Repetition priming reveals hemispheric differences in compound word processing

The left (LH) and right (RH) hemispheres are thought to implement different mechanisms for visual word recognition; the LH’s parallel encoding strategy is more efficient than the RH’s serial, letter-by-letter analysis. Here we examine differences in hemispheric language processing strategy by investigating repetition priming of compound words (e.g. buttercup) and their constituents (e.g. butter, cup). Eighty-eight right-handed participants (29 M, 59 F) completed a lexical decision experiment in which centrally-presented compounds primed related (whole compound, first constituent, second constituent) and unrelated targets presented laterally to the left or right visual field; participants made button-press word/nonword decisions. Consistent with the LH parallel/RH serial distinction, repetition priming prompted an RH advantage for first constituents, whereas the LH performed equally efficiently in response to both first and second constituents. These data thus highlight differences in the hemispheres’ language processing strategies, offering new evidence supporting a relative parallel/serial distinction in LH/RH visual word recognition.     

Attentional deployment in visual half-field tasks: the effect of cue position on word naming latency

Divided visual-field research suggests that attentional factors may contribute to the left hemisphere's (LH) superiority for language processing. The LH's parallel recognition strategy, specialised for whole word encoding, is largely unaffected by the distribution of spatial attention. In contrast, the right hemisphere's (RH) serial, letter-by-letter strategy places far greater demands on attentional resources. By manipulating spatial attention, the present study gauged the effect of cueing the beginning vs. the end of the word on LH and RH naming latency. Results indicated no effect of cue position on LH performance, consistent with research indicating that the LH enjoys an attentional advantage, deploying attention in parallel across the stimulus. As anticipated, the RH showed a facilitatory effect of beginning cue, which draws spatial attention to the initial letter cluster, enabling efficient implementation of the RH's sequential strategy. These findings suggest that differences in attentional deployment contribute to hemispheric asymmetries for word recognition.     

Hemispheric alpha asymmetries and behavioral responses of aphasic and normal subjects for the recall and recognition of active, passive, and negative sentences

The hemispheric alpha asymmetries of a group of normal males, a group of normal females, and a group of aphasic patients (fluent and dysfluent) were examined with electroencephalographic (EEG) techniques under memory conditions of recall and recognition of active, passive, and negative sentences. Aphasic patients, regardless of classification, showed right hemispheric alpha suppression across memory conditions and sentence types. Both normal groups were found to have greater left hemispheric alpha suppression for the recall memory condition and greater right hemispheric alpha suppression for the recognition memory condition (males significantly more than females). The aphasic subjects performed better on recognition tasks compared to recalled tasks and active sentences compared to transformed sentences. Results are discussed as providing evidence of the aphasic subjects' greater dependency on information processing resources of the right hemisphere in the recovery of language function. The findings are also discussed as providing support for a multiple-resources model of information processing.     

Emotional valence and arousal effects on memory and hemispheric asymmetries

This study examined predictions based upon the right hemisphere (RH) model, the valence–arousal model, and a recently proposed integrated model (Killgore & Yurgelun-Todd, 2007) of emotion processing by testing immediate recall and recognition memory for positive, negative, and neutral verbal stimuli among 35 right-handed women. Building upon methodologies of previous studies, we found that words presented to the right visual field/left hemisphere (RVF/LH) were recalled and recognized more accurately than words presented to the left visual field/right hemisphere (LVF/RH), and we found significant valence by visual field interactions. Some findings were consistent with one of the models evaluated whereas others were consistent with none of the models evaluated. Our findings suggest that an integration of the RH and valence–arousal models may best account for the findings with regard to hemispheric lateralization of memory for emotional stimuli.     

