Processing persuasive arguments: recall and recognition as a function of agreement and manipulated activation asymmetry

Righty-tighty, lefty-loosey: relation between societal tightness scores, left-handedness rates, and COVID-19 outcomes in US states

As the percentage of right-handers increases in a state, the tightness of that state's culture, as measured, also increases. The relations between handedness, tightness, and various COVID measures (cases per 100,000, vaccination rates, hospitalization rates, death rates, and mask wearing adherence) were examined. Left-handedness rates and tightness both marginally predicted COVID cases and significantly predicted vaccination rates (more right-handers and more tightness associated with higher COVID rates and lower vaccination rates), only left-handedness rates predicted mask wearing adherence (more left-handers associated with increased adherence), only tightness predicted death rates (more tightness associated with higher death rates), and neither handedness or tightness predicted hospitalizations. Results are discussed in terms of the connection between consistent right-handedness and decreased cognitive flexibility and its implication for sociopolitical outcomes, and implications for the framing of public health messaging are presented.

No Evidence That Lateral Preferences Predict Individual Differences in the Tendency to Update Mental Representations: A Replication-Extension Study

A growing body of evidence suggests that inconsistent hand preference is indicative of an increased disposition to update one’s beliefs upon exposure to novel information. This is attributed to a facilitated exchange of information between the two brain hemispheres among inconsistent handers, compared to consistent handers. Currently available studies provide only indirect evidence for such an effect, were mostly based on small sample sizes, and did not provide measures of effect size. Small sample size is a major factor contributing to low replicability of research findings and false-positive results. We thus attempted to replicate Experiment 1 of Westfall, Corser and Jasper (2014), which appears to be representative of research on degree of handedness and belief updating in terms of the employed methods. We utilized data from a sample more than 10 times the size (N = 1243) of the original study and contrasted the commonly applied median-split technique to classify inconsistent and consistent handers with an empirically grounded classification scheme. Following a replication-extension approach, besides handedness, footedness was also explored. Only one out of 12 chi-squared tests reached significance and supported the original hypothesis that inconsistent handers stay with, or switch more often from, the status quo than consistent handers, depending on the valence of novel information. A small-telescopes analysis suggested that the original study had too low analytic power to detect its reported effect reliably. These results cast doubt on the assumption that inconsistent and consistent-handers differ in the tendency to update mental representations. We discuss the use of the median-split technique in handedness research, available neuroscientific evidence on interhemispheric interaction and inconsistent handedness, and venues of future research.

Hemispheric lateralization in reasoning

A growing body of evidence suggests that reasoning in humans relies on a number of related processes whose neural loci are largely lateralized to one hemisphere or the other. A recent review of this evidence concluded that the patterns of lateralization observed are organized according to two complementary tendencies. The left hemisphere attempts to reduce uncertainty by drawing inferences or creating explanations, even at the cost of ignoring conflicting evidence or generating implausible explanations. Conversely, the right hemisphere aims to reduce conflict by rejecting or refining explanations that are no longer tenable in the face of new evidence. In healthy adults, the hemispheres work together to achieve a balance between certainty and consistency, and a wealth of neuropsychological research supports the notion that upsetting this balance results in various failures in reasoning, including delusions. However, support for this model from the neuroimaging literature is mixed. Here, we examine the evidence for this framework from multiple research domains, including an activation likelihood estimation analysis of functional magnetic resonance imaging studies of reasoning. Our results suggest a need to either revise this model as it applies to healthy adults or to develop better tools for assessing lateralization in these individuals.

