Sex Differences and Working Memory Performance

Sex Differences In Working Memory Tasks Using 2D:4D Ratio

Sarah Flynn

Monash University

Gender stereotypes related to cognition pervade social norms and stereotypes. While they provide an endless source of humour on social media, they can impact our values in negative ways. However, sex differences in cognition and memory do exist and their impact in clinical and research settings should understood. Although culture provides some insights into these differences, research currently does not understand the neurobiological mechanisms that underpin these stereotypes. The following study investigated the effect of sex difference on visual-spatial working memory performance.  

The term Working Memory (WM) was first used to refer to in 1960, to describe memory used to plan and carry out behaviour (Miller et al., 1960, as cited in Cowan, 2008). A person relies on working memory to retain partial results while solving an arithmetic problem without paper or to bake a cake without adding the same ingredient twice (Cowan, 2008).  “Working memory is not completely distinct from short-term memory, but rather allows for active ideas and memories to be manipulated whilst engaged in tasks” (Cowan, 2008). While there has been contention about its definition, the study of working memory gained momentum after it was found to be predictive of academic achievement and intelligence. It was correlated with learning outcomes in literacy and numeracy by Daneman and Carpenter (1980).  In fact it was found to correlate with intellectual aptitude better than any other measures of psychological process (Cowan, 2008). Engle et al. (2002) introduced the notion that aptitude and working memory both depend on the ability to control attention and it has since been used as a cognitive measure in a variety of clinical settings including ADHD, schizophrenia, anxiety and MS. WM training appears promising as an intervention in improving ADHD symptoms (Beck, 2010).  Given the important applications for WM measures, impacts of sex difference must be recognised and integrated into experimental designs and/or treatment models.  Currently the bulk of research simply ignores sex as a relevant variable in visual-spatial working memory research (Voyer, 2017).

Research into the brain structure and functioning of a WM model has identified networks that operate across genders but also gender specific networks (Hill, Laird and Robinson, 2014). Using fMRI, Goldstein (2005), demonstrated different patterns of activation across genders such that women demonstrated significant and greater activations in the prefrontal cortex (PFC) and surrounding regions identified as responsible for WM. No difference was found in performance of WM tasks however.

The effect of prenatal testosterone has been identified as effecting development of the PFC and can be measured using the 2D:4D ratio. This ratio is a measure of the length differences between the 2nd and 4th finger. It is a ratio that is evidenced to be a robust and stable measure of sex difference (Kalmady, 2013). Kalmady, 2013, used the ratio to examine sex difference in working memory performance. The n-back task, known for its strong sex difference effect test as it would differentially activate areas of the brain associated with WM. This did occur and Kalmady found that there was no difference in 2D:4D ratio and WM performance. They found small differences within sex groups however.

The 2D:4D ratio may provide a context to elucidate new relationships between WM and sex as it describes the influence of prenatal hormone exposure. It is clear from literature that hormones do effect WM in menstrual cycle and hormone replacement treatment investigations (Duff and Hampson, 2002). Whether this is true for prenatal will be investigated in this study. The literature is divided on the matter of sex difference and WM. Duff and Hampson (2001) reported a female advantage in memory location tasks, while meta-analysis review of 98 research papers by Voyer, (2017) showed a small but persistent male advantage.

The aim of the current study will be to extend current research and investigate whether there are differences between males and females in WM performance, measured in both percentage accuracy (%) and reaction time (ms) on n-back tasks. The difference between sex and 2D:4D ratio will also be tested for significance and finally the ratio 2D:4D will be tested for any relationship with working memory performance across both accuracy and reaction time.

Discussion

The aim of this study was to investigate the effects of sex difference on the performance of working memory tasks. Several secondary hypotheses were explored within the context of sex difference to further elucidate possible relationships. Sex was measured using both gender self-identification by the participant and the 2D:4D ratio; a sexually dimorphic trait indicative of prenatal exposure to testosterone. Working memory was tested using the n-back task, a well-known test of visual-spatial working memory (Voyer, 2017), with well-documented sex differences. (Kalmady, 2013). Participants were assessed on both their accuracy and reaction time (speed).  This study was limited in its use of WM tasks due to its design (a large-scale online environment). Hence a range of visual-spatial WM tasks could not be assessed. There was also a reliance on the participants to self-measure the 2D:4D ratio, however without a consistent sample wide error this would not be a true limitation to the study.

Sex difference with a female advantage was the main finding of the study. This difference was significant for both the accuracy and speed on the n-back task.  This finding was inconsistent with the most recent meta-analysis of 98 similar studies which demonstrated a small but persistent male advantage across the literature (Voyer, 2017). Duff and Hampson’s female advantage used a much wider range of WM tasks, specifically spatial location and verbal tasks which are known to deliver female advantage (2001).