A sinister subject: Quantifying handedness‐based recruitment biases in current neuroimaging research

Abstract

Approximately ten per cent of humans are left‐handed or ambidextrous (adextral). It has been suggested that, despite their sizable representation at the whole‐population level, this demographic is largely avoided by researchers within the neuroimaging community. To date, however, no formal effort has been made to quantify the extent to which adextrals are excluded from neuroimaging‐based research. Here, we aimed to address this question in a review of over 1,000 recent articles published in high‐impact, peer‐reviewed, neuroimaging‐focused journals. Specifically, we sought to ascertain whether, and the extent to which adextrals are underrepresented in neuroimaging study samples, and to delineate potential trends in this bias. Handedness data were available for over 30,000 research subjects; only around 3%–4% of these individuals were adextral—considerably less than the 10% benchmark one would expect if neuroimaging samples were truly representative of the general population. This observation was generally consistent across different areas of research, but was modulated by the demographic characteristics of neuroimaging participants. The epistemological and ethical implications of these findings are discussed.

Empirical assessment of changing sample‐characteristics in task‐fMRI over two decades: An example from gustatory and food studies

“…For articles that reported handedness of subjects, 89.1% of them recruited only right‐handed subjects. However, it should also be noted that 37.3% of the analyzed articles did not report subject handedness – this ratio is considerably much larger than the 9.2% of sensorimotor‐related articles as reported by Bailey et al ().…”

“…A recent survey, based on approximately 1,000 articles, reported that only 3–4% of over 30,000 research subjects recruited for neuroimaging experiments were left‐handed or ambidextrous, compared to their prevalence of 10–13% in the general population (Bailey et al, ). In this dataset, we also found that the subjects were mainly right‐handed.…”

“…Can results generated by those small samples be generalized to other populations and become relevant to us? A recent study surveyed approximately 1,000 neuroimaging articles, only to find that 3–4% of recruited subjects were left‐handed or ambidextrous (Bailey, McMillan, & Newman, ). In neuroscience, nearly half of the animal studies used males only, with 25% used both sexes and 9% used female only (Beery, ).…”

A systematic review of neurological impairments in myalgic encephalomyelitis/ chronic fatigue syndrome using neuroimaging techniques

“…In a VBM study of 465 healthy adult brains they found minimal effect of handedness on symmetry [68]. This is supported by a review article that assessed the effect of handedness on the findings from numerous different neuroimaging techniques [69]. Therefore, handedness matching may not be a necessary consideration for future imaging studies.…”

Handedness measures for the Human Connectome Project: Implications for data analysis

“…The use of some version of the EHI is now ubiquitous for subject screening and 4 participant exclusion in neuroimaging studies, often to the omission of other methods of 5 handedness assessment (Fazio & Cantor, 2015). The exclusion of left-handed subjects (defined as 6 those with either low or negative EHI scores) in neuroimaging contexts-specifically those 7 probing language or other lateralized functions-is largely justified, considering the effect of 8 subject lateralization on variance in activation patterns and resultant issues with common statistical 9 approaches (see Bailey, McMillan, & Newman, 2019;Króliczak, Gonzalez, & Carey, 2019;10 Vingerhoets, 2014). Still, some have argued that this is a misguided approach, claiming that the 11 inclusion of left-handers and other atypically lateralized individuals can tell us more, not less, 12 about cortical function, and especially, asymmetry (Willems et al, 2014).…”