Hemispheric differences in processing handwritten cursive

Hemispheric asymmetry was examined for native English speakers identifying consonant-vowel-consonant (CVC) non-words presented in standard printed form, in standard handwritten cursive form or in handwritten cursive with the letters separated by small gaps. For all three conditions, 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) and qualitative error patterns indicated that the last letter was missed more often than the first letter on LVF/RH trials but not on RVF/LH trials. Despite this overall similarity, the RVF/LH advantage was smaller for both types of cursive stimuli than for printed stimuli. In addition, the difference between first-letter and last-letter errors was smaller for handwritten cursive than for printed text, especially on LVF/RH trials. These results suggest a greater contribution of the right hemisphere to the identification of handwritten cursive, which is likely related visual complexity and to qualitative differences in the processing of cursive versus print.     

Is Happy Facial Expression Identified by the Left or Right Hemisphere？

1IntroductionCorrectly identifying other people′s facial ex-pressions of emotions is important to human socialinteraction in all societies.Many studies suggestthat the identification of facial expressions in par-ticular and perceptual processing of emotional infor-mation is carried out mainly by the right hemi-sphere of the brain[1￣7].Damage to the righthemisphere generally produces more significant im-pairment in recognition of all facial expressions ofemotion than damage to the left hemisp…     

Strategies of semantic categorization in the cerebral hemispheres

Strategies of semantic categorization in intact cerebral hemispheres were studied in two experiments by presenting names of typical and atypical category instances to the left visual field (LVF) (right hemisphere) or to the right visual field (RVF) (left hemisphere). The results revealed that the typicality of instances had a large effect on categorization times in the LVF in both experiments, suggesting that the right hemisphere relies strongly on a holistic, similarity-based comparison strategy. In Experiment 1, the typicality effect was weaker in the RVF than in the LVF. In Experiment 2, a typicality effect in the RVF was observed for the "four-footed animal" category but not for the "bird" category. The hypothesis that the left hemisphere employs a strategy based on defining or necessary features is not supported by the observed typicality effect in the "four-footed animal" category. Instead, it is suggested that the left hemisphere may be able to categorize on the basis of prestored instance-category knowledge. When such knowledge is not available (e.g., as for four-footed animals), a similarity-based comparison strategy is employed by the left hemisphere.     

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.     

Hemisphere specialization of Go experts in visuospatial processing

To investigate hemisphere function of experts, Go experts and novices were given two Salthouse-type visuospatial tasks. In Experiment 1, stimuli of 4 digits in 6 cells were projected to the left (LVF) or right visual field (RVF). There was no prominent group difference in identification of digits and locations. In Experiment 2, stimuli of 4 digits in 16 cells were projected to the LVF or RVF. Go experts showed more accurate performance than novices. Both groups showed the same laterality, an RVF advantage, in the number identification. However, in the location identification, Go experts showed no visual field difference, whereas novices showed an RVF advantage. Based on these findings, the relationship between task demand and hemisphere function of experts is discussed.     

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.     

Visual field effects in the discrimination of sine-wave gratings

The time needed to decide whether the second of two successively presented sinusoidal gratings was of a higher or lower spatial frequency than the first was measured for spatial frequencies of 1, 2, 4, 8, and 12 cycles per degree (cpd) presented in either the left visual field (LVF) or right visual field (RVF). A LVF advantage was found for discriminating within the low-spatial-frequency range (i.e., 1 and 2 cpd), whereas a RVF advantage was found for discriminating within the high-spatial-frequency range (i.e., 4-12 cpd). These findings support the conclusion that hemispheric asymmetries in the processing of gratings arise when comparisons are made between the output of spatial-frequency channels.     

Sequential processing in hemispheric word recognition: the impact of initial letter discriminability on the OUP naming effect

The cerebral hemispheres have been proposed to engage different word recognition strategies: the left hemisphere implementing a parallel, and the right hemisphere, a sequential, analysis. To investigate this notion, we asked participants to name words with an early or late orthographic uniqueness point (OUP), presented horizontally to their left (LVF), right (RVF), or both fields of vision (BVF). Consistent with past foveal research, Experiment 1 produced a robust facilitatory effect of early OUP for RVF/BVF presentations, indicating the presence of sequential processes in lexical retrieval. The effect was absent for LVF trials, which we argue results from the disadvantaged position of initial letters of words presented in the LVF. To test this proposition, Experiment 2 assessed the discriminability of various letter positions in the visual fields using a bar-probe task. The obtained error functions highlighted the poor discriminability of initial letters in the LVF and latter letters in the RVF. To confirm that this asymmetry in initial letter acuity was responsible for the absent OUP effect for LVF presentations, Experiment 3 replicated Experiment 1 using vertical stimulus presentations. Results indicated a marked facilitatory effect of early OUP across visual fields, supporting our contention that the lack of OUP effect for LVF presentations in Experiment 1 resulted from poor discriminability of the initial letters. These findings confirm the presence of sequential processes in both left and right hemisphere word recognition, casting doubt on parallel models of word processing.     

