Ordered short-term memory differs in signers and speakers: implications for models of short-term memory

Neurocognitive outcomes in young adults with cochlear implants: The role of early language access and crossmodal plasticity

Many children with profound hearing loss have received cochlear implants (CI) to help restore some sense of hearing. There is, however, limited research on long-term neurocognitive outcomes in young adults who have grown up hearing through a CI. This study compared the cognitive outcomes of early-implanted (n = 20) and late-implanted (n = 21) young adult CI users, and typically hearing (TH) controls (n=56), all of whom were enrolled in college. Cognitive fluidity, nonverbal intelligence, and American Sign Language (ASL) comprehension were assessed, revealing no significant differences in cognition and nonverbal intelligence between the early and late-implanted groups. However, there was a difference in ASL comprehension, with the late-implanted group having significantly higher ASL comprehension. Although young adult CI users showed significantly lower scores in a working memory and processing speed task than TH age-matched controls, there were no significant differences in tasks involving executive function shifting, inhibitory control, and episodic memory between young adult CI and young adult TH participants. In an exploratory analysis of a subset of CI participants (n = 17) in whom we were able to examine crossmodal plasticity, we saw greater evidence of crossmodal recruitment from the visual system in late-implanted compared with early-implanted CI young adults. However, cortical visual evoked potential latency biomarkers of crossmodal plasticity were not correlated with cognitive measures or ASL comprehension. The results suggest that in the late-implanted CI users, early access to sign language may have served as a scaffold for appropriate cognitive development, while in the early-implanted group early access to oral language benefited cognitive development. Furthermore, our results suggest that the persistence of crossmodal neuroplasticity into adulthood does not necessarily impact cognitive development. In conclusion, early access to language - spoken or signed - may be important for cognitive development, with no observable effect of crossmodal plasticity on cognitive outcomes.

Verbal and visual serial-order memory in deaf signers and hearing nonsigners: A systematic review and meta-analysis

Previous research suggests Deaf signers may have different short-term and working memory processes compared with hearing nonsigners due to prolonged auditory deprivation. The direction and magnitude of these reported differences, however, are variable and dependent on memory modality (e.g., visual, verbal), stimulus type, and research design. These discrepancies have made consensus difficult to reach which, in turn, slows progress in areas such as education, medical decision-making, and cognitive sciences. The present systematic review and meta-analysis included 35 studies (N = 1,701 participants) that examined verbal (n = 15), visuospatial (n = 10), or both verbal and visuospatial (n = 10) serial-memory tasks comparing nonimplanted, Deaf signers to hearing nonsigners across the life span. Multivariate meta-analyses indicated a significant, negative effect of deafness on verbal short-term memory (forward recall), g = -1.33, SE = 0.17, p < .001, 95% CI [-1.68, -0.98], and working memory (backward recall), g = -0.66, SE = 0.11, p < .001, 95% CI [-0.89, -0.45], but no significant effect of deafness on visuospatial short-term memory, g = -0.055, SE = 0.17, p = 0.75, 95% CI [-0.39, 0.28]. Visuospatial working memory was not analyzed due to limited power. Population estimates for verbal and visuospatial short-term memory were moderated by age wherein studies with adults demonstrated a stronger hearing advantage than studies with children/adolescents. Quality estimates indicated most studies were of fair quality, with only 38% of studies involving Deaf authors. Findings are discussed in the context of both Deaf equity and models of serial memory.

Effect of visual presentation format and recall direction on letter span and error patterns in Deaf signing and hearing adults

Deaf signers consistently show shorter memory spans than hearing nonsigners, but the scope and nature of this difference remain unclear. The present study tested whether Deaf signers are biased toward flexible use of visual aspects of linguistic items. Matched samples of adult Deaf signers (N = 33) and hearing nonsigners (N = 32) performed a letter-span task with visual serial presentation, to bias phonological processing, and a simultaneous presentation, to bias visuospatial processing. We also manipulated short-term memory by varying recall direction (forward, backward). Analyses revealed reduced spans for Deaf signers compared with hearing nonsigners, backward compared with forward recall, and sequential compared with simultaneous presentation. Item-level responses indicated that Deaf signers made more errors than hearing nonsigners across three error types. Deaf signers also showed reduced item position binding compared with hearing nonsigners, which indicates differences related to item order and sequencing in tasks with printed, linguistic stimuli. Deaf signers were the only group who demonstrated reduced omission errors when switching from sequential to simultaneous presentation, suggesting flexible processing mechanisms. No group differences were found for a secondary spatial span test, indicating the scope of group differences for ordered information was limited to verbal items. Overall, results are consistent with flexible use of different memory cues in Deaf signers. A core area for future research includes evaluating reduced activation of phonological representations of linguistic items in Deaf signers. These results amplify a novel M³ model approach for evaluating how errors contribute to short-term memory differences in Deaf signers.

