1. Understanding Metaphors: Is the RH uniquely involved? Natalie A. Kacinik 1 and Christine Chiarello 2 University of California, Davis 1, University of California, Riverside 2 Abstract Introduction Experiment 1 Research with brain-injured individuals suggests that the right hemisphere (RH) is preferentially involved in understanding figurative language, whereas evidence from non-injured participants has been mixed (Anaki et al., 1998; Coulson & Van Petten, 2000). We conducted several divided visual field priming experiments examining each hemisphere’s involvement in comprehending metaphors of increasing linguistic complexity. Experiments 1 and 2 investigated ambiguous words with literal and metaphoric meanings in single word and sentence contexts, while Experiment 3 involved standard metaphors (e.g., His girlfriend’s face was a storm). Although some RH metaphor priming was obtained in both sentence and single word priming conditions, results did not strongly support the RH figurative language hypothesis. Metaphor priming also occurred in the LH at early time- courses (100 ms SOA), or when supported by a sentence context. Results are discussed in terms of current theories of cerebral asymmetries for processing language, and theories of metaphor comprehension. Experiment 2 Experiment 3 General Conclusions Empirically, most research with brain-injured individuals suggests that the right hemisphere (RH) is preferentially involved in understanding figurative language (e.g., Brownell et al., 1990; Kempler et al., 1999). Although this hypothesis is supported by some investigations of non- injured participants (Anaki et al., 1998; Bottini et al., 1994), a growing number of studies have failed to provide evidence for this claim (e.g., Coulson & Van Petten, 2000; Lee & Dapretto, 2003). These investigations, however, have used widely different methodologies making it difficult to draw any firm conclusions. Theoretically, the RH is suggested to be better suited for comprehending figurative language because RH meaning activation is broader and maintained longer, even in the event of contextual inconsistency (Anaki et al., 1998 Beeman, 1998; Burgess & Simpson, 1988; Faust & Chiarello, 1998). The LH, in contrast, maintains the activation of only the most dominant, closely related, and contextually consistent aspects of meaning. The LH is also claimed to be better at grammatical and syntactic processing than the RH, which is less sensitive to sentence constraints (Faust, 1998). PURPOSE - The present study examined the extent to which each cerebral hemisphere is typically involved in understanding metaphors of increasing linguistic complexity. Non-brain-injured individuals were investigated using a divided visual field priming paradigm. PREDICTIONS - According to most previous empirical and theoretical claims, the LH was expected to have difficulties processing metaphoric meaning, particularly in minimal or ambiguous contexts, but not when presented in a supportive unambiguous sentence. RH meaning activation, on the other hand, was predicted to be generally broad and unconstrained. PURPOSE – To investigate cerebral asymmetries in the time- course of literal and metaphoric meaning activation of lexical metaphors (ambiguous words with literal and metaphoric meaning) in a single word priming paradigm. METHOD – Three SOAs (100, 200, & 800 ms) with 32 right- handed native English speakers run at each. Centrally presented primes and lateralized targets. The target task was lexical decision. Rel Word Prime Unrel Nonword Prime Literal Target Metaphor Target flaky grony CRUST SISTER grasped prolled RAILING IDEA bright glomed COLORS STUDENT Experiment 1: Results for RVF / LH Experiment 1: Results for LVF / RH PURPOSE – To investigate hemispheric differences for literal vs metaphoric meaning activation of lexical metaphors, going from ambiguous sentence contexts -> We all admired the bright COLORS vs STUDENT to more constrained unambiguous sentences -> It’s the building with the bright COLORS The teacher praised the bright STUDENT METHOD – 64 right-handed native English speakers performed lexical decisions to lateralized targets after incomplete sentence primes. Experiment 2: Results for RVF / LH Experiment 2: Results for LVF / RH PURPOSE – To investigate cerebral asymmetries for standard “an X is a Y” metaphors (e.g., His girlfriend’s face was a storm), and the extent to which each hemisphere maintains the activation of contextually appropriate (e.g., ANGRY) and inappropriate meanings (e.g., CLOUDS). METHOD – Literal and metaphoric sentences with targets related to the literal and metaphoric meaning were presented in a fully-crossed design: His girlfriend’s face was a storm – ANGRY His girlfriend’s face was a storm – CLOUDS