Hemispheric asymmetry and human associative learning: Interactions with attention

In a previous study (Hugdahl & Brobeck, 1986) it was shown that Pavlovian conditioning to an auditory verbal conditioned stimulus (CS) initially presented only to the left cerebral hemisphere was stronger than when the same CS was presented to the right hemisphere. This was followed up in the present study by controlling for the possibility that the effect was caused by laterally biased attention. The study was performed using the “dichotic extinction paradigm,” which consists of three different phases. During the habituation phase, the CS+ and CS- were presented binaurally and separated in time. During the acquisition phase, the CS+ was followed by a white-noise unconditioned stimulus (UCS). During the dichotic extinction phase, the CS+ and CS- were presented dichotically, i.e., simultaneous presentations on each trial. Half of the subjects had the CS+ in the right ear, and half had the CS+ in the left ear. Each group was further divided into two subgroups, with one subgroup instructed to attend only to the right ear input, and the other subgroup to attend only to the left ear input. During acquisition, larger electrodermal responses were obtained to the CS+ than to the CS-. During dichotic extinction, the CS+ right ear group showed superior resistance to extinction compared to the CS+ left ear group, with no effect of the manipulation of attention. The effect was, however, attenuated when levels of acquisition was used as covariates in an analysis of covariance. There were overall larger responses from the left hand recording.     

Hemispheric asymmetry and electrodermal activity in orienting and pavlovian conditioning paradigms

Three experiments on lateralization of electrodermal orienting and conditioned behavior are reported. The basic findings show effects of hemispheric asymmetry on initial magnitude and rate of habituation of phasic stimulus-elicited electrodermal responses. In summary, responses to verbal stimuli repeatedly flashed to the right visual half-field are larger than corresponding responses in the left half-field. Similarily, spatially relevant stimuli initially presented to the left half-field result in larger responses than when the same stimuli are repeatedly presented in the right half-field. In the auditory modality, data show asymmetrical control of responding to verbal material in a dichotic conditioning paradigm with greater resistance to extinction when the conditioned stimulus is initially fed only to the left hemisphere as compared to when it is fed only to the right hemisphere. It is argued that the present approach taps on basic mechanisms for the lateralization of attentional and associative functions.     

Hemispheric lateralization of functions related to emotion

We have reviewed the evidence that processes and functions related to perception and expression of emotions are represented asymmetrically in the cerebral hemispheres. The literature describes three possible aspects of emotional lateralization: that emotions are better recognized by the right hemisphere; that control of emotional expression and related behaviors takes place principally in the right hemisphere; and that the right hemisphere is specialized for dealing with negative emotions, while the left is specialized for dealing with positive emotions. Evidence for the three hypotheses derives from methodologically diverse studies in unimpaired, brain-lesioned, and mood-disordered populations. Relatively little of the work has been precisely replicated, and conclusions rest on parallel lines of evidence from diverse sources. The present level of knowledge suggests a model of emotional control based on interactive inhibition between a right negatively biased and left positively biased hemisphere. However, the details of such a model, including the precise conditions under which emotion-related functions are lateralized, and the mechanisms of such lateralization have yet to be elucidated.     

Hippocampal theta-dependent eyeblink classical conditioning: coordination of a distributed learning system

Richard F. Thompson's study of the neurobiological substrates of learning and memory has been a career-long endeavor, chosen early and pursued with uncompromising depth and breadth. His systematic mapping of the major brain systems and mechanisms involved in eyeblink classical conditioning (EBCC) established the essential role of the cerebellum. Investigations of the interactions between the hippocampus and cerebellum are critically important to this literature, given the essential involvement of these structures in trace EBCC as well as an important modulatory role of the hippocampus in delay EBCC. Hippocampal theta (3-7Hz) oscillations are known to reflect a functional state that influences both the timing of unit firing and the potential for neural plasticity in the hippocampus and other structures. Herein we present a brief summary of research demonstrating the behavioral enhancement due to theta and the underlying neurobiological correlates in both hippocampus and cerebellum during EBCC. Hippocampal and cerebellar local field potentials (LFPs) show that these distantly interconnected brain structures become precisely synchronized when conditions favor rapid behavioral acquisition. Our results suggest a major role for theta in coordinating the widely distributed memory system for trace EBCC. These and other important findings reflect Thompson's own work and his early-career mentoring of scientists whose contributions to the EBCC literature have ensured his major and lasting impact on the neurobiology of learning and memory.     