Individual differences in information order effects: the importance of right-hemisphere access in belief updating

The order in which information is received alters the evaluation of causal hypotheses. Specifically, research suggests that the last piece of information oftentimes has the greatest impact on the evaluation and that the difference in subjective value between two pieces of information is an important factor influencing the magnitude of this recency effect. The present paper extends this line of work by exploring individual differences in this phenomenon via one's degree of handedness. Two hundred and five participants were given two hypothetical scenarios and related causal hypotheses accompanied by two pieces of additional information and asked to revise their belief in each hypothesis as information accumulated. Results confirmed predictions that 1) inconsistent/mixed-handers (those who use their non-dominant hand for at least some activities) show a larger effect with two pieces of inconsistent weak or strong information, and 2) neither mixed-handers nor consistent/strong-handers (those who use their dominant hand for almost all activities) show an effect with strong and weak pieces of consistent information. Mixed-handers' susceptibility to persuasive arguments and Ramachandran's (1995; Ramachandran and Blakeslee, 1998) belief-updating theory centered around communication between the two halves of the brain and functional access to the right hemisphere are used to account for these data.

Unilateral muscle contractions enhance creative thinking

Following the notion of relative importance of the right hemisphere (RH) in creative thinking, we explored the possibility of enhancing creative problem solving by artificially activating the RH ahead of time using unilateral hand contractions. Participants attempted to complete the Remote Associates Test after squeezing a ball with either their left or right hand. As predicted, participants who contracted their left hand (thus activating the RH) achieved higher scores than those who used their right hand and those who did not contract either hand. Our findings indicate that tilting the hemispheric balance toward the processing mode of one hemisphere by motor activation can greatly influence the outcome of thought processes. Regardless of the specific mechanism involved, this technique has the potential for acting as a therapeutic or remedial manipulation and could have wide applications in aiding individuals with language impairments or other disorders that are believed to be related to hemispheric imbalances.

Side biases in humans (Homo sapiens): three ecological studies on hemispheric asymmetries

Hemispheric asymmetries and side biases have been studied in humans mostly in laboratory settings, and evidence obtained in naturalistic settings is scarce. We here report the results of three studies on human ear preference observed during social interactions in noisy environments, i.e., discotheques. In the first study, a spontaneous right-ear preference was observed during linguistic exchange between interacting individuals. This lateral bias was confirmed in a quasi-experimental study in which a confederate experimenter evoked an ear-orienting response in bystanders, under the pretext of approaching them with a whispered request. In the last study, subjects showed a greater proneness to meet an experimenter's request when it was directly addressed to the right rather than the left ear. Our findings are in agreement both with laboratory studies on hemispheric lateralization for language and approach/avoidance behavior in humans and with animal research. The present work is one of the few studies demonstrating the natural expression of hemispheric asymmetries, showing their effect in everyday human behavior.

Individual differences in risk perception versus risk taking: Handedness and interhemispheric interaction

Research indicates that right-hemisphere mechanisms are specifically sensitive to and averse to risk. Research also indicates that mixed degree of handedness is associated with increased access to right hemisphere processing. Accordingly, it was predicted that mixed-handers would exhibit greater risk aversion. Participants were presented with various risky activities and were asked to rate (i) the perceived risk, (ii) the perceived benefit, and (iii) their likelihood to engage in each activity. No handedness differences were found for any of these ratings. Regression analyses, however, indicated that the likelihood to engage in risky activities was predicted primarily by the perceived risks in mixed-handers and by the perceived benefits in strong-handers.

Manipulation of frontal brain asymmetry by cognitive tasks

The purpose of the present study was to evaluate whether verbal fluency tasks may specifically induce relatively greater left than right hemispheric activation in the dorsolateral prefrontal cortex. The effectiveness of the manipulation was evaluated by EEG, which was recorded during performance of the verbal fluency task and during two control conditions, i.e., a baseline condition without cognitive demands, and a mental arithmetic task, respectively. The results demonstrate that the desired effect can only be achieved in individuals with good performance on the verbal fluency task. Good and poor performers do not only differ in lateral asymmetry, but also in the most affected region within the prefrontal cortex. Whereas good performers show relatively increased activation in the cortical region and hemisphere putatively most specialized for this kind of task (i.e., the left dorsolateral frontal cortex), poor performers show a marked shift of frontopolar asymmetry to the right.

