Historical changes in everyday human lifestyles and their effects on hemispheric activation: Speculations on McGilchrist's The Master and His Emissary.

McGilchrist [McGilchrist, I. (2009). The master and His emissary: The divided brain and the making of the modern world. Yale University Press] argued that Western society has undergone a population-level shift from greater right hemisphere influence on cognition to increasingly greater left hemisphere influence over the past few centuries. Four historical lifestyle changes that replaced behaviours associated with right hemisphere activation with behaviours associated with left hemisphere activation may be responsible: (i) shifts from standing to sitting, (ii) from being outdoors to indoors, (iii) from communal to solitary activities, and (iv) from analogue/concrete to holistic/abstract representations.

Differences Between Consistent and Inconsistent Handedness Remain Consistently Interesting: Ten Years of Research on the Consistency of Handedness With the Edinburgh Handedness Inventory.

Almost 10 years ago Prichard et al. (2013) published a literature review on consistency of handedness. They described how consistency of handedness, typically measured by the Edinburgh Handedness Inventory (EHI), predicted outcomes in memory and decision-making paradigms better than direction of handedness. In the last 10 years, new research has extended these findings and added new theoretical perspectives. The goal of this short form review is to highlight and summarize some of these more intriguing findings and to encourage researchers in the fields of memory and decision making to incorporate handedness as a variable in future research.

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.

Predicting interactions in handedness research: The role of integrated versus independent dual-processes.

Over the past two decades, a new way of looking at handedness has emerged (see Prichard, E., Propper, R. E., & Christman, S. D. (2013). Degree of handedness, but not direction, is a systematic predictor of cognitive performance. Frontiers in Psychology, 4, 1-6), with an emphasis on degree (strong/consistent versus mixed/inconsistent) augmenting the traditional emphasis on direction (left versus right) of handedness. Much of this work has focused on main effects: e.g., inconsistent-handers show higher (or lower) performance than consistent-handers. However, many of these "main effects" are actually nested within higher order interactions: e.g., there are no handedness differences in a baseline/control condition, with handedness differences emerging in an experimental condition. Careful examination, though, of these interactions reveals an intriguing and predictable pattern: for integrated dual processes (e.g., episodic memory encoding versus retrieval), the interactions reflect larger effects in inconsistent-, relative to consistent-, handers. For independent, mutually exclusive dual processes (e.g., approach versus withdrawal), the interactions reflect larger effects in consistent-handers. It is argued that these patterns reflect the relative inability of (i) consistent-handers to integrate dual processes, and (ii) inconsistent-handers to keep independent dual processes separate. We also use this same theory to address higher order interactions involving changes in the experimental context as well as other individual difference factors, and make suggestions for future research.

Memory Effects of Manipulating Text Column Width: Eye-Movement Induced Attentional Processes Interfere With Prose Encoding Among Consistent Handers.

Performing bilateral saccadic eye-movements has enhanced subsequent verbal recall among consistent handers (people who use their dominant hands for virtually all tasks) but not inconsistent handers (people who use their non-dominant hands for some tasks); but eye-movements prior to encoding have disrupted recall in consistent handers. We sought to better understand how this research might be applied to recalling written text presented in ways that differentially affected eye movements. We manipulated text column width in order to test whether induced eye movements and resultant right hemisphere activations would lead consistent handed (versus inconsistent handed) readers to experience encoding disruptions and poorer recall of the written passage. We presented participants, divided by handedness consistency and gender, with a story about a fictional island in which the lines of text were either ∼28 or ∼120 characters wide. We later asked participants to answer 20 questions about the story and measured their memory performance by both their percentage of correct answers and by their correct answers adjusted for a guessing tendency. We found a handedness by text width interaction. Consistent handers who read the story in a narrower column width showed poorer recall than both inconsistent handers and consistent handers who read the story in the wider text column. We suggest a chain of events such that text width altered eye-movements that, in turn, activated right hemisphere brain processes associated with orienting attention and attentional control, competing with consistent handers' encoding.

Authoritarianism, Conspiracy Beliefs, Gender and COVID-19: Links Between Individual Differences and Concern About COVID-19, Mask Wearing Behaviors, and the Tendency to Blame China for the Virus.

