Performance on a free-recall verbal dichotic listening task and cerebral dominance determined by the carotid amytal test

Epileptic patients whose speech dominance had been ascertained using the carotid amytal technique were given a verbal dichotic listening test. Patients with left hemisphere speech dominance, like normal controls, showed a REA. Patients with right hemisphere speech representation, as a group, tended not to show a bias toward either ear. Moreover, repeated administrations of the verbal dichotic listening test yielded similar results.     

Lateral response dynamics and hemispheric dominance for speech perception

In this study, we investigated the mechanism for the left cerebral hemisphere's dominance for speech perception. We utilized the crossover of auditory pathways in the central nervous system to present speech stimuli more directly to the left hemisphere (via the right ear) and right hemisphere (via the left ear). Using functional MRI, we found that estimated duration of neural response in the left auditory cortex increased as more speech information was directly received from the right ear. Conversely, response duration in the right auditory cortex was not modulated when more speech information was directly received from the left ear. These data suggest that selective temporal responding distinguishes the dominant from nondominant hemisphere of the human brain during speech perception.     

Visual half-field testing for defining cerebral hemisphere speech laterality

The purpose of this study was to investigate to what extent the noninvasive visual half-field (VHF) test can reliably determine cerebral speech dominance for the individual patient with partial epilepsy considered for surgical treatment. The present VHF test consisted of a list of 36 words presented correctly and mirrored in the lateral visual fields to 13 right-handed and 14 left-handed control subjects and to 14 right-handed and 2 left-handed patients with partial epilepsy. In the controls, it was found that all right-handed and 10 out of 14 left-handed control subjects showed a right VHF (i.e., left hemisphere) advantage. Three of the left-handed control subjects showed the opposite pattern, and one showed no visual field advantage. All of the right-handed patients showed a right VHF advantage, except one who showed no VHF advantage. The two left-handed patients had both a left VHF advantage. Intracarotid amytal speech testing documented left hemisphere speech dominance in all right-handed patients. Of the two left-handed patients, one had right-sided, the other bilateral speech representation. The results suggest that the present VHF test reliably predicts cerebral hemisphere speech in patients with epilepsy.     

EYE-SIGHTING PREFERENCE OF NORMAL AND HEMIPLEGIC CHILDREN AND ADULTS

Monocular eye-sighting preference was examined in 32 children with hemiplegia, 51 adult-onset hemiplegic patients and 57 normal children and adults. Eye preference was compared with ear preference on dichotic listening for 25 of the hemiplegic children. No independent association could be detected between eye preference and ear preference. In both the children and adults with hemiplegia the preferred eye tended to be on the same side as the damaged hemisphere. Among the adults, this tendency was more pronounced with more extensive lesions, as manifested by aphasia and/or hemianopia. These findings are interpreted as indicating that eye-sighting preference is unrelated to unitary hemispheric dominance, and that, unlike dominance for hearing and speech, it is not irreversible after a critical period of development. A simpler explanation than incomplete hemispheric dominance is offered for the weakly positive association between mixed laterality and cerebral dysfunction.     

Speech-independent production of communicative gestures: evidence from patients with complete callosal disconnection

Recent neuropsychological, psycholinguistic, and evolutionary theories on language and gesture associate communicative gesture production exclusively with left hemisphere language production. An argument for this approach is the finding that right-handers with left hemisphere language dominance prefer the right hand for communicative gestures. However, several studies have reported distinct patterns of hand preferences for different gesture types, such as deictics, batons, or physiographs, and this calls for an alternative hypothesis. We investigated hand preference and gesture types in spontaneous gesticulation during three semi-standardized interviews of three right-handed patients and one left-handed patient with complete callosal disconnection, all with left hemisphere dominance for praxis. Three of them, with left hemisphere language dominance, exhibited a reliable left-hand preference for spontaneous communicative gestures despite their left hand agraphia and apraxia. The fourth patient, with presumed bihemispheric language representation, revealed a consistent right-hand preference for gestures. All four patients displayed batons, tosses, and shrugs more often with the left hand/shoulder, but exhibited a right hand preference for pantomime gestures. We conclude that the hand preference for certain gesture types cannot be predicted by hemispheric dominance for language or by handedness. We found distinct hand preferences for specific gesture types. This suggests a conceptual specificity of the left and right hand gestures. We propose that left hand gestures are related to specialized right hemisphere functions, such as prosody or emotion, and that they are generated independently of left hemisphere language production. Our findings challenge the traditional neuropsychological and psycholinguistic view on communicative gesture production.     

