Grammatical number agreement processing using the visual half-field paradigm: An event-related brain potential study

Despite indications in the split-brain and lesion literatures that the right hemisphere is capable of some syntactic analysis, few studies have investigated right hemisphere contributions to syntactic processing in people with intact brains. Here we used the visual half-field paradigm in healthy adults to examine each hemisphere's processing of correct and incorrect grammatical number agreement marked either lexically, e.g., antecedent/reflexive pronoun (“The grateful niece asked herself/*themselves…”) or morphologically, e.g., subject/verb (“Industrial scientists develop/*develops…”). For reflexives, response times and accuracy of grammaticality decisions suggested similar processing regardless of visual field of presentation. In the subject/verb condition, we observed similar response times and accuracies for central and right visual field (RVF) presentations. For left visual field (LVF) presentation, response times were longer and accuracy rates were reduced relative to RVF presentation. An event-related brain potential (ERP) study using the same materials revealed similar ERP responses to the reflexive pronouns in the two visual fields, but very different ERP effects to the subject/verb violations. For lexically marked violations on reflexives, P600 was elicited by stimuli in both the LVF and RVF; for morphologically marked violations on verbs, P600 was elicited only by RVF stimuli. These data suggest that both hemispheres can process lexically marked pronoun agreement violations, and do so in a similar fashion. Morphologically marked subject/verb agreement errors, however, showed a distinct LH advantage.     

Word position affects stimulus recognition: Evidence for early ERP short-term plastic modulation

The present study was aimed at investigating the short-term plastic changes that follow word learning at a neurophysiological level. The main hypothesis was that word position (left or right visual field, LVF/RH or RVF/LH) in the initial learning phase would leave a trace that affected, in the subsequent recognition phase, the Recognition Potential (i.e., the first negative component distinguishing words from other stimuli) elicited 220–240 ms after centrally presented stimuli. Forty-eight students were administered, in the learning phase, 125 words for 4 s, randomly presented half in the left and half in the right visual field. In the recognition phase, participants were split into two equal groups, one was assigned to the Word task, the other to the Picture task (in which half of the 125 pictures were new, and half matched prior studied words). During the Word task, old RVF/LH words elicited significantly greater negativity in left posterior sites with respect to old LVF/RH words, which in turn showed the same pattern of activation evoked by new words. Therefore, correspondence between stimulus spatial position and hemisphere specialized in automatic word recognition created a robust prime for subsequent recognition. During the Picture task, pictures matching old RVF/LH words showed no differences compared with new pictures, but evoked significantly greater negativity than pictures matching old LVF/RH words. Thus, the priming effect vanished when the task required a switch from visual analysis to stored linguistic information, whereas the lack of correspondence between stimulus position and network specialized in automatic word recognition (i.e., when words were presented to the LVF/RH) revealed the implicit costs for recognition. Results support the view that short-term plastic changes occurring in a linguistic learning task interact with both stimulus position and modality (written word vs. picture representation).     

Semantic priming within and between the visual fields: an event-related brain potential study

To investigate interhemispheric transfer of language information, event-related brain potentials (ERPs) were recorded during performance of a semantic matching task in which prime and target word pairs were sequentially presented to either the left (LVF) or the right (RVF) visual field. A posterior slow negative shift prior to the target presentation developed over both hemispheres for LVF primes, whereas for RVF primes the negative shift declined over the right hemisphere. An N400 attenuation was observed for targets semantically related to the primes and was predominant over the left parietal site. The N400 priming effect was significantly reduced for LVF targets preceded by RVF primes, compared to other patterns of presentation. These findings indicate that semantic priming is attenuated in the right hemisphere when information is transferred from the left hemisphere.     

On hemispheric specialisation and visual field effects in the perception of print: A comment on Jordan, Patching, and Thomas

Introduction Due to structural characteristics of the visual pathways, stimuli that are presented in the right half of the visual field (RVF) are initially projected to the left cerebral hemisphere, while those presented in the left half of the visual field (LVF) are projected to the right cerebral hemisphere. This anatomical feature has frequently been taken to support the notion that the well-documented RVF advantage in recognising printed words is a reflection of functional differences between the two hemispheres; notably that of the dominance of the left hemisphere for processing language. Word stimuli that are sent straight to the left hemisphere are believed to profit from more efficient processing than those sent initially to the right hemisphere, because the latter stimuli must follow a longer and more noisy pathway before reaching the language-dominant hemisphere. In the work by Jordan, Patching, and Thomas (2003) the above notion is further developed to speculate that the point of entry of visual information into the cortex may determine the procedure that will underlie the ensuing word recognition process: "... the left hemisphere can process words by mapping orthographic information in parallel onto lexical entries whereas the right hemisphere has a more rudimentary process, that can only map orthographic information sequentially" (p. 50).     