Deafness and early language deprivation influence arithmetic performances

It has been consistently reported that deaf individuals experience mathematical difficulties compared to their hearing peers. However, the idea that deafness and early language deprivation might differently affect verbal (i.e., multiplication) vs. visuospatial (i.e., subtraction) arithmetic performances is still under debate. In the present paper, three groups of 21 adults (i.e., deaf signers, hearing signers, and hearing controls) were therefore asked to perform, as fast and as accurately as possible, subtraction and multiplication operations. No significant group effect was found for accuracy performances. However, reaction time results demonstrated that the deaf group performed both arithmetic operations slower than the hearing groups. This group difference was even more pronounced for multiplication problems than for subtraction problems. Weaker language-based phonological representations for retrieving multiplication facts, and sensitivity to interference are two hypotheses discussed to explain the observed dissociation.

Functional connectivity alteration of the deprived auditory regions with cognitive networks in deaf and inattentive adolescents

Adolescents with early profound deafness may present with distractibility and inattentiveness. The brain mechanisms underlying these attention impairments remain unclear. We performed resting-state functional magnetic resonance imaging to investigate the functional connectivity of the superior temporal and transverse temporal gyri in 25 inattentive adolescents with bilateral prelingual profound deafness, and compared the results with those of 27 age-matched normal controls. Pearson and Spearman's rho correlation analyses were used to investigate the correlations of altered functional connectivity with the clinical parameters, including the duration of hearing loss sign language, and hearing aid usage. Compared with normal controls, prelingual profound deafness demonstrated mainly decreased resting-state functional connectivity between the deprived auditory regions and several other brain functional networks, including the attention control, language comprehension, default-mode, and sensorimotor networks. Moreover, we also found enhanced resting-state functional connectivity between the deprived auditory cortex and salience network. These results indicate a negative impact of early hearing loss on the attentional and other high cognitive networks, and the use of sign language and hearing aids normalized the participants' connectivity between the primary auditory cortex and attention networks, which is crucial for the early intervention and clinical care of deaf adolescents.

Early deafness leads to re-shaping of functional connectivity beyond the auditory cortex

Early sensory deprivation, such as deafness, shapes brain development in multiple ways. Deprived auditory areas become engaged in the processing of stimuli from the remaining modalities and in high-level cognitive tasks. Yet, structural and functional changes were also observed in non-deprived brain areas, which may suggest the whole-brain network changes in deaf individuals. To explore this possibility, we compared the resting-state functional network organization of the brain in early deaf adults and hearing controls and examined global network segregation and integration. Relative to hearing controls, deaf adults exhibited decreased network segregation and an altered modular structure. In the deaf, regions of the salience network were coupled with the fronto-parietal network, while in the hearing controls, they were coupled with other large-scale networks. Deaf adults showed weaker connections between auditory and somatomotor regions, stronger coupling between the fronto-parietal network and several other large-scale networks (visual, memory, cingulo-opercular and somatomotor), and an enlargement of the default mode network. Our findings suggest that brain plasticity in deaf adults is not limited to changes in the auditory cortex but additionally alters the coupling between other large-scale networks and the development of functional brain modules. These widespread functional connectivity changes may provide a mechanism for the superior behavioral performance of the deaf in visual and attentional tasks.

A Technology-based Intervention to Increase Reading Comprehension of Morphosyntax Structures

The purpose of this study was to examine the effectiveness of a technology-based intervention (LanguageLinks: Syntax Assessment and Intervention®; Laureate Learning Systems, Inc., 2013) to improve reading comprehension for d/Deaf and hard of hearing (DHH) elementary students. The intervention was a self-paced, interactive program designed to scaffold learning of morphosyntax structures. Participants included 37 DHH students with moderate to profound hearing levels, 7-12 years of age, in Grades 2-6. Assessment data were collected pre- and post- an 8-week intervention using a randomized control trial methodology. Findings indicate the intervention did not appear to be effective in improving performance, and 17 out of 36 morphosyntax structures were found difficult to comprehend for participants in the treatment group. These difficult structures included aspects of pronominalization, the verbal system, and number in nouns. Results are compared to previous research, with recommendations for future areas of research related to increasing knowledge of morphosyntax for learners who are DHH.

