Evidence for right hemisphere phonology in a backward masking task

The extent to which orthographic and phonological processes are available during the initial moments of word recognition within each hemisphere is under specified, particularly for the right hemisphere. Few studies have investigated whether each hemisphere uses orthography and phonology under constraints that restrict the viewing time of words and reduce overt phonological demands. The current study used backward masking in the divided visual field paradigm to explore hemisphere differences in the availability of orthographic and phonological word recognition processes. A 20 ms and 60 ms SOA were used to track the time course of how these processes develop during pre-lexical moments of word recognition. Nonword masks varied in similarity to the target words such that there were four types: orthographically and phonologically similar, orthographically but not phonologically similar, phonologically but not orthographically similar and unrelated. The results showed the left hemisphere has access to both orthography and phonology early in the word recognition process. With more time to process the stimulus, the left hemisphere is able to use phonology which benefits word recognition to a larger extent than orthography. The right hemisphere also demonstrates access to both orthography and phonology in the initial moments of word recognition, however, orthographic similarity improves word recognition to a greater extent than phonological similarity.     

Event-related potentials and the interaction between orthographic and phonological information in a rhyme-judgment task

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes in three experiments involving a rhyme-judgment task. Experiment 1 employed sequentially presented word pairs consisting of orthographically similar and dissimilar rhyming and nonrhyming items (RUNG-SUNG, MAKE-ACHE, BEAD-DEAD, GIFT-ROAD). Comparison of the ERPs elicited by the dissimilar pairs revealed a rhyme/nonrhyme difference in the form of an increase in the amplitude of a late negative component (N450) for nonrhyming pairs; this effect was confined almost entirely to right-hemisphere electrodes. By contrast, rhyme/nonrhyme differences in the ERPs to orthographically similar word pairs were smaller in magnitude, later in onset, and bilaterally distributed. Experiment 2 showed that this pattern of ERP effects with orthographically similar items depended upon orthographic and not visual similarity. Experiment 3 tested the hypothesis that the lack of a right-hemisphere based N450 effect with orthographically similar items resulted from the operation of an orthographic priming mechanism. ERPs to nonrhyming pairs containing a word with an inconsistent segment (COAST-FROST) were compared with visually matched controls (SPARSE-CREASE). The rhyme/nonrhyme differences in the N450 components from these two conditions were indistinguishable, although subjects found it as difficult to make nonrhyme responses to "COAST-FROST" pairs as to the orthographically similar nonrhyming items in Experiment 1. It was concluded that while "orthographic priming" accounted for the behavioral data from these experiments, it could not explain the interaction between phonology and orthography observed in the concurrently recorded ERP data.     

Rhyming and the right hemisphere

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.     

Orthography, phonology, short-term memory and the effects of concurrent articulation on rhyme and homophony judgements

The role of phonological short-term memory (pSTM) in phonological judgement tasks of print has been widely explored using concurrent articulation (CA). A number of studies have examined the effects of CA on written word/nonword rhyme and homophone judgements but the findings have been mixed and few studies have examined both tasks within subjects. Also important is the influence of orthographic similarity on such tasks (i.e., items that share phonology often strongly overlap on orthography). Although there are reports of orthographic similarity effects (e.g., LOAD-TOAD vs. DIAL-MILE) on rhyme judgements, it is unknown whether (a) similar orthographic effects are present with homophone judgements, (b) the degree to which such orthographic effects interact with CA, and (c) the degree to which such orthographic effects interact with lexical status (words vs. nonwords). The present work re-examines these three issues in a within subject design. CA and orthographic similarity yielded subtle differences across tasks. CA impaired accuracy for both homophone and rhyme judgement, but only slowed RTs on the rhyme judgement task, and then only for words. Orthographic similarity yielded an increase in false positives for similar items and vice versa for dissimilar items, suggesting a general impact of an orthographically based ‘bias’ in choosing similar or dissimilar sounding items. This pattern was amplified under CA but only on the homophone judgement task. These results highlight important interactions between phonological and orthographic representations in phonological judgement tasks, and the findings are considered both with reference to earlier studies and several models of pSTM.     