The present study investigated variables potentially associated with a lack of concern about COVID-19 and belief in the conspiracy theory that China is responsible for the virus. In particular, the study looked at Authoritarianism, Conspiracy Beliefs, gender, and consistency of handedness as predictors of nine Likert-type items gauging attitudes, behavior, and beliefs regarding the virus. Initial analyses showed that Authoritarianism predicted less concern about the impact of the virus on health, less mask wearing, and a stronger belief in China's responsibility for the illness. Conspiracy Beliefs were associated with a stronger belief in China's responsibility. Women expressed greater degrees of concern about their own and others' health and about the financial wellbeing of others. In order to reduce the number of dimensions, and thus the number of tests that could yield a type one error, the nine items were then submitted to a principal components analysis which yielded a "Concern about COVID" factor and a "Blame for China" factor. Authoritarianism is generally associated with less concern about the virus. In addition, men showed less concern about the virus overall than women. Both Authoritarianism and Conspiracy Beliefs accounted for unique variance in blame on China for the virus.

Handedness and the 2016 U.S. Primaries: consistent handedness predicts support for Donald Trump among republicans, but gender predicts support for Hillary Clinton among democrats.

A growing number of studies demonstrate that consistent handers, people who use their dominant hand for all or most manual tasks, are less cognitively flexible than inconsistent handers, people who use their non-dominant hands at least some of the time. A recent hypothesis suggests that differences in handedness emerged evolutionarily because populations benefited from a balance between cognitively rigid and cognitively flexible people. One expectation is that cognitively rigid consistent handers would support more authoritarian policies or candidates. To test this idea, we looked at handedness, gender, and political affiliation as predictors of support for Donald Trump, a candidate whose supporters self-report being more authoritarian, in the 2016 primary. Our data show that in the Republican Primary, consistent handers report more support than inconsistent for Donald Trump. When authoritarianism was added as a covariate, the handedness effect disappeared. Further analyses showed that authoritarianism mediates the relationship between handedness and support for Donald Trump. In the Democratic Primary, there was a main effect of gender. Women reported more support than men for Hillary Clinton.

The Pen Is Not Always Mightier: Different Ways of Measuring Handedness With the Edinburgh Handedness Inventory Yield Different Handedness Conclusions.

Although consistency of handedness (the strength of dominant hand preference) is increasingly recognized as an important individual difference, there are questions about how to best measure it. A recent meta-analysis showed that researchers have often failed to report details of responses and response formats to handedness test items. In addition to measuring handedness direction (i.e., left versus right handedness), there can be utility to dichotomizing the Edinburgh Handedness Inventory (EHI) into consistent and inconsistent dominant handedness, despite controversy over the best means of doing so. In this study, we performed a discriminant function analysis of EHI items to determine which items best predicted handedness consistency versus handedness direction. Although the same discriminant function accounted for most of the variance for both dependent measures, writing and drawing EHI items were the strongest predictors of handedness direction and combing and opening jars items were the strongest predictors of handedness consistency. As different items on the EHI predicted these different handedness dimensions, we discuss the implications of dichotomizing EHI items into both relevant dimensions for both biological and environmental theories of the basis of handedness and for future handedness research.

Superior categorical and coordinate spatial task performance in inconsistent-handers relative to consistent-right-handers.

Categorical versus coordinate spatial tasks rely differentially on the left versus right hemisphere. Given the neuroanatomical and neurophysiological differences between inconsistent- versus consistent-right-handers (ICH versus CRH, respectively), such that the former demonstrates increased access to right hemisphere processes relative to the latter, it was hypothesized that ICH would outperform CRH on a test of coordinate spatial knowledge. Previous work demonstrating reliance on the right hemisphere for both categorical and coordinate information in non-right-handers using lateralized stimuli of brief duration suggested ICH might also outperform CRH on a categorical task as well. Participants navigated a virtual environment, landmark-to-landmark, within a 3-dimensional first-person point of view with high ecological validity, and then were tested on either their categorical or coordinate spatial knowledge. ICH were superior relative to the CRH on both types of spatial knowledge. Additionally, ICH navigated the environment during learning more quickly, and reported being more confident in their knowledge of the location of landmarks within the environment, compared with CRH. Results are discussed in terms of potential handedness differences in spatial ability generally.

Mere ownership of memory: motor manipulation during encoding affects memory for words.