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.

The spatial representation of number, time, and serial order following sensory deprivation: A systematic review

The spatial representation of numerical and temporal information is thought to be rooted in our multisensory experiences. Accordingly, we may expect visual or auditory deprivation to affect the way we represent numerical magnitude and time spatially. Here, we systematically review recent findings on how blind and deaf individuals represent abstract concepts such as magnitude and time (e.g., past/future, serial order of events) in a spatial format. Interestingly, available evidence suggests that sensory deprivation does not prevent the spatial "re-mapping" of abstract information, but differences compared to normally sighted and hearing individuals may emerge depending on the specific dimension considered (i.e., numerical magnitude, time as past/future, serial order). Herein we discuss how the study of sensory deprived populations may shed light on the specific, and possibly distinct, mechanisms subserving the spatial representation of these concepts. Furthermore, we pinpoint unresolved issues that need to be addressed by future studies to grasp a full understanding of the spatial representation of abstract information associated with visual and auditory deprivation.

The relation between working memory and language comprehension in signers and speakers

This study investigated the relation between linguistic and spatial working memory (WM) resources and language comprehension for signed compared to spoken language. Sign languages are both linguistic and visual-spatial, and therefore provide a unique window on modality-specific versus modality-independent contributions of WM resources to language processing. Deaf users of American Sign Language (ASL), hearing monolingual English speakers, and hearing ASL-English bilinguals completed several spatial and linguistic serial recall tasks. Additionally, their comprehension of spatial and non-spatial information in ASL and spoken English narratives was assessed. Results from the linguistic serial recall tasks revealed that the often reported advantage for speakers on linguistic short-term memory tasks does not extend to complex WM tasks with a serial recall component. For English, linguistic WM predicted retention of non-spatial information, and both linguistic and spatial WM predicted retention of spatial information. For ASL, spatial WM predicted retention of spatial (but not non-spatial) information, and linguistic WM did not predict retention of either spatial or non-spatial information. Overall, our findings argue against strong assumptions of independent domain-specific subsystems for the storage and processing of linguistic and spatial information and furthermore suggest a less important role for serial encoding in signed than spoken language comprehension.

Articulatory Suppression Effects on Short-term Memory of Signed Digits and Lexical Items in Hearing Bimodal-Bilingual Adults

We can gain a better understanding of short-term memory processes by studying different language codes and modalities. Three experiments were conducted to investigate: (a) Taiwanese Sign Language (TSL) digit spans in Chinese/TSL hearing bilinguals (n = 32); (b) American Sign Language (ASL) digit spans in English/ASL hearing bilinguals (n = 15); and (c) TSL lexical sign spans in Chinese/TSL hearing bilinguals (n = 22). Articulatory suppression conditions were manipulated to determine if participants would use a speech- or sign-based code to rehearse lists of signed items. Results from all 3 experiments showed that oral suppression significantly reduced spans while manual suppression had no effect, revealing that participants were using speech-based rehearsal to retain lists of signed items in short-term memory. In addition, sub-vocal rehearsal using Chinese facilitated higher digit spans than English even though stimuli were perceived and recalled using signs. This difference was not found for lexical sign spans.

The contribution of phonological knowledge, memory, and language background to reading comprehension in deaf populations

While reading is challenging for many deaf individuals, some become proficient readers. Little is known about the component processes that support reading comprehension in these individuals. Speech-based phonological knowledge is one of the strongest predictors of reading comprehension in hearing individuals, yet its role in deaf readers is controversial. This could reflect the highly varied language backgrounds among deaf readers as well as the difficulty of disentangling the relative contribution of phonological versus orthographic knowledge of spoken language, in our case ‘English,’ in this population. Here we assessed the impact of language experience on reading comprehension in deaf readers by recruiting oral deaf individuals, who use spoken English as their primary mode of communication, and deaf native signers of American Sign Language. First, to address the contribution of spoken English phonological knowledge in deaf readers, we present novel tasks that evaluate phonological versus orthographic knowledge. Second, the impact of this knowledge, as well as memory measures that rely differentially on phonological (serial recall) and semantic (free recall) processing, on reading comprehension was evaluated. The best predictor of reading comprehension differed as a function of language experience, with free recall being a better predictor in deaf native signers than in oral deaf. In contrast, the measures of English phonological knowledge, independent of orthographic knowledge, best predicted reading comprehension in oral deaf individuals. These results suggest successful reading strategies differ across deaf readers as a function of their language experience, and highlight a possible alternative route to literacy in deaf native signers.

