Introversion and working memory: central executive differences
Introduction
Over the past half century, arousal accounts have dominated explanations of the differences between introverts and extraverts (Eysenck, 1967, Humphreys and Revelle, 1984). Because arousal is a noncognitive variable, it has been difficult for cognitive psychologists to bridge levels of analysis in attempting to understand the relation between the cognitive and the psychophysiological profiles of extraversion. Differences in neurochemistry and neuroanatomy are generally far more amenable to modular or neural circuitry-based views of cognition. The reticular formation in the brainstem, long cited as the anatomical source of arousal differences associated with extraversion (Eysenck, 1967), has recently been shown to exert control upstream over certain cortical and subcortical areas of the brain. Specifically, the pontine reticular nucleus projects to both the prefrontal cortex and the basal ganglia modulating the release of dopamine (DA; Martin, 1996, Robbins and Everitt, 1995). Each of these areas is central to higher cognitive functions. Dorsolateral prefrontal cortex (DLPFC) is involved in working memory (Cabeza & Nyberg, 1997), while the basal ganglia is central to procedural memory formation (Lieberman, submitted, Saint-Cyr and Taylor, 1992). Furthermore, both DLPFC and basal ganglia depend on DA for normal functioning (Cohen and Servan-Schreiber, 1992, Spitzer, 1993, Wickens and Kotter, 1995). These advances in mapping the neuroanatomical and neurochemical links from the reticular formation to other areas of the brain offer new avenues of insight into the cognitive consequences of arousal differences. Based on these findings, it should be expected that extraverts and introverts would differ both in their working memory and their procedural memory.
The expected difference in procedural memory has been found by Corr and colleagues (Corr, Pickering & Gray, 1995). In this study, subjects identified as quickly as possible, in which of four quadrants a target appeared. On 40% of the trials, a rule determined the location of the target and thus the location could be predicted, though only implicitly on the basis of procedural memory (Lewicki, Hill & Bizot, 1988). Introverts demonstrated a higher degree of procedural learning. This is consonant with Fischer, Wik and Fredrikson’s (1997) findings, using positron emission tomography, of greater subcortical activation in the basal ganglia of introverts than extraverts.
Section snippets
Introversion and working memory
The relationship of introversion and working memory has been nearly studied, or confounded with the investigation of other variables, a number of times. Only three experiments have directly assessed this relation. The unfortunate confound in most of the studies results from the historical progression of memory research. In the 1960s and 1970s, memory was conceptualized in terms of short- and long-term memory. Long-term memory denoted demonstration of memory after a retention interval of 10–20
Subjects
Twenty-eight individuals (Mean age=20.3 years) completed the Eysenck Personality Inventory scale for extraversion (Eysenck & Eysenck, 1968). The seven most extraverted (MEPI=15.78) and the seven most introverted (MEPI=9.98) individuals were brought in to complete the rest of the experiment. Data for one subject was lost due to a computer error. Thus, the final sample used was 10 females and 3 males. Ss were recruited from an introductory psychology course and received class credit for their
Results
The best fitting line for each subject’s reaction times was found by regressing each subject’s reaction times on memory set size. The y-intercepts associated with each subject’s line were compared revealing faster reaction times for extraverts than introverts, t(11)=2.28, P<0.05, r=−0.57 (MExtravert=341.19 ms, SEMExtravert =15.11 ms; MIntrovert=397.28 ms, SEMIntrovert =19.97 ms). As seen in Fig. 1, this difference is carried disproportionately by the two smallest memory set sizes, but is
Discussion
The results of the current study suggest that extraverts have better working memory skills than introverts. Furthermore, because the Sternberg paradigm (1975) was used, it is reasonable to conclude that the advantage is specifically located within the central executive component of working memory. This fits well with neuroscientific theories of working memory and the known neuroanatomical differences between introverts and extraverts. The central executive component of working memory is thought
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