Hemispheric Asymmetry In Processing Research Articles

A leftward bias for the arrangement of consumer items that differ in attractiveness

ABSTRACT People are frequently biased to use left-side information more than right-side information to inform their perceptual judgements. This research examined whether the leftward bias also applied to preferences for the arrangement of everyday consumer items. Pairs of consumer items were created where one item was more attractive than the other item. Using a two-alternative forced choice task, Experiment 1 found a robust preference for arrangements with the more attractive consumer item on the left side rather than the right side of a pair. Experiment 2 reversed the judgement decision, with participants asked to choose the arrangement they least preferred, and a bias for arrangements with the more attractive item on the right side emerged. Experiment 3 failed to find an effect of the “attractive left” preference on participants’ purchasing intentions. The preference for attractive left arrangements has implications for the display of consumer products and for the aesthetic arrangement of objects in general. The findings are discussed in relation to hemispheric asymmetries in processing and the role of left to right scanning.

Hemispheric Lateralization of Arithmetic Facts and Magnitude Processing for Two-Digit Numbers.

In the human brain, a (relative) functional asymmetry (i.e., laterality; functional and performance differences between the two cerebral hemispheres) exists for a variety of cognitive domains (e.g., language, visual-spatial processing, etc.). For numerical cognition, both bi-lateral and unilateral processing has been proposed with the retrieval of arithmetic facts postulated as being lateralized to the left hemisphere. In this study, we aimed at evaluating this claim by investigating whether processing of multiplicatively related triplets in a number bisection task (e.g., 12_16_20) in healthy participants (n = 23) shows a significant advantage when transmitted to the right hemisphere only as compared to transmission to the left hemisphere. As expected, a control task revealed that stimulus presentation to the left or both visual hemifields did not increase processing disadvantages of unit-decade incompatible number pairs in magnitude comparison. For the number bisection task, we replicated the multiplicativity effect. However, in contrast to the hypothesis deriving from the triple code model, we did not observe significant hemispheric processing asymmetries for multiplicative items. We suggest that participants resorted to keep number triplets in verbal working memory after perceiving them only very briefly for 150 ms. Rehearsal of the three numbers was probably slow and time-consuming so allowing for interhemispheric communication in the meantime. We suggest that an effect of lateralized presentation may only be expected for early effects when the task is sufficiently easy.

The face is the thing: Faces, not emotions, are responsible for chimeric perceptual asymmetry

ABSTRACTWe used factor analysis to examine relationships among tasks that have previously shown right hemispheric processing asymmetries. We were interested in whether processing emotion displayed by a face constitutes a distinct perceptual process from processing other facial characteristics. Interest in this topic arose after Boles [1991. Factor analysis and the cerebral hemispheres: Pilot study and parietal functions. Neuropsychologia, 29(1), 59–91] found evidence of a common process underlying face processing and then Boles [1992. Factor analysis and the cerebral hemispheres: Temporal, occipital and frontal functions. Neuropsychologia, 30(11), 963–988] found evidence of a distinct process for the processing of the facial emotion. We used seven tasks that measured both face and non-face perception. Analysis of the asymmetries revealed measures from the five face tasks resulted in a single factor, thus failing to support the hypothesis that emotional face perception would involve a separate process from non-emotional face perception. A second factor revealed a separate process underlying enumeration, and a third factor revealed yet another process underlying line bisection. The results indicate that perceiving facial emotion results in right hemisphere processing, and faces as a whole are responsible for such processing.

Hemispheric asymmetry in event knowledge activation during incremental language comprehension: A visual half-field ERP study

During incremental language comprehension, the brain activates knowledge of described events, including knowledge elements that constitute semantic anomalies in their linguistic context. The present study investigates hemispheric asymmetries in this process, with the aim of advancing our understanding of the neural basis and functional properties of event knowledge activation during incremental comprehension. In a visual half-field event-related brain potential (ERP) experiment, participants read brief discourses in which the third sentence contained a word that was either highly expected, semantically anomalous but related to the described event (Event-Related), or semantically anomalous but unrelated to the described event (Event-Unrelated). For both visual fields of target word presentation, semantically anomalous words elicited N400 ERP components of greater amplitude than did expected words. Crucially, Event-Related anomalous words elicited a reduced N400 relative to Event-Unrelated anomalous words only with left visual field/right hemisphere presentation. This result suggests that right hemisphere processes are critical to the activation of event knowledge elements that violate the linguistic context, and in doing so informs existing theories of hemispheric asymmetries in semantic processing during language comprehension. Additionally, this finding coincides with past research suggesting a crucial role for the right hemisphere in elaborative inference generation, raises interesting questions regarding hemispheric coordination in generating event-specific linguistic expectancies, and more generally highlights the possibility of functional dissociation of event knowledge activation for the generation of elaborative inferences and for linguistic expectancies.

An application of univariate and multivariate approaches in FMRI to quantifying the hemispheric lateralization of acoustic and linguistic processes.

The question of hemispheric lateralization of neural processes is one that is pertinent to a range of subdisciplines of cognitive neuroscience. Language is often assumed to be left-lateralized in the human brain, but there has been a long running debate about the underlying reasons for this. We addressed this problem with fMRI by identifying the neural responses to amplitude and spectral modulations in speech and how these interact with speech intelligibility to test previous claims for hemispheric asymmetries in acoustic and linguistic processes in speech perception. We used both univariate and multivariate analyses of the data, which enabled us to both identify the networks involved in processing these acoustic and linguistic factors and to test the significance of any apparent hemispheric asymmetries. We demonstrate bilateral activation of superior temporal cortex in response to speech-derived acoustic modulations in the absence of intelligibility. However, in a contrast of amplitude-modulated and spectrally modulated conditions that differed only in their intelligibility (where one was partially intelligible and the other unintelligible), we show a left dominant pattern of activation in STS, inferior frontal cortex, and insula. Crucially, multivariate pattern analysis showed that there were significant differences between the left and the right hemispheres only in the processing of intelligible speech. This result shows that the left hemisphere dominance in linguistic processing does not arise because of low-level, speech-derived acoustic factors and that multivariate pattern analysis provides a method for unbiased testing of hemispheric asymmetries in processing.

