Right Hemisphere Superiority Research Articles

Does face-selective cortex show a left visual field bias for centrally-viewed faces?

The left half of a centrally-viewed face contributes more strongly to recognition performance than the right. This left visual field (LVF) advantage is typically attributed to an untested assumption that face-selective cortex in the right hemisphere (RH) exhibits a contralateral bias, even for centrally-viewed faces. We tested the validity of this assumption using a behavioral measure of the LVF advantage and an fMRI experiment that measured laterality of face-selective cortex and neural contralateral bias. In the behavioral experiment, participants performed a chimeric face-matching task (Harrison and Strother, 2019). In the fMRI experiment, participants viewed chimeric faces comprised of face halves that either repeated or changed simultaneously in both hemifields, or repeated in one hemifield and changed in the other. This enabled us to measure lateralization of fMRI face-repetition suppression and hemifield-specific half-face sensitivity in face-selective cortex. We found that LVF bias in the fusiform face area (FFA) and right-lateralization of the FFA for changing versus repeated faces were both positively correlated with a behavioral measure of the LVF advantage for upright (but not inverted) faces. Results from regression analyses showed that LVF bias in the right FFA and FFA laterality make separable contributions to the prediction of our behavioral measure of the LVF bias for upright faces. Our results confirm a ubiquitous but previously untested assumption that RH superiority combined with contralateral bias in face-selective cortex explains the LVF advantage in face recognition. Specifically, our results show that neural LVF bias in the right FFA is sufficient to explain the relationship between FFA laterality and the perceptual LVF bias for centrally-viewed faces.

Voice gender categorization in the connected and disconnected hemispheres

ABSTRACT The role of the left and right hemispheres in processing the gender of voices is controversial, some evidence suggesting a bilateral involvement, some others suggesting a right-hemispheric superiority. We investigated this issue in a gender categorization task involving healthy participants and a male split-brain patient: female or male natural voices were presented in one ear during the simultaneous presentation of white noise in the other ear (dichotic listening paradigm). Results revealed faster responses by the healthy participants for stimuli presented in the left than in the right ear, although no asymmetries emerged between the two ears in the accuracy of both the patient and the control group. Healthy participants were also more accurate at categorizing female than male voices, and an opposite-gender bias emerged – at least in females – showing faster responses in categorizing voices of the opposite gender. The results support a bilateral hemispheric involvement in voice gender categorization, without asymmetries in the patient, but with a faster categorization when voices are directly presented to the right hemisphere in the healthy sample. Moreover, when the two hemispheres directly interact with one another, a faster categorization of voices of the opposite gender emerges, and it can be an evolutionary grounded bias.

Does right hemisphere superiority sufficiently explain the left visual field advantage in face recognition?

The tendency to perceive the identity of the left half of a centrally viewed face more strongly than that of the right half is associated with visual processing of faces in the right hemisphere (RH). Here we investigate conditions under which this well-known left visual field (LVF) half-face advantage fails to occur. Our findings challenge the sufficiency of its explanation as a function of RH specialization for face processing coupled with LVF-RH correspondence. In two experiments we show that the LVF half-face advantage occurs for normal faces and chimeric faces composed of different half-face identities. In a third experiment, we show that face inversion disrupts the LVF half-face advantage. In two additional experiments we show that half-faces viewed in isolation or paired with inverted half-faces fail to show the LVF advantage. Consistent with previous explanations of the LVF half-face advantage, our findings suggest that the LVF half-face advantage reflects RH superiority for processing faces and direct transfer of LVF face information to visual cortex in the RH. Critically, however, our findings also suggest the operation of a third factor, which involves the prioritization of face-processing resources to the LVF, but only when two upright face-halves compete for these resources. We therefore conclude that RH superiority alone does not suffice to explain the LVF advantage in face recognition. We also discuss the implications of our findings for specialized visual processing of faces by the right hemisphere, and we distinguish LVF advantages for faces viewed centrally and peripherally in divided field studies.

Right news, good news! The valence hypothesis and hemispheric asymmetries in auditory imagery

ABSTRACTA Right Ear Advantage (REA) has been found during dichotic listening, but also in tasks requiring the sole imagery of auditory content, due to the left-hemispheric specialisation for language. According to the Valence Hypothesis (VH) the left (right) hemisphere would be also specialised in processing stimuli with a positive (negative) emotional valence. In a single trial imagery task, we asked 200 right-handed participants to imagine hearing in one ear a sentence with a positive or a negative valence, either in first or in second person. Results confirmed an imagery REA for the positively-valenced sentences, but no hemispheric asymmetries emerged for the negatively-valenced sentences (both in first and second person). We conclude that hemispheric asymmetries for language and for emotions interact during imagery tasks: the right-hemispheric superiority for negative emotions balances the left-hemispheric superiority for language, resulting in the absence of hemispheric asymmetries when a negative emotional content is imagined.

