Effects of Age-of-Acquisition on Proficiency in Polish Sign Language: Insights to the Critical Period Hypothesis

Abstract

This study focuses on the relationship between the age of acquisition of Polish Sign Language (PJM) by deaf individuals and their receptive language skills at the phonological, morphological and syntactic levels. Sixty Deaf signers of PJM were recruited into three equal groups (n = 20): (1) a group exposed to PJM from birth from their deaf parents; (2) a group of childhood learners of PJM, who reported learning PJM between 4 and 8 years; (3) a group of adolescent learners of PJM, who reported learning PJM between 9 and 13 years. The PJM Perception and Comprehension Test was used to assess three aspects of language processing: phonological, morphological and syntactic. Participants were asked to decide whether a series of signs and sentences were acceptable in PJM. Results show that the age of PJM acquisition has a significant impact on performance on this task. The earlier deaf people acquire PJM, the more likely they were to distinguish signs and sentences considered permissible and impermissible in PJM by native signers. Native signers had significantly greater accuracy on the phonological, morphological, and syntactic items than either the Childhood or the Adolescent signers. Further, the Childhood signers had significantly greater accuracy than the Adolescent signers on all three parts of the test. Comparing performance on specific structures targeted within each part of the test revealed that multi-channel signs and negative suffixes posed the greatest challenge for Adolescent signers relative to the Native signers. The above results provide evidence from a less-commonly studied signed language that the age of onset of first language acquisition affects ultimate outcomes in language acquisition across all levels of grammatical structure. In addition, this research corroborates prior studies demonstrating that the critical period is independent of language modality. Contrary to a common public health assumption that early exposure to language is less vital to signed than to spoken language development, the results of this study demonstrate that early exposure to a signed language promotes sensitivity to phonological, morphological and syntactic patterns in language.

Unraveling the impact of congenital deafness on individual brain organization

“…An additional variable that may contribute to the observed outcomes is the comparable language abilities within our cohort of delayed signers. In fact, all deaf participants self-reported consistent levels of sign language proficiency, a factor that is typically affected following delayed language acquisition (Bogliotti et al, 2020; Caselli et al, 2021; Cheng & Mayberry, 2021; Tomaszewski et al, 2022). Furthermore, a subset of delayed deaf signers acquired sign language before the age of 6 (N = 6, see also Supplementary Table 2), potentially rendering them less susceptible to the impact of language deprivation.…”

Prosody of focus in Turkish Sign Language

“…It has also been found that neural processing of nonmanuals with topic structures in Austrian Sign Language (ÖGS) was increasingly delayed when the age of acquisition of the participants was increased (Malaia et al, 2020). Similarly, another study tested if the age of acquisition affected the grammaticality judgments of stimuli where nonmanual information was incrementally presented in Polish Sign Language (PJM) (Tomaszewski et al, 2022). Although all participants, including the native signers, had difficulty in detecting violations in nonmanual stimuli, signers with increased age of acquisition had more difficulty 'for multi-channel signs that required signers to split their attention between manual and non-manual features of the stimuli' (Tomaszewski et al, 2022, p. 10).…”

Early-life language deprivation affects specific neural mechanisms of semantic representations

“…These individuals usually acquired their first language (sign language) around school age, which is much later than the age of first language (L1) acquisition in typically developed children or native deaf signers who were born in deaf families and acquired sign language from birth. Previous research has shown that these delayed deaf signers have lower proficiency in phonological, morphological, and syntactic processing of sign language (Bogliotti et al, 2020; Caselli et al, 2021; Cheng and Mayberry, 2021; Lieberman et al, 2015; Mayberry et al, 2002; Mayberry and Fischer, 1989; Newport, 1990; Tomaszewski et al, 2022) and decreased neural activation in language areas (Mayberry et al, 2018, 2011; Richardson et al, 2020; Twomey et al, 2020) even after many years of sign language usage, indicating long-lasting hypofunction of the language system as a result of missing the critical period of language acquisition. The effects of early language deprivation on semantic processing have been scarcely studied and the extant pieces of evidence reported minimal influences in semantics-related behavioral or N400 measures in adult signers (Baus et al, 2008; Davidson and Mayberry, 2015; Skotara et al, 2012).…”