Victoria J. Bourne

The divided visual field paradigm: Methodological considerations

The divided visual field methodology has been used to examine a wide variety of lateralised processes. When conducting such studies it is important to employ a number of strict controls in order to maximise the effectiveness of the paradigm for examining the processing of stimuli by each hemisphere. The use of these controls is discussed in this paper. The following issues are discussed: selection of participants; methods of fixation control; presenting stimuli unilaterally; methods of responding; and measures that can be taken. The use of the divided visual field paradigm to examine interhemispheric cooperation is also discussed. Employing the recommended controls provides an effective and relatively easy method of examining the role of each hemisphere in the processing of stimuli.

Lateralised processing of positive facial emotion: sex differences in strength of hemispheric dominance

Sex differences in lateralisation have been examined frequently, but have found varying and contradictory results. The experiment presented in this paper examines the lateralisation of processing positive facial emotion in 276 right handed undergraduates (138 males, 138 females). All participants completed two behavioural tests of lateralisation: a handedness preference questionnaire and a chimeric faces emotion judgement task, which measured strength of lateralisation for the perception of positive facial emotion. A highly significant difference was found for the chimeric faces task only: males were more strongly lateralised than females, although both males and females tended to be right hemisphere dominant. The results suggest that females are more bilaterally distributed and hence have greater access to mechanisms located in each hemisphere.

Examining the Relationship Between Degree of Handedness and Degree of Cerebral Lateralization for Processing Facial Emotion

This paper examines the relationship between degree of handedness and degree of cerebral lateralization on a task of processing positive facial emotion in right-handed individuals. Three hundred and thirteen right-handed participants (157 women) were given two behavioral tests of lateralization: a handedness questionnaire and a chimeric faces test. Two further handedness measures were taken: familial left-handedness and writing posture. Regression analysis showed that both degree of handedness and sex were predictive of degree of lateralization. Individuals who were strongly right-handed were also more strongly lateralized to the right hemisphere for the task. Men were more strongly lateralized than women. Data were reanalyzed for men and women separately. The relationship between handedness and lateralization remained for men only. Neither familial left-handedness nor writing posture were associated with cerebral lateralization for men or women. The results suggest a positive relationship between degree of handedness and degree of cerebral lateralization, and further that there is a sex difference in this relationship.

How are emotions lateralised in the brain? Contrasting existing hypotheses using the Chimeric Faces Test

There are two contrasting hypotheses that attempt to explain how emotion perception might be organised in the brain. One suggests that all emotions are lateralised to the right hemisphere whereas the other suggests that emotions may be differently lateralised according to valence. Here these two theories are contrasted, in addition to considering the role of emotional intensity in explaining possible differences in strength of lateralisation across emotions. Participants completed a Chimeric Faces Test for each of the six basic emotions: anger, disgust, fear, happiness, sadness and surprise. All emotions showed significant lateralisation to the right hemisphere, however, differences in strength of lateralisation within the right hemisphere were found. Stronger patterns of right hemisphere lateralisation were found for positive emotions and for emotions of higher intensity. The results support the right-hemisphere hypothesis, but suggest that there may be variability in organisation within the right hemisphere across different types of emotion.

Examining the sex difference in lateralisation for processing facial emotion: Does biological sex or psychological gender identity matter?

The research examining sex differences in functional lateralisation has shown varying results. While some provide evidence for males being more strongly lateralised than females, a number have shown either no relationship or the opposite pattern of findings. In this study we consider whether psychological gender identity might clarify some of the conflicting results in this area of research. Eight five participants (39 males) aged from 18 to 49 years old were tested. We found that psychological masculinity was associated with stronger patterns of lateralisation for the processing of a range of emotional expressions. We also found an interaction between biological sex and psychological gender identity, with a positive relationship between psychological masculinity and lateralisation found for males, but a negative relationship found for females. The possible role of hormonal exposure in this relationship is discussed.