Hemispheric differences in the interference among components of compound gratings

The relationship between local/global and high/low spatial-frequency processing in hemispheric asymmetries was explored. Subjects were required to judge the orientation of a high- or low-spatial-frequency component of a compound grating presented in the left visual field (LVF) or right visual field (RVF). In Experiment 1, attention was focused on one or the other component. A signal detection analysis indicated that sensitivity (d′) to the high-spatial-frequency target was reduced more by the presence of the low-spatial-frequency component when both were presented in the LVF rather than in the RVF. In Experiment 2, subjects determined whether a target orientation was present, independent of spatial frequency at only a single level (i.e., at the high- or low-spatial-frequency level), as opposed to both or neither level. An RVF/LH (left hemisphere) advantage was found when the decision was based on the orientation of the high-frequency component. The asymmetrical influence of visual field of presentation and spatial frequency upon sensitivity is discussed in terms of hemispheric differences in the magnitude of inhibition between spatial-frequency channels and in the role of transient channel activity to capture and direct higher order attentional processes.     

Mixing metaphors in the cerebral hemispheres: what happens when careers collide?

Are processes of figurative comparison and figurative categorization different? An experiment combining alternative-sense and matched-sense metaphor priming with a divided visual field assessment technique sought to isolate processes of comparison and categorization in the 2 cerebral hemispheres. For target metaphors presented in the right visual field/left cerebral hemisphere (RVF/LH), only matched-sense primes were facilitative. Literal primes and alternative-sense primes had no effect on comprehension time compared to the unprimed baseline. The effects of matched-sense primes were additive with the rated conventionality of the targets. For target metaphors presented to the left visual field/right cerebral hemisphere (LVF/RH), matched-sense primes were again additively facilitative. However, alternative-sense primes, though facilitative overall, seemed to eliminate the preexisting advantages of conventional target metaphor senses in the LVF/RH in favor of metaphoric senses similar to those of the primes. These findings are consistent with tightly controlled categorical coding in the LH and coarse, flexible, context-dependent coding in the RH.     

Effects of Output Order on Hemispheric Asymmetry for Processing Letter Trigrams

Observers identified consonant–vowel–consonant trigrams with the letters arranged vertically by pronouncing the stimulus (treating the bottom letter as the first letter) and spelling it from bottom to top. On each trial, the trigram was presented to the left visual field/right hemisphere (LVF/RH), to the right visual field/left hemisphere (RVF/LH), or to both visual fields simultaneously (BILATERAL trials). Quantitative and qualitative visual field differences were identical to those found when observers used a more natural response output order, treating the top letter of the trigram as the first letter. The results suggest that, regardless of output order, attention is distributed across the three letters in a relatively slow, top-to-bottom fashion on LVF/RH and BILATERAL trials, whereas attention is distributed more rapidly and evenly across the three letters on RVF/LH trials.     

Facilitative orthographic neighborhood effects: the SERIOL model account

A large orthographic neighborhood (N) facilitates lexical decision for central and left visual field/right hemisphere (LVF/RH) presentation, but not for right visual field/left hemisphere (RVF/LH) presentation. Based on the SERIOL model of letter-position encoding, this asymmetric N effect is explained by differential activation patterns at the orthographic level. This analysis implies that it should be possible to negate the LVF/RH N effect and create an RVF/LH N effect by manipulating contrast levels in specific ways. In Experiment 1, these predictions were confirmed. In Experiment 2, we eliminated the N effect for both LVF/RH and central presentation. These results indicate that the letter level is the primary locus of the N effect under lexical decision, and that the hemispheric specificity of the N effect does not reflect differential processing at the lexical level.     

Changes in same-different laterality patterns as a function of practice and stimulus quality

Accuracy and reaction time (RT) of judgments about sameness vs. difference of (a) names of two letters and (b) shapes of two nonverbal forms were examined for stimuli presented to the center, left (LVF), and right (RVF) visual fields. For same-name letter pairs during Experiment I, responses were more accurate and faster for LVF than for RVF trials on an initial 90-trial block, but this difference was reversed by a third 90-trial block. The RVF advantage for RT was maintained over Trial Blocks 4 and 5, given during a second session, but had disappeared on Trial Blocks 6 through 9 as RT reached the same asymptotic level for both visual fields. No LVF-RVF differences were obtained at any level of practice for different-name letter pairs or for any of the form pairs. Experiment II replicated the shift from LVF toward RVF advantage that occurred over the first three trial blocks of Experiment I and demonstrated that such a shift does not occur when the letters are perceptually degraded. The results were discussed in terms of differences in cerebral hemisphere specialization for visuospatial vs. abstract stages of letter processing and changes with practice in the relative difficulty of these stages.     

Laterality effects in identification of caricatures and photographs of famous faces

Recent evidence suggests that memory representations of familiar faces may exaggerate distinctive information as do caricatures (G. Rhodes, S. Brennan, & S. Carey, Cognitive Psychology, 1987). Therefore caricatures should be effective representations of faces and should yield a right hemisphere processing advantage, as do photographs of faces. Photographs and caricatures of famous faces were presented to the left visual (LVF), the right visual field (RVF), and centrally (CVF), in a name-face verification task. There was a LVF (right hemisphere) advantage for both caricatures and photographs on name-face mismatches but no VF difference for matches. These results were true for both accuracy and reaction time. Processing strategy differences that may account for the difference between matches and mismatches are discussed. Performance was generally better for photographs than for caricatures, irrespective of visual field condition.     

