Assessing Lexical and Syntactic Comprehension in Deaf Signing Adults.

Among the existing sign language assessment tools, only a small number can be used in clinical settings. This contribution aims at presenting three comprehension assessment tests (two lexical and one syntactic) that offer a solid basis to build tools to assess language impairments in deaf signing adults. We provide the material and guidelines, based on psychometric analyses of the items, to make these tests suitable for clinical assessment. They are available for French Sign Language and Italian Sign Language. So far, the three tests were administered to three groups of deaf participants based on age of exposure (AoE) to sign language: native (AoE from birth), early (AoE = from 1 to 5 years), and late (AoE = from 6 to 15 years) signers. The results showed that the three tests are easy for the typical deaf signing population, and therefore, they can be adapted into tests that assess a deaf signing population with language impairments. Moreover, the results of the syntactic test reveal a categorial difference between native and non-native signers and therefore show the need for baselines that mirror the effect of AoE to sign language when assessing language competence, in particular in clinical assessment.

The role of verbal short-term memory in complex sentence comprehension: An observational study on aphasia.

BACKGROUND: The comprehension profile of people with agrammatism is a debated topic. Syntactic complexity and cognitive resources, in particular phonological short-term memory (pSTM), are considered as crucial components by different interpretative accounts. AIM: To investigate the interaction of syntactic complexity and of pSTM in sentence comprehension in a group of persons with aphasia with and without agrammatism. METHODS & PROCEDURES: A cohort of 30 participants presenting with aphasia was assessed for syntactic comprehension and for pSTM. A total of 15 presented with agrammatism and 15 had fluent aphasia. OUTCOMES & RESULTS: Linear nested mixed-model analyses revealed a significant interaction between sentence type and pSTM. In particular, participants with lower pSTM scores showed a reduced comprehension of centre-embedded object relatives and long coordinated sentences. Moreover, a significant interaction was found between sentence type and agrammatism, with a lower performance for passives within the agrammatic group. CONCLUSIONS & IMPLICATIONS: These results confirm that pSTM is involved in the comprehension of complex structures with an important computational load, in particular coordinated sentences, and long-distance filler gap dependencies. On the contrary, the specific deficit of the agrammatic group with passives is a pure syntactic deficit, with no involvement of pSTM.

On the Reliability of the Notion of Native Signer and Its Risks.

Who is a native signer? Since around 95% of deaf infants are born into a hearing family, deaf signers are exposed to a sign language at various moments of their life, and not only from birth. Moreover, the linguistic input they are exposed to is not always a fully fledged natural sign language. In this situation, is the notion of native signer as someone exposed to language from birth of any use? We review the results of the first large-scale cross-linguistic investigation on the effects of age of exposure to sign language. This research involved about 45 Deaf adult signers in each of three sign languages (Catalan Sign Language, French Sign Language, and Italian Sign Language). Across the three languages, participants were divided into three groups - those exposed from birth, those between 1 and 5 years of age, and those exposed between 6 and 15 years of age - and received a battery of tests designed for each language targeting various aspects of morphosyntactic competence. In particular, the tests focused on both those morphosyntactic phenomena that are known from the spoken language literature to be good detectors of language impairment or delay (i.e., wh-interrogatives and relative clauses) and on morphosyntactic phenomena that are sign language specific (i.e., role shift and directional verbs). The results showed a clear effect of being native, with significant differences across languages and tests between signers exposed to sign language from birth and those exposed in the 1st years of life. This confirms the life-long importance of language exposure from birth and the reliability of the notion of "nativeness", at least for syntax. On the other hand, while in most domains the differences observed between populations might be differences in performance, for some specific constructions, signers belonging to the three groups may have different grammars. This latter finding challenges the generalized use of native signers' grammar as the baseline for language description and language assessment.

Performance of Deaf Participants in an Abstract Visual Grammar Learning Task at Multiple Formal Levels: Evaluating the Auditory Scaffolding Hypothesis.

Previous research has hypothesized that human sequential processing may be dependent upon hearing experience (the "auditory scaffolding hypothesis"), predicting that sequential rule learning abilities should be hindered by congenital deafness. To test this hypothesis, we compared deaf signer and hearing individuals' ability to acquire rules of different computational complexity in a visual artificial grammar learning task using sequential stimuli. As a group, deaf participants succeeded at all levels of the task; Bayesian analysis indicates that they successfully acquired each of several target grammars at ascending levels of the formal language hierarchy. Overall, these results do not support the auditory scaffolding hypothesis. However, age- and education-matched hearing participants did outperform deaf participants in two out of three tested grammars. We suggest that this difference may be related to verbal recoding strategies in the two groups. Any verbal recoding strategies used by the deaf signers would be less effective because they would have to use the same visual channel required for the experimental task.

