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.     

Automatic semantic priming in the left and right hemispheres

We investigated hemispheric differences and inter-hemispheric transfer of facilitation in automatic semantic priming, using prime-target pairs composed of words of the same category but not associated (e.g. skirt-glove), and a blank-target baseline condition. Reaction time and accuracy were measured at short (300 ms) intervals between prime and target onsets, using a go/no-go task to discriminate between word or non-word targets. Reaction times were facilitated more for target words presented in the right visual field (RVF) compared to the left visual field (LVF), and targets presented in RVF were primed in both visual fields, whereas targets presented in LVF were primed by primes in the LVF only. These results suggest that both hemispheres are capable of automatic priming at very short stimulus onset asymmetries (SOA), but cross-hemisphere priming occurs only in the left hemisphere.     

Priming nouns and verbs: differential influences of semantic and grammatical cues in the two cerebral hemispheres

The current experiment investigated how sentential form-class expectancies influenced lexical-semantic priming within each hemisphere. Sentences were presented that led readers to expect a noun or a verb and the sentence-final target word was presented to one visual field/hemisphere for a lexical decision response. Noun and verb targets in the semantically related condition were compared to an unrelated prime condition, which also predicted part of speech but did not contain any lexical-semantic associates of the target word. The semantic priming effect was strongly modulated by form-class expectancy for RVF/LH targets, for both nouns and verbs. In the LVF/RH, semantic priming was obtained in all conditions, regardless of whether the form-class expectancy was violated. However, the nouns that were preceded by a noun-predicting sentence showed an extremely high priming value in the LVF/RH, suggesting that the RH may have some sensitivity to grammatical predictions for nouns. Comparisons of LVF/RH priming to calculations derived from the LSA model of language representation, which does not utilize word order, suggested that the RH might derive message-level meaning primarily from lexical-semantic relatedness.     

Right visual field advantage in parafoveal processing: Evidence from eye-fixation-related potentials

Readers acquire information outside the current eye fixation. Previous research indicates that having only the fixated word available slows reading, but when the next word is visible, reading is almost as fast as when the whole line is seen. Parafoveal-on-foveal effects are interpreted to reflect that the characteristics of a parafoveal word can influence fixation on a current word. Prior studies also show that words presented to the right visual field (RVF) are processed faster and more accurately than words in the left visual field (LVF). This asymmetry results either from an attentional bias, reading direction, or the cerebral asymmetry of language processing. We used eye-fixation-related potentials (EFRP), a technique that combines eye-tracking and electroencephalography, to investigate visual field differences in parafoveal-on-foveal effects. After a central fixation, a prime word appeared in the middle of the screen together with a parafoveal target that was presented either to the LVF or to the RVF. Both hemifield presentations included three semantic conditions: the words were either semantically associated, non-associated, or the target was a non-word. The participants began reading from the prime and then made a saccade towards the target, subsequently they judged the semantic association. Between 200 and 280 ms from the fixation onset, an occipital P2 EFRP-component differentiated between parafoveal word and non-word stimuli when the parafoveal word appeared in the RVF. The results suggest that the extraction of parafoveal information is affected by attention, which is oriented as a function of reading direction.     

Semantic and associative priming in the cerebral hemispheres: some words do, some words don't ... sometimes, some places

This study investigated spreading activation for words presented to the left and right hemispheres using an automatic semantic priming paradigm. Three types of semantic relations were used: similar-only (Deer-Pony), associated-only (Bee-Honey), and similar + associated (Doctor-Nurse). Priming of lexical decisions was symmetrical over visual fields for all semantic relations when prime words were centrally presented. However, when primes and targets were lateralized to the same visual field, similar-only priming was greater in the LVF than in the RVF, no priming was obtained for associated-only words, and priming was equivalent over visual fields for similar + associated words. Similar results were found using a naming task. These findings suggest that it is important to lateralize both prime and target information to assess hemisphere-specific spreading activation processes. Further, while spreading activation occurs in either hemisphere for the most highly related words (those related by category membership and association), our findings suggest that automatic access to semantic category relatedness occurs primarily in the right cerebral hemisphere. These results imply a unique role for the right hemisphere in the processing of word meanings. We relate our results to our previous proposal (Burgess & Simpson, 1988a; Chiarello, 1988c) that there is rapid selection of one meaning and suppression of other candidates in the left hemisphere, while activation spreads more diffusely in the right hemisphere. We also outline a new proposal that activation spreads in a different manner for associated words than for words related by semantic similarity.     

