From the one-word to the multi-word stage. Despite the difference in the modality of expression, developmental trajectories in L1 sign language and L1 spoken language acquisition have been found to be similar. After the transition from the babbling stage to the one-word stage, L1 sign language learners, like L1 spoken language learners, also go through a two-word stage before they produce more complex utterances (Baker et al. 2005). This evidence indicates that “the child’s discovery of the units and rules of grammar is an abstract process that transcends sensory-motor modality” (Mayberry & Squires 2006: 291).
Early production of signs combined with what is referred to as a point have been found to occur at age 12 months (Schick 2003: 222). Whether these combinations already represent multiword combinations remains controversial given the unclear status of the pointing (sign or gesture) at this stage. Schick (2003: 222), for example, remarks that “in young hearing children, who also point to objects and name them, the pointing is considered to be a gesture.” Multiword combinations of 2-3 signs appear about half a year later (between 12-18 months) (Schick 2003: 222 for ASL; Coerts & Mills 1994 for NGT).
Studies dedicated to mother-child interactions reveal that the early input provided to the children also contains few signs only (cf. Spencer & Harris 2006 for ASL; Van den Bogaerde 2000 for NGT). According to Spencer and Harris (2006: 81) mothers tend to produce short utterances (of 1-2 signs), but with multiple repetitions. Further the overall number of signed utterances was found to be lower if compared to the spoken utterances of hearing mothers. These observations are interpreted as evidence for “the mother’s sensitivity to their children’s immature patterns of visual attention” (Spencer & Harris 2006: 81).
Basic word order. With regard to the acquisition of the target word order, the studies undertaken reflect a lack of a clear picture about what would constitute the main developmental milestones. What can be gleaned from the available studies on ASL and NGT is that there is variation in the early learner data. With respect to the productions of young infants learning ASL, there is no consensus as to what they reveal regarding word order development. The focus of these studies is on the attainment of the canonical word order, that is, a surface word order (this needs to be distinguished from the investigation of the acquisition of the underlying structure and its specifications). Some authors have pointed out that early sequences follow a rigid linearisation pattern; other researchers have provided support for variable order at this stage (cf. Lillo-Martin 2006; and Lil- lo-Martin & Chen Pichler 2006 for detailed discussions).
In a study of children acquiring ASL (12 children aged 24 months), Schick (2006: 150-153), showed that L1 ASL learners did not follow any structural posi?tional pattern at this age (at which an average of 28% of the utterances consist of an NP and a point [= Index sign]. Although the children seemed to have a preference for the VERB-THEME order with some verbs and the THEME-VERB pattern with other verbs (similarly, the AGENT-VERB ordering was subject to variation). Interestingly, some of the children were also observed to use alternate orders in AGENT-VERB constructions, with an even percentage for the orderings AGENT- VERB and VERB-AGENT for one child. The examples in (75) illustrate the alternate verb position patterns in the productions of this child (cf. Schick 2002: 155).
Different hypotheses have been put forward to account for the variation observed. Lillo-Martin and Chen Pichler (2006), for example, speculate on the children’s knowledge of several grammatical processes responsible for word order rearrangements in ASL, apart from the target head-complement order parameter. Schick (2006), in turn, assumes that the children’s productions reflect variation in the input. Hence, Schick’s focus is on the children’s challenge to figure out the target word order regularities (e.g. concerning the use of topicalisation or non-manual markers). According to Schick (2006: 156) children might arrive at the conclusion that word order is free in ASL.
Word order variation in deaf children’s early sign language productions is also remarked upon in studies on the acquisition of NGT (cf. Coerts & Mills 1994; Coerts 2000; Van den Bogaerde 2000). NGT, like DGS, represents an SOV language. Although verb-final structures are acknowledged, the evidence obtained reveals that the frequency of this pattern in utterances with two or more signs equals that of verb-initial sequences, and is even slightly lower than that of V2 order (12%) (cf. Van den Bogaerde 2000: 205). Verb-only utterances in the children’s output during the time span covered by the study amount to 38%. Interestingly, verb-only utterances in the children’s input were found to make up 57% of the mothers’ NGT utterances directed to their deaf children aged 1;0-3;0 years
(Van den Bogaerde 2000: 201). Van den Bogaerde (2000: 201) remarks that “these verbs occurring by themselves give the children no clue as to the grammatical structure of SLN [= NGT, CPP].”
Complex structures. The development of complex structures in sign languages has received relatively little attention in the literature (Schick 2003). Some studies on the acquisition of ASL have focused on the development of non-manual markers in diverse constructions including conditional and interrogative clauses (Reilly & Anderson 2002; Schick 2002); others have been dedicated to the acquisition of referential shift in quotation environments and reported action (Emmorey & Reilly 1998). There is a general agreement that constructions with non-manual markers are acquired late (we will come back to this issue in section 126.96.36.199).
What is interesting is that prior to the productive use of non-manual markers in the respective constructions children produce conditional or interrogative clauses with lexical elements (Reilly & Anderson 2002). Based on the data obtained in a study of deaf children acquiring ASL (age 1-10) Reilly and Anderson (2002: 174) remark on an the early production of single sign utterances containing wh-signs accompanied by non-manual markers (furrowed brows). As children begin to produce sign combinations, they only use the manual signs in the interrogative utterances they produce (compare (76) and (77) (from Reilly & Anderson 2002: 174). According to Reilly & Anderson (2002: 174) children do not use the non-manual morphology appropriately until school age.
Hence, the pattern that emerges from developmental data is that “[d]eaf children consistently acquire the manual signals for a given linguistic structure before the acquire the required facial morphology. That is, children use free lexical morphemes, the manual signs, before they acquire the bound non-manual morphology” (Reilly & Anderson 2002: 175). To the best of our knowledge the acquisition of other complex clauses, such as constructions with modal or psychological verbs or rhetorical question-answer pairs remains unexplored thus far.
-  The examples are also worthy of further analysis in relation to child’s attempt to expressthe thematic structure of a verb like videotape, an issue that is not addressed by Schick (2002).