Hemispheric asymmetry for linguistic prosody: a study of stress perception in Croatian

The aim of the study was to test for possible functional cerebral asymmetry in processing one segment of linguistic prosody, namely word stress, in Croatian. The test material consisted of eight tokens of the word pas under a falling accent, varying only in vowel duration between 119 and 185 ms, attached to the end of a frame sentence. The sentence could, depending on the duration of the vowel, mean 'This is a beautiful dog' or 'This is a beautiful belt/waist.' Each sentence was presented eight times in three dichotic listening conditions (binaural, left ear only, right ear only), in random order. Fourty healthy female right-handers participated in a forced-choice lexical task. For each presented sentence they had to decide whether it referred to the animal (short vowel in the key word) or to the belt/waist (long vowel in the key word). Their oral responses were analyzed in terms of response time and categoricity. No consistent significant differences were found among listening conditions. The responses possibly reflect the nonlateralized activity of subcortical regions or a simultaneous activity of both hemispheres relying on different cues.     

Hemispheric asymmetry for alphabetic identification: Scaling analyses

In a test of the analytic-holistic theory of hemispheric asymmetry, 20 subjects saw brief presentations of upper-case letters in either the left or right visual half-field. A right half-field advantage was found for both accuracy of identification and vocal latency of erroneous responses. Multidimensional scaling, hierarchical clustering, and correlation analyses of the error patterns indicated similarities of processing between the hemispheres. The results were discussed in terms of loss of information from storage prior to processing.     

Hemispheric lateralization in aging: Interest of the verbal-manual concurrency paradigm

ABSTRACT

Introduction: The aim of this study was to evaluate whether the classic asymmetry seen in hemispheric functioning is modified in older adults by using a verbal-manual concurrency task. Method: Thirty-five right-handed participants divided into two groups according to age (15 older participants, mean age: 68 ± 8 years, without cognitive decline and 20 younger participants, mean age: 23 ± 2 years) had to perform a 30-second uni-manual tapping task, in both a single task (tapping alone) and dual task (tapping and performing a letter fluency task together) condition. Results: In younger participants, the letter fluency task disrupted the right hand more than the left hand whereas, in older participants, the letter fluency task disrupted both hands equally. Conclusion: These results should be considered preliminary data using a behavioral dual task condition, which might be useful for studying lateralized hemispheric functioning and the processes of divided attention during aging.     

Hemispheric asymmetry in the processing of negative and positive words: a divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Cognitive control of response inhibition and switching: Hemispheric lateralization and hand preference

Changing environmental constraints often make already prepared responses unnecessary or inappropriate. Under such circumstances, cognitive control enables to suppress the response or switch to alternative behavior. Here, we examine the neural dynamics of both functions in left- and right-handers who performed two variants of a paradigm that required either inhibition of the response or switching the response between hands. The EEG coherence data showed strengthening of interregional coupling in the alpha band (8–12 Hz) following the target cues with an essential contribution of fronto-medial circuitry and a specific involvement of parietal areas in response switching. Brain-behavioral correlations revealed the functional significance of left-sided regions for successful response inhibition and switching, underlining the significant role of the left hemisphere for the organization of goal-directed activities. This lateralization pattern was observed for both left- and right-handers and suggests dominance of higher-order aspects of action planning in the left hemisphere.     

Hemispheric asymmetry in the processing of negative and positive words: A divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Emotional modulation of attention orienting: A classical conditioning study

Emotional modulation of attention shifting was investigated in Posner's (1980) spatial orienting task by conditioning the attention cue to an aversive white noise. Prior to the attention task, the Conditioning group received a 90dB white noise unconditioned stimulus (UCS) contingent upon the frame-lit rectangle attention cue, while the Control group received non-contingent presentations. The Conditioning group evidenced greater skin conductance responses to the frame-lit rectangle in the conditioning phase, reflecting an electrodermal conditioned response. In the attention phase, the frame-lit rectangle served as the attention cue in the spatial orienting task. The Conditioning group showed equally fast reaction times (RTs) to targets presented outside the location of the cue as to targets at the same location as the cue, reflecting elimination of the cognitive cost usually involved in shifting attention. The Control group evidenced the regular cost of shifting attention away from the location of the cue. The Conditioning group also evidenced a larger N1-component with a parietal distribution of the event-related brain potentials to the cue and a larger N1-component at the frontal regions to targets presented outside the cued location. This suggests that both visual orienting to the cue and attention shifting from cue to target on invalid trials were amplified by the emotional salience attached to the cue through the classical conditioning procedure.     