Semantic context effects and priming in word association

Two experiments investigated priming in word association, an implicit memory task. In the study phase of Experiment 1, semantically ambiguous target words were presented in sentences that biased their interpretation. The appropriate interpretation of the target was either congruent or incongruent with the cue presented in a subsequent word association task. Priming (i.e., a higher proportion of target responses relative to a nonstudied baseline) was obtained for the congruent condition, but not for the incongruent condition. In Experiment 2, study sentences emphasized particular meaning aspects of nonambiguous targets. The word association task showed a higher proportion of target responses for targets studied in the more congruent sentence context than for targets studied in the less congruent sentence context. These results indicate that priming in word association depends largely on the storage of information relating the cue and target.     

Automatic semantic association between emotional valence and brightness in the right hemisphere

Positive words (e.g., faith) were recognised better when presented in white fonts than in black fonts, whereas the opposite was true for negative words (e.g., enemy). A neural basis for this type of association between emotional valence and brightness was investigated using a visual half-field paradigm. Positive and negative words were presented in black or white fonts and presented to the left visual field–right hemisphere (LVF–RH) or right visual field–left hemisphere (RVF–LH) in a word valence judgement task (i.e., positive vs. negative). A cross-over interaction between emotional valence and brightness was observed; valence judgements were facilitated when a positive word appeared in white and when a negative word appeared in black. This interaction was qualified by a higher-order interaction. The cross-over interaction appeared only for LVF–RH trials, suggesting that the right hemisphere was responsible for the association between emotional valence and brightness.     

语篇主题表征在大脑两半球的存贮

使用半视野速示技术和启动—再认探测方法,采用包含两个句子的短语篇作为前行信息、通过主题启动、歧义词启动探测语段阅读时主题表征在大脑两半球的存贮情况,结果发现,无论是主题启动还是歧义词启动,左视野／右半脑和右视野／左半脑对语境相关的目标词反应时间都比不一致目标词更长,说明语段阅读后两半脑对主题表征都有存贮。     

Memory scanning of described images and undescribed images: Hemispheric differences

Seamon (1972) has found that reaction times (RTs) to memory probes do not increase with memory set size (M) for words encoded in mental images in a memory scanning task. Rothstein and Atkinson (1975) have failed to replicate Seamon’s results. Experiment 1 investigated this discrepancy by manipulating one methodological difference (whether images were or were not described) between the two investigations. Results revealed that described images produced typical linear increases in RT with M. Undescribed images, however, revealed no change in RT with M for positive probes (i.e., the word presented was contained in the current memory set). Experiment 2 manipulated to which visual field probes were presented (RVF — right visual field; LVF = left visual field). Results showed that the imagery group showed no relation between RT and M for probes presented to the LVF, but a linear relation for probes presentedto the RVF. Described-image and repetition groups revealed a linear relation between RT and M no matter which visual field received the probe.     

The neural basis of the right visual field advantage in reading: an MEG analysis using virtual electrodes

Right-handed participants respond more quickly and more accurately to written words presented in the right visual field (RVF) than in the left visual field (LVF). Previous attempts to identify the neural basis of the RVF advantage have had limited success. Experiment 1 was a behavioral study of lateralized word naming which established that the words later used in Experiment 2 showed a reliable RVF advantage which persisted over multiple repetitions. In Experiment 2, the same words were interleaved with scrambled words and presented in the LVF and RVF to right-handed participants seated in an MEG scanner. Participants read the real words silently and responded "pattern" covertly to the scrambled words. A beamformer analysis created statistical maps of changes in oscillatory power within the brain. Those whole-brain maps revealed activation of the reading network by both LVF and RVF words. Virtual electrode analyses used the same beamforming method to reconstruct the responses to real and scrambled words in three regions of interest in both hemispheres. The middle occipital gyri showed faster and stronger responses to contralateral than to ipsilateral stimuli, with evidence of asymmetric channeling of information into the left hemisphere. The left mid fusiform gyrus at the site of the 'visual word form area' responded more strongly to RVF than to LVF words. Activity in speech-motor cortex was lateralized to the left hemisphere, and stronger to RVF than LVF words, which is interpreted as representing the proximal cause of the RVF advantage for naming written words.     

