Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Observers identified consonant-vowel-consonant (CVC) nonsense syllables with the letters arranged horizontally. In each of 2 experiments, there were fewer errors when stimuli were presented to the right visual field (RVF) and left hemisphere (LH) than when stimuli were presented to the left visual field (LVF) and right hemisphere (RH), and the extent to which the number of last-letter errors exceeded the number of first-letter errors was greater on LVF/RH than on RVF/LH trials. When the same stimulus was presented simultaneously to both visual fields (Experiment 2), the qualitative error pattern was very similar to the pattern obtained on LVF/RH trials. These effects replicate results obtained in earlier CVC identification experiments with letters arranged vertically. However. when a single stimulus was presented in the center of the visual field (Experiment 1), so that the first letter of the CVC projected to the LVF/RH and the last letter projected to the RVF/LH, the error pattern was a mixture of the LVF/RH and RVF/LH patterns, as if each hemisphere took the lead for processing the letter it received directly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interhemispheric cooperation: Left is left and right is right, but sometimes the twain shall meet.

Interhemispheric cooperation in the processing of nonsense syllables projected simultaneously to both hemispheres was investigated in 2 experiments. Stimuli were projected unilaterally in the left and right visual fields (LVF, RVF) and bilaterally (the same syllable in both fields, BVF; Exp 1, 64 right-handed Ss) or centrally (CVF; Exp 2, 32 right-handed Ss). Accuracy and error patterns differed for the LVF and RVF. Error patterns were intermediate for the BVF–CVF and were partly shifted toward the RVF for Ss with large RVF advantages and toward the LVF for those with small asymmetries. Regression analyses showed that variance in BVF–CVF error patterns was jointly predicted by LVF and RVF variances. Both hemispheres, as demonstrated by means and regression analyses, contribute to the processing of bihemispherically presented syllables. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bihemispheric processing of redundant bilateral lexical information

Cerebral asymmetries in lexical ambiguity resolution were studied. In 2 experiments, targets related to the dominant and subordinate meanings of ambiguous word primes were presented for lexical decision after a 750-ms stimulus onset asynchrony. Experiment 1 compared presentation of target words to the left visual field/right-hemisphere (LVF/RH), to the right visual field/left-hemisphere (RVF/LH), or after redundant bilateral visual field (BVF) presentation. Experiment 2 examined unilateral priming in the absence of a BVF condition. On unilateral trials, priming was observed for dominant meanings in both the LVF/RH and RVF/LH, whereas subordinate priming was obtained only in the RVF/LH. These results suggest a possible role of hemispheric interaction in the availability of ambiguous word meanings. BVF performance evidenced a bilateral redundancy gain and priming that resembled that obtained on RVF/LH trials. Additional BVF analyses were not consistent with a strict race model interpretation and appear to implicate hemispheric cooperation in the bihemisperic processing of lexical information.     

Psychopathy and laterality of cerebral function.

Used a tachistoscopic recognition task to test the hypothesis that psychopathy is associated with dysfunction of the dominant hemisphere. 55 prison inmates were divided into groups with high, medium, and low ratings of psychopathy. Ss were required to identify 3-letter words presented in a vertical arrangement either in the left visual half field (LVF) or the right visual half field (RVF) 1.5° from a central fixation point. Each of 24 words was presented twice, once in each visual half field, at an exposure time of 80 msec. The exposure time was then shortened to 40 msec, and a 2nd set of 24 words was presented twice, once in each visual half field. In general, words presented in the RVF were more readily identified than those presented in the LVF. There was no evidence that psychopathy was associated with any deficit in RVF performance even when handedness and writing position were taken into account. Further, based on responses to a laterality questionnaire, there were no group differences in "left-sidedness." Results do not support the hypothesis of dominant hemisphere dysfunction in psychopathy. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical priming in the cerebral hemispheres: automatic in the left hemisphere, postlexical in the right hemisphere?

