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

ABSTRACT

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.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Technically, consistent right- and left-handed individuals are different. Consistent right-handers typically have greater relative LH activation, while consistent left-handers tend to have greater relative RH activation, much like inconsistent handers (as outlined in Hardie & Wright, 2014). Nevertheless, while consistent left-handers are different, they are difficult to study because of their small numbers (as they represent only 2%–3% of the population (Lansky, Feinstein, & Peterson, 1988)), and their overall behavioral response patterns tend to be closer to consistent right-handers than inconsistent handers. Thus, they are usually categorized as consistent-handed, and at times they are excluded from data analyses altogether.

2 We should note here that the data in Figure 1.a do not involve the explicit manipulation of an independent variable, but there was nonetheless a larger effect on (not of) judgment type in inconsistent-handers.