Visual half-field experiments are a good measure of cerebral language dominance if used properly: evidence from fMRI

Traditional neuropsychology employs visual half-field (VHF) experiments to assess cerebral language dominance. This approach is based on the assumption that left cerebral dominance for language leads to faster and more accurate recognition of words in the right visual half-field (RVF) than in the left visual half-field (LVF) during tachistoscopic presentation. Information in the RVF is directly projected to the left hemisphere, whereas information presented in the LVF needs interhemispheric transfer to reach the left half of the brain. This interpretation of the RVF superiority for word recognition lacks direct evidence however, and a multitude of studies have lead to contradictory findings. To investigate this matter further we try to establish the ideal parameters for VHF experiments to measure language dominance, and subsequently compare laterality indices (LIs) obtained from RT patterns in bilateral VHF tasks to those LIs acquired in the same individuals during a mental word generation task in the fMRI scanner. Our results reveal a direct link between VHF advantages and individual language lateralization. Differences in behavioral performance between left-hemisphere dominant and right-hemisphere dominant individuals suggest that carefully designed VHF tests can be used as a reliable predictor of cerebral language dominance.     

Cross-modal asymmetries in perception related to asymmetry in cerebral function

Cross-modal correlations between left-right asymmetry on the Dichotic Listening (D-L) test and a visual half-field ((VHF) test were obtained for 30 right-handed subjects with no family history of left-handedness, 30 right handed subjects with a positive family history of left-handedness and 30 left-handed subjects. Both groups of right-handed subjects demonstrated significant cross-modal correlations between the D-L (auditory) asymmetry and the VHF (visual) asymmetry. The left-handed subjects displayed no correlation between D-L and VHF asymmetries. This suggests a dissociation between auditory and visual laterality in left-handers. Differences between this finding and two previous studies which found no cross-modal asymmetry for right-or-left-handers are discussed. The visual half-field test utilized in this experiment controlled fixation by presenting digits sequentially at fixation, while simultaneously presenting other digits to either the right or left VHF. This procedure minimizes the effect of directional scanning on VHF asymmetry. The reliability of the D-L and VHF asymmetries was also computed. The D-L asymmetry proved to be highly reliable (r = 0.86), while the VHF asymmetry was somewhat less reliable (r = 0.46). The asymmetry on both tests was attributed to asymmetry of cerebral function.     

A right visual field advantage for tool-recognition in the visual half-field paradigm

Neuropsychological and brain imaging studies have shown that the identification and use of tools mainly involve areas of the left hemisphere. We investigate whether this dominance can be observed in a behavioral visual half-field (VHF) task as well. To make sure that the VHF-effect was due to laterality and not due to attentional bias, we made use of two tasks: tool recognition and object recognition. On the basis of the existing literature, we predicted a right visual field (RVF) advantage for tool recognition, but not for object recognition. Twenty right-handed participants made judgments about whether one of two bilaterally presented stimuli was an object/non-object or a tool/non-tool. No VHF/hemisphere advantage was found for object recognition, whereas a significant RVF/left hemisphere advantage was observed for tool recognition. These findings show that VHF-tasks can be used as a valid laterality measure of tool recognition.     

Further fMRI validation of the visual half field technique as an indicator of language laterality: a large-group analysis

The best established lateralized cerebral function is speech production, with the majority of the population having left hemisphere dominance. An important question is how to best assess the laterality of this function. Neuroimaging techniques such as functional Magnetic Resonance Imaging (fMRI) are increasingly used in clinical settings to replace the invasive Wada-test. We evaluated the usefulness of behavioral visual half field (VHF) tasks for screening a large sample of healthy left-handers. Laterality indices (LIs) calculated on the basis of the latencies in a word and picture naming VHF task were compared to the brain activity measured in a silent word generation task in fMRI (pars opercularis/BA44 and pars triangularis/BA45). Results confirmed the usefulness of the VHF-tasks as a screening device. None of the left-handed participants with clear right visual field (RVF) advantages in the picture and word naming task showed right hemisphere dominance in the scanner. In contrast, 16/20 participants with a left visual field (LVF) advantage in both word and picture naming turned out to have atypical right brain dominance. Results were less clear for participants who failed to show clear VHF asymmetries (below 20 ms RVF advantage and below 60 ms LVF advantage) or who had inconsistent asymmetries in picture and word naming. These results indicate that the behavioral tasks can mainly provide useful information about the direction of speech dominance when both VHF differences clearly point in the same direction.     