A study on functional plasticity of the brain in childhood. II. Speech development and intelligence after the damage of cerebral hemisphere under 1 year of age]

To investigate the functional plasticity of the brain in childhood, the speech development, the intelligence test and dichotic listening test were performed on 27 patients who had suffered from hemiplegia under 1 year of age. Among 13 patients with right hemiplegia, 7 to 24 years old, 11 patients showed a left ear dominance suggesting the lateralization of language in the right hemisphere. All 14 patients with left hemiplegia, 5 to 37 years old, showed a right ear dominance suggesting the lateralization of language in the left hemisphere. All 27 patients acquired speech function enough to converse with other people during daily life. There were no differences in speech development or intelligence scores between both groups of hemiplegia. Although there was no correlation between the speech development and the age of onset of hemiplegia, there was a correlation between the speech development and the intelligence score in both groups of hemiplegia.     

Dichotic listening ear preference after childhood cerebral lesions

Patients with unilateral (right or left) nonprogressive cerebral lesions acquired in infancy (before age one) or childhood (ages one to fifteen) were given a dichotic listening test. The two groups of patients with the childhood lesions showed the pattern of ear preference typically seen after hemispheric lesions in adults; loss of right ear preference after left hemisphere (LH) lesions, and enhanced right ear preference after right hemisphere (RH) lesions. The two groups of patients with the very early lesions failed to show any consistent ear preference or to differ from one another in ear preference. It is postulated that this lack of a consistent lesion effect following very early lateralized brain lesions is due to the greater degree of functional reorganization that takes place after such lesions.     

A study of functional plasticity of the brain in childhood. I. Critical period dislodging lateralization of language in the brain]

To investigate the functional plasticity of the brain in childhood, the intelligence and language tests, brain CT and dichotic listening test were performed on 34 patients with hemiplegia. All 13 patients with left hemiplegia, 8 to 37 years old, showed a right ear dominance suggesting the lateralization of language in the left hemisphere. Among 21 patients with right hemiplegia, 7 to 22 years old, 16 patients who had suffered from the left hemispheric damage before 6 years and 1 month of age, showed the left ear dominance suggesting the lateralization of language in right hemisphere except 2 patients. On the contrary, 3 patients with right hemiplegia who had suffered from the left hemispheric damage after 6 years and 6 months of age showed a right ear dominance. It was concluded that the critical period for the dislodging of language lateralization in the brain from the damaged left hemisphere to the intact right hemisphere is the first half of 6 years after birth. Five patients out of 8 patients with right hemiplegia showed significantly lower scores in performance than in verbal WISC IQ. The compensation of language function rather than performance function was considered to be characteristic for the left-hemispheric damage in childhood.     

Left hemisphere dysfunction affects dichotic listening in patients with temporal lobe epilepsy

This study evaluated the relative effect of left hemisphere dysfunction and side of seizure onset on dichotic listening performance in patients with temporal lobe epilepsy and left hemisphere speech dominance. Seventeen patients were divided into groups based on side of seizure onset and based on scores on a composite measure revealing left hemisphere dysfunction. The group with left hemisphere dysfunction had more correct responses from the left ear, and a left ear advantage, on dichotic listening. The group with normal left hemisphere function showed the expected right ear advantage. Side of seizure onset did not affect dichotic listening performance significantly.     

LEFT HEMISPHERE DYSFUNCTION AFFECTS DICHOTIC LISTENING IN PATIENTS WITH TEMPORAL LOBE EPILEPSY

This study evaluated the relative effect of left hemisphere dysfunction and side of seizure onset on dichotic listening performance in patients with temporal lobe epilepsy and left hemisphere speech dominance. Seventeen patients were divided into groups based on side of seizure onset and based on scores on a composite measure revealing left hemisphere dysfunction. The group with left hemisphere dysfunction had more correct responses from the left ear, and a left ear advantage, on dichotic listening. The group with normal left hemisphere function showed the expected right ear advantage. Side of seizure onset did not affect dichotic listening performance significantly.­­     

Looking at eye dominance from a different angle: Is sighting strength related to hand preference?