The Impact of Aging on Spatial Abilities in Deaf Users of a Sign Language.

Research involving the general population of people who use a spoken language to communicate has demonstrated that older adults experience cognitive and physical changes associated with aging. Notwithstanding the differences in the cognitive processes involved in sign and spoken languages, it is possible that aging can also affect cognitive processing in deaf signers. This research aims to explore the impact of aging on spatial abilities among sign language users. Results showed that younger signers were more accurate than older signers on all spatial tasks. Therefore, the age-related impact on spatial abilities found in the older hearing population can be generalized to the population of signers. Potential implications for sign language production and comprehension are discussed.

Mind the stimulation site: Enhancing and diminishing sentence comprehension with anodal tDCS.

In a previous sham-controlled study, we showed the feasibility of increasing language comprehension in healthy participants by applying anodal transcranial direct current stimulation (atDCS) over the left inferior frontal gyrus (LIFG). In the present work, we present a follow-up experiment targeting with atDCS the left inferior parietal cortex (LIPC) while participants performed the same auditory comprehension task used in our previous experiment. Both neural sites (LIFG and LIPC) are crucial hubs of Baddeley's model of verbal short-term memory (vSTM). AtDCS over LIPC decreased accuracy as compared to sham and LIFG stimulation, suggesting the involvement of this area in sentence comprehension. Crucially, our results highlighted that applying tDCS over different hubs of the same neural network can lead to opposite behavioural results, with relevant implications from a clinical perspective.

Is STM involved in sentence comprehension?

We discuss the literature concerning the role of auditory-verbal short-term memory (phonological loop) in sentence comprehension. We critically analyze data concerning patients with a selective deficit of the phonological loop, then we examine aphasic patients with deficit of auditory-verbal short-term memory and we consider the effect of STM treatment on sentence comprehension. Finally, results from imaging and TMS studies are discussed. In our opinion, data from the literature suggest that both components of the phonological loop are involved in the comprehension of some type of sentence, namely syntactically complex sentences that load on memory, such as center-embedded object relative clauses. However, it is crucial to investigate further patients with a selective STM impairment or aphasic patients, by using extensive and sophisticated experimental material.

Spatial biases in deaf, blind, and deafblind individuals as revealed by a haptic line bisection task.

In this study, we investigated whether auditory deprivation leads to a more balanced bilateral control of spatial attention in the haptic space. We tested four groups of participants: early deaf, early blind, deafblind, and control (normally hearing and sighted) participants. Using a haptic line bisection task, we found that while normally hearing individuals (even when blind) showed a significant tendency to bisect to the left of the veridical midpoint (i.e., pseudoneglect), deaf individuals did not show any significant directional bias. This was the case of both deaf signers and non-signers, in line with prior findings obtained using a visual line bisection task. Interestingly, deafblind individuals also erred significantly to the left, resembling the pattern of early blind and control participants. Overall, these data critically suggest that deafness induces changes in the hemispheric asymmetry subtending the orientation of spatial attention also in the haptic modality. Moreover, our findings indicate that what counterbalances the right-hemisphere dominance in the control of spatial attention is not the lack of auditory input per se, nor sign language use, but rather the heavier reliance on visual experience induced by early auditory deprivation.

Artificial Grammar Learning Capabilities in an Abstract Visual Task Match Requirements for Linguistic Syntax.

Whether pattern-parsing mechanisms are specific to language or apply across multiple cognitive domains remains unresolved. Formal language theory provides a mathematical framework for classifying pattern-generating rule sets (or "grammars") according to complexity. This framework applies to patterns at any level of complexity, stretching from simple sequences, to highly complex tree-like or net-like structures, to any Turing-computable set of strings. Here, we explored human pattern-processing capabilities in the visual domain by generating abstract visual sequences made up of abstract tiles differing in form and color. We constructed different sets of sequences, using artificial "grammars" (rule sets) at three key complexity levels. Because human linguistic syntax is classed as "mildly context-sensitive," we specifically included a visual grammar at this complexity level. Acquisition of these three grammars was tested in an artificial grammar-learning paradigm: after exposure to a set of well-formed strings, participants were asked to discriminate novel grammatical patterns from non-grammatical patterns. Participants successfully acquired all three grammars after only minutes of exposure, correctly generalizing to novel stimuli and to novel stimulus lengths. A Bayesian analysis excluded multiple alternative hypotheses and shows that the success in rule acquisition applies both at the group level and for most participants analyzed individually. These experimental results demonstrate rapid pattern learning for abstract visual patterns, extending to the mildly context-sensitive level characterizing language. We suggest that a formal equivalence of processing at the mildly context sensitive level in the visual and linguistic domains implies that cognitive mechanisms with the computational power to process linguistic syntax are not specific to the domain of language, but extend to abstract visual patterns with no meaning.