Effects of a concurrent memory task on hemispheric asymmetries in categorization

Recent research on the division of processing between the two cerebral hemispheres has often employed two concurrent tasks to investigate the dynamic nature of hemispheric asymmetries. The experiment reported here explored the effects of two concurrent high-level cognitive tasks (memory retention and semantic categorization) on the direction and magnitude of hemispheric differences in the processing of words and pictures. Subjects were required to categorize words and pictures presented to either the left visual field-right hemisphere (LVF-RH) or the right visual field-left hemisphere (RVF-LH). The categorization could be performed while holding either verbal material in memory (digit span), pictorial material in memory (serial nonsense figure recognition), or with no concurrent memory task. The effects produced hemisphere-specific, material-nonspecific interference. The verbal task removed a RVF-LH advantage at word categorization and enhanced a LVF-RH advantage on picture categorization; the pictorial task interfered with picture categorization in the LVF-RH, while enhancing a RVF-LH advantage at word categorization. The results are discussed in terms of multiple resource models of hemisphere function, capacity limitations, and the functional locus of processing required to produce various dynamic hemispheric effects.     

The Modulation of Visual and Task Characteristics of a Writing System on Hemispheric Lateralization in Visual Word Recognition—A Computational Exploration

Through computational modeling, here we examine whether visual and task characteristics of writing systems alone can account for lateralization differences in visual word recognition between different languages without assuming influence from left hemisphere (LH) lateralized language processes. We apply a hemispheric processing model of face recognition to visual word recognition; the model implements a theory of hemispheric asymmetry in perception that posits low spatial frequency biases in the right hemisphere and high spatial frequency (HSF) biases in the LH. We show two factors that can influence lateralization: (a) Visual similarity among words: The more similar the words in the lexicon look visually, the more HSF/LH processing is required to distinguish them, and (b) Requirement to decompose words into graphemes for grapheme‐phoneme mapping: Alphabetic reading (involving grapheme‐phoneme conversion) requires more HSF/LH processing than logographic reading (no grapheme‐phoneme mapping). These factors may explain the difference in lateralization between English and Chinese orthographic processing.     

Qualitative hemispheric differences in semantic category matching.

A unilateral category matching task with words as stimuli was employed to investigate semantic processing in the right and left hemispheres (RH, LH). An overall right visual field (RVF)/LH dominance was observed and performances were better than chance, also in the left visual field (LVF)/RH. A qualitative analysis of reaction times with individual differences multidimensional scaling (INDSCAL) revealed that LVF/RH INDSCAL solutions were significantly more differentiated in structure than RVF/LH solutions in terms of number and size of dimensions. These findings support a depth of activation hypothesis of hemispheric processing, with the LH rapidly and focally and the RH slowly and diffusely activating the semantic network.     

Understanding metaphoric sentences in the two cerebral hemispheres

Previous studies indicate that the right hemisphere (RH) has a unique role in maintaining activation of metaphoric single word meanings. The present study investigated hemispheric asymmetries in comprehending metaphoric word meanings within a sentence context. Participants were presented with incomplete priming sentences followed by (literally) true, false, or metaphoric lateralized target words and were asked to decide whether each sentence is literally true or false. Results showed that responses to metaphoric sentences were slower and less accurate than to false sentences when target words were presented to the right visual field (RVF)-LH as well as to the left visual field (LVF)-RH. This suggests that the understanding of lexical metaphors within a sentence context involves LH as well as RH processing mechanisms and that the role of each hemisphere in processing nonliteral language is flexible and may depend on the linguistic task at hand.     

汉语名词、动词和动名兼类词语义加工的偏侧化现象——来自ERP的研究

将ERP技术和半视野技术相结合,采用词汇判断任务,对汉语名词、动词和动名兼类词在左脑和右脑中的加工机制进行了考察。实验结果显示,名词和动词的N400仅在左视野/右脑存在差异,名词和动词的N400在左视野/右脑和右视野/左脑中都比偏（动）和偏（名）更负。不同词类的LPC在右视野/左脑中没有显著差异;偏（名）和偏（动）的LPC在左视野/右脑中比名词和动词更正。实验结果表明,在没有语境条件下,汉语名词和动词的差异主要在具体性上,动名兼类词体现出不同于名词、动词的加工机制。     