Visual half-field presentations of incongruent color words: effects of gender and handedness

Right-handed (dextral) and left-handed (sinistral) males and females (N = 15) were compared for language lateralization in a visual half-field (VHF) incongruent color-words paradigm. The paradigm consists of repeated brief (less than 200 msec) presentations of color-words written in an incongruent color. Presentations are either to the right or to the left of center fixation. The task of the subject is to report the color the word is written in on each trial, ignoring the color-word. Color-bars and congruent color-words were used as control stimuli. Vocal reaction time (VRT) and error frequency were used as dependent measures. The logic behind the paradigm is that incongruent color-words should lead to a greater cognitive conflict when presented in the half-field contralateral to the dominant hemisphere. The results showed significantly longer VRTs in the right half-field for the dextral subjects. Furthermore, significantly more errors were observed in the male dextral group when the incongruent stimuli were presented in the right half-field. There was a similar trend in the data for the sinistral males. No differences between half-fields were observed for the female groups. It is concluded that the present results strengthen previous findings from our laboratory (Hugdahl and Franzon, 1985) that the incongruent color-words paradigm is a useful non-invasive technique for the study of lateralization in the intact brain.     

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.     

Perceptual and memory components of the superior recall of letters from the right visual half-fields

Right-hander's show consistently better recall from the right visual half-field (VHF) when digit sequences are presented simultaneously at fixation and in one of the visual half-fields. This right VHF superiority has been attributed to the more direct connection between the right VHF and the speech areas in the left hemisphere of the brain.The effect of amount of material to be remembered, interstimulas interval, and presentation time was studied in order to assess the importance of short-term memory, backward masking, and perceptual factors on this task. Sequences of five letter pairs were presented at two different interstimulas intervals (165 msec and 330 msec) and three presentation times (165 msec, 280 msec and 330 msec). Increasing the amount of material to be remembered and increasing the interstimulas interval appeared to increase the asymmetry between the VHF's. Changing presentation time (from 330 msec to 165 msec) had little effect on either the VHF asymmetry or recall efficiency. This suggests that the controlled fixation paradigm is a memory and backward masking task with the right VHF superiority resulting primarily from the memory aspect of the task.     

Hemispheric Lateralization and Aesthetic Judgement

Pairs of slides depicting works of art were presented tachistoscopically to the left or right visual half-fields. Subjects performed an aesthetic judgement task, selecting the better work of art in each pair. Subjects with highly lateralized cerebral organization, as inferred by handedness or sex, performed significantly better in response to slides presented in one visual half-field (VHF) than in response to slides presented in the opposite VHF. Some of these subjects showed a left VHF superiority, while others showed a right RHF superiority. Subjects who were less lateralized showed no significant tendency to perform better in response to slides presented in one VHF or the other. The results are interpreted as an indication that subjects will perform a given task in a lateralized or a non-lateralized manner as a function of the interaction between individual differences in cerebral organization and the cognitive processes used to perform the task.     

Visual half-field presentations of incongruent color-words reveal mirror-reversal of language lateralization in dextral and sinistral subjects

Two experiments are reported concerning identification of left and right hemisphere dominance for language in dextral and sinistral subjects. A visual half-field (VHF) incongruent color-words paradigm was used. Color-words written in incongruent colors were presented either to the right or left half-field. Subjects were instructed to report the color, ignoring the color-word. Vocal reaction time (VRT) and frequency of errors were measured. Twenty dextral adult males were tested in Experiment 1. Results showed significantly more errors and a trend towards longer VRT:s when the words were presented in the right half-field, i.e. initially to the left hemisphere. No differences between half-fields were observed to color-stripes serving as control-stimuli. The results were followed up in Experiment 2 with a preselected sinistral group. All subjects in the sinistral group had revealed a left-ear-advantage (LEA) in a previous dichotic listening test, i.e. right hemisphere language dominance. The results from the VHF inconguent color-words test showed a reverse pattern of responding compared to the dextral group, i.e. more errors and longer VRTs when the color-words were initially presented to the right hemisphere.     

Abnormal cerebral laterality in bipolar depression: convergence of behavioral and brain event-related potential findings.

Cerebral laterality in bipolar and unipolar major depression was compared using visual half-field and dichotic listening measures of perceptual asymmetry. The results replicate our prior finding of abnormal laterality in bipolar depressed patients on a visuospatial test. Bipolar patients (n = 11) failed to show the left visual field (right hemisphere) advantage for dot enumeration seen for both unipolar patients (n = 43) and normal controls (n = 24). Bipolar patients performed significantly poorer than unipolar patients on normal controls for left visual field, but not right visual field stimuli. An electrophysiological correlate of abnormal visual field asymmetry in bipolar depression was found in brain event-related potentials recorded during audiospatial and temporal discrimination tasks. Bipolar patients had smaller N100 amplitudes for test stimuli in the left than right hemifield, whereas unipolar patients and normals did not. The origins of left hemifield deficits in bipolar depression are discussed in terms of right-sided dysfunction of an arousal/attentional system involving temporoparietal and possibly frontal regions.     

