Complexity and hemispheric abilities: evidence for a differential impact on semantics and phonology

Phonological processing in psychopathic offenders

Recent research has demonstrated that psychopathic offenders exhibit dynamic cognitive and behavioral deficits on a variety of lab tasks that differentially activate left hemisphere resources. The Left Hemisphere Activation (LHA) hypothesis is a cognitive perspective that aims to address these deficits by conceptualizing psychopathy as a disorder in which behavior and cognitive processing change dynamically as a function of the differential taxation of left hemisphere resources. This study aimed to investigate whether psychopathic traits are associated with electrophysiological anomalies under conditions that place differential demands on left hemisphere language processing systems. We examined in a sample of 43 incarcerated indivdiuals the evocation of the N320, an event-related potential (ERP) elicited by nontarget stimuli during a phonological/phonetic decision task that has been shown to elicit greater activation and cognitive processing within the left hemisphere than the right hemisphere. Findings for a subsample of 18 offenders low in psychopathic traits were generally consistent with previous findings in healthy individuals, suggesting similar electrophysiological activity during phonological processing. However, psychopathic traits impacted the amplitude of the N320. Higher levels of psychopathic traits were associated with reduced left-lateralization in phonological processing as well as enhanced ERP differentiation between pronounceable and nonpronounceable stimuli. These findings provide physiological evidence of a relationship between psychopathic traits and anomalous language processing at the phonological level of word processing.

Hemispheric processing of lexical information in Chinese character recognition and its relationship to reading performance

Hemispheric predominance has been well documented in the visual perception of alphabetic words. However, the hemispheric processing of lexical information in Chinese character recognition and its relationship to reading performance are far from clear. In the divided visual field paradigm, participants were required to judge the orthography, phonology, or semantics of Chinese characters, which were presented randomly in the left or right visual field. The results showed a right visual field/left hemispheric superiority in the phonological judgment task, but no hemispheric advantage in the orthographic or semantic task was found. In addition, reaction times in the right visual field for phonological and semantic tasks were significantly correlated with the reading test score. These results suggest that both hemispheres involved in the orthographic and semantic processing of Chinese characters, and that the left lateralized phonological processing is important for Chinese fluent reading.

Information properties of morphologically complex words modulate brain activity during word reading

Neuroimaging studies of the reading process point to functionally distinct stages in word recognition. Yet, current understanding of the operations linked to those various stages is mainly descriptive in nature. Approaches developed in the field of computational linguistics may offer a more quantitative approach for understanding brain dynamics. Our aim was to evaluate whether a statistical model of morphology, with well‐defined computational principles, can capture the neural dynamics of reading, using the concept of surprisal from information theory as the common measure. The Morfessor model, created for unsupervised discovery of morphemes, is based on the minimum description length principle and attempts to find optimal units of representation for complex words. In a word recognition task, we correlated brain responses to word surprisal values derived from Morfessor and from other psycholinguistic variables that have been linked with various levels of linguistic abstraction. The magnetoencephalography data analysis focused on spatially, temporally and functionally distinct components of cortical activation observed in reading tasks. The early occipital and occipito‐temporal responses were correlated with parameters relating to visual complexity and orthographic properties, whereas the later bilateral superior temporal activation was correlated with whole‐word based and morphological models. The results show that the word processing costs estimated by the statistical Morfessor model are relevant for brain dynamics of reading during late processing stages.

Enhancing the ecological validity of tests of lateralization and hemispheric interaction: Evidence from fixated displays of letters or symbols of varying complexity

