Ágnes Lukács

Impaired procedural learning in language impairment: Results from probabilistic categorization

The Weather Prediction (WP) Task is a classical task of probabilistic category learning generally used for examining the dissociation of procedural and declarative memory. The current study focuses on performance of children with language impairment (LI) and compares their performance to that of typically developing (TD) children and adults with the aim of testing the procedural deficit hypothesis of LI (PDH; Ullman & Pierpont, 2005), which states that language impairment is not a specific linguistic phenomenon, but results from the dysfunction of a more general cognitive system: the procedural system. To test the generality of the procedural impairment, we needed a task that is dissimilar from language in that it does not build on sequential information. Children with language impairment show deficient learning on the Weather Prediction Task, which already appears at the early stages of the task. These results, in line with the PDH, point to the deficit of the procedural system in language impairment going beyond the language system. Whether this deficit is selective to the procedural system or is complemented by deficits in the declarative system is the subject of future studies.

Domain-general sequence learning deficit in specific language impairment.

OBJECTIVE Grammar-specific accounts of specific language impairment (SLI) have been challenged by recent claims that language problems are a consequence of impairments in domain-general mechanisms of learning that also play a key role in the process of language acquisition. Our studies were designed to test the generality and nature of this learning deficit by focusing on both sequential and nonsequential, and on verbal and nonverbal, domains. METHOD Twenty-nine children with SLI were compared with age-matched typically developing (TD) control children using (a) a serial reaction time task (SRT), testing the learning of motor sequences; (b) an artificial grammar learning (AGL) task, testing the extraction of regularities from auditory sequences; and (c) a weather prediction task (WP), testing probabilistic category learning in a nonsequential task. RESULTS For the 2 sequence learning tasks, a significantly smaller proportion of children showed evidence of learning in the SLI than in the TD group (χ2 tests, p < .001 for the SRT task, p < .05 for the AGL task), whereas the proportion of learners on the WP task was the same in the 2 groups. The level of learning for SLI learners was comparable with that of TD children on all tasks (with great individual variation). CONCLUSIONS Taken together, these findings suggest that domain-general processes of implicit sequence learning tend to be impaired in SLI. Further research is needed to clarify the relationship of deficits in implicit learning and language.

Development of Different Forms of Skill Learning throughout the Lifespan.

The acquisition of complex motor, cognitive, and social skills, like playing a musical instrument or mastering sports or a language, is generally associated with implicit skill learning (SL). Although it is a general view that SL is most effective in childhood, and such skills are best acquired if learning starts early, this idea has rarely been tested by systematic empirical studies on the developmental pathways of SL from childhood to old age. In this paper, we challenge the view that childhood and early school years are the prime time for skill learning by tracking age-related changes in performance in three different paradigms of SL. We collected data from participants between 7 and 87 years for (1) a Serial Reaction Time Task (SRT) testing the learning of motor sequences, (2) an Artificial Grammar Learning (AGL) task testing the extraction of regularities from auditory sequences, and (3) Probabilistic Category Learning in the Weather Prediction task (WP), a non-sequential categorization task. Results on all three tasks show that adolescence and adulthood are the most efficient periods for skill learning, since instead of becoming less and less effective with age, SL improves from childhood into adulthood and then later declines with aging.

Self-Insight in Probabilistic Category Learning

ABSTRACT The Weather Prediction (WP) task is one of the most extensively used Probabilistic Category Learning tasks. Although it has been usually treated as an implicit task, its implicit nature has been questioned with focus on the structural knowledge of the acquired information. The goal of the current studies is to test if participants acquire explicit knowledge on the WP task. Experiment 1 addresses this question directly with the help of a subjective measure on self-insight in two groups: an experimental group facing the WP task and a control group with a task lacking predictive structure. Participants in the experimental group produced more explicit reports than the control group, and only on trials with explicit knowledge was their performance higher. Experiment 2 provided further evidence against the implicitness of the task by showing that decreasing stimulus presentation times extends the learning process, but does not result in more implicit processes.

Lateralized processing of novel metaphors: disentangling figurativeness and novelty.

One of the intriguing and sometimes controversial findings in figurative language research is a right-hemisphere processing advantage for novel metaphors. The current divided visual field study introduced novel literal expressions as a control condition to assess processing novelty independent of figurativeness. Participants evaluated word pairs belonging to one of the five categories: (1) conventional metaphorical, (2) conventional literal, (3) novel metaphorical, (4) novel literal, and (5) unrelated expressions in a semantic decision task. We presented expressions without sentence context and controlled for additional factors including emotional valence, arousal, and imageability that could potentially influence hemispheric processing. We also utilized an eye-tracker to ensure lateralized presentation. We did not find the previously reported right-hemispherical processing advantage for novel metaphors. Processing was faster in the left hemisphere for all types of word pairs, and accuracy was also higher in the right visual field - left hemisphere. Novel metaphors were processed just as fast as novel literal expressions, suggesting that the primary challenge during the comprehension of novel expressions is not a serial processing of salience, but perhaps a more left hemisphere weighted semantic integration. Our results cast doubt on the right-hemisphere theory of metaphors, and raise the possibility that other uncontrolled variables were responsible for previous results. The lateralization of processing of two word expressions seems to be more contingent on the specific task at hand than their figurativeness or saliency.

