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.     

Progressive dysfluency associated with right hemisphere disease

A late onset progressive dysfluency following a right hemisphere stroke occurred in a 62-year-old male. Dysfluency was characterized by pronounced word and phrase reiterations, and sound and syllable reiterations to a lesser degree. Spontaneous speech was significantly more dysfluent than oral reading and repetition. Recitation and singing were minimally dysfluent. Reiterations were accompanied by reduced vocal loudness and increased rate of speech. Reiterations occurred in initial, medial, and final sentence position. Secondary symptoms such as facial grimacing were absent. In contrast to acquired cortical stuttering which is characterized by a preponderance of sound and syllable sentence initial repetitions, dysfluency was more closely characteristic of palilalia. The dysfluency occurred as a symptom of a diffuse nonspecific subcortical projection system defect related to massive infarction in the right middle cerebral artery distribution with associated atrophy.     

Probability matching in the right hemisphere

Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.     

Hemihypokinesia after right hemisphere stroke

We tested the hypothesis that the right hemisphere is dominant for motor activation of "intention." If the right hemisphere is dominant for intention and if intention is a prerequisite for movement, motor impairment should be worse after an infarct in the right hemisphere than in the left. We asked nine subjects with right and nine with left hemisphere infarcts to elevate each shoulder independently. Subjects with right hemisphere lesions had more trouble moving the contralateral shoulder. The data are consistent with the hypothesis that the right hemisphere is dominant for motor activation or intention.     

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

Speech production is inextricably linked to speech perception, yet they are usually investigated in isolation. In this study, we employed a verbal-repetition task to identify the neural substrates of speech processing with two ends active simultaneously using functional MRI. Subjects verbally repeated auditory stimuli containing an ambiguous vowel sound that could be perceived as either a word or a pseudoword depending on the interpretation of the vowel. We found verbal repetition commonly activated the audition-articulation interface bilaterally at Sylvian fissures and superior temporal sulci. Contrasting word-versus-pseudoword trials revealed neural activities unique to word repetition in the left posterior middle temporal areas and activities unique to pseudoword repetition in the left inferior frontal gyrus. These findings imply that the tasks are carried out using different speech codes: an articulation-based code of pseudowords and an acoustic-phonetic code of words. It also supports the dual-stream model and imitative learning of vocabulary.     

Personal relevance and the human right hemisphere.

Brain damage can selectively disrupt or distort information and ability across the range of human behaviors. One domain that has not been considered as an independent attribute consists of acquisition and maintenance of personal relevant entities such as "familiar" faces, persons, voices, names, linguistic expressions, handwriting, topography, and so on. In experimental studies of normal mentation, personal relevance is revealed in studies of emotion, arousal, affect, preference and familiarity judgments, and memory. Following focal brain damage, deficits and distortions in the experience of personal relevance, as well as in recognizing formerly personally relevant phenomena, are well known to occur. A review and interpretation of these data lead to a proposal that the right hemisphere has a special role in establishing, maintaining, and processing personally relevant aspects of the individual's world.     

Flexible contrast gain control in the right hemisphere

This study investigates whether the right hemisphere has more flexible contrast gain control settings for the identification of spatial frequency. Right-handed participants identified 1 and 9 cycles per degree sinusoidal gratings presented either to the left visual field-right hemisphere (LVF-RH) or the right visual field-left hemisphere (RVF-LH). When luminance contrast was randomized across a wide range (20-60%), performance gradually improved with contrast in the LVF-RH. Conversely, performance in the RVF-LH was disrupted and saturated for 20 and 60% of contrast, respectively, leading to a LVF-RH advantage for these contrast levels. When contrast was blocked or randomized for a smaller range (30-50%), the LVF-RH advantage was diminished. Flexible contrast gain control is needed when contrast is randomized across a wide range, but not when it is blocked or randomized across a smaller range. The results therefore suggest that the right hemisphere is able to process spatial frequency information across a wider range of contrast levels than is the left hemisphere.     

Aha! Insight experience correlates with solution activation in the right hemisphere

In one experiment, we tested for an association between semantic activation in the right hemisphere (RH) and left hemisphere (LH) and the Aha! experience when people recognize solutions to insight-like problems. The compound remote associate problems used in this experiment sometimes evoke an Aha! experience and sometimes do not. On each trial, participants (N = 44) attempted to solve these problems and, after 7 sec, named a target word, made a solution decision, and rated their insight experience of recognizing the solution. As in prior studies, the participants demonstrated more solution priming for solutions presented to the left visual field-RH (lvf-RH) than for solutions presented to the right visual field-LH (rvf-LH). As was predicted, following unsolved problems the participants showed greater priming for solutions that they rated as evoking an insight experience on the subsequent solution decision than for solutions that did not evoke an insight experience. This association was stronger for solutions presented to the lvf-RH than for those presented to the rvf-LH. These results tie the subjective experience of insight to an objective measure-semantic priming-and suggest that people have an Aha! experience in part because they already had semantic activation that could lead them to recognize the solution quickly. We believe semantic activation in both hemispheres cooperatively contributes to problem solving, but weak solution activation that contributes to the Aha! experience is more likely to occur in the RH than in the LH.     