Automatic and postlexical semantic processing in the cerebral hemispheres was studied by presenting categorically related but nonassociated word pairs (e.g., TABLE-BED) to the left visual field (LVF) or to the right visual field (RVF) in semantic priming experiments. Experiment 1 examined automatic priming across stimulus onset asynchronies (SOAs) of 165 and 750 ms with a low proportion of related pairs and a low nonword ratio, employing a GO-NOGO lexical decision task. In contrast to an earlier view that a larger range of meanings is automatically activated in the right than in the left hemisphere, priming was observed in the RVF/left hemisphere only. SOA did not exert any effects. In Experiment 2, postlexical semantic matching of the prime and the target was encouraged by requiring subjects to respond to both of them at the same time. Now there was priming in the LVF, suggesting that a postlexical matching process works in the right hemisphere. The earlier studies showing a right hemisphere advantage in categorical priming are reinterpreted according to the postlexical right hemisphere hypothesis.     

Word repetition within- and across-visual fields: an event-related potential study

A divided visual field (DVF) procedure was used to investigate the scalp distribution of the event-related potential (ERP) repetition effect. ERPs were recorded from 27 scalp sites whilst subjects (n = 20) discriminated between words and non-words presented to either the left (LVF) or the right (RVF) visual field. A proportion of the words were repeated on the trial immediately following their first presentation. In two within-field repetition conditions the two encounters with a word occurred in the same visual field (LVF or RVF). In two across-field repetition conditions, the two encounters with a word occurred in different visual fields. For both words and non-words, task performance was better for RVF presentations than for LVF presentations. In each repetition condition there was a positive-going shift in the ERP elicited by repeated words compared to that elicited by words on their first presentation. This ERP repetition effect was equivalent in magnitude and lateralised to the right hemisphere to an equivalent degree in all four repetition conditions. It is suggested that the ERP effects largely reflect the processing of visual form thought to occur predominately in the right hemisphere.     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of nicotine and depressive traits on affective priming of lateralized emotional word identification.

Based on evidence suggesting that depressive traits, emotional information processing, and the effects of nicotine may be mediated by lateralized brain mechanisms, analyses assessed the influence of depressive traits and nicotine patch on emotional priming of lateralized emotional word identification in 61 habitual smokers. Consistent with hypotheses, nicotine as compared to placebo patch enhanced right visual field (RVF) emotional word identification while decreasing performance of emotional word identification in the left visual field (LVF). Nicotine also enhanced positive affect and decreased negative affect. Consistent with the Heller model of depression, scoring high in depressive traits was associated with a general decrease in LVF emotional word identification. Additionally, this general LVF deficit was especially pronounced for positive word identification in individuals scoring high in trait depression. Positive primes facilitated positive target identification in the RVF and negative primes facilitated negative target identification in the LVF. Thus, nicotine promoted a LVF word-identification deficit similar to that observed in those with depressive traits. However, nicotine also enhanced RVF processing and reduced negative affect, whereas it enhanced positive affect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mirror-image matching and mental rotation problem solving by baboons (Papio papio): Unilateral input enhances performance.

Three experiments, using a matching-to-sample procedure, were conducted to examine hemispheric specialization in mirror-image discrimination and mental rotation in baboons. In Exp 1, no significant difference was found in discrimination of mirror-image and asymmetric pattern stimuli. In Exp 2, orientation was assessed within the left (LVF) and right (RVF) visual half-fields. An RVF advantage was found in accuracy for asymmetric patterns, whereas an LVF advantage was found for discrimination of mirror-image stimuli. No significant relation was found between angular disparity of the stimuli and response time. Exp 3 examined the effect of bilateral visual input on accuracy and response time. Significantly lower accuracy and longer response times were found for bilateral compared with unilateral visual input. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of clustering solutions for cognitive heterogeneity in schizophrenia

This study investigated semantic priming for literal (stinging-mosquito) and metaphoric (stinging-insult) associates presented to either the left or right visual fields (RVF/LVF) across stimulus-onset-asynchronies (SOA) of 200 and 800 ms. For the short SOA condition, facilitation was found for metaphorically related targets in both visual fields (VFs) while literally related targets were facilitated only in the RVF. For the long SOA condition, metaphorically related targets were facilitated in the LVF whereas literally related targets were facilitated in the RVF. These results support previous findings indicating an enhanced role of the RH in metaphoric comprehension. In addition, the present results are in accordance with current models of hemispheric semantic processing.     

