Research has shown that verb agreement in American Sign Language (ASL), which is manifested through movement and spatial displacement of verb signs, is not fully acquired until age three (Meier 1982).  This late acquisition has been hypothesized to be due to the simultaneous occurrence of agreement markers with the verb stem, whereas morphemes which are acquired early in spoken languages are temporally and phonologically distinct from the stem (Meier 1982; Newport and Meier 1985).  Using evidence from action gestures and verb signs produced during the acquisition of ASL by deaf children of deaf parents, it is argued that simultaneity cannot account for this late acquisition.

Analogous to the use of verb agreement in ASL, deaf children aged 0;8-2;11 produce pre-linguistic, directional action gestures (i.e. incorporating movement or spatial displacement) to indicate additional referents.  It is proposed that simultaneity is not a factor in the late acquisition of verb agreement based on evidence that: 1) directional gestures and signs are produced throughout acquisition, 2) agreement is produced in at least 70% of obligatory contexts as early as age 1;11, 3) first recorded productions of specific verbs are not more likely to be produced without directionality, and 4) directionality errors (Bellugi 1988; Fischer 1973; Meier 1982) can be accounted for by difficulty with
factors other than simultaneity.

Analysis of children's directionality errors indicates other possible causes for this late acquisition.  These errors display problems related to: 1) the irregularity of verb agreement (Lillo-Martin 1991; Newport and Meier 1985; Slobin 1982), in that not all verbs can occur with agreement, 2) at which endpoint an argument should occur (Lillo-Martin 1991), 3) with which semantic roles a verb can agree (Lillo-Martin 1991), and 4) the subtle use of role shift, in which the signer takes on the role of a third person (Lillo-Martin 1991).

Based on these data, it is suggested that the use of directionality for referential purposes has gestural origins.  This proposal of a link between pre-linguistic gestures and verb agreement in ASL is additionally claimed to account for this use of directionality in various signed languages (T. Supalla and Webb 1995), the emergence of a new signed language (Kegl, Senghas, and Coppola, in press; Senghas 1995), gestures of deaf children with no ASL input (Goldin-Meadow and Mylander 1990; S.  Supalla 1991), and gestures of hearing adults when not permitted to speak (Dufour 1993).

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