Decision strategies and visual-field asymmetries in same-different judgments of word meaning

The accuracy with which observers judged whether two words belonged to the same semantic category was determined from a detection-theoretic analysis ofsame-different judgments. In Experiment 1, one word was presented centrally and the other word in either the left visual field (LVF) or the right visual field (RVF); in Experiment 2, both words were presented to either the LVF or the RVF. In order to obtain receiver-operating characteristics (ROCs) of performance, observers were asked to rate their confidence that the two words belonged to the same semantic category. Two models of the decision strategy were fitted to the obtained characteristics: a differencing model, in which the decision variable was the difference between the two observations; and an optimal model, in which each observation was judged in relation to a criterion. In both experiments, the optimal model provided a better fit than the differencing model to the obtained characteristics. Maximum-likelihood estimates of both the criterion-free parameter,d′, and the area under the operating characteristic,p(A), were greater for words presented in the RVF than for those presented in the LVF.     

Hemisphere dynamics in lexical access: automatic and controlled priming

Hemisphere differences in lexical processing may be due to asymmetry in the organization of lexical information, in procedures used to access the lexicon, or both. Six lateralized lexical decision experiments employed various types of priming to distinguish among these possibilities. In three controlled (high probability) priming experiments, prime words could be used as lexical access clues. Larger priming was obtained for orthographically similar stimuli (BEAK-BEAR) when presented to the left visual field (LVF). Controlled priming based on phonological relatedness (JUICE-MOOSE) was equally effective in either visual field (VF). Semantic similarity (INCH-YARD) produced larger priming for right visual field (RVF) stimuli. These results suggest that the hemispheres may utilize different information to achieve lexical access. Spread of activation through the lexicon was measured in complementary automatic (low probability) priming experiments. Priming was restricted to LVF stimuli for orthographically similar words, while priming for phonologically related stimuli was only obtained in the RVF. Automatic semantic priming was present bilaterally, but was larger in the LVF. These results imply hemisphere differences in lexical organization, with orthographic and semantic relationships available to the right hemisphere, and phonological and semantic relations available to the left hemisphere. Support was obtained for hemisphere asymmetries in both lexical organization and directed lexical processing.     

Both sides get the point: Hemispheric sensitivities to sentential constraint

Behavioral studies have consistently reported striking differences in the impact of sentence-level information on the processing of words presented in the right (RVF) versus the left (LVF) visual field, with context effects apparent only for RVF items. The consistent lack of such effects in the LVF has been taken to mean that right hemisphere language comprehension is largely insensitive to message-level meaning. We used the functional specificity afforded by event-related potential measures to assess this claim. Target words completing strongly and weakly constraining sentence contexts, in which constraint arose at the sentence level rather than from lexical associations, were presented laterally in the LVF or RVF. Increased constraint significantly reduced N400 amplitudes with presentation in both VFs, with no differences in the timing or amplitude of these effects. These results are inconsistent with the view that the VF asymmetries found in behavioral measures reflect differential hemispheric capacities at the level of semantic analysis and integration, although VF-based differences on earlier components (P2) suggest asymmetries in the impact of sentential context on perceptual aspects of word processing in the two hemispheres.     

Interhemispheric cooperation and non-cooperation during word recognition: evidence for callosal transfer dysfunction in dyslexic adults

Participants report briefly-presented words more accurately when two copies are presented, one in the left visual field (LVF) and another in the right visual field (RVF), than when only a single copy is presented. This effect is known as the 'redundant bilateral advantage' and has been interpreted as evidence for interhemispheric cooperation. We investigated the redundant bilateral advantage in dyslexic adults and matched controls as a means of assessing communication between the hemispheres in dyslexia. Consistent with previous research, normal adult readers in Experiment 1 showed significantly higher accuracy on a word report task when identical word stimuli were presented bilaterally, compared to unilateral RVF or LVF presentation. Dyslexics, however, did not show the bilateral advantage. In Experiment 2, words were presented above fixation, below fixation or in both positions. In this experiment both dyslexics and controls benefited from the redundant presentation. Experiment 3 combined whole words in one visual field with word fragments in the other visual field (the initial and final letters separated by spaces). Controls showed a bilateral advantage but dyslexics did not. In Experiments 1 and 3, the dyslexics showed significantly lower accuracy for LVF trials than controls, but the groups did not differ for RVF trials. The findings suggest that dyslexics have a problem of interhemispheric integration and not a general problem of processing two lexical inputs simultaneously.     

Visual field asymmetries in numerical size comparisons of digits, words, and signs

Visual field asymmetries were examined in American Sign Language-English bilinguals for speeded numerical size judgments of pairs of digits, number words, and number signs. Physical size of the number pairs was either congruent or incongruent with their numerical size. The results revealed a greater left visual field (LVF) interference for numbers represented as digits and a greater right visual field (RVF) interference for numbers represented as words or signs. Subjects' performance on number words and signs was also influenced by their skill in English and ASL: interference was greater in the RVF in the subjects' better language but was greater in the LVF for the less skilled language. These findings suggest that lateralization of numerical size judgments is moderated by the mode of number presentation and by prior language experience.     