Unilateral hf-tRNS over the temporal cortex does not influence pleasantness of musical chords

The “consonance effect” is the pleasant and unpleasant evaluation attributed to consonant and dissonant music, respectively. Different studies in this domain revealed a left-hemispheric superiority for dissonance and a right-hemispheric superiority for consonance. We investigated the causal relationship between the consonance effect and the activity of the cerebral hemispheres by applying high frequency transcranial Random Noise Stimulation (hf-tRNS) over the left or right auditory cortex in a group of 24 healthy volunteers. Results confirm the consonance effect, dissonant chords being judged as more unpleasant than consonant chords, and show that hf-tRNS does not influence the pleasantness evaluations of chords. We speculate that the auditory cortex is directly involved in consonance and dissonance processing, but that pleasantness evaluations could take place in the anterior areas of the brain. This is the first evidence concerning the effects of the modulatory activity in each cerebral hemisphere and the consonance effect.

Right hemisphere superiority for executive control of attention

Over forty years have passed since the first evidence showing the unbalanced attentional allocation of humans across the two visual fields, and since then, a wealth of behavioral, neurophysiological, and clinical data increasingly showed a right hemisphere dominance for orienting of attention. However, inconsistent evidence exists regarding the right-hemisphere dominance for executive control of attention, possibly due to a lack of consideration of its dynamics with the alerting and orienting functions. In this study, we used a version of the Attentional Network Test with lateralized presentation of the stimuli to the left visual field (processed by the right hemisphere, RH) and right visual field (processed by the left hemisphere, LH) to examine visual field differences in executive control of attention under alerting and orienting of attention. Analyses of behavioral performance (reaction time and error rate) showed a more efficient executive control (reduced conflict effect) in the RH compared to the LH for the reaction time, under conditions of increased alerting and of informative spatial orienting. These results demonstrate the right-hemisphere superiority for executive control, and that this effect depends on the involvement of the alerting and orienting functions.

Contrasting hemispheric asymmetries for emotional processing from event-related potentials and behavioral responses.

Four main theories concerning hemispheric asymmetries for emotional processing have been proposed: the right hemisphere hypothesis (RHH; the right hemisphere is specialized in processing all emotions), the valence hypothesis (VH; the left and the right hemispheres are superior in positive and negative emotion processing, respectively), the modified VH (the right-hemispheric superiority at posterior sites is followed by a valence-specific activity at frontal sites), and the motivational model (the left and the right hemispheres are superior in approaching-related and avoidance-related emotions, respectively). In a divided visual field paradigm, we presented happy and angry faces to 16 healthy participants, either unilaterally or bilaterally, in order to test the aforementioned theories. Behavioral results provided support for the VH and correlational analysis revealed that handedness influences the rightward bias for positive emotions. The amplitude of P1, N170, and P2 event-related potential components at parietal sites (selected by means of topographic maps) was larger in the right than in the left hemisphere, independently of the emotional expression of the stimuli, supporting the RHH. At frontal sites, no asymmetry was found in bilateral conditions, whereas in unilateral conditions, a mixed pattern of hemispheric asymmetries emerged. We conclude that there is no correspondence between behavioral and electrophysiological results concerning asymmetries for emotion processing, and that the VH and the RHH are not mutually exclusive. (PsycINFO Database Record

Split-brain patients: Visual biases for faces.

Split-brain patients constitute a small subpopulation of epileptic patients who have received the surgical resection of the callosal fibers in an attempt to reduce the spread of epileptic foci between the cerebral hemispheres. The study of callosotomy patients allowed neuropsychologists to investigate the effects of the hemispheric disconnection, shedding more light on the perceptual and cognitive abilities of each hemisphere in isolation. This view that callosotomy completely isolates the hemispheres has now been revised, in favor of the idea of a dynamic functional reorganization of the two sides of the brain; however, the evidence collected from split-brain patients is still a milestone in the neurosciences. The right-hemispheric superiority found in the healthy population concerning face perception has been further supported with split-brains, and it has been shown that the right disconnected hemisphere appears superior to the left hemisphere in recognizing and processing faces with similar characteristics as the observers' (e.g., gender, identity, etc.). Even more controversial is the field of hemispheric asymmetries for processing facial emotion, some evidence suggesting a right-hemispheric superiority for all emotions, some others showing a complementary hemispheric asymmetry depending on the positive or negative emotional valence. Although the practice of callosotomy is mostly abandoned today in favor of pharmacological alternatives, further studies on the remaining split-brain patients could help advance our understanding of hemispheric specialization for social stimuli.