On hemispheric specialisation and visual field effects in the perception of print: A comment on Jordan,Patching, and Thomas

Introduction Due to structural characteristics of the visual pathways, stimuli that are presented in the right half of the visual field (RVF) are initially projected to the left cerebral hemisphere, while those presented in the left half of the visual field (LVF) are projected to the right cerebral hemisphere. This anatomical feature has frequently been taken to support the notion that the well-documented RVF advantage in recognising printed words is a reflection of functional differences between the two hemispheres; notably that of the dominance of the left hemisphere for processing language. Word stimuli that are sent straight to the left hemisphere are believed to profit from more efficient processing than those sent initially to the right hemisphere, because the latter stimuli must follow a longer and more noisy pathway before reaching the language-dominant hemisphere. In the work by Jordan, Patching, and Thomas (2003) the above notion is further developed to speculate that the point of entry of visual information into the cortex may determine the procedure that will underlie the ensuing word recognition process: "... the left hemisphere can process words by mapping orthographic information in parallel onto lexical entries whereas the right hemisphere has a more rudimentary process, that can only map orthographic information sequentially" (p. 50).     

Hemispheric differences for identification of words and nonwords in Urdu-English bilinguals

Hemispheric asymmetry was examined for Urdu-English bilinguals identifying printed Urdu words and nonwords, separated Urdu letter strings, digits, and English nonwords. In all cases, fewer errors occurred when stimuli were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH). Qualitative error patterns suggested that separated Urdu letter strings were processed more serially than Urdu letter strings joined to form words or pronounceable nonwords and more serially on RVF/LH than on LVF/RH trials. This qualitative laterality effect is similar to that found for Hebrew and Arabic but opposite that found for English and suggests that the qualitative manner of processing printed verbal material is influenced by language-specific factors such as scanning direction, orthographic-to-phonological mapping rules, and morphology.     

Event‐related potentials reveal the effects of aging on meaning selection and revision

ERPs were recorded as older adults decided if a target word was related to a lateralized ambiguous or unambiguous prime; prime‐target pairs were preceded by a related or unrelated context word. In an unrelated context, N400 facilitation effects differed from those seen in young adults, with older adults showing priming for the dominant meaning (e.g., BOOM‐BANK‐DEPOSIT) on right visual field/left hemisphere (RVF/LH) trials and priming for the subordinate meaning (e.g., BOOM‐BANK‐RIVER) on LVF/RH trials. Higher‐functioning older adults, especially those with better inhibition, were more likely to show bilateral activation of the dominant meaning and unilateral activation of the subordinate meaning, suggesting a retention of young‐like activation. In a biasing context (e.g., RIVER‐BANK‐DEPOSIT), older adults selected the contextually‐consistent meaning, but were less likely than young adults to revise their selection.     

Assessing the Role of Hemispheric Specialisation, Serial-Position Processing, and Retinal Eccentricity in Lateralised Word RecognitioN

The advantage for words in the right visual hemifield (RVF) has been assigned parallel orthographic processing by the left hemisphere and sequential by the right. However, an examination of previous studies of serial position performance suggests that orthographic processing in each hemifield is modulated by retinal eccentricity. To investigate this issue, we presented words at eccentricities of 1, 2, 3, and 4 degrees. Serial position performance was measured using the Reicher-Wheeler task to suppress influences of guesswork and an eye-tracker controlled fixation location. Greater eccentricities produced lower overall levels of performance in each hemifield although RVF advantages for words obtained at each eccentricity (Experiments 1 and 2). However, performance in both hemifields revealed similar U-shaped serial position performance at all eccentricities. Moreover, this performance was not influenced by lexical constraint (high, low; Experiment 2) or status (word, nonword; Experiment 3), although only words (not nonwords) produced an RVF advantage. These findings suggest that although each RVF advantage was produced by left-hemisphere function, the same pattern of orthographic analysis was used by each hemisphere at each eccentricity.     

Lateralization of repetition effects in event-related potentials to words in left- and right-handed women

In our previous event-related potential (ERP) study [A. Nowicka, I. Szatkowska, Memory-induced modulation of event-related potentials in frontal cortex of human subjects: a divided visual field study, Neurosci. Lett. 359 (2004) 171-174], word repetition effects in right-handed males were observed only in case of the direct stimulation of the left (competent) hemisphere. Since the left-handedness and the factor of female gender may determine the lateralization of verbal functions, the goal of the present study was to test the sensitivity of the ERP repetition effects to the visual field of word presentation in the group of left- and right-handed women. ERPs were recorded from symmetrical sites over the left and right hemisphere. Target words were presented in the left (LVF) or right (RVF) visual hemifield. Subjects' were instructed to recognize the target word on a response card. A substantial portion of words was repeated twice. Words elicited different ERPs at frontal sites when presented the first and second times: ERPs were more positive to the repeated stimulus than to its first occurrence. However, in right-handed participants, repetition effects were only observed when target words were presented to the RVF whereas in left-handed participants, repetition effects were only observed when target words were presented to the LVF. These findings are indicative of the asymmetrical involvement of the two hemispheres in memory-induced modulation of brain activity related to verbal processing in left- and right-handed women.     