Sighting dominance (the behavioural preference for one eye over the other under monocular viewing conditions) has traditionally been thought of as a robust individual trait. However, Khan and Crawford (2001) have shown that, under certain viewing conditions, eye preference reverses as a function of horizontal gaze angle. Remarkably, the reversal of sighting from one eye to the other depends on which hand is used to reach out and grasp the target. Their procedure provides an ideal way to measure the strength of monocular preference for sighting, which may be related to other indicators of hemispheric specialisation for speech, language and motor function. Therefore, we hypothesised that individuals with consistent side preferences (e.g., right hand, right eye) should have more robust sighting dominance than those with crossed lateral preferences. To test this idea, we compared strength of eye dominance in individuals who are consistently right or left sided for hand and foot preference with those who are not. We also modified their procedure in order to minimise a potential image size confound, suggested by Banks et al. (2004) as an explanation of Khan and Crawford’s results. We found that the sighting dominance switch occurred at similar eccentricities when we controlled for effects of hand occlusion and target size differences. We also found that sighting dominance thresholds change predictably with the hand used. However, we found no evidence for relationships between strength of hand preference as assessed by questionnaire or by pegboard performance and strength of sighting dominance. Similarly, participants with consistent hand and foot preferences did not show stronger eye preference as assessed using the Khan and Crawford procedure. These data are discussed in terms of indirect relationships between sighting dominance, hand preference and cerebral specialisation for language and motor control.     

Mouth asymmetry during speech of epileptic patients who have undergone carotid amytal testing

Asymmetry in the opening of the two sides of the mouth during speech has been suggested as an observable correlate of lateralization of cerebral speech motor control. For 24 epileptic patients who suffered speech disturbance only during left hemisphere carotid amytal anesthetization, 22 showed the expected greater opening of the right side of the mouth during a repetition task. However, all four of the patients who suffered speech disturbance following only right hemisphere anesthetization, and 8 of the 11 "bilateral speech" patients, also showed greater opening of the right side of the mouth. The speech dominant patients may, however, have genetic left speech dominance but a pathology-forced shift of some components of language to the right hemisphere. Basic mouth asymmetry, as measured here, may primarily reflect lateralization of a component of the motor/speech/language control system that may not be shifted by pathology in epileptic patients sustaining early brain insult. Relative change in mouth asymmetry as the speech task becomes more demanding may, however, be a more sensitive indicator or cerebral asymmetries for language in pathological cases.     

Atypical hemispheric language dominance in left temporal lobe epilepsy as a result of the reorganization of language functions

Hemispheric language dominance, as determined by intracarotid short-acting barbiturate injections (Wada testing), was retrospectively evaluated in 44 right-handed patients with medically intractable left (n=26) or right (n=18) temporal lobe epilepsy (TLE). Atypical hemispheric language dominance (right or bilateral) was revealed in 13.6% of all patients investigated. A significantly higher rate of deviance from complete left hemisphere dominance was observed in left TLE (23.1%) than in right TLE (0%). Patient age at the time of seizure onset was proven a critical variable affecting atypical speech development in left TLE. The mean patient age at the time of seizure onset in left TLE patients with atypical language representation was 5.61 years, but was 13.13 years in patients with left hemisphere language dominance. Our results strongly support the influential impact of epileptiform activity spreading from the left temporal lobe structures on the reorganization of language functions in patients with early brain injury.     

Cerebral Organization in a Right-handed Trilingual Patient with Right-hemisphere Speech: a Positron Emission Tomography Study

Using the method of positron emission tomography, combined with word-generation tasks, we had the opportunity to examine the cerebral representation of multiple languages in the brain in a right-handed patient, RA, with known right-hemisphere speech representation as determined by intracarotid sodium amobarbital testing. Similar patterns of cerebral blood flow were observed across all three languages (French, Spanish and English), when synonym generation was compared with a silent resting baseline. In particular, several regions in the right inferior frontal cortex were activated. These foci are in locations corresponding to those observed in the left hemisphere in normal right-handed volunteers with presumed left-hemisphere dominance, and in patients known to be left-hemisphere dominant for speech. The lack of anatomical separation of the three languages within the same individual, who acquired two languages early and one language later in life, suggests that at least at this single-word level of analysis, age of acquisition was not a significant factor in the determining of functional organization in the brain.     

Cerebral organization in a right-handed trilingual patient with right-hemisphere speech: a positron emission tomography study

Using the method of positron emission tomography, combined with word-generation tasks, we had the opportunity to examine the cerebral representation of multiple languages in the brain in a right-handed patient, RA, with known right-hemisphere speech representation as determined by intracarotid sodium amobarbital testing. Similar patterns of cerebral blood flow were observed across all three languages (French, Spanish and English), when synonym generation was compared with a silent resting baseline. In particular, several regions in the right inferior frontal cortex were activated. These foci are in locations corresponding to those observed in the left hemisphere in normal right-handed volunteers with presumed left-hemisphere dominance, and in patients known to be left-hemisphere dominant for speech. The lack of anatomical separation of the three languages within the same individual, who acquired two languages early and one language later in life, suggests that at least at this single-word level of analysis, age of acquisition was not a significant factor in the determining of functional organization in the brain.     

