The study examined correlations between incidental learning of foreign words and interhemispheric connectivity, operationalized as consistency of hand preference, using pooled data of five experiments on adult foreign language learning (N = 242). Inconsistent hand preference was found to be positively correlated with vocabulary learning even after effects of cognitive variables (verbal working memory capacity and nonverbal IQ), identified previously as predictive of successful foreign-language vocabulary learning, were partialled out. This observed relationship between handedness consistency and vocabulary learning persisted when left-handed and right-handed individuals were analyzed separately, and there was no overall difference in performance between left- and right-handers. The findings confirm an association between degree of handedness and verbal episodic memory.
Individuals differ in their ability to learn words in a new language. One obvious source of this variability is working memory capacity, which may constrain the extent to which new phonological strings are encoded and retained. Specifically, the phonological loop, a subsystem of verbal working memory, may serve as a word-learning device controlling the storage of phonological strings (Baddeley, Gathercole, & Papagno, 1998) via a sequence memory that encodes the serial order of phonemes, syllables, and words (Gupta, 2003). Consequently, measures of short-term verbal working memory capacity correlate with vocabulary acquisition in children (Gathercole, Hitch, Service, & Martin, 1997) and foreign language learners (Service, 1992).
However, in natural learning situations novel words are encountered in specific semantic and referential contexts. There is good evidence that memory for newly learned vocabulary has a strong episodic component. Using evoked response potentials, Perfetti, Wlotko, and Hart (2005) demonstrated that, unlike unfamiliar words or words well established in the learner's vocabulary, recently encountered words, the meanings of which had been provided in a word-learning task, produced a late positive wave peaking at around 600 msec after word onset, which is considered to be a marker of an episodic memory trace (Curran, 1999). This suggests that over a lifetime an individual accumulates episodic memory traces representing specific experiences with words, which collectively constitute the rich knowledge base of native language vocabulary (Perfetti & Hart, 2002; Reichle & Perfetti, 2003). Indeed, amnesic individuals who have lost their ability to form episodic memories tend to be unsuccessful at learning new vocabulary (Temple & Richardson, 2006).
Recent evidence shows asymmetrical involvement of the cortical hemispheres in episodic memory tasks. The hemispheric encoding/retrieval asymmetry model was developed to account for greater activation in the left prefrontal cortex during encoding and greater activation in the right prefrontal cortex during recall or recognition (Tulving, Kapur, Craik, Moscovitch, & Houle, 1994)1. The model predicts that interhemispheric connectivity modulates performance in episodic memory tasks; indeed, splitbrain patients demonstrate deficits in episodic but not in semantic memory (Cronin-Golomb, Gabrieli, & Keane, 1996). One way to operationalize degree of interhemispheric connectivity is to utilize individual differences in consistency of hand preference;2 this is assumed to be negatively related to interhemispheric connectivity since the size of the corpus callosum is significantly smaller in consistent right-handers (Witelson, 1989). Inconsistently handed individuals are advantaged in a variety of episodic memory tasks, including earlier offset of childhood amnesia (Christman, Propper, & Brown, 2006), better source memory (Christman, Propper, & Dion, 2004; Lyle, Mc- Cabe, & Roediger, 2008), and better episodic recall of laboratory and real-world memories (Lyle, Logan, & Roediger, 2008; Propper, Christman, & Phaneuf, 2005). …