Memory for hand-use depends on consistency of handedness

The Italian version of Edinburgh Handedness Inventory: Translation, transcultural adaptation, and validation in healthy subjects

Lateralization is a key aspect of brain architecture and handedness is its primary manifestation. The Edinburgh Handedness Inventory (EHI) and the laterality quotient (LQ) assess the direction and consistency of handedness and require translation and cross-cultural adaptation to guarantee construct validity. We developed a standardized Italian EHI version. The developed Italian version was tested on 202 Italian subjects, classified into three hand types based on their LQs: right, mixed, and left. The frequency of left-handedness in Italians and other populations was compared to previous data. LQs from the twenty- and the ten-item original inventories were also compared. We conducted a factorial analysis. Mcdonald's Omega tested internal consistency. The prevalence of left-handedness was 6.4%, consistent with prior findings in Italian samples and other EHI translations. Age was the only socio-demographic variable that significantly affected the LQ. The internal consistency of the Italian EHI was excellent. Handedness is a feature of several cognitive functions and some neuropsychological diseases; it is influenced by socio-demographic and cultural factors and the instrument used to assess it. To provide a consistent and comparable evaluation of the construct, we recommend using this validated Italian translation of the EHI.

Hand preference for unimanual and bimanual tasks: Evidence from questionnaires and preferential reaching

The current research compared hand selection in a preferential reaching paradigm with unimanual (i.e., pick-up cup) and bimanual (pick-up cup and pour from pitcher) tasks. In addition, relationships between self-report, questionnaire-based hand preference (unimanual and bimanual) and patterns of hand selection were assessed. Data offer support for a division of labour between the hands in at the midline; however, bimanual selection otherwise reflects consideration of object proximity (i.e., location) and comfort (i.e., biomechanical constraints). When grasping cups in right space, the right-hand was used to stabilize the cup and left-hand to mobilize the pitcher, whereas the opposite pattern was observed in left-space. Unimanual hand selection was also driven by object location. Subsequent analyses revealed a relationship between unimanual measures, but not bimanual measures of hand preference. Overall, findings support the notion that questionnaire data are associated with hand preference for grasping to a certain extent; however, use of a comprehensive battery of assessments is recommended when assessing and/or predicting handedness.

Do cerebral motivational asymmetries mediate the relationship between handedness and personality?

Handedness has long been tied to personality, but detailed explanations for the association are lacking. Importantly for purposes of theory development, measures of approach and withdrawal associated with Big Five personality traits have also been traced back to activity in brain areas that relate to handedness. Specifically, increased right-hemisphere frontal activity appears to be linked to both withdrawal motivation and left/inconsistent-handedness, while increased left-hemisphere frontal activity is associated with approach motivation and right/consistent-handedness. Cerebral motivational asymmetries therefore present one plausible mechanism by which approach and withdrawal motivation could mediate the relationship between handedness and personality. We tested this possibility in a large online study (N = 499) in which participants completed multiple survey measures. Results indicated that approach/withdrawal motivation partially accounts for relationships between handedness and personality.

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.

Motor behavior-induced prefrontal cortex activation and episodic memory function

BACKGROUND

The objective of this paper was to evaluate the potential individual and combined effects of acute exercise coupled with bilateral interhemispheric activation on episodic memory function. Six experiments were conducted.

METHODS

Experiment 1 was a within-subject, counterbalanced experiment. Participants completed four visits, including 1) exercise and saccadic eye movements, 2) exercise only, 3) saccadic eye movements only, and 4) no exercise and no saccadic eye movements (control). A word-list memory assessment was employed, including a long-term (20-min delay) memory evaluation. In Experiment 2, we evaluated the effects of saccadic eye movements on prefrontal cortex oxygenation, a proxy for neuronal activity. Similarly, in our third experiment, we evaluated the effects of acute exercise on prefrontal cortex oxygenation. Thus, experiments 2 and 3 were employed to provide mechanistic insights from the results shown in experiment 1. Experiment 4 replicated Experiment 1, but instead of increasing prefrontal cortex activation via saccadic eye movements, we used a fist clenching protocol. Experiment 5 evaluated the effects of fist clenching on prefrontal cortex oxygenation.

RESULTS

Collectively, these 5 experimental studies showed that acute exercise (Experiment 1), saccadic eye movements (Experiment 1), and fist clenching (Experiment 4) enhanced memory function, and that acute exercise (Experiment 3), saccadic eye movements (Experiment 2) and fist clenching (Experiment 5) all increased prefrontal cortex oxygenation. Experiment 6 demonstrated that prefrontal cortex oxygenation was positively associated with episodic memory function.

CONCLUSION

These six experiments suggest that several behaviors, such as acute exercise, saccadic eye movements and fist clenching may improve memory function and may, potentially, do so via increases in prefrontal cortex oxygenation.

Why are consistently-handed individuals more authoritarian? The role of need for cognitive closure

Recent studies indicate that individuals with consistent hand preference are more authoritarian than individuals whose preference is relatively inconsistent. We explored the role of epistemic needs in the handedness-authoritarianism relationship. Based on findings that consistent individuals are less cognitively flexible than inconsistent individuals, we hypothesized that consistent-handers would report greater need for definite knowledge. To measure this, we administered the revised Need for Cognitive Closure scale to a sample of undergraduates (N = 235), along with measures of handedness consistency and authoritarian submission. Consistent individuals scored significantly higher on authoritarian submission and need for closure. Need for closure fully mediated the relationship between consistency and submission. Consistent individuals also expressed greater prejudice against authoritarian out-groups such as immigrants and liberals. This effect was partially mediated by authoritarian submission. We theorize that consistent-handers' cognitive inflexibility leads them to covet definite knowledge. These individuals turn to authoritarianism because it promises to stifle dissent and protect existing (conventional) knowledge.