Dexamethasone induces chondrogenesis in organoid culture of cell mixtures from mouse embryos

Previous studies have shown that verbal processing in both normal individuals and a split-brain patient can be strongly affected by the semantic category of an unattended word presented to the left visual field (LVF). The effect was interpreted in terms of inhibition, since responses were slower when the unattended LVF word belonged to the same category as the target word. The present experiment discriminated between two alternative explanations for this finding. Subjects were presented with two letter strings, one in central vision and one to the left or right of centre. Subjects made a speeded lexical decision to the central string, and were instructed to ignore the lateral string. When a word was presented to the LVF subjects responded more slowly when it was semantically related to the central word. When an unattended word was presented to the RVF, its semantic relationship to the central word had no effect on decision latency. This finding is discussed in relation to views of performance laterality and selective attention.     

Lateralized word recognition: Assessing the role of hemispheric specialization, modes of lexical access, and perceptual asymmetry.

The processing advantage for words in the right visual field (RVF) has often been assigned to parallel orthographic analysis by the left hemisphere and sequential by the right. The authors investigated this notion using the Reicher-Wheeler task to suppress influences of guesswork and an eye-tracker to ensure central fixation. RVF advantages obtained for all serial positions and identical U-shaped serial-position curves obtained for both visual fields (Experiments 1–4). These findings were not influenced by lexical constraint (Experiment 2) and were obtained with masked and nonmasked displays (Experiment 3). Moreover, words and nonwords produced similar serial-position effects in each field, but only RVF stimuli produced a word-nonword effect (Experiment 4). These findings support the notion that left-hemisphere function underlies the RVF advantage but not the notion that each hemisphere uses a different mode of orthographic analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 (RT) paradigm. Ss 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 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 2 semantic categories: food and tools. A 3rd set of warning stimuli were familiar geometric symbols. Dependent measures included RT and the number of false-positive responses. RT 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 Ss 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple modes of right-hemisphere information processing: Age and sex differences in facial recognition.

Examined hemispheric differences in processing tachistoscopically presented faces in 8-, 11-, and 13-yr-old children of above-average intelligence. Ss viewed 4 female faces and were then asked to point to the face presented on each trial. The finding of a bimodal distribution of error scores among those Ss who showed a left visual-field (LVF) advantage supports the view that there are 2 types of information processing associated with the right hemisphere. The error scores of the younger Ss with an LVF advantage were unimodal and those of the 13-yr-olds bimodal. This bimodality characterized only the older girls. Since the unimodal error scores for the younger Ss were at a relatively high level, the data were interpreted as indicating that younger children and males at all ages use a diffuse right-hemisphere processing strategy in recognizing faces, whereas some older females use a more integrated right-hemisphere strategy. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric priming in a reading task

Some theories of reading and of reading disorders assume that the right hemisphere plays an important role in reading. However, despite the evidence supporting the competence of the right hemisphere in recognizing isolate words, there is little direct evidence to support the claim that the right hemisphere is involved in the continuous reading of connected text. This study used a stationary window technique to present text passages in a continuous reading task. At intervals during the reading of the text, a lexical decision was required to a target projected to the left or right side of the visual field. On some trials, the target was primed by a semantic associate which appeared in the passage immediately prior to the presentation of the target. It was found that these associative primes facilitated responses to LVF and RVF targets to an equal degree. It was also found, in agreement with previous investigations, that overall RTs to LVF targets were longer than RTs to RVF targets. It is suggested that these results indicate that the right hemisphere is actively involved in the comprehension of text in normal reading. However, the right hemisphere may not acquire text information directly, but may instead receive most of its information following initial analysis and decoding by the left.     

Perceptual Interactions Between Bilaterally Presented Words: What You Get Is Often Not What You See.