Executive functions and the contribution of short-term memory span in children with specific language impairment.

OBJECTIVE An increasing number of results show that specific language impairment (SLI) is often associated with impairments in executive functions (EF), but the nature, extent, and generality of these deficits is yet unclear. The aim of the paper is to present results from verbal and nonverbal tasks examining EF in children with SLI and their age-matched typically developing (TD) peers. METHOD 31 children with SLI were tested on verbal and nonverbal versions of simple and complex span, fluency, N-back, and Stroop tasks. Their performance was compared with 31 TD children matched on age and nonverbal IQ. The design allows us to examine whether executive functions are similarly affected in SLI in verbal and nonverbal tasks. RESULTS The SLI group showed difficulties in verbal versions of complex span (listening span task) and fluency but not in inhibition (Stroop tasks) relative to TD age-matched children. Including simple verbal span (digit span) as a covariate eliminated group differences on both verbal tasks. CONCLUSIONS Children with SLI were found to be impaired on several verbal measures of EF, but these differences were largely due to more fundamental deficits in verbal short-term span.

Perceptual Effect on Motor Learning in the Serial Reaction-Time Task

ABSTRACT Although the Serial Reaction-Time Task has been an effective tool in studying procedural learning, there is still a debate as to whether learning in the task is effector-based, stimulus-based, or response-based. In this article, the authors contribute to this debate by contrasting response- and stimulus-based learning by manipulating them selectively and simultaneously. Results show that (a) participants learned response sequences in the absence of stimulus-specific perceptual sequence information but (b) not stimulus sequences without corresponding response information. In a third condition, response sequence and stimulus frequency information were in conflict, and each effect decreased learning in the other domain. Overall, our findings show that learning in these tasks is primarily motor-based, but it is also constrained by relatively salient perceptual information. Together with earlier findings in the literature, the findings also suggest a task and stimulus-arrangement-specific interaction between motor and perceptual learning, where relevance and salience of the specific information plays a crucial role.

A specific pattern of executive dysfunctions in transcortical motor aphasia

Background: Recent studies imply that executive functions (EF) are closely related to our ability to comprehend and produce language. A number of findings suggest that functional communication and language recovery in aphasia depend not only on intact language abilities but on EF as well. Some patients with transcortical motor aphasia (TMA) show language deficits only in tasks in which conflicting representations must be resolved by executive processes. In line with these results, others have proposed that TMA should be referred to as “dysexecutive aphasia”. EF in aphasia have mostly been studied using neuropsychological tests, therefore there is a need for systematic experimental investigations of these skills. Aims: 1. To investigate EF in TMA, and to test whether executive dysfunctions are specific to TMA. 2. To experimentally measure different components of EF: updating working memory representations and inhibition of prepotent responses. Methods & Procedures: Five individuals with TMA, five patients with conduction aphasia and ten healthy controls participated. We designed four nonverbal tasks: to measure updating of working memory representations, we used a visual and an auditory n-back task. To assess inhibition of prepotent responses, we designed a Stop-signal and a nonverbal Stroop task. All tasks involved within-subject baseline conditions. Outcomes & Results: We found certain EF deficits in both groups of individuals with aphasia as compared to healthy controls. Individuals with TMA showed impaired inhibition as indexed by the Stop-signal and the nonverbal Stroop tasks, as well as a deficit of updating of working memory representations as indexed by the auditory n-back task. Participants with conduction aphasia had difficulties in only one of the tasks measuring inhibition, but no clear evidence for impairment of updating of working memory representations was found. Conclusions: Although the results show different patterns of EF deficits in the groups with aphasia, the findings clearly demonstrate that EF deficits are not specific to participants with TMA. Based on these results, and on earlier data highlighting the role of executive processes in functional communication and language recovery, we suggest that tests of EF should be an inherent part of clinical aphasia assessment.

Tense and Aspect in Childhood Language Impairment: Contributions from Hungarian

Previous studies of children with language impairment (LI) reveal an insensitivity to aspect that may constitute part of the childrens deficit. In this study, we examine aspect as well as tense in Hungarian-speaking children with LI. Twenty-one children with LI, 21 typically developing children matched for age, and 21 typically developing children matched for receptive vocabulary scores were tested on their comprehension and production of both imperfective and perfective verb forms in past tense contexts. Although the groups did not differ in their comprehension performance, the children with LI were less accurate than both comparison groups in producing both imperfective and perfective forms. Based on these results, it appears that children with LI have difficulties selecting the appropriate aspectual marking in past tense contexts.

Stimulus dependence in probabilistic category learning.

The current study investigates whether probabilistic categorization on the Weather Prediction task involves a single, modality/domain general learning mechanism or there are modality/domain differences. The same probabilistic categorization task was used in three modalities/domains and two modes of presentation. Cues consisted of visual, auditory-verbal or auditory-nonverbal stimuli, and were presented either sequentially or simultaneously. Results show that while there was no general difference in performance across modalities/domains, the mode of presentation affected them differently. In the visual modality, simultaneous performance had a general advantage over sequential presentation, while in the auditory conditions, there was an initial advantage of simultaneous presentation, which disappeared, and in the non-verbal condition, gave over to a sequential advantage in the later stages of learning. Data suggest that there are strong peripheral modality effects; however, there are no signs of modality/domain of stimuli centrally affecting categorization.