Telling right from right: the influence of handedness in the mental rotation of hands

BACKGROUND

This study investigated the impact of handedness on a common spatial abilities task, the mental rotation task (MRT). The influence of a right-handed world was contrasted with people's embodied experience with their own hands by testing both left- and right-handed people on an MRT of right- and left-hand stimuli. An additional consideration is the influence of matching the shape of the hand stimuli with the proprioception of one's own hands. Two orthogonal hypothesis axes were crossed to yield four competing hypotheses. One axis contrasted (i) embodied experience versus (ii) world knowledge; the other axis contrasted (a) the match between the visual image of a hand on the screen and one's own hand versus (b) the resemblance of the shape outline information from the hand stimuli with the proprioception of one's own hands.

RESULTS

Among people with mixed handedness, right-handers performed more accurately for left-hand stimuli, while left-handers had a trend for higher accuracy for right-hand stimuli. For people with extreme handedness, right-handers outperformed left-handers. Regardless of group, there was no significant variation in performance for left-hand stimuli, with only right-hand stimuli producing significant variation.

CONCLUSIONS

No hypothesis fully aligned with all the data. For left-hand stimuli, the consistent performance across groups does not provide support for embodied experience, while world knowledge might influence all groups similarly. Alternatively, the within-group variation for mixed-handed people supports embodied experience in the hand MRT, likely processed through visual-proprioceptive integration.

Is self-report a valid measure of unimanual object-based task performance?

Hand preference is commonly measured via self-report using instruments known as handedness inventories. These instruments query which hand subjects use to perform unimanual object-based tasks and also the consistency of usage. Scores reveal which hand people report using most (i.e., which hand is preferred). Some people report highly consistent usage of their preferred hand while others report relatively inconsistent usage. These reports are often assumed to be accurate descriptions of people's actual behavior, but empirical evidence concerning their validity is surprisingly scant. In the present research, subjects completed a handedness inventory on which higher scores indicated more consistent usage of the preferred hand. After a brief filled interval, subjects performed tasks listed on the inventory, spontaneously choosing which hand to use for each task. Subjects who scored higher on the inventory used the preferred hand more often. Subjects were then timed while performing the tasks as fast as they could with each hand. Subjects were faster when using their preferred hand and the magnitude of the preferred hand advantage was positively correlated with self-reported consistency. These results support the validity of inventory scores by showing that they are related to spontaneous hand choice and manual fluency when performing inventory tasks.

Interhemispheric Activation and Memory Function: Considerations and Recommendations in the Context of Cardiovascular Exercise Research

The field of neurobiology of learning and memory has demonstrated that interhemispheric activation plays an important role in subserving episodic memory function. A common behavioral technique to induce interhemispheric activation includes saccadic eye movements, with a common behavioral marker being the degree of handedness. Importantly, however, the field of exercise neurobiology has yet to consider these behavioral techniques and markers in exercise-based studies. This review highlights the effects of these techniques and markers on episodic memory function and discusses the implications of this for exercise studies. We discuss the physiological and neurological mechanisms of interhemispheric activation on memory. We also discuss the role this may play in cardiorespiratory exercise studies. Our understanding of the role of both exercise and interhemispheric activation on memory function is improving. The interplay between these two factors on memory, however, is unknown. We discuss these implications and provide recommendations for future research.

Effects of handedness consistency and saccade execution on eyewitness memory in cued- and free-recall procedures

Identifying characteristics that distinguish between people with relatively good versus poor episodic memory is an important goal of eyewitness-memory research, as is identifying activities that can improve people's ability to retrieve episodic memories. Consistency of hand preference is a trait associated with the quality of people's episodic memory and repetitive saccade execution is an activity known to improve people's ability to retrieve episodic memories. These factors were examined in relation to cued and free recall of a staged criminal event. Individuals with inconsistent hand preference (versus consistent) remembered more on a cued-recall test and also freely recalled a larger amount of victim information. Repetitive saccade execution did not increase cued recall but did increase free recall of victim information. Theoretical implications are discussed, as is potential practical significance, with an emphasis on the size of the observed effects.

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.

Bimanual coordination positively predicts episodic memory: A combined behavioral and MRI investigation

Some people remember events more completely and accurately than other people, but the origins of individual differences in episodic memory are poorly understood. One way to advance understanding is by identifying characteristics of individuals that reliably covary with memory performance. Recent research suggests motor behavior is related to memory performance, with individuals who consistently use a single preferred hand for unimanual actions performing worse than individuals who make greater use of both hands. This research has relied on self-reports of behavior. It is unknown whether objective measures of motor behavior also predict memory performance. Here, we tested the predictive power of bimanual coordination, an important form of manual dexterity. Bimanual coordination, as measured objectively on the Purdue Pegboard Test, was positively related to correct recall on the California Verbal Learning Test-II and negatively related to false recall. Furthermore, MRI data revealed that cortical surface area in right lateral prefrontal regions was positively related to correct recall. In one of these regions, cortical thickness was negatively related to bimanual coordination. These results suggest that individual differences in episodic memory may partially reflect morphological variation in right lateral prefrontal cortex and suggest a relationship between neural correlates of episodic memory and motor behavior.

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.

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.