Highlights:

1. Deaf individuals vary in their orthographic and phonological knowledge of English as a function of their language experience.

2. Reading comprehension was best predicted by different factors in oral deaf and deaf native signers.

3. Free recall memory (primacy effect) better predicted reading comprehension in deaf native signers as compared to oral deaf or hearing individuals.

4. Language experience should be taken into account when considering cognitive processes that mediate reading in deaf individuals.

Deaf children's non-verbal working memory is impacted by their language experience

Several recent studies have suggested that deaf children perform more poorly on working memory tasks compared to hearing children, but these studies have not been able to determine whether this poorer performance arises directly from deafness itself or from deaf children's reduced language exposure. The issue remains unresolved because findings come mostly from (1) tasks that are verbal as opposed to non-verbal, and (2) involve deaf children who use spoken communication and therefore may have experienced impoverished input and delayed language acquisition. This is in contrast to deaf children who have been exposed to a sign language since birth from Deaf parents (and who therefore have native language-learning opportunities within a normal developmental timeframe for language acquisition). A more direct, and therefore stronger, test of the hypothesis that the type and quality of language exposure impact working memory is to use measures of non-verbal working memory (NVWM) and to compare hearing children with two groups of deaf signing children: those who have had native exposure to a sign language, and those who have experienced delayed acquisition and reduced quality of language input compared to their native-signing peers. In this study we investigated the relationship between NVWM and language in three groups aged 6-11 years: hearing children (n = 28), deaf children who were native users of British Sign Language (BSL; n = 8), and deaf children who used BSL but who were not native signers (n = 19). We administered a battery of non-verbal reasoning, NVWM, and language tasks. We examined whether the groups differed on NVWM scores, and whether scores on language tasks predicted scores on NVWM tasks. For the two executive-loaded NVWM tasks included in our battery, the non-native signers performed less accurately than the native signer and hearing groups (who did not differ from one another). Multiple regression analysis revealed that scores on the vocabulary measure predicted scores on those two executive-loaded NVWM tasks (with age and non-verbal reasoning partialled out). Our results suggest that whatever the language modality-spoken or signed-rich language experience from birth, and the good language skills that result from this early age of acquisition, play a critical role in the development of NVWM and in performance on NVWM tasks.

Generating a lexicon without a language model: Do words for number count?

Homesigns are communication systems created by deaf individuals without access to conventional linguistic input. To investigate how homesign gestures for number function in short-term memory compared to homesign gestures for objects, actions, or attributes, we conducted memory span tasks with adult homesigners in Nicaragua, and with comparison groups of unschooled hearing Spanish speakers and deaf Nicaraguan Sign Language signers. There was no difference between groups in recall of gestures or words for objects, actions or attributes; homesign gestures therefore can function as word units in short-term memory. However, homesigners showed poorer recall of numbers than the other groups. Unlike the other groups, increasing the numerical value of the to-be-remembered quantities negatively affected recall in homesigners, but not controls. When developed without linguistic input, gestures for number do not seem to function as summaries of the cardinal values of the sets (four), but rather as indexes of items within a set (one-one-one-one).

Signed language working memory capacity of signed language interpreters and deaf signers

This study investigated the effects of hearing status and age of signed language acquisition on signed language working memory capacity. Professional Auslan (Australian sign language)/English interpreters (hearing native signers and hearing nonnative signers) and deaf Auslan signers (deaf native signers and deaf nonnative signers) completed an Auslan working memory (WM) span task. The results revealed that the hearing signers (i.e., the professional interpreters) significantly outperformed the deaf signers on the Auslan WM span task. However, the results showed no significant differences between the native signers and the nonnative signers in their Auslan working memory capacity. Furthermore, there was no significant interaction between hearing status and age of signed language acquisition. Additionally, the study found no significant differences between the deaf native signers (adults) and the deaf nonnative signers (adults) in their Auslan working memory capacity. The findings are discussed in relation to the participants' memory strategies and their early language experience. The findings present challenges for WM theories.

Verbal short-term memory development and spoken language outcomes in deaf children with cochlear implants

OBJECTIVES

Cochlear implants (CIs) help many deaf children achieve near-normal speech and language (S/L) milestones. Nevertheless, high levels of unexplained variability in S/L outcomes are limiting factors in improving the effectiveness of CIs in deaf children. The objective of this study was to longitudinally assess the role of verbal short-term memory (STM) and working memory (WM) capacity as a progress-limiting source of variability in S/L outcomes after CI in children.