Bilateral presentations of words, 1 in the left visual hemifield (LVF) and 1 in the right (RVF), are used widely in studies of hemispheric asymmetry. However, although words shown centrally (i.e., nonlaterally) produce perceptual interactions in which 1 word alters the perceived identity of the other, perceptual interactions between bilaterally presented words have never been reported. To investigate this issue, the authors used brief, bilateral displays of words (e.g., romp-ramp) presented simultaneously. An eye tracker and forced-choice task ensured appropriate presentation and testing. Report accuracy was greatest for RVF words. However, this was accompanied by perceptual interactions that occurred almost exclusively in responses to LVF words, indicating that RVF words often altered the perceived identity of LVF words but not vice versa. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric contributions to the integration of visual and auditory information in speech perception

Differential hemispheric contributions to the perceptual phenomenon known as the McGurk effect were examined in normal subjects, 1 callosotomy patient, and 4 patients with intractable epilepsy. Twenty-five right-handed subjects were more likely to demonstrate an influence of a mouthed word on identification of a dubbed acoustic word when the speaker's face was lateralized to the LVF as compared with the RVF. In contrast, display of printed response alternatives in the RVF elicited a greater percentage of McGurk responses than display in the LVF. Visual field differences were absent in a group of 15 left-handed subjects. These results suggest that in right-handers, the two hemispheres may make distinct contributions to the McGurk effect. The callosotomy patient demonstrated reliable McGurk effects, but at a lower rate than the normal subjects and the epileptic control subjects. These data support the view that both the right and left hemisphere can make significant contributions to the McGurk effect.     

Processing of global and local visual information and hemispheric specialization in humans (Homo sapiens) and baboons (Papio papio).

Global precedence was examined in 8 baboons and 14 humans using compound stimuli presented in the left visual hemifield (LVF) or the right visual hemifield (RVF). Humans showed a global advantage and global-to-local interference. Baboons showed a local advantage and no interference. For humans and baboons, a LVF advantage appeared for global matching and an insignificant RVF advantage appeared for local matching. The local advantage in baboons still emerged when the memory load of the task was removed and when the local elements were connected by lines or were adjacent. Moreover, global precedence in humans persisted with unfamiliar forms. Species differences suggest that global precedence is not a universal trait and that this effect in humans does not have a purely perceptual or sensory basis. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perceptual laterality and iconic recognition of visual materials by Korsakoff patients and normal adults.

Compared 9 male patients with Korsakoff's syndrome to 19 normal and 11 alcoholic control Ss on their threshold for recognition of words or patterns presented monocularly to the lateral visual fields. Ss were then tested on backward visual masking of the same (target) stimuli to determine the interstimulus interval (ISI) needed to escape the masking effect (critical ISI) in each lateral field. Threshold for recognition and critical ISI were elevated in Korsakoff Ss. For all Ss, the right visual field was superior to the left for word recognition but not for pattern recognition. The critical ISIs were shorter in the right visual field for both types of material, suggesting that the dominant hemisphere is more efficient in the early (iconic) stages of information processing. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laterality for visual-spatial processing in two language-trained chimpanzees (Pan troglodytes).

Most reviews of laterality in nonhuman primates indicate that hemispheric asymmetries, similar to those found in humans, are not evident. With the growing evidence for cognitive processes germane to language in apes, in addition to their phylogenetic similarity to humans, they appear to be useful candidates for studies of laterality. Laterality for visual-spatial processing in 2 language-trained chimpanzees was investigated with a visual half-field paradigm. Initially, Ss were taught to manipulate a joystick that controlled the movement of a cursor on a computer monitor to a central fixation point. Ss were then taught a visual discrimination based on the location of a short line contained within a geometric form. Testing consisted of systematic presentation rates of 15, 122, and 226 ms to the left and right visual fields. For half of the trials, Ss used their left hand to respond and used the right hand for the remaining trials. Accuracy and reaction time (RT) were the dependent measures. One S demonstrated significantly faster RTs to stimuli presented to the left visual field (LVF) regardless of which hand was used to respond. The other S demonstrated a significant LVF bias when using the left hand to respond. Results are discussed in the context of current theories on the evolution of laterality and its relation to linguistic functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)