Right-hemisphere language dominance in right-handed epileptic patients

Hemispheric language dominance, as determined by intracarotid amobarbital sodium injections, and handedness, as reflected by writing and drawing preference, were evaluated in a select group of patients with intractable seizures who had documented focal epilepsy originating from one temporal lobe. Of the patients with left temporal lobe seizure focus, an unusually high percentage of right-handed patients (4/26 [15%]) had right hemisphere language dominance. Pathologic findings of the resected temporal lobe in these patients revealed microscopic damage (hippocampal sclerosis) of the hippocampus in three of three cases; one patient also had a small hamartoma in the midtemporal gyrus. We hypothesize that crossed dominance resulted from disruption by epileptiform activity during early development of selective areas of the left hemisphere.     

Language laterality assessed by unilateral ECT and dichotic monitoring

A dichotic monitoring test for the lateralisation of speech dominance was compared with testing for dysphasia after unilateral electroconvulsive therapy to each side of the head in 31 patients, and the intracarotid amylobarbitone test in four epileptic patients. Twenty-eight patients shown to be left speech dominant also showed right ear advantages in the dichotic test. Four of the five right speech dominant patients showed left ear advantages. Two patients with bilateral speech representation showed nonsignificant ear asymmetries. The noninvasive dichotic monitoring task is quick and simple and produces large mean ear advantages (14 to 25%) in normal subjects as well as patients.     

Auditory perception in early lateralized brain damage

In a study of hemispheric dominance for the perception of speech the performance of 28 young children with congenital or infantile hemiplegia was compared with that of their normal peers and recently brain damage nonaphasic adults. Our results confirm Goodglass's findings that in children with early left hemisphere damage the transfer of dominance for speech processing is completed in childhood, and they show that this process of hemispheric transfer can be completed by 3 years of age. Comparison with results on adults with CVA provides additional evidence that in early lateralized brain cognitive functions normally dominant in one cerebral hemisphere are developed in the alternative hemisphere in a way that apparently does not happen later in life.     

Symmetry detection in typically and atypically speech lateralized individuals: A visual half-field study

Visuospatial functions are typically lateralized to the right cerebral hemisphere, giving rise to a left visual field advantage in visual half-field tasks. In a first study we investigated whether this is also true for symmetry detection off fixation. Twenty right-handed participants with left hemisphere speech dominance took part in a visual half-field experiment requiring them to judge the symmetry of 2-dimensional figures made by joining rectangles in symmetrical or asymmetrical ways. As expected, a significant left visual field advantage was observed for the symmetrical figures. In a second study, we replicated the study with 37 left-handed participants and left hemisphere speech dominance. We again found a left visual field advantage. Finally, in a third study, we included 17 participants with known right hemisphere dominance for speech (speech dominance had been identified with fMRI in an earlier study; Van der Haegen, Cai, Seurinck, & Brysbaert, 2011). Around half of these individuals showed a reversed pattern, i.e. a right visual half-field advantage for symmetric figures while the other half replicated the left visual-field advantage. These findings suggest that symmetry detection is indeed a cognitive function lateralized to the right hemisphere for the majority of the population. The data of the participants with atypical speech dominance are more in line with the idea that language and visuospatial functions are lateralized in opposite brain hemispheres than with the idea that different functions lateralize independently, although there seems to be more variability in this group.     

Speech lateralization and attention/executive functions in a Finnish family with specific language impairment (SLI)

Hemisphere lateralization for speech perception was investigated in a Finnish family with specific language impairment. We used dichotic presentations of consonant-vowel (CV) syllables, consisting of the six stop-consonants paired with the vowel /a/, under three different attentional instructions. The dichotic listening technique means that two different speech stimuli are presented simultaneously, one in each ear. Left hemisphere dominance for speech perception is assessed from a preference for the right ear stimulus. Response accuracy was compared in five members, over three generations, of a family with SLI with 5 healthy control subjects. The dichotic listening task was performed under three different instructions, to attend only to the right ear stimulus, to attend only to the left ear stimulus, or with no instruction about attention. The subjects indicated orally which of the six CV-syllables they heard on each trial. There were 36 dichotic presentations of the CV-syllables for each instruction. The CV-syllables were played from a CD with digitized stimuli. The results showed no difference between the groups during the no instruction condition, indicating normal speech lateralization in the SLI group. However, the SLI group was deficient in modifying the ear advantage through focused attention to the left ear, thus indicating an attentional/executive deficit in addition to a deficit in left hemisphere lateralization. It is concluded that individuals with specific language impairment may have a cognitive deficit related to attention in addition to a language processing deficit related to left hemisphere function.