The direction of hemispheric asymmetries for object categorization at different levels of abstraction depends on the task

In this study hemispheric asymmetries for categorizing objects at the basic versus subordinate level of abstraction were investigated. As predictions derived from different theoretical approaches are contradictory and experimental evidence is inconclusive in this regard, we conducted two categorization experiments, where we contrasted two experimental paradigms. In the first experiment, subjects had to verify whether a word and a laterally presented picture matched or not. In the second experiment, subjects had to identify laterally presented pictures of animals either at the basic or subordinate level by pressing a corresponding response key. Whereas the first experiment revealed an advantage of the left hemisphere (LH) for categorizing objects at the basic level and of the right hemisphere (RH) for categorizing at the subordinate level, just the opposite brain asymmetry was found in the second experiment. As the stimuli were identical in both experiments, hemispheric asymmetries seem to be strongly task dependent.     

False recognition of emotional stimuli is lateralised in the brain: An fMRI study

We have investigated whether the left (LH) and right (RH) hemisphere play a different role in eliciting false recognition (FR) and whether their involvement in this memory illusion depends on the emotional content of stimuli. Negative and neutral pictures (taken from IAPS) were presented in the divided-visual field paradigm. Subjects task was to indicate whether the pictures had already been presented or not during the preceding study phase. FR rate was much higher for the RH than the LH presentations. In line, FR resulted in activations mainly in the right prefrontal cortex (PFC) for either RH or LH presentations. Emotional content of stimuli facilitated the formation of false memories and strengthened the involvement of the right PFC in FR induction.     

Hemispheric specialization for emotional word processing is a function of SSRI responsiveness

Vulnerability to depression and non-response to Selective Serotonin Reuptake Inhibitors (SSRIs) are associated with specific neurophysiological characteristics including greater right hemisphere (RH) relative to left hemisphere (LH) activity. The present study investigated the relationship between hemispheric specialization and processing of emotional words using a divided visual field paradigm administered to never-depressed and previously-depressed individuals, who were subdivided into SSRI responders and non-responders. SSRI responders and never-depressed participants were similar in their left hemispheric lateralization for evaluating emotional words. In contrast, SSRI non-responders showed a relative shift towards RH processing of negative words, and a strong bias toward negative evaluation of words presented to the RH. The results are discussed within the context of a biological-cognitive model of vulnerability to depression.     

Hemispheric Differences in the Processing of Words Learned Early Versus Later in Childhood

The research investigated whether there are hemispheric differences in processing for words acquired early in childhood (early AoA) and words acquired later in childhood (late AoA). We hypothesized that because of recent evidence suggesting that there is a right hemisphere dominance in early childhood, early AoA words would be represented in the right hemisphere, and late AoA words would be represented in the left hemisphere. This hypothesis differs from an early view that late AoA words would be represented in the left hemisphere, and early AoA words would be represented in both hemispheres (Gazzaniga, 1974). We report two experiments using the divided visual field (DVF) technique. The results showed that there was a right visual field (RVF)/left hemisphere (LH) advantage only for late AoA words. For early AoA words, there was a left visual field (LVF)/right hemisphere advantage (RH). Implications for theories of hemispheric differences in word processing are discussed.     

Evaluating a split processing model of visual word recognition: effects of orthographic neighborhood size

The split fovea theory proposes that visual word recognition of centrally presented words is mediated by the splitting of the foveal image, with letters to the left of fixation being projected to the right hemisphere (RH) and letters to the right of fixation being projected to the left hemisphere (LH). Two lexical decision experiments aimed to elucidate word recognition processes under the split fovea theory are described. The first experiment showed that when words were presented centrally, such that the initial letters were in the left visual field (LVF/RH), there were effects of orthographic neighborhood, i.e., there were faster responses to words with high rather than low orthographic neighborhoods for the initial letters ('lead neighbors'). This effect was limited to lead-neighbors but not end-neighbors (orthographic neighbors sharing the same final letters). When the same words were fully presented in the LVF/RH or right visual field (RVF/LH, Experiment 2), there was no effect of orthographic neighborhood size. We argue that the lack of an effect in Experiment 2 was due to exposure to all of the letters of the words, the words being matched for overall orthographic neighborhood count and the sub-parts no longer having a unique effect. We concluded that the orthographic activation found in Experiment 1 occurred because the initial letters of centrally presented words were projected to the RH. The results support the split fovea theory, where the RH has primacy in representing lead neighbors of a written word.     