Hemispheric differences in the perception of words and faces in deaf and hearing children

The purpose of this study was to investigate hemispheric functional asymmetry in 18 normal hearing children and 18 congenitally deaf children aged 13-14 years. The task was identification of a visual stimulus (3-letter word or photograph of a face) presented in either the left or right visual field. The children responded by pointing to the target stimulus on a response card which contained four different words or three different faces. The percentage of errors for presentations to the two visual fields were analysed to determine hemispheric dominance. The pattern of hemispheric differences for the hearing children was consistent with that from previous investigations. The results for the deaf children differed from those of the normals. In word perception we observed a right hemisphere advantage and in the face recognition a lack of hemispheric differences. These results point to a lack of auditory experiences which is affecting the functional organization of the two hemispheres. It is suggested that the necessity to make use of visuo-spatial information in the process of communication causes right hemisphere dominance in verbal tasks. This may influence the perception of other visuo-spatial stimuli which may yield a lack of hemispheric asymmetry in face recognition.     

Hemispheric differences in the time-course of semantic priming processes: evidence from event-related potentials (ERPs)

To investigate hemispheric differences in the timing of word priming, the modulation of event-related potentials by semantic word relationships was examined in each cerebral hemisphere. Primes and targets, either categorically (silk-wool) or associatively (needle-sewing) related, were presented to the left or right visual field in a go/no-go lexical decision task. The results revealed significant reaction-time and physiological differences in both visual fields only for associatively related word pairs, but an electrophysiological difference also tended to reach significance for categorically related words when presented in the left visual field. ERP waveforms showed a different time-course of associative priming effects according to the field of presentation. In the right visual field/left hemisphere, both N400 and Late Positive Component (LPC/P600) were modulated by semantic relatedness, while only a late effect was present in the left visual field/ right hemisphere.     

Hemispheric asymmetry in recognition memory: effects of retention level on the recognition of Portuguese words

Early findings from Broca and Wernicke led to the classical view of hemispheric specialization, where the main idea relates to left-hemisphere language capabilities compared to right-hemisphere visual capabilities. Federmeier and Benjamin (2005) have suggested that semantic encoding for verbal information in the right hemisphere can be more effective when memory demands are higher. In light of this, our main goal was to study the effect of retention level of verbal information on hemispheric processes. However, regarding the cross-linguistic differences in orthography and their subsequent effects on word recognition (Frost, Katz, & Bentin, 1987), our intent was also to test prior predictions of Federmeier and Benjamin (2005) for a "shallow" orthography language, where words have a clear correspondence between graphemes and phonemes, as opposed to English, which is a "deep" orthography language. Portuguese concrete nouns were selected. The participants were submitted to a visual half-field word presentation using a continuous recognition memory paradigm. The retention level included 1, 2, 4, 8, 20 or 40 words. Results showed that recognition accuracy was higher for words studied in the right visual field, compared to those studied in the left visual field, when the retention interval included 2, 4, or 20 words. No significant differences were found for the remaining intervals. Further analysis on accuracy data for intermediate retention levels showed that recognition accuracy was higher for the 2 words retention level than for the levels including 4, 8, or 20 words; it was higher for left-hemisphere encoding as well. Our results also indicated that reaction times were slower for left-hemisphere encoding and for the 40 words retention level when compared to that of 20 words. In summary, the current results are in partial agreement with those of Federmeier and Benjamin (2005) and suggest different hemispheric memory strategies for the semantic encoding of verbal information.     

Hemispheric differences in semantic processing: Category matching is not the same as category membership

Two closely related semantic processing tasks were studied under identical procedural conditions in order to examine lateral visual field effects on reaction times. In Experiment 1, reaction times did not differ as a function of visual field when subjects decided whether a lateral word was a member of a foveally presented category word (category membership task). On the other hand, reaction times were faster for right than for left visual field stimulus presentations when subjects decided whether two words, one lateral and one foveal, belonged to the same category (category matching task), although this advantage did not occur immediately. In Experiment 2, the laterality effect in the category matching task was studied as a function of word familiarity. Two groups of subjects performed the matching task for two blocks of trials, one group receiving the same word list in each block and the other receiving different lists. No visual field differences in reaction times were observed for either group during the first block of trials, but a distinct right field advantage appeared for both during the second block. The data from these experiments suggest that category matching strategies rely upon structures or processes localized in the left hemisphere, although their influence is not immediate. Category membership strategies, on the other hand, do not depend upon such localized structures.     