Lateral word recognition: Effects of unilateral and bilateral presentation, asynchrony of bilateral presentation, and forced order of report

This experiment enquired: (1) whether right visual field (RVF) recognition superiority was greater in bilateral than in unilateral word presentation; (2) whether left field-favouring attentional or recall sets could be induced by presenting left visual field (LVF) words 20 msec prior to RVF words or by instructions to report LVF words prior to RVF words. Results showed: (1) all conditions studied yielded significant RVF superiority; (2) RVF superiority magnitude was significantly greater in bilateral than in unilateral presentation, suggesting the tenability of hypotheses that different mechanisms operate in these conditions; (3) neither earlier delivery nor earlier report of LVF words altered the pattern of RVF superiority in bilateral presentation, the later result demonstrating that differential receptive organization rather than differential recall of the two stimuli is responsible for RVF superiority in bilateral presentation.     

Length, formats, neighbours, hemispheres, and the processing of words presented laterally or at fixation

It has long been known that the number of letters in a word has more of an effect on recognition speed and accuracy in the left visual field (LVF) than in the right visual field (RVF) provided that the word is presented in a standard, horizontal format. After considering the basis of the length by visual field interaction two further differences between the visual fields/hemispheres are discussed: (a) the greater impact of format distortion (including case alternation) in the RVF than in the LVF and (b) the greater facilitation of lexical decision by orthographic neighbourhood size (N) in the LVF than in the RVF. In the context of split fovea accounts of word recognition, evidence is summarised which indicates that the processing of words presented at fixation is affected by the number of letters to the left of fixation but not by the number of letters to the right and by the number of orthographic neighbours activated by letters to the left of fixation but not by the number of orthographic neighbours activated by letters to the right of fixation. A model of word recognition is presented which incorporates the notion that the left hemisphere has sole access to a mode of word recognition that involves parallel access from letter forms to the visual input lexicon, is disrupted by format distortion, and does not employ top-down support of the letter level by the word level.     

Interhemispheric communication via direct connections for alternative meanings of ambiguous words

A priming experiment was used to investigate Burgess and Simpson's (1988) claim that interhemispheric cooperation plays an essential role in the interpretation of ambiguous text. In doing so, the merits of two models of interhemispheric cooperation, the homotopic inhibition theory (Cook, 1986) and the direct connections model (Collins & Coney, 1998), were examined. Priming of alternative meanings of ambiguous words was measured using homographs and their dominant (e.g., BARK-DOG) and subordinate meanings (e.g., BARK-TREE) as related pairs in a lexical decision task, with normal university students as subjects. Stimulus pairs were temporally separated by stimulus onset asynchronies (SOAs) of 180 and 350 ms and were independently projected to the left or right visual fields (LVF or RVF). At the shorter SOA, priming was restricted to LVF-RVF presentations, with homograph primes directed to the LVF equally facilitating responses to RVF targets which were associated with their dominant and subordinate meanings. This suggests that within 180 ms, a homograph projected to the right hemisphere activates a range of alternative meanings in the left hemisphere. At an SOA of 350 ms, LVF-RVF priming was obtained along with RVF-LVF and RVF-RVF priming. Evidently at this stage of processing, an ambiguous word directed to either hemisphere activates a range of alternative meanings in the contralateral hemisphere, while RVF primes also activate subordinate, but not dominant meanings in the left hemisphere. A homograph directed to the LVF did not activate dominant or subordinate meanings within the right hemisphere at either SOA. Generally, ambiguous words directed to either hemisphere activated a more extensive array of meanings in the contralateral hemisphere than in the hemisphere to which the prime was directed. This confirms the importance of interhemispheric cooperation in generating alternate meanings of ambiguous words. Strong support was found for the direct connections model (Collins & Coney, 1998), but no support for the homotopic inhibition theory (Cook, 1986).     

Word length and orthographic neighborhood size effects in the left and right cerebral hemispheres

Previous studies have reported an interaction between visual field (VF) and word length such that word recognition is affected more by length in the left VF (LVF) than in the right VF (RVF). A reanalysis showed that the previously reported effects of length were confounded with orthographic neighborhood size (N). In three experiments we manipulated length and N in lateralized lexical decision tasks. Results showed that length and VF interacted even with N controlled (Experiment 1); that N affected responses to words in the LVF but not the RVF (Experiment 2); and that when length and N were combined, length only affected performance in the LVF for words with few neighbors.