Hemispheric specialization for emotional word processing is a function of SSRI responsiveness

Vulnerability to depression and non-response to Selective Serotonin Reuptake Inhibitors (SSRIs) are associated with specific neurophysiological characteristics including greater right hemisphere (RH) relative to left hemisphere (LH) activity. The present study investigated the relationship between hemispheric specialization and processing of emotional words using a divided visual field paradigm administered to never-depressed and previously-depressed individuals, who were subdivided into SSRI responders and non-responders. SSRI responders and never-depressed participants were similar in their left hemispheric lateralization for evaluating emotional words. In contrast, SSRI non-responders showed a relative shift towards RH processing of negative words, and a strong bias toward negative evaluation of words presented to the RH. The results are discussed within the context of a biological–cognitive model of vulnerability to depression.     

Hemispheric differences in picture-word interference

In a picture-word version of the Stroop task, 30 right-handed subjects were tested under each of six conditions in which a picture alone or a picture plus a word were presented to the left, the right, or both hemispheres. In two additional conditions the picture was presented to the right hemisphere and the word was simultaneously presented to the left hemisphere, or vice versa. For all conditions, subjects were instructed to name the picture only, as rapidly as possible. Picture naming times were significantly slower for the conditions in which the pictures were accompanied by words than in the respective picture alone conditions. Moreover, simultaneous presentation of a picture and a word to both hemispheres resulted in greater interference (slower picture naming times) than did the simultaneous presentation of the picture and the word to either the left hemisphere alone or the right hemisphere alone. The latter two conditions, in turn, resulted in significantly more interference than did the simultaneous presentation of the picture to one hemisphere and the word to the other hemisphere. This pattern of results suggests that the Stroop effect obtained under normal circumstances is in large part a function of the interference caused by the simultaneous processing of items in the same hemisphere. In contrast to hemispheric differences reported for the color-word Stroop task, the effect of presenting a picture and word simultaneously to the right hemisphere did not differ reliably from that of presenting a picture and word to the left hemisphere. The failure to replicate this aspect of the color-word Stroop is attributed to differences in the abilities of the two hemispheres to process the respective target items (the color or the picture) of the two tasks.     

Reevaluating split-fovea processing in word recognition: Hemispheric dominance, retinal location, and the word-nonword effect

Many studies have claimed that hemispheric projections are split precisely at the foveal midline and so hemispheric asymmetry affects word recognition right up to the point of fixation. To investigate this claim, four-letter words and nonwords were presented to the left or right of fixation, either close to fixation in foveal vision or farther from fixation in extrafoveal vision. Presentation accuracy was controlled using an eyetracker linked to a fixation-contingent display. Words presented foveally produced identical performance on each side of fixation, but words presented extrafoveally showed a clear left-hemisphere (LH) advantage. Nonwords produced no evidence of hemispheric asymmetry in any location. Foveal stimuli also produced an identical word-nonword effect on each side of fixation, whereas extrafoveal stimuli produced a word-nonword effect only for LH (not right-hemisphere) displays. These findings indicate that functional unilateral projections to contralateral hemispheres exist in extrafoveal locations but provide no evidence of a functional division in hemispheric processing at fixation.     

Effects of right and left hemisphere cerebrovascular lesions on discrimination of prosodic and semantic aspects of affect in sentences.