Orienting asymmetries and lateralized processing of sounds in humans

BackgroundLateralized processing of speech is a well studied phenomenon in humans. Both anatomical and neurophysiological studies support the view that nonhuman primates and other animal species also reveal hemispheric differences in areas involved in sound processing. In recent years, an increasing number of studies on a range of taxa have employed an orienting paradigm to investigate lateralized acoustic processing. In this paradigm, sounds are played directly from behind and the direction of turn is recorded. This assay rests on the assumption that a hemispheric asymmetry in processing is coupled to an orienting bias towards the contralateral side. To examine this largely untested assumption, speech stimuli as well as artificial sounds were presented to 224 right-handed human subjects shopping in supermarkets in Germany and in the UK. To verify the lateralized processing of the speech stimuli, we additionally assessed the brain activation in response to presentation of the different stimuli using functional magnetic resonance imaging (fMRI).ResultsIn the naturalistic behavioural experiments, there was no difference in orienting behaviour in relation to the stimulus material (speech, artificial sounds). Contrary to our predictions, subjects revealed a significant left bias, irrespective of the sound category. This left bias was slightly but not significantly stronger in German subjects. The fMRI experiments confirmed that the speech stimuli evoked a significant left lateralized activation in BA44 compared to the artificial sounds.ConclusionThese findings suggest that in adult humans, orienting biases are not necessarily coupled with lateralized processing of acoustic stimuli. Our results – as well as the inconsistent orienting biases found in different animal species – suggest that the orienting assay should be used with caution. Apparently, attention biases, experience, and experimental conditions may all affect head turning responses. Because of the complexity of the interaction of factors, the use of the orienting assay to determine lateralized processing of sound stimuli is discouraged.

Hemispheric processing asymmetries: Implications for memory

Recent research has demonstrated that memory for words elicits left hemisphere activation, faces right hemisphere activation, and nameable objects bilateral activation. This pattern of results was attributed to dual coding of information, with the left hemisphere employing a verbal code and the right a nonverbal code. Nameable objects can be encoded either verbally or nonverbally and this accounts for their bilateral activation. We investigated this hypothesis in a callosotomy patient. Consistent with dual coding, the left hemisphere was superior to the right in memory for words, whereas the right was superior for faces. Contrary to prediction, performance on nameable pictures was not equivalent in the two hemispheres, but rather resulted in a right hemisphere superiority. In addition, memory for pictures was significantly better than for either words or faces. These findings suggest that the dual code hypothesis is an oversimplification of the processing capabilities of the two hemispheres.

Hemispheric asymmetries in global⧹local processing are modulated by perceptual salience

It has been claimed that a left hemisphere bias toward local and right hemisphere bias toward global visual processing can be explained in terms of specialization for relatively high and low spatial frequencies, respectively. Using non-representational figures, we tested this hypothesis in experiment 1 using positron emission tomography (PET) measures of cerebral activity in 10 normal volunteers. In each block of trials subjects viewed either a relatively high or a relatively low spatial frequency grating. The orientation (vertical or horizontal) of the grating changed from trial to trial. In a directed attention task, subjects reported the orientation of either the whole stimulus (globally directed attention) or the orientation of the component parts thereof (locally directed attention). A significant interaction between hierarchical processing level (global or local) and stimulus level (relatively high or relatively low spatial frequency within the absolute low spatial frequency range) was found. Globally directed attention led to significantly increased cerebral activity in the right hemisphere when relatively high spatial frequency stimuli were used but not when relatively low spatial frequency stimuli were used. Likewise, locally directed attention increased cerebral activity when low but not high spatial frequency stimuli were used. On the basis of these results we suggest that perceptual salience of the global or local form modulates hemispheric processing asymmetries in early visual cortex. In experiment 2, the perceptual salience of global form in relatively high spatial frequency stimuli and of local form in relatively low spatial frequency stimuli was confirmed in a reaction time (RT) study. In combination, the results of the two experiments suggest that perceptual salience takes precedence over spatial frequency (within the range studied here) in determining the cerebral organization of global⧹local processing.

Validity and temporal stability of the chimeric face technique for studying hemispheric processing asymmetries: Data from 6-through 14-year-old children

The validity and temporal stability of the chimeric face technique as a measure of cerebral hemispheric functioning in children were investigated. The method is based upon the observation that when a subject encounters a representation of the human face, the left side (from the observer's point of view) of the face dominates his or her perception of it. This bias was shown to be present in a majority of children ranging from 6 through 14 years old, and it was stronger for right-handers than for left-handers. The 1-month temporal stability of the bias was 67%, which is comparable to that of other surface methods. As in other split-message techniques, the typical left visual field bias was more reliable than the unusual right visual field bias. The implications of these data are discussed.

Hemispheric processing in differential classical eyelid conditioning

During both stages of a two-stage differential classical eyelid conditioning study, visual CSs were projected randomly either to the right or to the left of a central fixation point in order to investigate a hypothesis relating the differences between V-form and C-form responders to cerebral hemispheric processing asymmetries. Failing to extend the findings of an earlier investigation, the present set of results provided little evidence in support of the hemispheric point of view.