DESIGN

Longitudinal study of 66 children with CIs for prelingual severe-to-profound hearing loss. Outcome measures included performance on digit span forward (DSF), digit span backward (DSB), and four conventional S/L measures that examined spoken-word recognition (Phonetically Balanced Kindergarten word test), receptive vocabulary (Peabody Picture Vocabulary Test ), sentence-recognition skills (Hearing in Noise Test), and receptive and expressive language functioning (Clinical Evaluation of Language Fundamentals Fourth Edition Core Language Score; CELF).

RESULTS

Growth curves for DSF and DSB in the CI sample over time were comparable in slope, but consistently lagged in magnitude relative to norms for normal-hearing peers of the same age. For DSF and DSB, 50.5% and 44.0%, respectively, of the CI sample scored more than 1 SD below the normative mean for raw scores across all ages. The first (baseline) DSF score significantly predicted all endpoint scores for the four S/L measures, and DSF slope (growth) over time predicted CELF scores. DSF baseline and slope accounted for an additional 13 to 31% of variance in S/L scores after controlling for conventional predictor variables such as: chronological age at time of testing, age at time of implantation, communication mode (auditory-oral communication versus total communication), and maternal education. Only DSB baseline scores predicted endpoint language scores on Peabody Picture Vocabulary Test and CELF. DSB slopes were not significantly related to any endpoint S/L measures. DSB baseline scores and slopes taken together accounted for an additional 4 to 19% of variance in S/L endpoint measures after controlling for the conventional predictor variables.

CONCLUSIONS

Verbal STM/WM scores, process measures of information capacity, develop at an average rate in the years after cochlear implantation, but were found to consistently lag in absolute magnitude behind those reported for normal-hearing peers. Baseline verbal STM/WM predicted long-term endpoint S/L outcomes, but verbal STM slopes predicted only endpoint language outcomes. Verbal STM/WM processing skills reflect important underlying core elementary neurocognitive functions and represent potential intervention targets for improving endpoint S/L outcomes in pediatric CI users.

Routes to short-term memory indexing: lessons from deaf native users of American Sign Language

Models of working memory (WM) have been instrumental in understanding foundational cognitive processes and sources of individual differences. However, current models cannot conclusively explain the consistent group differences between deaf signers and hearing speakers on a number of short-term memory (STM) tasks. Here we take the perspective that these results are not due to a temporal order-processing deficit in deaf individuals, but rather reflect different biases in how different types of memory cues are used to do a given task. We further argue that the main driving force behind the shifts in relative biasing is a consequence of language modality (sign vs. speech) and the processing they afford, and not deafness, per se.

Developmental trajectories of forward and backward digit spans in deaf children with cochlear implants

BACKGROUND

Accounting for outcome variability among pediatric cochlear implant (CI) recipients is an enduring clinical challenge. Short-term memory and working memory (STM/WM), as indexed by digit span forward (DSF) and digit span backward (DSB), have been shown to be strongly correlated with speech and language (S/L) outcomes. The enormous variability observed in conventional outcome measures of S/L may reflect individual differences in STM/WM.

METHODS

Repeated measure auditory digit spans were obtained from 110 children (age 3-15 years; mean 7.2 years) with at least 2 years of CI use. Growth curves were computed for each child, and linear functions were fit to both DSF and DSB. Slopes and intercepts were used as parameters in mixed-models to assess relations between STM/WM capacity change over time and S/L outcome measures including vocabulary (PPVT), open-set set spoken word recognition (PBK), and sentence perception (HINT-C).

RESULTS

For DSF, the percent of the sample more than 1 SD below the norm at each age ranged from 54 to 90% (mean = 66.5%). For DSB, the percent of the sample more than 1 SD below the norm at each age ranged from 23 to 42% (mean = 34.5%) at ages where there were at least five children. Four subgroups within our CI sample emerged: (Subgroup 1) children demonstrating age-appropriate growth in both DSF and DSB scores over time (49/110, 44.55%); (Subgroup 2) children demonstrating age appropriate growth in DSF over time but below average growth in DSB over time (23/110, 20.91%); (Subgroup 3) children demonstrating below average growth in DSF over time but age-appropriate growth in DSB over time (19/110, 17.27%); and (Subgroup 4) children demonstrating below average growth in both DSF and DSB over time (19/110, 17.27%). For all tests except CELF-3, Subgroup 4 demonstrated the poorest performance among the four DS slope subgroups. Significant differences were observed between Subgroup 1 and Subgroup 4 on last visit PBK-Word (P = 0.029), PPVT (P = 0.018), and HINT-C in Quiet (P = 0.001), but not CELF-3 (P = 0.433).