Ten nonaphasic left cerebrovascular accident (CVA) patients, 12 right CVA patients, and 16 normals were matched for age, education, lesion sizes, and postonset intervals; all were right handed. One task consisted of 36 sentences connoting one of six primary emotions (joy, sadness, fear, surprise, disgust, anger) presented binaurally with a neutral emotional tone. Subjects were required to point to the appropriate emotion name on a vertically arranged list. A second task consisted of the same 36 sentences voiced emotionally by humming with a closed mouth, presented binaurally, and requiring the same response as for the preceding task. A third task consisted of 18 of the sentences spoken with concordant emotional tone and the remaining 18 sentences spoken with discordant emotional tone, presented binaurally and requiring pointing to the word "SAME" or "DIFFERENT" arrayed vertically. The right hemisphere (RH) patients were significantly impaired, relative to the left hemisphere (LH) patients and normals, on the pure prosody task (2) and on the emotional concordance task (3), the latter effect being significant only for mismatch categorization. The LH patients performed (nonsignificantly) less well than the RH patients and normals on the verbal contextual task (1). Performances on the three tasks were not significantly correlated in the patient groups. It was concluded that the RH probably dominates for phonetic discrimination of vowel trains (fundamental frequency and/or single vowel or multivowel contour) and that the RH probably dominates for certain forms of selective attention in the verbal domain perhaps involving simultaneous mismatch treatment of ongoing sentence-level, distracting, complementary, verbal processes. Comparison of similar right and left, cortical (frontoparietal), and subcortical (capsule and basal ganglia) lesions suggested, but did not prove, that the RH pure prosody impairment is cortical whereas the RH tonal-semantic mismatch categorization impairment involves subcortical as well as cortical contributions.     

Sex task and processing strategy effects in hemispheric alpha asymmetries for the recall and recognition of arousal words: results from perceptual and motor tasks in males and females

Hemispheric alpha asymmetries of males and females were observed during perceptual and motor tasks requiring recall and recognition of words controlled for level of arousal (positive, negative, and neutral). Verbal reports of individual processing strategy were collected and analyzed relative to hemispheric alpha ratios. Results showed greater alpha suppression in the left relative to right hemisphere for recall as compared to recognition tasks and for word presentation when contrasted with motor conditions. High positive correlations were found between narrative report of processing strategy and hemispheric alpha data. A separate analysis revealed that seven subjects identified as highly analytic processors showed greater alpha suppression in the left relative to right hemisphere across tasks, conditions, and stimuli than did seven highly visual processors who, in contrast, demonstrated greater right hemispheric alpha suppression. Task difficulty and individual differences in processing style that modify cerebral laterality effects are discussed.     

The right hemisphere maintains solution-related activation for yet-to-be-solved problems

In five experiments, we examined the time course of hemispheric differences in solution activation for insight-like problems. We propose that solving insight problems requires retrieval of unusual interpretations of problem elements, and that right-hemisphere (RH) coarse semantic coding is more likely than left-hemisphere (LH) fine semantic coding to maintain semantic activation of such interpretations. In four experiments, participants attempted word problems for 7 sec (Experiments 1A and 1B) or 2 sec (Experiments 2A and 2B), and 750 msec later responded to lateralized target words. After 7 sec of solving effort, Experiment 1A participants showed greater solution-related priming (i.e., they named solutions faster than unrelated words) for left visual field-RH (lvf-RH) targets than for right visual field-LH (rvf-LH) targets, and Experiment 1B participants made faster solution decisions on target words presented to the RH, as previously demonstrated following 15 sec of effort. After 2 sec of solving effort in Experiment 2A, women showed symmetric solution-related priming, although men showed a slight lvf-RH advantage in priming; and in Experiment 2B participants made equally quick solution decisions for targets presented to the LH and to the RH. In Experiment 3, participants viewed the problems for 1,250 msec then named lateralized target words; they showed symmetric solution-related priming. These experiments demonstrate solution activation initially in both hemispheres, but maintained solution activation only in the RH.