EEG Multiscale Complexity in Schizophrenia During Picture Naming.

Introduction: Patients with schizophrenia show cognitive deficits that are evident both behaviourally and with EEG recordings. Recent studies have suggested that non-linear analyses of EEG might more adequately reflect the complex, irregular, non-stationary behavior of neural processes than more traditional ERP measures. Non-linear analyses have been mainly applied to EEGs from patients at rest, whereas differences in complexity might be more evident during task performance. Objective: We aimed to investigate changes in non-linear brain dynamics of patients with schizophrenia during cognitive processing. Method: 18 patients and 17 matched healthy controls were asked to name pictures. EEG data were collected at rest and while they were performing a naming task. EEGs were analyzed with the classical Lempel-Ziv Complexity (LZC) and with the Multiscale LZC. Electrodes were grouped in seven regions of interest (ROI). Results: As expected, controls had fewer naming errors than patients. Regarding EEG complexity, the interaction between Group, Task and ROI indicated that patients showed higher complexity values in right frontal regions only at rest, where no differences in complexity between patients and controls were found during the naming task. EEG complexity increased from rest to task in controls in left temporal-parietal regions, while no changes from rest to task were observed in patients. Finally, differences in complexity between patients and controls depended on the frequency bands: higher values of complexity in patients at rest were only observed in fast bands, indicating greater heterogeneity in patients in local dynamics of neuronal assemblies. Conclusion: Consistent with previous studies, schizophrenic patients showed higher complexity than controls in frontal regions at rest. Interestingly, we found different modulations of brain complexity during a simple cognitive task between patients and controls. These data can be interpreted as indicating schizophrenia-related failures to adapt brain functioning to the task, which is reflected in poorer behavioral performance. HIGHLIGHTS:     - We measured classical and multiscale Lempel-Ziv Complexity (LZCN and MLZC) of the EEG signal of patients with schizophrenia and controls at rest and while performing a cognitive task.    - We found that patients and controls showed a different pattern of brain complexity depending on their cognitive state (at rest or under cognitive challenge).    - Our results illustrate the value of the MLZC in the characterization of the pattern of brain complexity in schizophrenia on function of frequency bands.    - Nonlinear methodologies of EEG analysis can help to characterize brain dysfunction in schizophrenia.

Language access and language selection in professional translators.

Two experiments were conducted measuring self-paced reading to study language access and language selection in professional translators and bilinguals when they understood sentences randomly presented in their first language (L1, Spanish) and second language (L2, English). These sentences contained a critical cognate word or a control matched word. The effect of cognate words was considered an index of between-language activation while the inhibition of the non-target language was examined with the asymmetrical switching cost. In Experiment 1, participants read and repeated sentences while in Experiment 2 participants read sentences without repeating them after reading. The results indicated that lexical processing depended on the experience of participants in professional translation and the demands imposed by the understanding task (reading and repeating or only reading).

Intentional inhibition in memory and hallucinations: directed forgetting and updating.

Hallucinations have been recently associated with inhibitory deficits in memory. In this study, the authors investigated whether hallucinations were related to difficulties to inhibit irrelevant information from episodic memory (Experiment 1) and working memory (Experiment 2). In Experiment 1, a directed forgetting task was used. This task measures participants' ability to intentionally forget some recently learned material, when instructions indicate that it is no longer relevant. In Experiment 2, an updating task was used. This task requires participants to intentionally suppress irrelevant information from working memory. Results showed that patients with schizophrenia with hallucinations presented inhibitory deficits in the directed forgetting task and an increase in the number of intrusions in the updating task, compared to patients without hallucinations and healthy controls. No correlations were found between indices of inhibition and other general, negative or positive symptoms. These findings support the existence of an association between intentional inhibition in memory and hallucinations, and they suggest that problems to suppress memory representations can underlie hallucinations in schizophrenia.

Cognitive substrates in semantic memory of formal thought disorder in schizophrenia.

