather fix, more cookie, miss (imitated), harmonica, sleep please, ix frog hopping + hiding, some more shown in the video above, and other ASL words mentioned in the past months.
Also see verb inflection based on role-shifting pronouns at age 3.