Matthew L. Hall

Persistent Difference in Short-Term Memory Span Between Sign and Speech Implications for Cross-Linguistic Comparisons

Short-term memory (STM) is thought to be limited in capacity to about 7 ± 2 items for linguistic materials and 4 ± 1 items for visuospatial information (Baddeley & Logie, 1999; Cowan, 2001). Recently, we (Boutla, Supalla, Newport, & Bavelier, 2004) challenged this dichotomy between linguistic and visuospatial STM by showing that STM capacity in users of American Sign Language (ASL) is also limited to about 4 or 5 items. This finding suggests that although longer spans appear for speech, spans are not necessarily longer for linguistic materials across all modalities. Wilson and Emmorey (2006) responded that because we evaluated span using digits for English speakers and letters for ASL signers, the difference we reported might have stemmed from stimulus selection rather than language modality. Here we address this claim by reporting an experiment in which we reexamined STM span in English speakers using letters and compared the outcome with results we and Wilson and Emmorey have obtained for ASL signers. It is important to note that the discrepancy between our previous results and those of Wilson and Emmorey is not in the obtained span in signers found by all parties to be around 4 to 5 items (Fig. la). Rather, Wilson and Emmorey disputed whether the digit span of 7 ± 2 in speakers is an appropriate benchmark for comparison with signers. Using letters to measure span in speakers, they found a span of only 5.3, comparable to that of signers. They suggested that there is no difference in span between the two languages. Here we show that their result is not due to their use of letters instead of digits. Rather, in selecting letters that are translations of one another in English and ASL, Wilson and Emmorey failed to control the stimuli in each language for phonological factors known to affect span size. One such crucial factor is phonological similarity. The finding that span is longer for digits than for letters in English speakers is not new (Cavanaugh, 1972). However, this difference has been attributed to the greater phonological similarity of letter names than digit names in English (Conrad & Hull, 1964; Mueller, Seymour, Kieras, & Meyer, 2003). In our previous study, we used letters with signers and digits with speakers to match stimuli in this important regard. Finger-spelled letters are less phonologically similar than number signs in ASL and therefore are more comparable to digits in English speakers. To demonstrate that there is nothing special about letters versus digits, other than the fact that many letter names are highly similar in English (e.g., bee, dee, ee, gee) and thus prone to produce shorter spans, we show here that when phonologically controlled letter materials are used with English speakers, the span of speakers returns to the typical 7 ± 2 range and continues to contrast with the span of signers.

Short-term memory stages in sign vs. speech: the source of the serial span discrepancy.

Speakers generally outperform signers when asked to recall a list of unrelated verbal items. This phenomenon is well established, but its source has remained unclear. In this study, we evaluate the relative contribution of the three main processing stages of short-term memory--perception, encoding, and recall--in this effect. The present study factorially manipulates whether American Sign Language (ASL) or English is used for perception, memory encoding, and recall in hearing ASL-English bilinguals. Results indicate that using ASL during both perception and encoding contributes to the serial span discrepancy. Interestingly, performing recall in ASL slightly increased span, ruling out the view that signing is in general a poor choice for short-term memory. These results suggest that despite the general equivalence of sign and speech in other memory domains, speech-based representations are better suited for the specific task of perception and memory encoding of a series of unrelated verbal items in serial order through the phonological loop. This work suggests that interpretation of performance on serial recall tasks in English may not translate straightforwardly to serial tasks in sign language.

Bilingual picture-word studies constrain theories of lexical selection

Whether lexical selection is by competition is the subject of current debate in studies of monolingual language production. Here, I consider whether extant data from bilinguals can inform this debate. In bilinguals, theories that accept the notion of lexical selection by competition are divided between those positing competition among all lexical nodes vs. those that restrict competition to nodes in the target language only. An alternative view rejects selection by competition altogether, putting the locus of selection in a phonological output buffer, where some potential responses are easier to exclude than others. These theories make contrasting predictions about how quickly bilinguals should name pictures when non-target responses are activated. In Part 1, I establish the empirical facts for which any successful theory must account. In Part 2, I evaluate how well each theory accounts for the data. I argue that the data do not support theories that reject lexical selection by competition, and that although theories where competition for selection is restricted to the target language can be altered to fit the data, doing so would fundamentally undermine the distinctness of their position. Theories where selection is by competition throughout both target and non-target language lexicons must also be modified to account for the data, but these modifications are relatively peripheral to the theoretical impetus of the model. Throughout, I identify areas where our empirical facts are sparse, weak, or absent, and propose additional experiments that should help to further establish how lexical selection works, in both monolinguals and bilinguals.