Picture-name priming in the cerebral hemispheres: evidence for phonological access in the right hemisphere

This study investigated right hemisphere involvement in access to phonology, using a picture-naming priming paradigm where pictures and names of common objects printed in Japanese Kana were presented in succession to the same visual field or different visual fields with a stimulus onset asynchrony of 250 msec. A naming task was used for this purpose. The result showed that, when primes and targets were presented to the same visual field, facilitation for related pairs was observed in each hemisphere, with overall naming latencies being slower in the right hemisphere than in the left hemisphere. This result indicates that the prior access to phonology for a picture in the right hemisphere facilitates phonological activation of a word that names the picture in this hemisphere, suggesting that the right hemisphere is involved in access to phonology. On the other hand, when primes and targets were presented to different visual fields, there was no facilitation for related pairs with inhibition for unrelated pairs, irrespective of prime and target visual fields. It is suggested that this inhibition-dominant pattern of priming may occur due to homotopic inhibition processes proposed by N. D. Cook.     

Brain potentials as indices of orthographic and phonological interaction during word matching

The interaction between orthographic and phonological codes in a same-different judgment task was studied by requiring subjects to decide if two visually presented words either looked alike or rhymed. Word pairs were selected from four different lists. Words rhymed and looked alike, rhymed but did not look alike, looked alike but did not rhyme, or neither looked alike nor rhymed. Reaction time and percent error increased whenever there was a conflict between the orthography and phonology of the words. The N200 component of the event-related brain potential (ERP) indicated that subjects were capable of detecting phonological differences between words within 260 ms from the presentation of a word pair. The amplitude of the N200s also varied with the degree of mismatch between words. N200s were largest when both the orthography and phonology mismatched, of intermediate amplitude when either orthography or phonology mismatched, and smallest when both orthography and phonology matched. P300 latency was consistent with reaction time, increasing whenever there was a conflict between the two codes. Taken together, behavioral measures and the ERP data suggest that the extraction of the orthographic and phonological aspects of words occurs early in the information processing sequence.     

Hemispheric differences for feature perception

Summary Hemisphere differences for featural processing were investigated in three experiments. Stimulus arrays composed of the same background letter were presented tachistoscopically and the subject instructed to detect an embedded target letter. Background and target letter features were manipulated across studies, while stimulus arrays were presented at different retinal loci within experiments. Signal detection analysis revealed that left hemisphere stimulus presentations demonstrated slightly better detection when target and background features were relatively dissimilar, while right hemisphere stimulus presentations demonstrated better detection when target and background features were highly similar. Retinal locus generally decreased detection performance when the stimulus letters were dissimilar and interacted with hemispheric advantages. Both of these factors also were affected by changes in response criterion across experiments which were linked to target/background perceptual confusions. The findings suggest that the left and right hemispheres differ in their feature extraction capabilities during the early stages of visual stimulus processing.     

Hemispheric patterns in visual search

A visual search paradigm was employed to examine hemispheric serial and parallel processing. Stimulus arrays containing 4, 9, or 16 elements were tachistoscopically presented to the right visual field-left hemisphere (RVF-LH) or left visual field-right hemisphere (LVF-RH). Subjects judged whether all of the elements within an array were physically the same (all X's) or whether one (O) was different from the rest. Left hemisphere presentations were processed more quickly and accurately than LVF-RH presentations for all stimulus conditions. As the number of array elements increased, more errors and longer response times were obtained for different stimulus items whereas fewer errors and somewhat shorter response times were obtained for same stimulus items. These and previous results suggest that the left hemisphere obtains an advantage for visual search because of that hemisphere's superiority for fine-grained feature analysis rather than because of a fundamental hemispheric serial/parallel processing dichotomy.     

Hemispheric specialization in reading and word recognition

Three experiments dealing with hemispheric specialization are presented. In Experiment 1, words and/or faces were presented tachistoscopically to the left or right of fixation. Words were more accurately identified in the right visual field and faces were more accurately identified in the left visual field. A forced choice error analysis for words indicated that errors made for word stimuli were most frequently visually similar words and this effect was particularly pronounced in the left visual field. Two additional experiments supported this finding. On the basis of the results, it was argued that word identification is a multistage process, with visual feature analysis carried out by the right hemisphere and identification and naming by the left hemisphere. In addition, Kinsbourne's attentional model of brain function was rejected in favor of an anatomical model which suggests that simultaneous processing of verbal and nonverbal information does not constrict the attention of either hemisphere.     