Hemispheric specialization and creative thinking: A meta-analytic review of lateralization of creativity

In the last two decades research on the neurophysiological processes of creativity has found contradicting results. Whereas most research suggests right hemisphere dominance in creative thinking, left-hemisphere dominance has also been reported. The present research is a meta-analytic review of the literature to establish how creative thinking relates to relative hemispheric dominance. The analysis was performed on the basis of a non-parametric vote-counting approach and effect-size calculations of Cramer’s phi suggest relative dominance of the right hemisphere during creative thinking. Moderator analyses revealed no difference in predominant right-hemispheric activation for verbal vs. figural tasks, holistic vs. analytical tasks, and context-dependent vs. context-independent tasks. Suggestions for further investigations with the meta-analytic and neuroscience methodologies to answer the questions of left hemispheric activation and further moderation of the effects are discussed.     

An asymmetry in transmodal perceptual learning

Transmodal perceptual learning was examined in a canonical same/different paradigm. Subjects naive to vibrotactile stimulation and unfamiliar with the task were asked to discriminate sequentially presented shapes moving laterally across an aperture. On all trials, the shapes were presented either visually and then vibrotactually or in the opposite modality order, and on all trials the shapes moved in opposite directions. Analyses of the data revealed that although perceptual learning was evident in both groups, the rate of the learning was more rapid in the visual-vibrotactile group. This interaction of modality order and practice was significant and was considered in terms of E.J. Gibson's theory of perceptual learning and in terms of the constructs, suggested by J.J. Gibson, of available and accessible information-in-stimulation and the education of attention.     

Hemispheric asymmetry and pun comprehension: when cowboys have sore calves

Event-related potentials (ERPs) were recorded as healthy participants listened to puns such as "During branding, cowboys have sore calves." To assess hemispheric differences in pun comprehension, visually presented probes that were either highly related (COW), moderately related (LEG), or unrelated, were presented in either the left or right visual half field (LVF/RVF). The sensitivity of each hemisphere to the different meanings evoked by the pun was assessed by ERP relatedness effects with presentation to the LVF and the RVF. In Experiment 1, the inter-stimulus interval between the pun and the onset of the visual probe was 0 ms; in Experiment 2, this value was 500 ms. In Experiment 1, both highly and moderately related probes elicited similar priming effects with RVF presentation. Relative to their unrelated counterparts, related probes elicited less negative ERPs in the N400 interval (300-600 ms post-onset), and more positive ERPs 600-900 ms post-onset, suggesting both meanings of the pun were equally active in the left hemisphere. LVF presentation yielded similar priming effects (less negative N400 and a larger positivity thereafter) for the highly related probes, but no effects for moderately related probes. In Experiment 2, similar N400 priming effects were observed for highly and moderately related probes presented to both visual fields. Compared to unrelated probes 600-900 ms post-onset, related probes elicited a centro-parietal positivity with RVF presentation, but a fronto-polar positivity with LVF presentation. Results suggest that initially, the different meanings evoked by a pun are both active in the left hemisphere, but only the most highly related meaning is active in the right hemisphere. By 500 ms, both meanings are active in both hemispheres.     

Brain asymmetry and autonomic conditioning: Sensitization control

In the present experiment we report effects of cerebral asymmetry, or laterality, during classical conditioning to facial emotional stimuli. Twenty-five female subjects were presented with slides of a happy face in one visual half-field (VHF), and simultaneously a slide of an angry face in the other VHF, followed by shock as the unconditioned stimulus (UCS). To control for effects of sensitization, a new stimulus, never associated with the UCS, was introduced in the extinction phase. Dependent measures were phasic heart rate responses (HR) and skin conductance responses (SCR). The HR results showed a significant right hemisphere effect for the CS-UCS association, that was not attributable to UCS sensitization. No significant effects were found for the SCRs. The basic HR finding was a right hemisphere superiority for learning of a conditioned association.