Spatial probability cuing and right hemisphere damage

In this experiment we studied statistical learning, inter-trial priming, and visual attention. We assessed healthy controls and right brain damaged (RBD) patients with and without neglect, on a simple visual discrimination task designed to measure priming effects and probability learning. All participants showed a preserved priming effect for item color. Contrary to healthy controls and RBD participants without neglect, RBD participants with neglect did not show positional priming and both RBD groups learned the underlying spatial probability distribution of target locations to a lesser degree. To see if the latter deficiency could be improved, we tested a patient with long standing chronic spatial neglect on three separate days and observed improved identification times for left sided, high probability, targets. In summary, we found preservation of priming per se in people with spatial neglect. However, this was only clearly demonstrable for color priming and not for positional priming. Associated with this impairment was a difficulty in learning the overall statistical structure of target locations. In a patient with severe persistent neglect we were able to demonstrate that the deficit in statistical learning was not absolute, as this subject improved his identification times for targets appearing in high probability regions of the test display.     

Neuropsychological syndromes in right hemisphere stroke patients

A specific set of syndromes, based on different intrahemispheric lesion locations, has not yet been described in patients with right hemisphere lesions. To explore whether statistically derived clusters could give clues to a syndrome structure, neuropsychological data from a sample of 106 patients with right hemisphere stroke were studied. CT data were available for 58 of the patients. Based on factor analysis of eight test and four ratings variables, six variables were chosen for a cluster analysis. A structure of 13 clusters was considered statistically valid. Combining clusters with parallel test profiles into main cluster classes, five right hemisphere syndromes proved clinically valid: an above average syndrome ( n =46), denial perseverance (frontal) syndrome ( n =14). a depressed mood syndrome ( n = 14), a focal RH syndrome ( n =18) and a global RH syndrome ( n =9). It is suggested that syndromes are related to intrahemispheric location of the lesion, such as the extent of anterior and posterior damage.     

Spontaneous humor among right hemisphere stroke survivors

We analyzed spontaneous conversational humor production and response among 11 right hemisphere-damaged (RHD) patients, 10 left hemisphere-damaged (LHD) patients, 7 normal controls (NC), and their spouses. RHD patients and their spouses reported a statistically significant decline in the patients' orientation to humor post-stroke. Also, we found a significant positive association between a RHD patient's ability to decode prosody and their self-reported orientation to humor post-stroke.     

Form-specific visual priming in the right cerebral hemisphere.

Results of 4 experiments indicate that both within-modality and case-specific visual priming for words are greater when test stimuli are presented initially to the right cerebral hemisphere (RH). In contrast, neither within-modality nor case-specific explicit memory for words is greater when stimuli are presented initially to the RH. Priming is measured using word-stem completion, and explicit memory is measured using word-stem cued recall. In both cases, Ss first rate how much they like words, and then word stems are presented briefly to the RH (in the left visual field) or to the left hemisphere (in the right visual field). Results suggest that at least 2 separate systems encode the visual representations that produce priming. The system that is more effective in the RH is better at representing form-specific information, whereas another system that is not more effective in the RH does not distinguish among distinct instances of word forms.     

Left hemisphere sensitivity to consonant sounds not displayed by the right hemisphere: electrophysiological correlates

Auditory evoked responses (AER) to a series of consonant-vowel syllables were recorded from frontal, temporal, and parietal scalp locations from 14 right-handed college students. Averaged AERs were submitted to principal components analysis and analysis of variance. Six components of the group's AERs were found to reflect various aspects of the stimulus parameters. One component reflected changes over only the left hemisphere to different consonants. A second component changed systematically over both hemispheres but did not discriminate between all consonants.     

Evidence for differentiation of right hemisphere visual-perceptual functions

Performance on tasks sensitive to right hemisphere dysfunction (facial discrimination and perceptual closure) are reported in eight patients with right hemisphere lesions. Patients demonstrated an apparent double dissociation of performance on the two measures. Site-by-task specificity for the closure task was strongly suggested. Implications for right hemisphere organization and underlying psychological processes are considered.     

The role of the right hemisphere in speech act comprehension

In this research the role of the RH in the comprehension of speech acts (or illocutionary force) was examined. Two split-screen experiments were conducted in which participants made lexical decisions for lateralized targets after reading a brief conversation remark. On one-half of the trials the target word named the speech act performed with the preceding conversation remark; on the remaining trials the target did not name the speech act that the remark performed. In both experiments, lexical decisions were facilitated for targets representing the speech act performed with the prior utterance, but only when the target was presented to the left visual field (and hence initially processed by the RH) and not when presented to the right visual field. This effect occurred at both short (Experiment 1: 250 ms) and long (Experiment 2: 1000 ms) delays. The results demonstrate the critical role played by the RH in conversation processing.     

Gender differences in empathy: the role of the right hemisphere

The relationship between activation of the right cerebral hemisphere (RH) and empathy was investigated. Twenty-two men and 73 women participated by completing a chimeric face task and empathy questionnaire. For the face task, participants were asked to pick which of the two chimeric faces looked happier. Both men and women were significantly more likely to say the chimera with the smile to their left was happier, suggesting activation of the RH. As expected, men scored significantly lower than women on the empathy questionnaire, p = .003. A correlation was found between RH activation on the face task and empathy for women only, p = .037, suggesting a possible neural basis for gender differences in empathy.