Hemispheric organization in disorders of development

ABSTRACTA recent theoretical account posits that, during the acquisition of word recognition in childhood, the pressure to couple visual and language representations in the left hemisphere (LH) results in competition with the LH representation of faces, which consequently become largely, albeit not exclusively, lateralized to the right hemisphere (RH). We explore predictions from this hypothesis using a hemifield behavioural paradigm with words and faces as stimuli, with concurrent event-related potential (ERP) measurement, in a group of adults with developmental dyslexia (DD) or with congenital prosopagnosia (CP) and matched control participants. Behaviourally, the DD group exhibited clear deficits in both word and face processing relative to controls, while the CP group showed a specific deficit in face processing only. This pattern was mirrored in the ERP data too. The DD group evinced neither the normal ERP pattern of RH dominance for faces nor the LH dominance for words. In contrast, the CP group showed the typical ERP superiority for words in the LH but did not show the typical RH superiority for faces. These findings are consistent with the hypothesis that the typical hemispheric organization for words can develop in the absence of typical hemispheric organization for faces but not vice versa, supporting the account of interactive perceptual development.

Asymmetry for Symmetry: Right-Hemispheric Superiority in Bi-Dimensional Symmetry Perception

A right-hemispheric superiority has been shown for spatial symmetry perception with mono-dimensional stimuli (e.g., bisected lines). Nevertheless, the cerebral imbalance for bi-dimensional stimuli is still controversial, and the aim of the present study is to investigate this issue. Healthy participants and a split-brain patient (D.D.C.) were tested in a divided visual field paradigm, in which a square shape was presented either in the left or right visual field and they were asked to judge whether a dot was placed exactly in the center of the square or off-center, by using the left/right hand in two separate sessions. The performance of healthy participants was better when the stimuli presented in the left visual field (LVF) were on-center rather than off-center. The performance of D.D.C. was higher than chance only when on-center stimuli were presented in the LVF in the left hand session. Only in this condition did his accuracy not differ with respect to that of the control group, whereas in all of the other conditions, it was lower than the controls’ accuracy. We conclude that the right-hemispheric advantage already shown for mono-dimensional stimuli can be extended also to bi-dimensional configurations, confirming the right-hemispheric superiority for spatial symmetry perception.

Geometry, landmarks and the cerebral hemispheres: 2D spatial reorientation in split-brain patients.

A right-hemispheric superiority in spatial encoding based on geometric cues has been largely documented in a variety of species, together with a left-hemispheric specialization for encoding based on landmarks. In humans, hemispheric asymmetries for spatial encoding have been little explored. In this study, we compared a patient with a complete callosal resection (D.D.C.) and a patient with a wide callosal resection saving the splenium (A.P.), with healthy participants. In two 2D versions of the 'reorientation task', participants were asked to find the target corner of a rectangle-shaped environment, by exploiting either geometric information alone or the combination of geometric and landmark information. In Experiment 1, the landmark consisted of a coloured side of the rectangle; in Experiment 2, this cue was replaced by a coloured disc located inside the rectangle. In both experiments, the rectangular shape ensured the geometric cue. D.D.C. was always unable to recall the target, whereas A.P. correctly solved the task when only the geometric information was available, without difference with respect to the controls. Importantly, the performance of A.P. did not differ from controls' when the right hemisphere was tested with the landmark cues (the task being carried out using the left hand), whereas when the left hemisphere was tested (right-hand session) his performance was worse than controls' with the coloured side of the space, but it was better than controls' with the coloured disc. The results are discussed comparing them with data collected on other species, and with theories of spatial processing.

Face gender categorization and hemispheric asymmetries: Contrasting evidence from connected and disconnected brains

We investigated hemispheric asymmetries in categorization of face gender by means of a divided visual field paradigm, in which female and male faces were presented unilaterally for 150ms each. A group of 60 healthy participants (30 males) and a male split-brain patient (D.D.C.) were asked to categorize the gender of the stimuli. Healthy participants categorized male faces presented in the right visual field (RVF) better and faster than when presented in the left visual field (LVF), and female faces presented in the LVF than in the RVF, independently of the participants’ sex. Surprisingly, the recognition rates of D.D.C. were at chance levels – and significantly lower than those of the healthy participants – for both female and male faces presented in the RVF, as well as for female faces presented in the LVF. His performance was higher than expected by chance – and did not differ from controls – only for male faces presented in the LVF. The residual right-hemispheric ability of the split-brain patient in categorizing male faces reveals an own-gender bias lateralized in the right hemisphere, in line with the rightward own-identity and own-age bias previously shown in split-brain patients. The gender-contingent hemispheric dominance found in healthy participants confirms the previously shown right-hemispheric superiority in recognizing female faces, and also reveals a left-hemispheric superiority in recognizing male faces, adding an important evidence of hemispheric imbalance in the field of face and gender perception.