Anodal transcranial direct current stimulation over left inferior frontal gyrus enhances sentence comprehension.

We tested the possibility of enhancing natural language comprehension through the application of anodal tDCS (a-tDCS) over the left inferior frontal gyrus, a key region for verbal short-term memory and language comprehension. We designed a between subjects sham- and task-controlled study. During tDCS stimulation, participants performed a sentence to picture matching task in which targets were sentences with different load on short-term memory. Regardless of load on short-term memory, the Anodal group performed significantly better than the Sham group, thus providing evidence that a-tDCS over LIFG enhances natural language comprehension. To our knowledge, we apply for the first time tDCS to boost sentence comprehension. This result is of special interest also from a clinical perspective: applying a-tDCS in patients manifesting problems at the sentence level due to brain damage could enhance the effects of behavioral rehabilitation procedures aimed to improve language comprehension.

Tactile short-term memory in sensory-deprived individuals.

To verify whether loosing a sense or two has consequences on a spared sensory modality, namely touch, and whether these consequences depend on practice or are biologically determined, we investigated 13 deafblind participants, 16 deaf participants, 15 blind participants, and 13 matched normally sighted and hearing controls on a tactile short-term memory task, using checkerboard matrices of increasing length in which half of the squares were made up of a rough texture and half of a smooth one. Time of execution of a fixed matrix, number of correctly reproduced matrices, largest matrix correctly reproduced and tactile span were recorded. The three groups of sensory-deprived individuals did not differ in any measure, while blind and deaf participants outscored controls in all parameters except time of execution; the difference approached significance for deafblind people compared to controls only in one measure, namely correctly reproduced matrices. In blind and deafblind participants, performance negatively correlated with age of Braille acquisition, the older being the subject when acquiring Braille, the lower the performance, suggesting that practice plays a role. However, the fact that deaf participants, who did not share tactile experience, performed similarly to blind participants and significantly better than controls highlights that practice cannot be the only contribution to better tactile memory.

Deaf Individuals Show a Leftward Bias in Numerical Bisection.

Consistent evidence suggests that deaf individuals conceive of numerical magnitude as a left-to-right-oriented mental number line, as typically observed in hearing individuals. When accessing this spatial representation of numbers, normally hearing individuals typically show an attentional bias to the left (pseudoneglect), resembling the attentional bias they show in physical space. Deaf individuals do not show pseudoneglect in representing external space, as assessed by a visual line bisection task. However, whether deaf individuals show attentional biases in representing numerical space has never been investigated before. Here we instructed groups of deaf and hearing individuals to quickly estimate (without calculating) the midpoint of a series of numerical intervals presented in ascending and descending order. Both hearing and deaf individuals were significantly biased toward lower numbers (i.e., the leftward side of the mental number line) in their estimations. Nonetheless, the underestimation bias was smaller in deaf individuals than in the hearing when bisecting pairs of numbers given in descending order. This result may depend on the use of different strategies by deaf and hearing participants or a less pronounced lateralization of deaf individuals in the control of spatial attention.

Deaf, blind or deaf-blind: Is touch enhanced?

When someone looses one type of sensory input, s/he may compensate by using the sensory information conveyed by other senses. To verify whether loosing a sense or two has consequences on a spared sensory modality, namely touch, and whether these consequences depend on the type of sensory loss, we investigated the effects of deafness and blindness on temporal and spatial tactile tasks in deaf, blind and deaf-blind people. Deaf and deaf-blind people performed the spatial tactile task better than the temporal one, while blind and controls showed the opposite pattern. Deaf and deaf-blind participants were impaired in temporal discrimination as compared to controls, while deaf-blind individuals outperformed blind participants in the spatial tactile task. Overall, sensory-deprived participants did not show an enhanced tactile performance. We speculate that discriminative touch is not so relevant in humans, while social touch is. Probably, more complex tactile tasks would have revealed an increased performance in sensory-deprived people.

When meaning is useless.

The aim of this study is to disentangle the relative contribution of semantic and phonological representation in immediate serial recall. Indeed, short-term memory (STM) performance could be enhanced by familiarity with the phonological form of the word only or together with semantic information. Participants learned two sets of words in an unknown language: for one set they acquired both phonology and semantics, while for the other only phonology. After that, they performed two immediate serial recall tasks involving either "phonology and semantics" or "only phonology" words and one with untrained words. The analyses showed that the trained lists did not differ from each other, while they did from the untrained one. These data confirm that familiarity with the phonological form is sufficient for immediate serial recall. Therefore, we argue that semantics is not required for verbal STM, but knowledge of the phonological form is what matters.

Making sense of an unexpected detrimental effect of sign language use in a visual task.