Divided Visual Attention and Left Hemisphere Activation Among Psychopathic and Nonpsychopathic Offenders

Recent divided attention studies suggest the impulsive antisocial behavior of psychopaths may be related to deficient processing of information under conditions that place substantial demands on left-hemisphere-specific processing resources (left hemisphere activation (LHA) hypothesis; D. S. Kosson [1996, 1998]). To examine performance under conditions constraining eye movements and covert shifts of attention, 26 psychopathic and 46 nonpsychopathic inmates completed a divided attention task in which lateralized stimuli appeared briefly and simultaneously in the left visual field (LVF) and right visual field (RVF) of a monitor. Targets were either presented primarily in the RVF to induce LHA or were equiprobable in LVF and RVF to promote equal activation (EA) of left and right hemisphere resources. Psychopaths were less accurate than nonpsychopaths only under LHA conditions; within-group comparisons also revealed a substantial decrement from EA to LHA only in psychopaths. Thus, psychopaths’ performance deficits were specific to conditions priming left hemisphere resources asymmetrically.     

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.     

Hemispheric asymmetry and pun comprehension: when cowboys have sore calves

Event-related potentials (ERPs) were recorded as healthy participants listened to puns such as "During branding, cowboys have sore calves." To assess hemispheric differences in pun comprehension, visually presented probes that were either highly related (COW), moderately related (LEG), or unrelated, were presented in either the left or right visual half field (LVF/RVF). The sensitivity of each hemisphere to the different meanings evoked by the pun was assessed by ERP relatedness effects with presentation to the LVF and the RVF. In Experiment 1, the inter-stimulus interval between the pun and the onset of the visual probe was 0 ms; in Experiment 2, this value was 500 ms. In Experiment 1, both highly and moderately related probes elicited similar priming effects with RVF presentation. Relative to their unrelated counterparts, related probes elicited less negative ERPs in the N400 interval (300-600 ms post-onset), and more positive ERPs 600-900 ms post-onset, suggesting both meanings of the pun were equally active in the left hemisphere. LVF presentation yielded similar priming effects (less negative N400 and a larger positivity thereafter) for the highly related probes, but no effects for moderately related probes. In Experiment 2, similar N400 priming effects were observed for highly and moderately related probes presented to both visual fields. Compared to unrelated probes 600-900 ms post-onset, related probes elicited a centro-parietal positivity with RVF presentation, but a fronto-polar positivity with LVF presentation. Results suggest that initially, the different meanings evoked by a pun are both active in the left hemisphere, but only the most highly related meaning is active in the right hemisphere. By 500 ms, both meanings are active in both hemispheres.     

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.     

The brain's hemispheres and controlled search of the lexicon: evidence from fixated words and pseudowords

Difference between the brain's hemispheres in efficiency of intentional search of the mental lexicon with phonological, orthographic, and semantic strategies was investigated. Letter strings for lexical decision were presented at fixation, with a lateralized distractor to the LVF or RVF. Word results revealed that both hemispheres were capable of using each of the three strategies, but the right hemisphere had better baseline processing of orthography and was better at processing semantics. Pseudoword results supported the right hemisphere advantage for orthography and showed a left hemisphere advantage for phonology and assessment of possible semantic relationships. Taken together, the data support the idea that the right hemisphere uses orthography to make efficient decisions about novelty of an item, while the left engages in grapheme-to-phoneme conversion to test hypotheses about unfamiliar items. The convergence of data with previous research reveals that the procedure, as well as analyses of pseudowords, inform laterality research.     

Hemispheric Differences for Visual Matrix Processing: Stimulus Size and Spatial Frequency Effects

Hemispheric processing differences were assessed by presenting square matrices that varied in size and the number of filled-in cells. Subjects judged whether the matrix contained an even or odd number of filled cells. Experiment 1 employed relatively small matrix sizes (2 x 2, 3 x 3, and 4 x 4), and Experiment 2 employed relatively large matrix sizes (4 x 4, 6 x 6, and 8 x 8). Response time was shorter and error rates lower for left visual field/right hemisphere (LVF/RH) presentations compared to right visual field/left hemisphere (RVF/LH) presentations, with the larger matrices demonstrating the strongest visual field/hemispheric effects. Increases in the number of filled cells contributed to increases for the LVF/RH response time advantage only for the larger arrays. Analysis of the data from both studies collapsed across the number of filled cells produced highly consistent LVF/RH advantages for both response time and error rate, with stronger LVF/RH advantages found for the larger matrix sizes of both studies. The findings suggest that visual stimulus spatial frequency is a key determinant of hemispheric processing advantages, but that this factor is constrained by stimulus size variation. Theoretical implications with respect to the hemispheric processing double filtering by frequency model are discussed.