Academic journal article Memory & Cognition

Hemispheric Processing of Inferences: The Effects of Textual Constraint and Working Memory Capacity

Academic journal article Memory & Cognition

Hemispheric Processing of Inferences: The Effects of Textual Constraint and Working Memory Capacity

Article excerpt

In this study, we investigated hemispheric differences in the generation of bridging and predictive inferences. Participants read texts that provided either strong or weak causal constraints for a particular bridging (Experiment 1) or predictive (Experiment 2) inference and performed a lexical decision task to inference-related targets presented to the left or the right hemisphere. Facilitation for strongly constrained bridging and predictive inferences was found in both hemispheres. In contrast, facilitation for weakly constrained inferences was stronger in the right than in the left hemisphere for both bridging and predictive inferences, although for the latter there was some facilitation in the left hemisphere as well. We also considered whether these effects differ as a function of the working memory capacity of the reader. High working memory capacity readers showed greater facilitation for strongly constrained inferences than for weakly constrained inferences in both hemispheres, whereas low working memory capacity readers showed this same pattern in the left hemisphere but showed equal facilitation for strongly and weakly constrained inferences in the right hemisphere. These results suggest that hemispheric processing, textual constraint, and working memory capacity interact to affect how readers generate causal inferences.

Much of our comprehension of text is derived from the making of inferences. To make inferences, we must connect explicit text events with other text events or with our background knowledge. The result of this process is the formation of a coherent mental representation. One important factor influencing inference generation is the causal structure of text events (see, e.g., Graesser, Singer, & Trabasso, 1994; van den Broek, 1994). Little is known, however, about how the cerebral hemispheres respond to causal information when generating inferences to form coherence. In this study, we investigated whether the left and right hemispheres play unique roles in causal inference generation. Specifically, we examined two factors that could affect inference generation in the hemispheres: whether an inference is bridging or predictive and whether the inference is strongly or weakly constrained by the text's causal structure. We also explored how the effects of these two factors might differ as a function of the working memory capacity of the reader, an individual-differences component known to affect the causal inferential process.

Although the left hemisphere is considered the dominant hemisphere in the processing of language, the right hemisphere is involved in processes that could contribute to the generation of inferences. For example, right-hemisphere-damaged patients have difficulty answering true/false questions about inferable information, despite being able to answer questions about explicitly stated information (Brownell, Potter, Bihrle, & Gardner, 1986). Furthermore, unlike non-brain-damaged readers, they show longer response times to inference-related words than to unrelated words after reading stories that promote inferences (Beeman, 1993). In addition, the right hemisphere is highly activated when participants comprehend metaphors versus literal sentences (Bottini etal., 1994), read untitled texts versus titled texts (St. George, Kutas, Martinez, & Sereno, 1999), and process connected discourse versus unrelated discourse (Robertson et al., 2000). Thus, the right hemisphere may be important in helping readers maintain coherence while they comprehend texts.

The idea that the right hemisphere is involved in maintaining coherence leads to interesting hypotheses about how the hemispheres process inferences. It is possible that the two hemispheres differ in the activation of semantic information during inference generation. One generally accepted method for studying the activation of semantic information in the hemispheres is the divided visual field paradigm. The divided visual field paradigm is useful because it allows researchers to present material in isolation to one visual field, which leads to processing in the contralateral hemisphere (Church & Chiarello, 1988; Iacoboni & Zaidel, 1996). …

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