What supports deaf signers advantage over nonsigners on visuospatial short-term memory (STM) tasks is still a matter of debate. We compared the performance of 18 deaf Italian Sign Language (LIS) users with that of a matched group of Italian hearing nonsigners in three different tasks: two versions of the Corsi Block test, namely span forward and span backward, and the Visual Pattern Test (VPT). Although the Corsi forward and backward are dynamic and mainly involve a spatial component, the VPT is static and taps primarily the visual component of STM. Signers significantly outperformed nonsigners on both versions of the Corsi Block test, whereas they performed significantly worse on the VPT. We suggest that the source of the different pattern lies in the static nature of the VPT versus the dynamic nature of the Corsi spans.

Auditory deprivation affects biases of visuospatial attention as measured by line bisection.

In this study, we investigated whether early deafness affects the typical pattern of hemispheric lateralization [i.e., right hemisphere (RH) dominance] in the control of spatial attention. To this aim, deaf signers, deaf non-signers, hearing signers, and hearing non-signers were required to bisect a series of centrally presented visual lines. The directional bisection bias was found to be significantly different between hearing and deaf participants, irrespective of sign language use. Hearing participants (both signers and non-signers) showed a consistent leftward bias, reflecting RH dominance. Conversely, we observed no evidence of a clear directional bias in deaf signers or non-signers (deaf participants overall showing a non-significant tendency to deviate rightward), suggesting that deafness may be associated to a more bilateral hemispheric engagement in visuospatial tasks.

Phonology without semantics? Good enough for verbal short-term memory. Evidence from a patient with semantic dementia.

INTRODUCTION: There is considerable evidence that long-term knowledge has an influence on short-term memory (STM) performance. This reflects the activation of long-term representations involved in perceiving and comprehending spoken language. Still, this type of long-term knowledge might be of two different kinds. STM performance might be facilitated by information about the meaning of the word, or, alternatively, by familiarity with its phonological form. METHODS: We investigated these two alternatives by assessing word span in MC, a patient with semantic dementia. Four different lists of words were used: known words, words whose phonological form was known by the patient although she could not report its meaning, words that the patient did not recognize as words and judged as nonwords, nonwords. The patient's performance was compared to that of six matched controls. RESULTS: MC did not differ from controls in the first two types of lists and performed at the same level with both, while for words whose phonological form was unknown (and therefore not recognized as words) her performance was comparable to that with nonwords; also, with this type of item, she produced significantly more phonemic substitutions than controls. CONCLUSIONS: The results show that long-term knowledge facilitates immediate serial recall. However, this facilitation is due to familiarity with phonological representations rather than to knowledge of meaning.

Hearing shapes our perception of time: temporal discrimination of tactile stimuli in deaf people.

Confronted with the loss of one type of sensory input, we compensate using information conveyed by other senses. However, losing one type of sensory information at specific developmental times may lead to deficits across all sensory modalities. We addressed the effect of auditory deprivation on the development of tactile abilities, taking into account changes occurring at the behavioral and cortical level. Congenitally deaf and hearing individuals performed two tactile tasks, the first requiring the discrimination of the temporal duration of touches and the second requiring the discrimination of their spatial length. Compared with hearing individuals, deaf individuals were impaired only in tactile temporal processing. To explore the neural substrate of this difference, we ran a TMS experiment. In deaf individuals, the auditory association cortex was involved in temporal and spatial tactile processing, with the same chronometry as the primary somatosensory cortex. In hearing participants, the involvement of auditory association cortex occurred at a later stage and selectively for temporal discrimination. The different chronometry in the recruitment of the auditory cortex in deaf individuals correlated with the tactile temporal impairment. Thus, early hearing experience seems to be crucial to develop an efficient temporal processing across modalities, suggesting that plasticity does not necessarily result in behavioral compensation.

Looking for an explanation for the low sign span. Is order involved?

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.

A case for the involvement of phonological loop in sentence comprehension.

The specific role of the phonological loop in sentence comprehension is still a matter of debate. We tested the behavioural consequences of activity disruption in left BA40 and BA44, key regions of the phonological loop, on language comprehension using 1Hz rTMS. Comprehension was assessed by means of two tasks: a sentence-to-picture matching task, with sentences varying in length and syntactic complexity (Experiment 1), and a sentence verification task (Experiment 2). rTMS over left BA40 significantly reduced accuracy for syntactically complex sentences and long, but syntactically simpler sentences, while rTMS over left BA44 significantly reduced accuracy only for syntactically complex sentences. rTMS applied over left BA40 also impaired performance on sentences in which word order was crucial. We suggest that the neural correlates of the phonological loop, left BA40 and BA44, are both involved in the comprehension of syntactically complex sentences, while only left BA40, corresponding to the short-term store, is recruited for the comprehension of long but syntactically simple sentences. Therefore, in contrast with the dominant view, we showed that sentence comprehension is a function of the phonological loop.