Formal thought disorder (FTD) has been associated with abnormalities in the semantic memory system. However, it is still unclear whether these abnormalities are related to the organization of the semantic system, or to the automatic spread of activation-inhibition in semantic networks. In this paper these alternative proposals are examined. Schizophrenic patients and healthy matched controls were given two semantic memory tasks. In the first task, participants were required to judge the similarity between pairs of natural concepts. These ratings are assumed to reflect the underlying knowledge organization. In the second task, participants were required to name pictures that were preceded by related or unrelated word primes. Interference is typically observed when pictures are preceded by semantically related primes, and it is explained as due to inhibitory processes from the word prime to the related picture target. The results showed that the semantic structures derived from the similarity ratings were similar for patients with and without FTD and for control participants. However, results from the picture-naming task indicated that both non-FTD and control participants showed the normal interference/inhibition effects from the related prime words, whereas the patients with FTD showed similar performance for pictures preceded by related words than for pictures preceded by unrelated words. These findings support the hypothesis that abnormalities in inhibitory processes in semantic memory underlie FTD.

Activation of lexical and syntactic target language properties in translation.

Is reading for translation equal to reading in monolingual contexts? Horizontal/parallel theories of translation propose that normal reading and reading for translation differ because the translator engages in partial reformulation while reading for translating the source text. In contrast, vertical/serial theories assume that the translators first extract the meaning of the message, and only then they proceed to reformulate it. In two experiments, we manipulated lexical and syntactic properties of the target language (TL) while translators read for repetition or for translation. On-line sentence comprehension was affected by the lexical frequency of words in the TL (Experiment 1) and the syntactic congruency between the source language (SL) and TL sentences (Experiment 2). However, the influence of lexical and syntactic TL properties was restricted to the reading for translation task. According to our results, the horizontal view of translation includes code-to-code links between the SL and TL involving at least the lexical and syntactic level of processing.

Differential allocation of study time: incomplete compensation for the difficulty of the materials.

The results of many experiments have shown that although people distribute their study time depending on the perceived difficulty of the materials, they do not succeed in compensating for this difficulty (e.g., Mazzoni & Cornoldi, 1993). The purpose of this paper was to explore possible ways to induce compensation. The objective difficulty of the items was varied by manipulating their concreteness. In Experiment 1, we explored whether compensation could be increased through practice. In Experiment 2, predictive memory judgements were obtained to determine to what extent participants were sensitive to the characteristics of the material that made it difficult. Finally, in Experiment 3, participants were given instructions designed to achieve complete compensation. Results showed that although participants' judgements of learning and their allocation of time were sensitive to the objective difficulty of the materials, this knowledge was not spontaneously used to compensate. Thus, even with practice participants recalled more easy items than difficult ones. Only instructions that induced greater awareness of the nature of the material were able to produce complete compensation.

Prior knowledge: the effects of natural category size on memory for implicitly encoded concepts.

Studying a familiar word activates its associates, and these associates affect the likelihood of recalling the studied word in a cued recall task. These experiments examined variables that normally affect memory for the studied word to determine if they have similar effects on memory for the word's associates. Memory for associates was tested by cued recall (Experiments 1-3) or by recognition (Experiments 4-5), with the number and strength of the associates varied in all experiments. In different experiments, test instructions (direct-indirect), distractor tasks, lag, and amount of practice were manipulated. Provided that subjects were not distracted prior to test, the probability of recalling associates of the studied word decreased with the number of associates activated and with their strength under all conditions. The strength of the associates but not their number affected recognition. In general, variables that affected recall and recognition of studied words had parallel effects on their associates.

Semantic facilitation with pictures and words.

The present experiments explored the role of processing level and strategic factors in cross-form (word-picture and picture-word) and within-form (picture-picture and word-word) semantic facilitation. Previous studies have produced mixed results. The findings presented in this article indicate that semantic facilitation depends on the task and on the subjects' strategies. When the task required semantic processing of both picture and word targets (e.g., category verification), equivalent facilitation was obtained across all modality combinations. When the task required name processing (e.g., name verification, naming), facilitation was obtained for the picture targets. In contrast, with word targets, facilitation was obtained only when the situation emphasized semantic processing. The results are consistent with models that propose a common semantic representation for both picture and words but that also include assumptions regarding differential order of access to semantic and phonemic features for these stimulus modalities.

Lexical and semantic search in cued recall, fragment completion, perceptual identification, and recognition.