CONCLUSION

The findings from this longitudinal study suggest that differences in the rate of development of STM/WM may influence S/L outcomes in children with CIs. The clinical implications of these findings are significant because they indicate that the rate of development of STM/WM, and not just the actual level of STM/WM at a single time point, predicts later S/L development in this clinical population. Targeted interventions to improve developmental rate of verbal STM/WM may hold promise for enhancing S/L skills in children with CIs.

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.

CNS activation and regional connectivity during pantomime observation: no engagement of the mirror neuron system for deaf signers

Deaf signers have extensive experience using their hands to communicate. Using fMRI, we examined the neural systems engaged during the perception of manual communication in 14 deaf signers and 14 hearing non-signers. Participants passively viewed blocked video clips of pantomimes (e.g., peeling an imaginary banana) and action verbs in American Sign Language (ASL) that were rated as meaningless by non-signers (e.g., TO-DANCE). In contrast to visual fixation, pantomimes strongly activated fronto-parietal regions (the mirror neuron system, MNS) in hearing non-signers, but only bilateral middle temporal regions in deaf signers. When contrasted with ASL verbs, pantomimes selectively engaged inferior and superior parietal regions in hearing non-signers, but right superior temporal cortex in deaf signers. The perception of ASL verbs recruited similar regions as pantomimes for deaf signers, with some evidence of greater involvement of left inferior frontal gyrus for ASL verbs. Functional connectivity analyses with left hemisphere seed voxels (ventral premotor, inferior parietal lobule, fusiform gyrus) revealed robust connectivity with the MNS for the hearing non-signers. Deaf signers exhibited functional connectivity with the right hemisphere that was not observed for the hearing group for the fusiform gyrus seed voxel. We suggest that life-long experience with manual communication, and/or auditory deprivation, may alter regional connectivity and brain activation when viewing pantomimes. We conclude that the lack of activation within the MNS for deaf signers does not support an account of human communication that depends upon automatic sensorimotor resonance between perception and action.

Effects of age on the temporal organization of working memory in deaf signers

Deaf native signers have a general working memory (WM) capacity similar to that of hearing non-signers but are less sensitive to the temporal order of stored items at retrieval. General WM capacity declines with age, but little is known of how cognitive aging affects WM function in deaf signers. We investigated WM function in elderly deaf signers (EDS) and an age-matched comparison group of hearing non-signers (EHN) using a paradigm designed to highlight differences in temporal and spatial processing of item and order information. EDS performed worse than EHN on both item and order recognition using a temporal style of presentation. Reanalysis together with earlier data showed that with the temporal style of presentation, order recognition performance for EDS was also lower than for young adult deaf signers. Older participants responded more slowly than younger participants. These findings suggest that apart from age-related slowing irrespective of sensory and language status, there is an age-related difference specific to deaf signers in the ability to retain order information in WM when temporal processing demands are high. This may be due to neural reorganisation arising from sign language use. Concurrent spatial information with the Mixed style of presentation resulted in enhanced order processing for all groups, suggesting that concurrent temporal and spatial cues may enhance learning for both deaf and hearing groups. These findings support and extend the WM model for Ease of Language Understanding.

Encoding, rehearsal, and recall in signers and speakers: shared network but differential engagement

Short-term memory (STM), or the ability to hold verbal information in mind for a few seconds, is known to rely on the integrity of a frontoparietal network of areas. Here, we used functional magnetic resonance imaging to ask whether a similar network is engaged when verbal information is conveyed through a visuospatial language, American Sign Language, rather than speech. Deaf native signers and hearing native English speakers performed a verbal recall task, where they had to first encode a list of letters in memory, maintain it for a few seconds, and finally recall it in the order presented. The frontoparietal network described to mediate STM in speakers was also observed in signers, with its recruitment appearing independent of the modality of the language. This finding supports the view that signed and spoken STM rely on similar mechanisms. However, deaf signers and hearing speakers differentially engaged key structures of the frontoparietal network as the stages of STM unfold. In particular, deaf signers relied to a greater extent than hearing speakers on passive memory storage areas during encoding and maintenance, but on executive process areas during recall. This work opens new avenues for understanding similarities and differences in STM performance in signers and speakers.