Lateralized repetition priming for familiar faces: Evidence for asymmetric interhemispheric cooperation

Repetition priming refers to facilitated recognition of stimuli that have been seen previously. Although a great deal of work has examined the properties of repetition priming for familiar faces, little has examined the neuroanatomical basis of the effect. Two experiments are presented in this paper that combine the repetition priming paradigm with a divided visual field methodology to examine lateralized recognition of familiar faces. In the first experiment participants were presented with prime faces unilaterally to each visual field and target faces foveally. A significant priming effect was found for prime faces presented to the right hemisphere, but not for prime faces presented to the left hemisphere. In Experiment 2, prime and target faces were presented unilaterally, either to the same visual field or to the opposite visual field (i.e., either within hemisphere or across hemispheres). A significant priming effect was found for the within right hemisphere condition, but not for the within left hemisphere condition, replicating the findings of the first experiment. Priming was also found in both of the across hemispheres conditions, suggesting that interhemispheric cooperation occurs to aid recognition. Taken in combination these experiments provide two main findings. First, an asymmetric repetition priming effect was found, possibly as a result of asymmetric levels of activation following recognition of a prime face, with greater priming occurring within the right hemisphere. Second, there is evidence for asymmetric interhemispheric cooperation with transfer of information from the right hemisphere to the left hemisphere to facilitate recognition.

Chimeric faces, visual field bias, and reaction time bias: Have we been missing a trick?

The chimeric faces test is a frequently used behavioural test of lateralisation for cognitive processing. Performance on this task is typically quantified in terms of bias towards selecting faces where positive facial emotion is expressed in the viewers left visual field, indicating right hemisphere dominance for the task. This paper examines an alternative measure that may be extracted from responses to the chimeric faces test: reaction time bias. There was a strong positive correlation between the two asymmetry measures, which remained even after controlling for sex and handedness. The possible uses of reaction time bias in the measurement of cerebral lateralisation are discussed.

Hormone exposure and functional lateralisation: Examining the contributions of prenatal and later life hormonal exposure

An increasing amount of research has shown a relationship between hormonal exposure and functional lateralisation. In this study different sources of hormonal exposure were examined: prenatal exposure, estimated using the 2D:4D ratio, and later life exposure through examining the effects of hormone replacement therapy. In addition to considering multiple sources of hormonal exposure, three tests of functional lateralisation were used: two versions of the chimeric faces test, one using positive emotion and the other using negative emotion, and the landmark task. The same effects were found across all three measures of lateralisation. Lower 2D:4D ratios, which indicate high levels of prenatal testosterone exposure, were associated with stronger right hemisphere dominance. Later life hormonal exposure was not found to be associated with any of the lateralisation measures. This finding suggests a relationship between prenatal hormonal exposure and brain organisation.

Examining the effects of inversion on lateralisation for processing facial emotion.

There is an increasing amount of evidence which suggests that each hemisphere is differently specialised for processing facial stimuli, with the right hemisphere specialised for the processing of configural information and the left hemisphere specialised for the processing of featural information. While there is evidence for this distinction from studies of face recognition, it has not been shown in studies of lateralisation for processing facial emotion. In this study the chimeric faces test was used with faces expressing anger, disgust, fear, happiness, sadness or surprise, presented in either an upright or an inverted orientation. When presented upright, a significant right hemisphere bias was found for all six emotions. However, when inverted, a significant left hemisphere bias was found for the processing of happiness and surprise, but not for the processing of negative emotions (although the analysis was approaching significance for anger). These findings support the hypothesis that each hemisphere is differently specialised for processing facial emotion, but contradicts previous work that examined the effects of inversion on chimeric face stimuli.

Lateralised repetition priming for featurally and configurally manipulated familiar faces: Evidence for differentially lateralised processing mechanisms

Although early research suggested that the right hemisphere was dominant for processing faces, more recent studies have provided evidence for both hemispheres being involved, at least to some extent. In this experiment we examined hemispheric specialisations by using a lateralised repetition-priming paradigm with selectively degraded faces. Configurally degraded prime faces produced negative priming when presented to the left visual field (right hemisphere) and positive priming (facilitation) when presented to the right visual field (left hemisphere). Featurally degraded prime faces produced the opposite pattern of effects: positive priming when presented to the left visual field (right hemisphere) and negative priming when presented to the right visual field (left hemisphere). These results support the proposal that each hemisphere is differentially specialised for processing distinct forms of facial information: the right hemisphere for configural information and the left hemisphere for featural information.