Investigating constituent order change with elicited pantomime: a functional account of SVO emergence.

One of the most basic functions of human language is to convey who did what to whom. In the worlds languages, the order of these three constituents (subject [S], verb [V], and object [O]) is uneven, with SOV and SVO being most common. Recent experiments using experimentally elicited pantomime provide a possible explanation of the prevalence of SOV, but extant explanations for the prevalence of SVO could benefit from further empirical support. Here, we test whether SVO might emerge because (a) SOV is not well suited for describing reversible events (a woman pushing a boy) and (b) pressures to be efficient and mention subjects before objects conspire to rule out many other alternatives. We tested this by asking participants to describe reversible and non-reversible events in pantomime, and we instructed some participants to be consistent in the form of their gestures and to teach them to the experimenter. These manipulations led to the emergence of SVO in speakers of both English (SVO) and Turkish (SOV).

Auditory Deprivation Does Not Impair Executive Function, But Language Deprivation Might: Evidence From a Parent-Report Measure in Deaf Native Signing Children

Deaf children are often described as having difficulty with executive function (EF), often manifesting in behavioral problems. Some researchers view these problems as a consequence of auditory deprivation; however, the behavioral problems observed in previous studies may not be due to deafness but to some other factor, such as lack of early language exposure. Here, we distinguish these accounts by using the BRIEF EF parent report questionnaire to test for behavioral problems in a group of Deaf children from Deaf families, who have a history of auditory but not language deprivation. For these children, the auditory deprivation hypothesis predicts behavioral impairments; the language deprivation hypothesis predicts no group differences in behavioral control. Results indicated that scores among the Deaf native signers (n = 42) were age-appropriate and similar to scores among the typically developing hearing sample (n = 45). These findings are most consistent with the language deprivation hypothesis, and provide a foundation for continued research on outcomes of children with early exposure to sign language.

Syntactic Priming in American Sign Language

Psycholinguistic studies of sign language processing provide valuable opportunities to assess whether language phenomena, which are primarily studied in spoken language, are fundamentally shaped by peripheral biology. For example, we know that when given a choice between two syntactically permissible ways to express the same proposition, speakers tend to choose structures that were recently used, a phenomenon known as syntactic priming. Here, we report two experiments testing syntactic priming of a noun phrase construction in American Sign Language (ASL). Experiment 1 shows that second language (L2) signers with normal hearing exhibit syntactic priming in ASL and that priming is stronger when the head noun is repeated between prime and target (the lexical boost effect). Experiment 2 shows that syntactic priming is equally strong among deaf native L1 signers, deaf late L1 learners, and hearing L2 signers. Experiment 2 also tested for, but did not find evidence of, phonological or semantic boosts to syntactic priming in ASL. These results show that despite the profound differences between spoken and signed languages in terms of how they are produced and perceived, the psychological representation of sentence structure (as assessed by syntactic priming) operates similarly in sign and speech.

Executive Function in Deaf Children: Auditory Access and Language Access

Purpose Deaf children are frequently reported to be at risk for difficulties in executive function (EF); however, the literature is divided over whether these difficulties are the result of deafness itself or of delays/deficits in language that often co-occur with deafness. The purpose of this study is to discriminate these hypotheses by assessing EF in populations where the 2 accounts make contrasting predictions. Method We use a between-groups design involving 116 children, ages 5-12 years, across 3 groups: (a) participants with normal hearing (n = 45), (b) deaf native signers who had access to American Sign Language from birth (n = 45), and (c) oral cochlear implant users who did not have full access to language prior to cochlear implantation (n = 26). Measures include both parent report and performance-based assessments of EF. Results Parent report results suggest that early access to language has a stronger impact on EF than early access to sound. Performance-based results trended in a similar direction, but no between-group differences were significant. Conclusions These results indicate that healthy EF skills do not require audition and therefore that difficulties in this domain do not result primarily from a lack of auditory experience. Instead, results are consistent with the hypothesis that language proficiency, whether in sign or speech, is crucial for the development of healthy EF. Further research is needed to test whether sign language proficiency also confers benefits to deaf children from hearing families.