Executive Functions and Theory-of-Mind Among Deaf Children: Different Routes to Understanding Other Minds?

The aim of the present study was to investigate the role of executive functions (EF) in theory-of-mind (ToM) performance in deaf children and adolescents. Four groups of deaf children aged 7–16 years, with different language backgrounds at home and at school, that is, bilingually instructed native signers, oralist-instructed native signers, and two groups of bilingually instructed late signers from Sweden and Estonia, respectively, were given eight ToM and four EF measures. The bilingually instructed native signers performed at a significantly higher level on the ToM measures than the other groups of deaf children. On the EF measures, there were no significant differences found between any of the groups, with one exception—the Swedish bilingual late signers had a significantly shorter average reaction time on the go-no-go inhibition task than the oralist native signers and the Estonian bilingual late signers. However, the Swedish children's better EF performance was not mirrored in better performance on ToM tasks. Our results indicate that despite all deaf children's good general cognitive abilities, there were still differences in their performance on ToM tasks that need to be explained in other terms. Thus, whatever the cause of late signers' difficulties with ToM, poor EF-skills seem to be of minor importance.     

How grammar can cope with limited short-term memory: simultaneity and seriality in sign languages

It is known that in American Sign Language (ASL) span is shorter than in English, but this discrepancy has never been systematically investigated using other pairs of signed and spoken languages. This finding is at odds with results showing that short-term memory (STM) for signs has an internal organization similar to STM for words. Moreover, some methodological questions remain open. Thus, we measured span of deaf and matched hearing participants for Italian Sign Language (LIS) and Italian, respectively, controlling for all the possible variables that might be responsible for the discrepancy: yet, a difference in span between deaf signers and hearing speakers was found. However, the advantage of hearing subjects was removed in a visuo-spatial STM task. We attribute the source of the lower span to the internal structure of signs: indeed, unlike English (or Italian) words, signs contain both simultaneous and sequential components. Nonetheless, sign languages are fully-fledged grammatical systems, probably because the overall architecture of the grammar of signed languages reduces the STM load. Our hypothesis is that the faculty of language is dependent on STM, being however flexible enough to develop even in a relatively hostile environment.     

Effects of language experience on the perception of American Sign Language

Perception of American Sign Language (ASL) handshape and place of articulation parameters was investigated in three groups of signers: deaf native signers, deaf non-native signers who acquired ASL between the ages of 10 and 18, and hearing non-native signers who acquired ASL as a second language between the ages of 10 and 26. Participants were asked to identify and discriminate dynamic synthetic signs on forced choice identification and similarity judgement tasks. No differences were found in identification performance, but there were effects of language experience on discrimination of the handshape stimuli. Participants were significantly less likely to discriminate handshape stimuli drawn from the region of the category prototype than stimuli that were peripheral to the category or that straddled a category boundary. This pattern was significant for both groups of deaf signers, but was more pronounced for the native signers. The hearing L2 signers exhibited a similar pattern of discrimination, but results did not reach significance. An effect of category structure on the discrimination of place of articulation stimuli was also found, but it did not interact with language background. We conclude that early experience with a signed language magnifies the influence of category prototypes on the perceptual processing of handshape primes, leading to differences in the distribution of attentional resources between native and non-native signers during language comprehension.     

Spoken Language Activation Alters Subsequent Sign Language Activation in L2 Learners of American Sign Language

A large body of literature has characterized unimodal monolingual and bilingual lexicons and how neighborhood density affects lexical access; however there have been relatively fewer studies that generalize these findings to bimodal (M2) second language (L2) learners of sign languages. The goal of the current study was to investigate parallel language activation in M2L2 learners of sign language and to characterize the influence of spoken language and sign language neighborhood density on the activation of ASL signs. A priming paradigm was used in which the neighbors of the sign target were activated with a spoken English word and compared the activation of the targets in sparse and dense neighborhoods. Neighborhood density effects in auditory primed lexical decision task were then compared to previous reports of native deaf signers who were only processing sign language. Results indicated reversed neighborhood density effects in M2L2 learners relative to those in deaf signers such that there were inhibitory effects of handshape density and facilitatory effects of location density. Additionally, increased inhibition for signs in dense handshape neighborhoods was greater for high proficiency L2 learners. These findings support recent models of the hearing bimodal bilingual lexicon, which posit lateral links between spoken language and sign language lexical representations.     