Individual analysis of laterality data

Graphical and statistical analyses are presented that allow one to check for an individual subject whether the performance during a session is stable, whether the difference between the left and the right visual half-field is significant, and whether the performance is uniform over different sessions. Analyses are given for accuracy data and for latency data. Though the analyses are described for a visual half-field experiment, they can easily be adapted for other laterality tasks.     

Auditory naming and temporal lobe epilepsy.

Patients with left (i.e. language-dominant) temporal lobe epilepsy (TLE) typically report word finding difficulties. However, these deficits are not reliably detected with traditional visual object naming tests. We administered both visual and auditory naming tests to left and right TLE patients and normal controls. We hypothesized that an auditory naming test might be more sensitive since it better simulates the conditions under which word finding problems occur in daily living. The left TLE group obtained significantly lower scores than other groups on auditory naming, whereas their performance on visual naming was indistinguishable from that of right TLE patients and normals. Furthermore, whereas cut-off scores on the auditory naming task predicted seizure focus laterality in 85% of patients, performance on the visual naming task predicted laterality in only 60% of patients. These findings suggest that compared with visual naming, as assessed in the present study, auditory naming may more accurately characterize and lateralize TLE-associated language dysfunction. These results also propose a more complex understanding of word retrieval that incorporates modality and contextual information.     

Using functional transcranial Doppler ultrasonography to assess language lateralisation: Influence of task and difficulty level

Language is lateralised to the left hemisphere in most people, but it is unclear whether the same degree and direction of lateralisation is found for all verbal tasks and whether laterality is affected by task difficulty. We used functional transcranial Doppler ultrasonography (fTCD) to assess the lateralisation of language processing in 27 young adults using three tasks: word generation (WG), auditory naming (AN), and picture story (PS). WG and AN are active tasks requiring behavioural responses whereas PS is a passive task that involves listening to an auditory story accompanied by pictures. We also examined the effect of task difficulty by a post hoc behavioural categorisation of trials in the WG task and a word frequency manipulation in the AN task. fTCD was used to measure task-dependent blood flow velocity changes in the left and right middle cerebral arteries. All of these tasks were significantly left lateralised: WG, 77% of individuals left, 5% right; AN, 72% left: 4% right; PS, 56% left: 0% right. There were significant positive relationships between WG and AN (r=0.56) as well as AN and PS (r=.76) but not WG and PS (r = ?0.22). The task difficulty manipulation affected accuracy in both WG and AN tasks, as well as reaction time in the AN task, but did not significantly influence laterality indices in either task. It is concluded that verbal tasks are not interchangeable when assessing cerebral lateralisation, but that differences between tasks are not a consequence of task difficulty.     

Reliability of non-verbal laterality effects in the visual modality

The present experiment investigated the reliability and magnitude of laterality effects in a non-verbal task in the visual modality. The use of a bilateral discrimination task in which participants indicated whether a centrally presented probe stimulus matched either of the bilaterally presented targets was presumed to provide control over attention deployment. This led to the prediction that a reliable left visual field advantage (LVFA) would be obtained. A total of 40 right-handed undergraduate students completed the bilateral discrimination task twice in a test-retest design. Although relatively large test-retest correlations suggested that the laterality effect was quite reliable, a significant LVFA was obtained in the first testing session, and a right visual field advantage in the second one. This finding parallels results obtained in previous work with non-verbal tasks and supports the notion that practice affects the direction of laterality effects. The discussion examines alternative explanations with emphasis on practice effects and possible attentional factors. A possible shift in the bivariate distribution of laterality scores is used as a tentative explanation of the apparent contradiction between the high test-retest reliability and the shift in laterality with practice.     

Reliability of non-verbal laterality effects in the visual modality

The present experiment investigated the reliability and magnitude of laterality effects in a non-verbal task in the visual modality. The use of a bilateral discrimination task in which participants indicated whether a centrally presented probe stimulus matched either of the bilaterally presented targets was presumed to provide control over attention deployment. This led to the prediction that a reliable left visual field advantage (LVFA) would be obtained. A total of 40 right-handed undergraduate students completed the bilateral discrimination task twice in a test-retest design. Although relatively large test-retest correlations suggested that the laterality effect was quite reliable, a significant LVFA was obtained in the first testing session, and a right visual field advantage in the second one. This finding parallels results obtained in previous work with non-verbal tasks and supports the notion that practice affects the direction of laterality effects. The discussion examines alternative explanations with emphasis on practice effects and possible attentional factors. A possible shift in the bivariate distribution of laterality scores is used as a tentative explanation of the apparent contradiction between the high test-retest reliability and the shift in laterality with practice.     