The ship was headed toward a storm – CLOUDS The ship was headed toward a storm - ANGRY 48 right-handed native English participants were presented with the full sentences as primes and performed lexical decisions on the lateralized targets. Experiment 3: Results for RVF / LH Experiment 3: Results for LVF / RH Experiment 1: Results & Discussion RVF/LH - Equivalent priming for literal and metaphor targets at brief SOAs, but no metaphoric priming at long SOA. This indicates that ALL aspects of meaning are initially activated by the LH, but ONLY the literal meaning is selected and maintained later in time-course. LVF/RH - Literal priming across SOAs (RT & ACC). Metaphoric priming only in ACC, but constant over time. Thus, the degree of RH semantic activation varies for different aspects of meaning. Literal meanings were activated more strongly than the metaphoric sense, although this weak metaphoric activation was maintained across time. CONCLUSIONS - Time-course and the type of semantic relation modulate the extent of literal and metaphoric meaning activation in BOTH hemispheres. Minimal evidence for preferential RH involvement in metaphor comprehension resulting from more bottom-up semantic activation processes. This experiment, HOWEVER, was limited to the literal and metaphoric meanings of individual words. Experiment 2: Results & Discussion RVF/LH – Similar literal and metaphor priming with both contexts, but greater facilitation following unambiguous sentences. LH processes thus take advantage of semantic, grammatical, and syntactic constraints to maintain the activation of ALL aspects of meaning (literal or metaphoric) consistent with the sentence context, even if it is ambiguous, rather than selecting and maintaining the activation of only the dominant literal meaning. LVF/RH – Very similar to RVF/LH results. Equivalent literal and metaphor priming with both contexts, but greater facilitation after unambiguous sentences. In contrast to Experiment 1, these findings show that the RH can strongly activate and maintain the activation of metaphoric meanings if there is contextual support, indicating that RH processes also benefit from the activation of words in the sentence, even if the context is vague. CONCLUSIONS – This experiment still fails to support the hypothesis of the RH as preferentially involved in metaphor comprehension because the LH was also able to understand and activate metaphoric meaning to a similar degree, even after ambiguous sentences. Experiment 3: Results & Discussion RVF/LH – Literal and metaphor targets primed to similar degree when consistent with sentence, but no priming for either target when contextually inappropriate. LH processes thus select and maintain the activation of only contextually relevant aspects of meaning, regardless of whether they are literal or metaphoric per se. LVF/RH – Similar literal and metaphor priming when contextually consistent. No priming for inconsistent metaphor targets, but irrelevant literal aspects of meaning were primed. RH processing of metaphoric sentences results in a broader activation of meaning than the comprehension of literal sentences, such that inconsistent literal aspects of meaning remain active. This could be advantageous if an initial interpretation needed to be revised. CONCLUSIONS - As in Experiment 2, literal and metaphor aspects of meaning were active in both hemispheres when targets were consistent with the meaning of the sentence, indicating that both hemispheres are able to understand metaphors involving more complex sentence integration processes. Metaphoric aspects of meaning were not primed after literal sentences (in either hemisphere) indicating that metaphoric meaning only emerges upon comprehension of the metaphoric expression as a whole. LH processes were extensively involved in understanding metaphors, and RH meaning activation was considerably affected by different sentence contexts. Any hemisphere differences for understanding literal and metaphoric language can’t be explained according to general differences in the breadth of meaning activation because time-course, and especially sentence contexts, significantly modulated the degree of literal and metaphoric meaning activation in both hemispheres although in slightly different ways. Indeed, literal and metaphor priming effects in each hemisphere were remarkably similar across the study as a whole. The RH can’t generally be considered the preferred substrate for metaphor comprehension, but it is involved (as is the LH) and may play a unique role in maintaining broadly activated meanings in the event an original interpretation needs to be modified. Referemces Anaki, D., Faust, M., & Kravetz, S. (1998). 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