Lateralization effects during semantic and rhyme judgement tasks in deaf and hearing subjects

A visual hemifield experiment investigated hemispheric specialization among hearing children and adults and prelingually, profoundly deaf youngsters who were exposed intensively to Cued Speech (CS). Of interest was whether deaf CS users, who undergo a development of phonology and grammar of the spoken language similar to that of hearing youngsters, would display similar laterality patterns in the processing of written language. Semantic, rhyme, and visual judgement tasks were used. In the visual task no VF advantage was observed. A RVF (left hemisphere) advantage was obtained for both the deaf and the hearing subjects for the semantic task, supporting Neville's claim that the acquisition of competence in the grammar of language is critical in establishing the specialization of the left hemisphere for language. For the rhyme task, however, a RVF advantage was obtained for the hearing subjects, but not for the deaf ones, suggesting that different neural resources are recruited by deaf and hearing subjects. Hearing the sounds of language may be necessary to develop left lateralised processing of rhymes.     

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.     

Quantitative and Qualitative Hemispheric Asymmetry for Processing Japanese Kana

Native Japanese speakers identified three-letter kana stimuli presented to the left visual field and right hemisphere (LVF/RH), to the right visual field and left hemisphere (RVF/LH), or to both visual fields and hemispheres simultaneously (BILATERAL trials). There were fewer errors on RVF/LH and BILATERAL trials than on LVF/RH trials. Qualitative analysis of error patterns indicated that there were many fewer errors of first-letter identification than of last-letter identification, suggesting top-to-bottom scanning of the kana characters. In contrast to similar studies presenting nonword letter trigrams to native English speakers, qualitative error patterns were identical for the three visual field conditions. Taken together with the results of earlier studies, the results of the present experiment indicate that the ubiquitous RVF/LH advantage reflects a left-hemisphere superiority for phonetic processing that generalizes across specific languages. At the same time, qualitative aspects of hemispheric asymmetry differ from one language to the next and may depend on such things as the way in which individual characters map onto the pronunciation of words and nonwords.     

Disruption of spelling-to-sound correspondence mapping during single-word reading in patients with temporal lobe epilepsy

Processing and/or hemispheric differences in the neural bases of word recognition were examined in patients with long-standing, medically-intractable epilepsy localized to the left (N=18) or right (N=7) temporal lobe. Participants were asked to read words that varied in the frequency of their spelling-to-sound correspondences. For the right temporal lobe group, reaction times (RTs) showed the same pattern across spelling-to-sound correspondence conditions as previously reported for normal participants. For the left temporal lobe group, however, the pattern of RTs suggested a greater relative influence of orthographic frequency than rime frequency, such that performance was worse on words whose orthographic body was less frequent in the language. We discuss these results in terms of differences in processing between the two cerebral hemispheres: the results for the right-temporal lobe patients are taken to support connectionist models of reading as described for the dominant (left) hemisphere, while results for the left-temporal lobe patients support a view of the right hemisphere as relatively less sensitive to phonology and relatively more sensitive to orthography.     

Suppression effects in rhyme judgement tasks

Orthographic and phonological similarity were orthogonally manipulated in a rhyme judgement task. The effects were assessed of paced versus very rapid articulatory suppression on subjects' ability to make rhyme judgements when pairs of words were presented either simultaneously or successively. It was found that there were consistent suppression effects on the accuracy of subjects' judgements to visually similar non-rhyming pairs (e.g. “pint-tint”), visually dissimilar rhyming pairs (e.g. “fare-wear”) and visually similar rhyming pairs (e.g. “fall-tall), regardless of mode of presentation or speed of suppression. The size of the suppression effect was greatest for the visually similar non-rhyming word pairs. It was argued that subjects need to carry out a recheck for phonological similarity when word pairs are visually but not phonologically similar, and that encoding the words in articulatory form is particularly beneficial for making accurate rhyme judgements to such pairs.     

The effect of associative strength on priming in the cerebral hemispheres

Recent studies have suggested that semantic memory is more diffusely organized in the right hemisphere of the brain and that words directed to this hemisphere are more likely to activate meanings distantly related to the input. It is argued that this model of language processes predicts that variations in the associative strength of word pairs should give rise to different patterns of priming in each hemisphere. Specifically, the right hemisphere should exhibit relatively more facilitation than the left in response to weaker associative relationships, whereas the left hemisphere should exhibit relatively more facilitation than the right in the context of stronger relationships. This study varied the strength of the semantic association between prime and target in a divided visual field priming procedure. The results were unequivocal in demonstrating similar associative strength functions in each hemisphere, under conditions that encouraged either automatic or controlled processing. Visual field differences in absolute RTs to words and in magnitude of facilitation effects support the claim that the data collected in this study are veridical with respect to priming processes in the hemispheres. It is suggested that current models of hemispheric language processes require further refinement.     

Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.