Visual-spatial processing in deaf brain-damaged signers

Sign language displays all the complex linguistic structure found in spoken languages, but conveys its syntax in large part by manipulating spatial relations. This study investigated whether deaf signers who rely on a visual-spatial language nonetheless show a principled cortical separation for language and nonlanguage visual-spatial functioning. Four unilaterally brain-damaged deaf signers, fluent in American Sign Language (ASL) before their strokes, served as subjects. Three had damage to the left hemisphere and one had damage to the right hemisphere. They were administered selected tests of nonlanguage visual-spatial processing. The pattern of performance of the four patients across this series of tests suggests that deaf signers show hemispheric specialization for nonlanguage visual-spatial processing that is similar to hearing speaking individuals. The patients with damage to the left hemisphere, in general, appropriately processed visual-spatial relationships, whereas, in contrast, the patient with damage to the right hemisphere showed consistent and severe visual-spatial impairment. The language behavior of these patients was much the opposite, however. Indeed, the most striking separation between linguistic and nonlanguage visual-spatial functions occurred in the left-hemisphere patient who was most severely aphasic for sign language. Her signing was grossly impaired, yet her visual-spatial capacities across the series of tests were surprisingly normal. These data suggest that the two cerebral hemispheres of congenitally deaf signers can develop separate functional specialization for nonlanguage visual-spatial processing and for language processing, even though sign language is conveyed in large part via visual-spatial manipulation.     

Looking through phonological shape to lexical meaning: The bottleneck of non-native sign language processing

In two studies, we find that native and non-native acquisition show different effects on sign language processing. Subjects were all born deaf and used sign language for interpersonal communication, but first acquired it at ages ranging from birth to 18. In the first study, deaf signers shadowed (simultaneously watched and reproduced) sign language narratives given in two dialects, American Sign Language (ASL) and Pidgin Sign English (PSE), in both good and poor viewing conditions. In the second study, deaf signers recalled and shadowed grammatical and ungrammatical ASL sentences. In comparison with non-native signers, natives were more accurate, comprehended better, and made different kinds of lexical changes; natives primarily changed signs in relation to sign meaning independent of the phonological characteristics of the stimulus. In contrast, non-native signers primarily changed signs in relation to the phonological characteristics of the stimulus independent of lexical and sentential meaning. Semantic lexical changes were positively correlated to processing accuracy and comprehension, whereas phonological lexical changes were negatively correlated. The effects of non-native acquisition were similar across variations in the sign dialect, viewing condition, and processing task. The results suggest that native signers process lexical structural automatically, such that they can attend to and remember lexical and sentential meaning. In contrast, non-native signers appear to allocate more attention to the task of identifying phonological shape such that they have less attention available for retrieval and memory of lexical meaning.     

Memory for Faces and Objects by Deaf and Hearing Signers and Hearing Nonsigners

The memory of 11 deaf and 11 hearing British Sign Language users and 11 hearing nonsigners for pictures of faces of and verbalizable objects was measured using the game Concentration. The three groups performed at the same level for the objects. In contrast the deaf signers were better for faces than the hearing signers, who in turn were superior to the hearing nonsigners, who were the worst. Three hypotheses were made: That there would be no significant difference in terms of the number of attempts between the three groups on the verbalizable object task, that the hearing and deaf signers would demonstrate superior performance to that of the hearing nonsigners on the matching faces task, and that the hearing and deaf signers would exhibit similar performance levels on the matching faces task. The first two hypotheses were supported, but the third was not. Deaf signers were found to be superior for memory for faces to hearing signers and hearing nonsigners. Possible explanations for the findings are discussed, including the possibility that deafness and the long use of sign language have additive effects.     