Two experiments expand upon behavioural evidence of interactions among lateralization, hemispheric interaction, and task complexity with findings from an ecologically valid procedure. Target displays of letters or symbols were presented at fixation in go/no-go matching tasks of physical or categorical identity. Simultaneously with the target, a distractor appeared in the left visual field or right visual field to weight processing of the target to the hemisphere ipsilateral to the distractor, or the distractor did not appear at all. Comparison of the respective distractor-present trials with distractor-absent trials measures the relative costs or benefits of hemispheric interaction. Both experiments found that 3-item displays were processed faster and more accurately than displays of 5 items, suggesting they are relatively simple. Accuracy to the simple tasks showed left-hemisphere lateralization in the lexical task, right-hemisphere lateralization in the spatial task, a cost of hemispheric interaction compared to the advantaged hemisphere, and a benefit of hemispheric interaction compared to the less-advantaged hemisphere, suggesting that the contributions of the less-advantaged hemisphere interfere with processing, and that the advantaged hemisphere controls the lion's share. In contrast, 5-item displays for physical match in both experiments showed a significant benefit to accuracy of hemispheric interaction compared to the left hemisphere, an insignificant benefit compared to the right hemisphere, no lateralization, no cost of hemispheric interaction, and a consequence to performance that was more costly to the hemisphere that had been advantaged in simple tasks, suggesting that the advantaged hemisphere relinquishes control as tasks become more complex and complementary processing results from both increased collaboration and decreased lateralization between the hemispheres. The findings expand upon behavioural evidence, converge with imaging evidence, and suggest future directions for brain mapping.

List constituency and orthographic and phonological processing: a shift to high familiarity words from low familiarity words

Two lexical decision experiments build on established patterns of laterality and hemispheric interaction to test whether the presence of low familiarity words dynamically affects the use of an orthographic or phonological strategy for high familiarity words; and, if so, whether the hemispheres are similarly flexible in adapting to the constituency change. Experiment 1 restricted word strings to the highly familiar. Experiment 2 presented the same high familiarity words, along with an equal number of low familiarity words. Targets for lexical decision were presented at fixation to approximate normal viewing behaviour, either with or without a non-lexical distractor lateralized left visual field (LVF) or right visual field (RVF). Response time and accuracy were measured. Responses were faster in Experiment 1 than Experiment 2 to high familiarity words, pseudowords (orthographically correct), and non-words (orthographically incorrect), suggesting that a different strategy was used. A main effect of distractor location in Experiment 1 was due to more accurate responses to letter strings accompanied by a RVF distractor than no distractor, revealing a cost from hemispheric interaction compared to the right hemisphere when a task is simple. Experiment 2 found an interaction between distractor location and string type in both the response time and accuracy data. Separate analyses of word strings revealed a shift to a left hemisphere advantage: Accuracy to low familiarity words and speed to high familiarity words was better when accompanied by a LVF than a RVF distractor. Critical to a dynamic effect of list constituency is that the right hemisphere slowed to the same high familiarity words that had provoked speedier responses in Experiment 1. The findings are consistent with the use of an orthographic strategy in Experiment 1 and a phonological strategy in Experiment 2, and support the idea that right hemisphere access to familiar phonology is slower than the left hemisphere. Taken together, the findings suggest that the strategy used by both hemispheres is flexible, that both adapt to list constituency by adopting a strategy that is optimal for the task as a whole, and that there are different timelines of phonological activation in the two cerebral hemispheres.

Hemispheric interaction, task complexity, and emotional valence: evidence from naturalistic images

Two experiments extend the ecological validity of tests of hemispheric interaction in three novel ways. First, we present a broad class of naturalistic stimuli that have not yet been used in tests of hemispheric interaction. Second, we test whether probable differences in complexity within the class of stimuli are supported by outcomes from measures of hemispheric interaction. Third, we use a procedure that presents target stimuli at fixation rather than at a lateralized location in order to more closely approximate normal viewing behavior. Images of positive or negative valence were presented with a lateralized distractor or no distractor at all. Response time and accuracy to determine whether an image was pleasant or unpleasant was measured. Results found that positive images were more quickly and accurately processed by the left hemisphere alone, while negative images were more quickly processed when the hemispheres interacted, and were more accurately processed when the hemispheres interacted than the left hemisphere alone. The findings support the idea that hemispheric interaction costs the performance of a simple task and benefits the performance of a complex task, and that the respective cost or gain is mediated by the pattern of laterality for emotional processing.