Involving the body in learning increases the impact information has on memory (Johnson-Glenberg et al. in Front Psychol 7(1819):1-22, 2016), especially when that information is self-relevant (Truong et al. in J Exp Psychol Hum Percept Perform 42(3):375-385, 2016). Yet, prior research has only examined the effect of self-relevant movement (i.e., toward the self or away from the self) on memory through passive joystick flexion or extension (Oakes and Onyper in Cognit Process 18:325-333, 2017). Therefore, the current research sought to replicate the "toward: remember" and "away: forget" motor-induced self-reference effects on memory with actual body movement. Participants in two experiments took notes on a word list and either pushed notes away, pulled notes toward them, moved notes laterally, or wrote the words in a list. Results showed that participants who pulled hand-written notes toward them had better recall than those who pushed notes away from them or moved them laterally. Results suggest implicitly taking ownership of material in an embodied manner may influence how much is recalled.

Superior episodic memory in inconsistent-handers: a replication and extension using fNIRS.

A large body of evidence supports the existence of a robust handedness difference in episodic memory retrieval, with inconsistent-handedness being associated with superior memory across a wide variety of paradigms, including superior retrieval of lab-based and real world memories. Despite superior episidoc memory in inconsistent-handers, and despite neuroanatomical and neurophysiological differences in cortical regions between inconsistent- and consistent-handers, we are aware of no studies to date that have examined physiological activity in the brains of inconsistent- versus consistent-handers while engaged in memory tasks. The purpose of this paper, therefore, is to present a first look at this issue, using functional near-infrared spectroscopy (fNIRS) as a simple, non-invasive measure of frontal lobe activity during encoding and recall of list words in inconsistent- and consistent-handers. Behaviourally, we replicated prior studies, finding a significant inconsistent-handed advantage in free recall. Using fNIRS-derived oxygenated haemoglobin (O2Hb) as a measure of frontal lobe activity, we found the first evidence for handedness differences in brain activity that are associated with the handedness differences in episodic retrieval. Specifically, the primary finding was that increased O2Hb in the right hemisphere during recall was associated with better retrieval, but for consistent-handers only.

Relationship between sustained unilateral hand clench, emotional state, line bisection performance, and prefrontal cortical activity: A functional near-infrared spectroscopy study.

Sustained unilateral hand clenching alters perceptual processing and affective/motivational state, with these alterations presumed to reflect increased hemispheric activity contralateral to the side of motor movement. However, data from electroencephalographic and imaging studies are contradictory regarding the relationship between sustained hand clenching and brain activity. In order to investigate the relationship between brain activity, sustained unilateral hand clenching, and changes in affect and perceptual processing, frontal hemispheric activity was measured via functional near-infrared spectroscopy (fNIRS), using derived O2Hb prior to, during, and post-sustained unilateral hand clench. Participants' mood and spatial perception were recorded pre- and post-clenching. Sustained unilateral hand clenching altered brain activity and mood, but not spatial perception. Results revealed increased O2Hb bilaterally following sustained unilateral hand clenching, relative to baseline, regardless of hand. In agreement with previous fNIRS studies, sustained unilateral hand clenching resulted in greater ipsilateral, compared with contralateral, O2Hb. An interaction between side of hand clench and change in mood was in the direction predicted by theories of hemispheric lateralization of emotion: Following left-hand clenching, individuals became more affectively negative, and following right-hand clenching, they became more affectively positive.

Inconsistent-handed advantage in episodic memory extends to paragraph-level materials.

Past research using handedness as a proxy for functional access to the right hemisphere demonstrates that individuals who are mixed/inconsistently handed outperform strong/consistently handed individuals when performing episodic recall tasks. However, research has generally been restricted to stimuli presented in a list format. In the present paper, we present two studies in which participants were presented with paragraph-level material and then asked to recall material from the passages. The first study was based on a classic study looking at retroactive interference with prose materials. The second was modelled on a classic experiment looking at perspective taking and the content of memory. In both studies, the classic effects were replicated and the general finding that mixed/inconsistent-handers outperform strong/consistent-handers was replicated. This suggests that considering degree of handedness may be an empirically useful means of reducing error variance in paradigms looking at memory for prose level material.

The contributions of handedness and working memory to episodic memory.

Past studies have independently shown associations of working memory and degree of handedness with episodic memory retrieval. The current study takes a step ahead by examining whether handedness and working memory independently predict episodic memory. In agreement with past studies, there was an inconsistent-handed advantage for episodic memory; however, this advantage was absent for working memory tasks. Furthermore, regression analyses showed handedness, and complex working memory predicted episodic memory performance at different times. Results are discussed in light of theories of episodic memory and hemispheric interaction.

Need for cognition moderates paranormal beliefs and magical ideation in inconsistent-handers.