Perception of movement in American Sign Language: Effects of linguistic structure and linguistic experience

In order to reveal the psychological representation of movement from American Sign Language (ASL), deaf native signers and hearing subjects unfamiliar with sign were asked to make triadic comparisons of movements that had been isolated from lexical and from grammatically inflected signs. An analysis of the similarity judgments revealed a small set of physically specifiable dimensions that accounted for most of the variance. The dimensions underlying the perception of lexical movement were in general different from those underlying inflectional movement, for both groups of subjects. Most strikingly, deaf and hearing subjects significantly differed in their patterns of dimensional salience for movements, both at the lexical and at the inflectional levels. Linguistically relevant dimensions were of increased salience to native signers. The difference in perception of linguistic movement by native signers and by naive observers demonstrates that modification of natural perceptual categories after language acquisition is not bound to a particular transmission modality, but rather can be a more general consequence of acquiring a formal linguistic system.     

Visual field asymmetries for motion processing in deaf and hearing signers

Recently, we reported a strong right visual field/left hemisphere advantage for motion processing in deaf signers and a slight reverse asymmetry in hearing nonsigners (Bosworth & Dobkins, 1999). This visual field asymmetry in deaf signers may be due to auditory deprivation or to experience with a visual-manual language, American Sign Language (ASL). In order to separate these two possible sources, in this study we added a third group, hearing native signers, who have normal hearing and have learned ASL from their deaf parents. As in our previous study, subjects performed a direction-of-motion discrimination task at different locations across the visual field. In addition to investigating differences in left vs right visual field asymmetries across subject groups, we also asked whether performance differences exist for superior vs inferior visual fields and peripheral vs central visual fields. Replicating our previous study, a robust right visual field advantage was observed in deaf signers, but not in hearing nonsigners. Like deaf signers, hearing signers also exhibited a strong right visual field advantage, suggesting that this effect is related to experience with sign language. These results suggest that perceptual processes required for the acquisition and comprehension of language (motion processing in the case of ASL) are recruited by the left, language-dominant, hemisphere. Deaf subjects also exhibited an inferior visual field advantage that was significantly larger than that observed in either hearing group. In addition, there was a trend for deaf subjects to perform relatively better on peripheral than on central stimuli, while both hearing groups showed the reverse pattern. Because deaf signers differed from hearing signers and nonsigners along these domains, the inferior and peripheral visual field advantages observed in deaf subjects is presumably related to auditory deprivation. Finally, these visual field asymmetries were not modulated by attention for any subject group, suggesting they are a result of sensory, and not attentional, factors.     

Brain activations associated with sign production using word and picture inputs in deaf signers

Effective literacy education in deaf students calls for psycholinguistic research revealing the cognitive and neural mechanisms underlying their written language processing. When learning a written language, deaf students are often instructed to sign out printed text. The present fMRI study was intended to reveal the neural substrates associated with word signing by comparing it with picture signing. Native deaf signers were asked to overtly sign in Chinese Sign Language (CSL) common objects indicated with written words or presented as pictures. Except in left inferior frontal gyrus and inferior parietal lobule where word signing elicited greater activation than picture signing, the two tasks engaged a highly overlapping set of brain regions previously implicated in sign production. The results suggest that word signing in the deaf signers relies on meaning activation from printed visual forms, followed by similar production processes from meaning to signs as in picture signing. The present study also documents the basic brain activation pattern for sign production in CSL and supports the notion of a universal core neural network for sign production across different sign languages.     

Correlations Between Handshape and Movement in Sign Languages

Sign language phonological parameters are somewhat analogous to phonemes in spoken language. Unlike phonemes, however, there is little linguistic literature arguing that these parameters interact at the sublexical level. This situation raises the question of whether such interaction in spoken language phonology is an artifact of the modality or whether sign language phonology has not been approached in a way that allows one to recognize sublexical parameter interaction. We present three studies in favor of the latter alternative: a shape-drawing study with deaf signers from six countries, an online dictionary study of American Sign Language, and a study of selected lexical items across 34 sign languages. These studies show that, once iconicity is considered, handshape and movement parameters interact at the sublexical level. Thus, consideration of iconicity makes transparent similarities in grammar across both modalities, allowing us to maintain certain key findings of phonological theory as evidence of cognitive architecture.     