Response format,magnitude of laterality effects,and sex differences in laterality

The present study examined the evidence for the claim that response format might affect the magnitude of laterality effects by means of a meta-analysis. The analysis included the 396 effect sizes drawn from 266 studies retrieved by Voyer (1996) and relevant to the main effect of laterality and sex differences in laterality for verbal and non-verbal tasks in the auditory, tactile, and visual sensory modality. The response format used in specific studies was the only moderator variable of interest in the present analysis, resulting in four broad response categories (oral, written, computer, and pointing). A meta-analysis analogue to ANOVA showed no significant influence of response format on either the main effect of laterality or sex differences in laterality when all sensory modalities were combined. However, when modalities were considered separately, response format affected the main effect of laterality in the visual modality, with a clear advantage for written responses. Further pointed analyses revealed some specific differences among response formats. Results are discussed in terms of their implications for the measurement of laterality.     

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.     

Response format, magnitude of laterality effects, and sex differences in laterality

The present study examined the evidence for the claim that response format might affect the magnitude of laterality effects by means of a meta-analysis. The analysis included the 396 effect sizes drawn from 266 studies retrieved by Voyer (1996) and relevant to the main effect of laterality and sex differences in laterality for verbal and non-verbal tasks in the auditory, tactile, and visual sensory modality. The response format used in specific studies was the only moderator variable of interest in the present analysis, resulting in four broad response categories (oral, written, computer, and pointing). A meta-analysis analogue to ANOVA showed no significant influence of response format on either the main effect of laterality or sex differences in laterality when all sensory modalities were combined. However, when modalities were considered separately, response format affected the main effect of laterality in the visual modality, with a clear advantage for written responses. Further pointed analyses revealed some specific differences among response formats. Results are discussed in terms of their implications for the measurement of laterality.     

Manual laterality in haptic and visual reaching tasks by tufted capuchin monkeys (Cebus apella). An association between hand preference and hand accuracy for food discrimination

Manual laterality was examined in 26 tufted capuchins (Cebus apella) in three tasks differing in their sensorimotor demands and the availability of visual cues. The Haptic discrimination task required the monkeys to discriminate haptically between two pumpkin seeds and two tinfoil items stuck into a tray inside an opaque box. The other two tasks required the monkeys to reach for two pumpkin seeds stuck into the tray within a transparent box with vision (Visually guided reaching task) or without vision (Visual-Tactual reaching task) during reaching. A significant group-level left hand bias was found for food retrieval in both the Haptic discrimination and Visual-Tactual tasks, and a significant group-level right hand bias in the Visually guided reaching task. The strength of hand preferences did not differ among the tasks. It was found that the accuracy of food recognition in the Haptic discrimination task was greater for the left than the right hand. The results suggest that the differences in the manipulo-spatial requirements of the tasks and in the availability of visual cues can variously affect manual laterality in capuchins. The left-hand preferences for the Haptic discrimination and Visual-Tactual tasks as well as the left-hand advantage for food discrimination may reflect a greater involvement of the right hemisphere in processing haptic information.     

The effect of unimodal affective priming on dichotic emotion recognition

The present report concerns two experiments extending to unimodal priming the cross-modal priming effects observed with auditory emotions by Harding and Voyer [(2016). Laterality effects in cross-modal affective priming. Laterality: Asymmetries of Body, Brain and Cognition, 21, 585–605]. Experiment 1 used binaural targets to establish the presence of the priming effect and Experiment 2 used dichotically presented targets to examine auditory asymmetries. In Experiment 1, 82 university students completed a task in which binaural targets consisting of one of 4 English words inflected in one of 4 emotional tones were preceded by binaural primes consisting of one of 4 Mandarin words pronounced in the same (congruent) or different (incongruent) emotional tones. Trials where the prime emotion was congruent with the target emotion showed faster responses and higher accuracy in identifying the target emotion. In Experiment 2, 60 undergraduate students participated and the target was presented dichotically instead of binaurally. Primes congruent with the left ear produced a large left ear advantage, whereas right congruent primes produced a right ear advantage. These results indicate that unimodal priming produces stronger effects than those observed under cross-modal priming. The findings suggest that priming should likely be considered a strong top-down influence on laterality effects.