Assimilation processes in sign language
Like all languages, both signed and spoken, word formation evolves over generations. Among different patterns of historical change of the ASL signs, two types of assimilation will be focused on in this discussion about how an ASL compound has evolved into a single word.
In assimilation process, the first part (handshape) of the compound sign is influenced by the second part (handshape). The video clips below illustrate an example of anticipatory assimilation.
The original compound was GIRL+MARRY, meaning WIFE. This became assimilated into a single-like sign WIFE.
The handshape of the second part of the sign WIFE influences the first part which evolves into the same handshape as the second part. In this sign, there is only one handshape.
More examples: HUSBAND, SISTER (multiple assimilation), BROTHER, LAST (from dominant handshape "1" to "i"), REMEMBER (KNOW+CONTINUE), GOLD (EARRING+YELLOW), and so on.
The old ASL word "REMEMBER" signed by George Veditz in his 1913 film, "The Preservation of American Sign Language", shows two handshapes in this ASL sign. Today, there is only one handshape.
In this assimilation process, the first part (handshape) of a sign influences the second part (handshape) of the sign. It's the opposite from anticipatory assimilation.
In this single sign TOMATO, there are two different handshapes between the passive hand and the dominant hand.
In this perseverative assimilation process, the first part ("1" handshape) of the sign TOMATO influences the second part ("O" handshape). In this sign, there is only one handshape.
Other examples of perseverative assimilation are HOME (EAT+BED), etc.
Understanding the reason behind historical change of some ASL signs may help students understand why there are some conventional variations of the signs.
Baker-Shenk, Charlotte; Cokely, Dennis (1991). American Sign Language: A Teacher's Resource Text on Grammar and Culture. Gallaudet University Press, pp 92-95.
You may be interested in Word formation in Japanese Sign Language.