Short-term memory coding by deaf signers: the primary language coding hypothesis reconsidered

Shand (Cognitive Psychology, 1982, 14, 1-12) hypothesized that strong reliance on a phonetic code by hearing individuals in short-term memory situations reflects their primary language experience. As support for this proposal, Shand reported an experiment in which deaf signers' recall of lists of printed English words was poorer when the American Sign Language translations of those words were structurally similar than when they were structurally unrelated. He interpreted this result as evidence that the deaf subjects were recoding the printed words into sign, reflecting their primary language experience. This primary language interpretation is challenged in the present article first by an experiment in which a group of hearing subjects showed a similar recall pattern on Shand's lists of words, and second by a review of the literature on short-term memory studies with deaf subjects. The literature survey reveals that whether or not deaf signers recode into sign depends on a variety of task and subject factors, and that, contrary to the primary language hypothesis, deaf signers may recode into a phonetic code in short-term recall.     

Narrative Skills in Written Texts by Deaf and Hearing Bilingual Adolescents

Most studies on narrative competence have focused on monolingual subjects, and there are very few studies which address this issue in bilingual subjects dealing with two language systems. In the present case study we analyzed and compared the textual and narrative written skills of three deaf and three hearing adolescents attending eighth grade at a bilingual school (Italian and Italian Sign Language), characterized by a pragmatic approach to writing (based on production and the interpretation of texts in genuine and meaningful situations).Their competences were assessed through a well-known narrative task, the Frog Story (Mayer, 1969), and the following parameters were examined: complex syntax, narrative structure and evaluation devices. Results show that there were not significant differences in the texts written by the deaf students compared to the hearing students and that being immersed in a bilingual context did not interfere with the development of textual and narrative competence in either hearing or deaf students.     

Neural responses to meaningless pseudosigns: evidence for sign-based phonetic processing in superior temporal cortex

To identify neural regions that automatically respond to linguistically structured, but meaningless manual gestures, 14 deaf native users of American Sign Language (ASL) and 14 hearing non-signers passively viewed pseudosigns (possible but non-existent ASL signs) and non-iconic ASL signs, in addition to a fixation baseline. For the contrast between pseudosigns and baseline, greater activation was observed in left posterior superior temporal sulcus (STS), but not in left inferior frontal gyrus (BA 44/45), for deaf signers compared to hearing non-signers, based on VOI analyses. We hypothesize that left STS is more engaged for signers because this region becomes tuned to human body movements that conform the phonological constraints of sign language. For deaf signers, the contrast between pseudosigns and known ASL signs revealed increased activation for pseudosigns in left posterior superior temporal gyrus (STG) and in left inferior frontal cortex, but no regions were found to be more engaged for known signs than for pseudosigns. This contrast revealed no significant differences in activation for hearing non-signers. We hypothesize that left STG is involved in recognizing linguistic phonetic units within a dynamic visual or auditory signal, such that less familiar structural combinations produce increased neural activation in this region for both pseudosigns and pseudowords.     

聋人手语视觉表象生成能力的实验研究

通过视觉表象判断实验,对聋手语使用者和听力正常人两类被试视觉表象生成的能力进行了比较。实验发现：与听力正常的人相比,聋手语使用者学习和记忆大写字母的时间短于听力正常的被试,并且两组被试记忆复杂字母的时间都较长;聋被试和听力正常被试采用了相同的字母表征方式。但是,习得手语的年龄对聋手语者生成表象的能力没有明显的影响。     

Silent reading: Insights from second-generation deaf readers

Previous studies indicate that hearing readers sometimes convert printed text into a phonological form during silent reading. The experiments reported here investigated whether second-generation congenitally deaf readers use any analogous recoding strategy. Fourteen congenitally and profoundly deaf adults who were native signers of American Sign Language (ASL) served as subjects. Fourteen hearing people of comparable reading levels were control subjects. These subjects participated in four experiments that tested for the possibilities of (a) recoding into articulation, (b) recoding into fingerspelling, (c) recoding into ASL, or (d) no recoding at all. The experiments employed paradigms analogous to those previously used to test for phonological recoding in hearing populations. Interviews with the deaf subjects provided supplementary information about their reading strategies. The results suggest that these deaf subjects as a group do not recode into articulation or fingerspelling, but do recode into sign.     