A growing literature suggests that degree of handedness predicts gullibility and magical ideation. Inconsistent-handers (people who use their non-dominant hand for at least one common manual activity) report more magical ideation and are more gullible. The current study tested whether this effect is moderated by need for cognition. One hundred eighteen university students completed questionnaires assessing handedness, self-reported paranormal beliefs, and self-reported need for cognition. Handedness (Inconsistent vs. Consistent Right) and Need for Cognition (High vs. Low) were treated as categorical predictors. Both paranormal beliefs and magical ideation served as dependent variable's in separate analyses. Neither set of tests yielded main effects for handedness or need for cognition. However, there were a significant handedness by need for cognition interactions. Post-hoc comparisons revealed that low, but not high, need for cognition inconsistent-handers reported relatively elevated levels of paranormal belief and magical ideation. A secondary set of tests treating the predictor variables as continuous instead of categorical obtained the same overall pattern.

Factor analysis of the Edinburgh Handedness Inventory: Inconsistent handedness yields a two-factor solution.

While neuropsychology has long focused on direction (left versus right) of handedness, a growing body of evidence indicates that degree (inconsistent versus consistent) of handedness is at least as important. A promising feature of this new emphasis on degree of handedness is its greater concordance with extant genetic models of handedness, which posit a continuum from inconsistent-handedness to consistent right-handedness, not a continuum from left- to right-handedness. Specifically, departures away from consistent-right-handedness are thought to reflect the action of a neutral genetic factor that leaves handedness up to random environmental influences. To test whether handedness in inconsistent-handers reflects the presence of multiple factors (compared to the presence of a single factor only in consistent-right-handers), factor analyses of handedness inventory scores were conducted on data from 987 right-handers, divided into consistent- versus inconsistent-handers. Consistent with predictions, analyses of inconsistent- versus consistent-handers yielded two versus one factor solutions, respectively. Results are discussed in terms of their potential implications for genetic models of handedness and for researchers interested in consistency of handedness as a neuropsychological variable.

Handedness differences observed in episodic memory retrieval do not extend to the domain of prospective memory.

A robust inconsistent handed advantage exists for episodic retrospective memory processes. The current study was undertaken to test whether this handedness difference extends to the domain of prospective memory (PM). Two studies, one based on a self-report measure (the Prospective and Retrospective Memory Questionnaire) and the second involving a performance-based test (Memory for Intentions Screening Test), were carried out. Handedness effects were absent for both measures of PM. The absence of a handedness effect strongly suggests that PM processes are primarily characterized by executing intentions that depend on semantic networks for retrieval and do not necessarily rely on recalling spatio-temporal context, as is the case with episodic retrospective memory.

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.

Responding to framed health messages: different strokes for different (handedness) folks.

Research has shown that strength of handedness - a proxy variable for the degree of interaction between the left and right brain hemispheres - predicts differences in a variety of cognitive domains. The present paper extends this work to message (or goal) framing effects in which persuasive health communications emphasise positive vs. negative outcomes. One hundred fifty-six participants read pamphlets containing statements emphasising either the gains of using or the losses of not using sunscreen. Replicating previous research, non-users of sunscreen were more affected by framed messages than users. However, we found a loss- rather than gain-framed advantage, and mixed (inconsistent)-handers seemed to drive these effects more so than strong (consistent)-handers. These results suggest that a 'one-size-fits-all' approach may be inadequate in crafting effective educational messages about health behaviours, and that theories centring around one's regulatory focus orientation as well as new methods in laterality research may be useful in reaching the widest range of individuals.

Handedness differences in information framing.

Previous research has shown that strength of handedness predicts differences in sensory illusions, Stroop interference, episodic memory, and beliefs about body image. Recent evidence also suggests handedness differences in the susceptibility to common decision biases such as anchoring and sunk cost. The present paper extends this line of work to attribute framing effects. Sixty-three undergraduates were asked to advise a friend concerning the use of a safe allergy medication during pregnancy. A third of the participants received negatively-framed information concerning the fetal risk of the drug (1-3% chance of having a malformed child); another third received positively-framed information (97-99% chance of having a normal child); and the final third received no counseling information and served as the control. Results indicated that, as predicted, inconsistent (mixed)-handers were more responsive than consistent (strong)-handers to information changes and readily update their beliefs. Although not significant, the data also suggested that only inconsistent handers were affected by information framing. Theoretical implications as well as ongoing work in holistic versus analytic processing, contextual sensitivity, and brain asymmetry will be discussed.