The left visual-field advantage in rapid visual presentation is amplified rather than reduced by posterior-parietal rTMS

In the present task, series of visual stimuli are rapidly presented left and right, containing two target stimuli, T1 and T2. In previous studies, T2 was better identified in the left than in the right visual field. This advantage of the left visual field might reflect dominance exerted by the right over the left hemisphere. If so, then repetitive transcranial magnetic stimulation (rTMS) to the right parietal cortex might release the left hemisphere from right-hemispheric control, thereby improving T2 identification in the right visual field. Alternatively or additionally, the asymmetry in T2 identification might reflect capacity limitations of the left hemisphere, which might be aggravated by rTMS to the left parietal cortex. Therefore, rTMS pulses were applied during each trial, beginning simultaneously with T1 presentation. rTMS was directed either to P4 or to P3 (right or left parietal cortex) either as effective or as sham stimulation. In two experiments, either one of these two factors, hemisphere and effectiveness of rTMS, was varied within or between participants. Again, T2 was much better identified in the left than in the right visual field. This advantage of the left visual field was indeed modified by rTMS, being further increased by rTMS to the left hemisphere rather than being reduced by rTMS to the right. It may be concluded that superiority of the right hemisphere in this task implies that this hemisphere is less irritable by external interference than the left hemisphere.     

Emotion and space: lateralized emotional word detection depends on line bisection bias

There is converging evidence, from various independent areas of neuroscience, for a functional specialization of the left and right cerebral hemispheres for positive and negative emotions, respectively (“valence theory” of emotional processing). One subfield, however, has produced mixed results, i.e. work on the detection of parafoveally presented positively or negatively emotional words by healthy subjects. Right or left visual field advantages were described and interpreted as reflecting the superiority of either the left hemisphere (LH) for linguistic material, or of the right hemisphere (RH) for highly emotional stimuli. Here we show that 48 healthy, right-handed participants' performance on a lateralized lexical decision task depends on their individual inclination to bisect a line to the left or right of the objective center. Only those with a bisection bias to the right showed the LH advantage for word detection known from the neuropsychological literature. Negative emotional words were processed with comparable accuracy in the two visual fields. However, a recognition advantage for negative over positive emotional words was found exclusively for those participants with a leftward line bisection bias. These results suggest that in work on functional hemispheric differences state variables like stimulus lateralization and word emotionality may be less decisive than the trait variable of lateral hemispatial attention. We propose a cautious reconsideration of the concept of “hemisphericity,” which once emphasized individual differences in baseline hemispheric arousal, but was later dismissed in a reaction to oversimplifications in popular science accounts.     

Laterality, word valence, and visual attention: a comparison of depressed and non-depressed individuals.

Thirteen depressed and 13 non-depressed college students attended to valence-loaded word pairs (euphoric/dysphoric, euphoric/neutral, and neutral/dysphoric) on a computer screen. Each pair was observed through a viewing box with a vertical partition, each word in a different visual field. As a prior-entry task (Titchener, 1908) the words were simultaneously replaced by colored bars. Participants indicated which color bar (left or right) was seen first. As predicted, identifications of color bars following euphoric words in the right visual field (left hemisphere) exceeded their identification in the left visual field (right hemisphere). Also, as predicted, the non-depressed participants made identifications following the euphoric word of a pair more often than did the depressed participants. No interaction occurred between laterality and participant classification. Implications for research and therapy are discussed.     

Hemispheric differences in a categorization matching task

The laterality difference in the execution of the higher-order cognitive task, categorization utilizing a superordinate concept, was examined. The subjects decided whether the two stimuli serially presented in the right or left visual field came under an identical category. In Exp. I, outline drawing stimuli were used and the RVF condition superiority in latency in the "same" response and LVF condition superiority in the "different" responses were demonstrated. These results were similar to those in the previous physical matching task and suggested that a superordinate concept was not in use to execute the present task. In Exp. II, vertically written verbal stimuli were used and the RVF condition superiority in both the "same" and the "different" responses were demonstrated. These results would suggest the superiority of the left hemisphere in the higher-order cognitive tasks.     

Hemispheric priming by meaningful and nonmeaningful symbols in language-trained chimpanzees (Pan troglodytes): further evidence of a left hemisphere advantage.

Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time paradigm. Subjects were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field (LVF) or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from two semantic categories: foods and tools. A third set of warning stimuli were familiar geometric symbols. Dependent measures included reaction time and the number of false-positive responses. Reaction-time data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when subjects responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees.     

Visual memory for shapes in deaf signers and nonsigners and in hearing signers and nonsigners: atypical lateralization and enhancement

Deaf and hearing individuals who either used sign language (signers) or not (nonsigners) were tested on visual memory for objects and shapes that were difficult to describe verbally with a same/different matching paradigm. The use of 4 groups was designed to permit a separation of effects related to sign language use (signers vs. nonsigners) and effects related to auditory deprivation (deaf vs. hearing). Forty deaf native signers and nonsigners and 51 hearing signers and nonsigners participated in the study. Signing individuals (both deaf and hearing) were more accurate than nonsigning individuals (deaf and hearing) at memorizing shapes. For the shape memory task but not the object task, deaf signers and nonsigners displayed right hemisphere (RH) advantage over the left hemisphere (LH). Conversely, both hearing groups displayed a memory advantage for shapes in the LH over the RH. Results indicate that enhanced memory performance for shapes in signers (deaf and hearing) stems from the visual skills acquired through sign language use and that deafness, irrespective of language background, leads to the use of a visually based strategy for memory of difficult-to-describe items.     

Asymmetrical hemispheric EEG activation evoked by stimulus position during the Simon task

The Simon effect has been previously shown to be asymmetric at both the behavioral and electrophysiological levels. The present investigation was aimed to clarify whether, during a Simon task, hemispheric asymmetry is also observed in the early phases of stimulus processing. In a group of healthy subjects performing the Simon task, we analyzed scalp potentials evoked by the first lateralized cue (left or right), instead of the classical readiness potential preceding the motor response. ERP results showed a significant left cortical activation to stimuli presented in the right visual field at the 140–160 ms time window. Instead, left stimuli elicited a significant activation of the right versus left hemisphere starting at the next 160–180 ms time interval. We linked this asymmetry to that observed in behavioral data: the Simon effect recorded with left stimuli is smaller than the Simon effect recorded with right stimuli. Results confirm the hypothesis that in right handed subjects, left hemisphere is specialized for motor response selection and is able to process right stimuli faster than the right hemisphere does for left stimuli.     

Differential asymmetries for recognizing nouns and verbs: where are they?

To support categorical representation in the brain for grammatical class, it is necessary to show that noun-verb differences are attributable to parts of speech and not to covarying semantic factors. Prior visual-half field investigations of noun-verb processing have confounded grammatical class with imageability. The current study included numerous tests of differential noun-verb processing across visual fields for stimuli equated for imageability. Task (lexical decision, pronunciation) and list context (blocked vs. mixed lists) variables were examined in 168 right-handed participants. There was no reliable reduction of the right visual field advantage for moderately imageable nouns as compared with verbs. If there are qualitative hemisphere differences in single-word noun and verb recognition, these may be attributable to semantic dimensions that tend to covary with grammatical class.     

Processing of form stimuli presented unilaterally in humans, chimpanzees (Pan troglodytes), and monkeys (Macaca mulatta)

Visual forms were unilaterally presented using a video-task paradigm to 10 humans, 3 chimpanzees, and 2 rhesus monkeys to determine whether hemispheric advantages existed in the processing of these stimuli. Both accuracy and reaction time served as dependent measures. For the chimpanzees, a significant right hemisphere advantage was found within the first 3 test sessions. The humans and monkeys failed to show a hemispheric advantage as determined by accuracy scores. Analysis of reaction time data revealed a significant left hemisphere advantage for the monkeys. A Visual Half-Field x Block interaction was found for the chimpanzees, with a significant left visual field advantage in Block 2, whereas a right visual field advantage was found in Block 4. In the human subjects, a left visual field advantage was found in Block 3 when they used their right hands to respond. The results are discussed in relation to recent reports of hemispheric advantages for nonhuman primates.     

Hemispheric asymmetry in the analysis of stroop stimuli: A developmental approach

This experiment was designed to investigate hemisphere differences in the processing of Stroop color‐word stimuli in 7‐ to 15‐year‐olds. One hundred eight normal, right‐handed males were tested. Each participated in three experimental conditions: reading, naming, and interference. Vocal reaction times and error rates were recorded. Results showed a right‐visual‐field advantage invariant with age in the reading condition and a left‐visual‐field advantage invariant with age in the naming condition. In the interference condition, however, age‐related variations in the pattern of visual asymmetry were observed. I propose that differences in visual asymmetries result from changes in subsets of cognitive components used to carry out different cognitive strategies.