Upright or inverted, entire or exploded: right-hemispheric superiority in face recognition withstands multiple spatial manipulations.

Background. The ability to identify faces has been interpreted as a cerebral specialization based on the evolutionary importance of these social stimuli, and a number of studies have shown that this function is mainly lateralized in the right hemisphere. The aim of this study was to assess the right-hemispheric specialization in face recognition in unfamiliar circumstances.Methods. Using a divided visual field paradigm, we investigated hemispheric asymmetries in the matching of two subsequent faces, using two types of transformation hindering identity recognition, namely upside-down rotation and spatial “explosion” (female and male faces were fractured into parts so that their mutual spatial relations were left intact), as well as their combination.Results. We confirmed the right-hemispheric superiority in face processing. Moreover, we found a decrease of the identity recognition for more extreme “levels of explosion” and for faces presented upside-down (either as sample or target stimuli) than for faces presented upright, as well as an advantage in the matching of female compared to male faces.Discussion. We conclude that the right-hemispheric superiority for face processing is not an epiphenomenon of our expertise, because we are not often exposed to inverted and “exploded” faces, but rather a robust hemispheric lateralization. We speculate that these results could be attributable to the prevalence of right-handedness in humans and/or to early biases in social interactions.

Variable left-hemisphere language and orthographic lateralization reduces right-hemisphere face lateralization.

It is commonly believed that, in right-handed individuals, words and faces are processed by distinct neural systems: one in the left hemisphere (LH) for words and the other in the right hemisphere (RH) for faces. Emerging evidence suggests, however, that hemispheric selectivity for words and for faces may not be independent of each other. One recent account suggests that words become lateralized to the LH to interact more effectively with language regions, and subsequently, as a result of competition with words for representational space, faces become lateralized to the RH. On this interactive account, left-handed individuals, who as a group show greater variability with respect to hemispheric language dominance, might be expected to show greater variability in their degree of RH lateralization of faces as well. The current study uses behavioral measures and ERPs to compare the hemispheric specialization for both words and faces in right- and left-handed adult individuals. Although both right- and left-handed groups demonstrated LH over RH superiority in discrimination accuracy for words, only the right-handed group demonstrated RH over LH advantage in discrimination accuracy for faces. Consistent with this, increased right-handedness was related to an increase in RH superiority for face processing, as measured by the strength of the N170 ERP component. Interestingly, the degree of RH behavioral superiority for face processing and the amplitude of the RH N170 for faces could be predicted by the magnitude of the N170 ERP response to words in the LH. These results are discussed in terms of a theoretical account in which the typical RH face lateralization fails to emerge in individuals with atypical language lateralization because of weakened competition from the LH representation of words.

The “consonance effect” and the hemispheres: A study on a split-brain patient

The association between musical consonance and pleasantness, and between musical dissonance and unpleasantness (“consonance effect”) is well established. Furthermore, a number of studies suggest the main involvement of the left hemisphere in the perception of dissonance and that of the right hemisphere in the perception of consonance. In the present study, the consonance effect was studied in a callosotomized patient, D. D. C. and in a control group. In binaural presentations, the patient did not attribute different pleasantness judgements to consonant and dissonant chords, differently from the control group who showed the consonance effect. However, in dichotic presentations (e.g. a chord in one ear and white noise in the other ear), a trend towards the consonance effect was found in D. D. C., but only when chords were presented in his right ear (left hemisphere), whereas the control group confirmed the known hemispheric asymmetry in labelling the pleasantness of consonant and dissonant chords. These results suggest that the right-hemispheric superiority in appreciating consonance might hide the inability of the right hemisphere to classify dissonant chords as unpleasant in the split-brain, whereas the left hemisphere seems capable to differently label the pleasantness of consonant and dissonant chords, even if it is more sensitive to dissonance.