Bisecting and behavior: lateral inattention predicts 8-week academic performance

Converging evidence supports a left hemisphere role in defensive repression and sensation seeking. This led to the hypothesis that students with a relatively active left hemisphere would perform poorly during 8 weeks of a college class. The measure of relative hemispheric activation was the visual line-bisecting task given early in the course. The hypothesis was supported. Previous evidence that activation asymmetry is stable over time was supported because the single measurement of line bisecting was a longitudinal predictor of multiple behaviors. A temporal pattern of increasing correlation between the bisecting and performance measures favors a feedback repression model. Alternative explanations based on sensation seeking, subject-matter repression, and cooperation were considered but not eliminated.

Hemispheric interaction and consciousness: Degree of handedness predicts the intensity of a sensory illusion

It has been suggested that the two cerebral hemispheres play different roles in the maintenance and updating of an individual's beliefs. In particular it has been suggested that the left hemisphere (LH) forms consistent beliefs, whereas the right hemisphere (RH) monitors for inconsistencies or anomalies in reference to these beliefs. If some threshold of inconsistencies is detected, the role of the RH is to update the LH's belief system accordingly. Handedness may reflect the degree to which the two hemispheres exchange information such that the more strongly handed an individual is, the less interhemispheric communication may take place, thus attenuating this updating process. Two studies were carried out that confronted participants with conflicting, anomalous sensory information by tapping on both the participant's real hand and a fake hand in synchrony. One conclusion would be to update the LH belief system to include the fake hand as their own and consciously experience the taps as coming from the fake hand. It was predicted that this experience would vary with handedness such that the more strongly handed a participant was, the less they would experience the sensory illusion. Study 1 supported this, with more strongly handed participants reporting lesser degrees of the illusion. A second study replicated this effect and included a variable that measured the time it took for a participant to experience the illusion. A non-significant trend was present such that more strongly handed participants were slower to experience the illusion. Last, although the illusion was felt equally in both the left and right hand conditions, correlations between handedness and the illusion were only present in the left hand condition. A model of how interhemispheric interaction may function in maintaining beliefs and consciousness is presented.

Relationship between attentional orientation and associative learning

This study presents experimental evidence for a relationship between attentional orientation and associative learning. Learning to establish contingencies between warning signals and subsequent task stimuli is a phenomenon which we know from previous studies to be more associated with the left hemisphere. We investigated how hemispheric priming, i.e., activating one hemisphere by directing attention towards the contralateral hemispace, affected both the rate and the extent of associative and nonassociative learning. When attention was directed towards the right while perceiving a discrimination task stimulus, the rate of learning through contingency formation was increased since the relative activation of the left hemisphere was increased. Such a relationship was not found for relative activation of the right hemisphere following leftward orientation of attention.

The role of hemispheric activation in person perception: evidence for an attentional focus model

Two studies assessed the role of hemispheric activation in person perception. Results of Study 1 supported an attentional focus model of hemispheric differences in person perception as opposed to a stereotyping/individuating model. Relative to left hemisphere-activated participants, right hemisphere-activated participants made more individuating judgments and engaged in more trait level stereotyping, whereas left hemisphere-activated participants engaged in more global stereotyping. In Study 2, greater individuation by participants under higher levels of motivation and ability was shown to be mediated by relatively greater right hemisphere activation. Results of both studies are interpreted in terms of an attentional focus model of person perception. Implications for dual process models of social perception are also discussed.

Line bisecting as a predictor of personal optimism and desirability of risky behaviors

Our goal was to test whether current hemisphere predominance is a predictor of scores on standardized measures of personal optimism and preference for risk. In two between-subject experiments, current hemisphere predominance was measured by the direction and extent of line bisecting errors. Pearson correlations and median splits of the line bisecting errors showed significantly greater personal optimism and preference for risk with left hemisphere predominance. These results support previous research in which manipulation of hemisphere predominance produced similar effects on personal optimism in normal individuals and on risk taking in lesioned and normal samples. We conclude that the association of optimism and risk with left hemisphere predominance can be observed in resting as well as in manipulated situations.