Search processes in word-stem cued recall, fragment completion, perceptual identification, and recognition are contrasted. These retention tests involve letters as cues, but the lexical characteristics of these cues vary considerably. In word-stem cued recall, ending letters are presented as recall cues for studied targets (e.g., ONEY as a cue for HONEY). In fragment completion, the test cues consist of letters and spaces (e.g., HO__Y); in perceptual identification, they consist of letter features that survive the mask; and in recognition, they consist of all the letters of the studied word (e.g., HONEY). These differences in retention tests and lexical characteristics were evaluated by manipulating three variables with known effects in cued recall: (a) the presence of study context words emphasizing lexical information, (b) lexical set size corresponding to the number of words that fit the letter cue, and (c) meaning set size corresponding to the number of meaningful associates linked to the studied targets. The results indicated that (a) the presence of study contexts emphasizing lexical information reduced accuracy and response time equally in all tasks, (b) larger lexical set sizes reduced accuracy and response time in all tasks except recognition, and (c) larger meaning set size reduced accuracy in cued recall but not in the other tasks. Lexical search appears to be a significant component process in word-stem cued recall, fragment completion, and identification. Searching through meaning-related concepts encoded during study is a significant component process only in cued recall.

Comparing word fragment completion and cued recall with letter cues.

Cued recall with word stems as cues and fragment completion rely on different types of letter cues and also differ in the explicit-implicit nature of the retrieval orientation. Despite these differences, variables effective in one task may be effective in the other because both rely on letter cues. Two variables known to affect cued recall were manipulated: Lexical set size (number of words that fit the letter cue) and meaning set size (number of associates generated to the studied words). Across four experiments, subjects in each task were less likely to recover targets from larger lexical sets. However, meaning set size affected cued recall but not fragment completion. These results indicate that fragment completion and letter-cued recall are based on lexical search but that cued recall also involves a semantic search component. Furthermore, type of retrieval cue had a greater effect than type of retrieval orientation.

Prior knowledge and memory: the episodic encoding of implicitly activated associates and rhymes.

The presentation of a familiar word activates related concepts, and, once encoded, related concepts interfere with memory for the work actually presented. Presented words that activate larger numbers of related concepts are generally more difficult to recall than those that activate smaller numbers. The purpose of the present experiments was to explore the effects of study-trial orientation and test delay on the encoding of both rhyme- and meaning-related concepts. The results of Experiments 1 and 2 indicate that meaning-related concepts are encoded and interfere with memory for the presented target regardless of study-trial orientation. Interference is obtained even when the study-trial context emphasizes phonemic information and subjects are incidentally oriented to rating rhyme properties. However, this interference effect disappears when the test trial is delayed. In contrast, the results of Experiments 1-4 indicate that rhyme-related concepts are encoded and interfere with memory for the presented target only when subjects explicitly attend to the rhyme dimension. Once oriented, this interference effect is found after a relatively long delay. These differences are attributed to differences in attentional processing. The encoding of meaning-related concepts results from relatively automatic processes and the encoding of rhyme-related concepts requires subjects to attend to rhyme.

Prior knowledge and memory: the influence of natural category size as a function of intention and distraction.

Words having larger numbers of related associates are more difficult to recall under conditions of intentional learning. This finding indicates that memory performance is inversely related to natural category size. The purpose of the experiments presented in this article was to evaluate the potential influence of orienting task and attention shifts associated with delayed testing on the natural category size effect. The results of Experiments 1 and 2 indicate that it is obtained regardless of task orientation. However, the results of Experiments 2 and 3 indicate that the effect is easily disrupted. Even after only 5 min of solving multiplication problems, words having larger sets of associates are no more difficult to recall than those having smaller sets. These findings suggest that related associates are automatically activated and encoded whenever a familiar concept is experienced in the absence of specific semantic cues. However, words having larger sets will be more difficult to recall only when these related associates are in a state of current activation.

Prior knowledge and cued recall: category size and dominance.

Previous work indicates that our ability to recall a recently experienced word is reduced by the number of related concepts that it activates in permanent memory. The purpose of this research was to evaluate the possibility that dominance of primary associates, and not category size, is responsible for this observation. The results of three experiments involving manipulations of target and cue set size, as well as meaning and rhyme, indicate that category size effects are independent of dominance. In fact, the advantage of smaller categories and fewer activated items is substantially reduced for words having very dominant primary associates. The findings are discussed in relation to the Sensory-Semantic model.