Effects of age, sex and arm on the precision of arm position sense—left-arm superiority in healthy right-handers

Position sense is an important proprioceptive ability. Disorders of arm position sense (APS) often occur after unilateral stroke, and are associated with a negative functional outcome. In the present study we assessed horizontal APS by measuring angular deviations from a visually defined target separately for each arm in a large group of healthy subjects. We analyzed the accuracy and instability of horizontal APS as a function of age, sex and arm. Subjects were required to specify verbally the position of their unseen arm on a 0-90° circuit by comparing the current position with the target position indicated by a LED lamp, while the arm was passively moved by the examiner. Eighty-seven healthy subjects participated in the study, ranging from 20 to 77 years, subdivided into three age groups. The results revealed that APS was not a function of age or sex, but was significantly better in the non-dominant (left) arm in absolute errors (AE) but not in constant errors (CE) across all age groups of right-handed healthy subjects. This indicates a right-hemisphere superiority for left APS in right-handers and neatly fits to the more frequent and more severe left-sided body-related deficits in patients with unilateral stroke (i.e. impaired APS in left spatial neglect, somatoparaphrenia) or in individuals with abnormalities of the right cerebral hemisphere. These clinical issues will be discussed.

A left-hand superiority for the implicit detection of a rule

We set out to test the hypothesis of right-hemisphere superiority for the implicit detection of a rule. Forty healthy men provided speeded manual responses to randomly presented digits from 1 to 6 (left hand to 1–3, right hand to 4–6). Red digits on trial n signaled that the response on trial n+1 should be made with one hand, blue digits with the other hand. White digits gave no signal (control trials). Half the participants were told that the stimulus color conveyed a rule that could be exploited to improve performance, the other half were not. After completing the first run, participants' awareness of the presence and nature of the rule was assessed and all were debriefed. Participants then performed a second run with identical stimulus conditions. In Run 1, none of the participants reported being aware of the nature of the rule. Reaction times (RTs) were longer after signal than no-signal trials, but only for the left hand. Participants informed about the presence of a rule tended to have longer RTs, irrespective of hand. In Run 2, RTs were shorter after signal than no-signal trials, and there were no differences between hands. The observed RT effect for the left-hand points to a right-hemisphere superiority for the detection and application of a rule in the absence of verbal awareness. Longer (instead of shorter) RTs in the signal trials are discussed in the framework of interhemispheric inhibition.

The right hemisphere advantage in visual change detection depends on temporal factors

What accounts for the Right Hemisphere (RH) functional superiority in visual change detection? An original task which combines one-shot and divided visual field paradigms allowed us to direct change information initially to the RH or the Left Hemisphere (LH) by deleting, respectively, an object included in the left or right half of a scene presented centrally. We manipulated the perceptual salience and semantic relevance of the change as well as the duration of the Inter-Stimulus Interval (ISI) between the scenes in order to clarify the role of the RH in memory and attention processes, and to explore whether lengthening the ISI would enhance the contribution of the LH. When analyzing data collapsed over the two levels (high vs. low) of salience and of relevance, changes were better detected in the left visual field (lvf) than in the right visual field (rvf) in the case of a short ISI, while no difference emerged in the case of a long ISI. Moreover, lengthening the ISI resulted in a performance decrement in the lvf, both for accuracy and response speed. The fact that the RH superiority was limited to short intervals indicates that stimulus-driven orienting contributes more than perceptual processing to this hemispheric asymmetry. When considering perceptual and semantic properties of the change, the effect of the ISI duration seemed to specifically emerge in the case of low relevance, with an enhancement of accuracy in the rvf when comparing the long with the short ISI. This suggests that the ISI influence on hemispheric performance operates on different levels.

Right Hemisphere Dysfunction and Metaphor Comprehension in Young Adults with Asperger Syndrome

This study examined whether the known difficulties in metaphor comprehension exhibited by persons with Asperger syndrome (AS) can be explained by a dysfunctional right hemisphere (RH). Using the divided visual field paradigm, 27 AS participants and 36 matched controls were presented with word pairs of four types (literal, conventional metaphors, novel metaphors, and unrelated word pairs), and were asked to perform a semantic judgment task. The main hypothesis was that whereas the control group participants will show RH superiority for novel metaphor processing, no RH superiority will be found in the AS group. Results indeed indicate much less RH contribution to novel metaphor comprehension in AS, and are discussed in light of linguistic models and the neurobiology of autism.

Hemispheric dominance for mental rotation: it is a matter of time

Mental rotation is often said to be a right-hemisphere function. The evidence for this claim, however, remains equivocal. To investigate whether right-hemispheric superiority relates to speed of processing, we measured the latencies and amplitudes of individual participant's mental-rotation event-related potential effects over the parietal electrodes. The results suggest that increases in parietal negativity begin around 400 ms after stimulus onset, and continue until 550 ms over the right hemisphere, and 610 ms over the left hemisphere. The effect of orientation on event-related potential amplitudes during those times do not differ between hemispheres. These results indicate that the lateralization effect is primarily related to timing, rather than the extent of cortical involvement.