The goal of this article is to explore the utility of experimental syntax techniques in the investigation of syntactic variation. To that end, we applied the factorial definition of island effects made available by experimental syntax (e.g., Sprouse et al. 2012) to four island types (wh/whether, complex NP, subject, and adjunct), two dependency types (wh-interrogative clause dependencies and relative clause dependencies) and two languages (English and Italian). The results of 8 primary experiments suggest that there is indeed variation across dependency types, suggesting that wh-interrogative clause dependencies and relative clause dependencies cannot be identical at every level of analysis; however, the pattern of variation observed in these experiments is not exactly the pattern of variation previously reported in the literature (e.g., Rizzi 1982). We review six major syntactic approaches to the analysis of island effects (Subjacency, CED, Barriers, Relativized Minimality, Structure-building, and Phases) and discuss the implications of these results for these analyses. We also present 4 supplemental experiments testing complex wh-phrases (also called D-linked or lexically restricted wh-phrases) for all four island types using the factorial design in order to tease apart the contribution of dependency type from featural specification. The results of the supplemental experiments confirm that dependency type is the major source of variation, not featural specification, while providing a concrete quantification of what exactly the effect of complex wh-phrases on island effects is.

Tactile sign languages used by Deafblind signers are most often acquired by signers competent in a visual sign language who can no longer rely on the grammatical system of the visual language as it is, since some of its features are lost due to the loss of vision. A natural question is which repair strategies are adopted to compensate for the loss of the grammatical features of the visual language that can no longer be perceived. We argue that the transformation of LIS (Italian Sign Language) into tactile Italian Sign Language (LISt) is constrained by grammatical principles, rather than reflecting communication strategies that in principle might compensate for the visual loss equally well. Certain innovations are introduced to carry over the grammatical features of LIS to LISt. Even when LISt undergoes processes that make it diverge from LIS, these processes are attested in other natural languages. For example, among the innovations unconsciously introduced by LISt signers we found an instance of cross-modal grammaticalization. Our research suggests that tactile languages have the potential of becoming complete grammatical systems, at least when they build on previous knowledge of a visual sign language.

Although signed and speech-based languages have a similar internal organization of verbal short-term memory, sign span is lower than word span. We investigated whether this is due to the fact that signs are not suited for serial recall, as proposed by Bavelier, Newport, Hall, Supalla, and Boutla (2008. Ordered short-term memory differs in signers and speakers: Implications for models of short-term memory. Cognition, 107, 433–459). We administered a serial recall task with stimuli in Italian Sign Language to 12 deaf people, and we compared their performance with that of twelve age-, gender-, and education-matched hearing participants who performed the task in Italian. The results do not offer evidence for the hypothesis that serial order per se is a detrimental factor for deaf participants. An alternative explanation for the lower sign span based on signs being phonologically heavier than words is considered.