Deaf signers and serial recall in the visual modality: Memory for signs,fingerspelling, and print

This study investigated serial recall by congenitally, profoundly deaf signers for visually specified linguistic information presented in their primary language, American Sign Language (ASL), and in printed or fingerspelled English. There were three main findings. First, differences in the serial-position curves across these conditions distinguished the changing-state stimuli from the static stimuli. These differences were a recency advantage and a primacy disadvantage for the ASL signs and fingerspelled English words, relative to the printed English words. Second, the deaf subjects, who were college students and graduates, used a sign-based code to recall ASL signs, but not to recall English words; this result suggests that well-educated deaf signers do not translate into their primary language when the information to be recalled is in English. Finally, mean recall of the deaf subjects for ordered lists of ASL signs and fingerspelled and printed English words was significantly less than that of hearing control subjects for the printed words; this difference may be explained by the particular efficacy of a speech-based code used by hearing individuals for retention of ordered linguistic information and by the relatively limited speech experience of congenitally, profoundly deaf individuals.     

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

Capacity limits in linguistic short-term memory (STM) are typically measured with forward span tasks in which participants are asked to recall lists of words in the order presented. Using such tasks, native signers of American Sign Language (ASL) exhibit smaller spans than native speakers ([Boutla, M., Supalla, T., Newport, E. L., & Bavelier, D. (2004). Short-term memory span: Insights from sign language. Nature Neuroscience, 7(9), 997-1002]). Here, we test the hypothesis that this population difference reflects differences in the way speakers and signers maintain temporal order information in short-term memory. We show that native signers differ from speakers on measures of short-term memory that require maintenance of temporal order of the tested materials, but not on those in which temporal order is not required. In addition, we show that, in a recall task with free order, bilingual subjects are more likely to recall in temporal order when using English than ASL. We conclude that speakers and signers do share common short-term memory processes. However, whereas short-term memory for spoken English is predominantly organized in terms of temporal order, we argue that this dimension does not play as great a role in signers' short-term memory. Other factors that may affect STM processes in signers are discussed.     

Temporal processing in deaf signers

The auditory and visual modalities differ in their capacities for temporal analysis, and speech relies on more rapid temporal contrasts than does sign language. We examined whether congenitally deaf signers show enhanced or diminished capacities for processing rapidly varying visual signals in light of the differences in sensory and language experience of deaf and hearing individuals. Four experiments compared rapid temporal analysis in deaf signers and hearing subjects at three different levels: sensation, perception, and memory. Experiment 1 measured critical flicker frequency thresholds and Experiment 2, two-point thresholds to a flashing light. Experiments 3-4 investigated perception and memory for the temporal order of rapidly varying nonlinguistic visual forms. In contrast to certain previous studies, specifically those investigating the effects of short-term sensory deprivation, no significant differences between deaf and hearing subjects were found at any level. Deaf signers do not show diminished capacities for rapid temporal analysis, in comparison to hearing individuals. The data also suggest that the deficits in rapid temporal analysis reported previously for children with developmental language delay cannot be attributed to lack of experience with speech processing and production.     

Memory in deaf signers and embodied cognition of sign languages

Abstract:  In the first half of this paper, the experimental investigations on memory and cognition in deaf signers are reviewed in order to reveal how deaf signers rely on sign-based coding when they process linguistic information. It is suggested that deaf signers tactically employ a set of originally separate memory strategies relying on multiple components of working memory. In the second half of this paper, the author shows possible factors that could contribute to a sign language advantage. It is indicated that deaf signers' cognitive activities are deeply rooted in the signers' interaction with the environment. Some concrete examples of Japanese Sign Language signs and their use are provided to support this hypothesis.