The Limits of the Left Hemisphere Interpreter in a Split Brain patient

Rami H. GabrielUniversity of California, Santa BarbaraDepartment of Psychology – Cognitive and Perceptual Sciences

The basis of this experiment is the question: can the RH make inferences? The literature indicates that the RH has trouble creating narratives, whereas the left hemisphere is adept to the point of making illusory connections (Phelps & Gazzaniga, 1992).Our stimuli consists of specially drawn comic strip sequences (ranging from 3-12 pictures in length) which conclude in a two alternative forced choice between the actual ending, which follows through its inferential relations to the previous images, and another image that contains the same elements but is not inferentially related to the narrative at hand. The results of the inference task within a narrative situation are contrasted with sequences of spatial patterns (3 frames long) concluding with a two alternative forced choice of either the correct next step in the pattern or an image not consistent with the pattern. The motivation for this comparison is that the RH has been found to be adept at tasks of spatial reasoning (Gazzaniga, 2000). Spatial reasoning necessitates inferential capabilities but not in the form of a narrative. There are 28 narrative sequences and 9 spatial sequences.

Introduction

Research has shown that the Right Hemisphere is superior at tasks which necessitate spatial reasoning while the Left Hemisphere is superior at tasks that necessitate higher level cognitive processing. I investigate these findings by exposing a Split Brain patient to two types of sequences of images: a) narrative events (viz. comic strips) and b) spatial patterns. After viewing a given spatial or narrative sequence, the patient is given a two alternative forced choice asking her to decide “what comes next” in a given sequence. Each hemisphere is tested separately using both types of sequences. In this way I am able to compare narrative vs. spatial interpretation across hemispheres. Normal participant responses will be used as control data. I hypothesize that the Right Hemisphere will be able to correctly complete the spatial, but not the narrative sequences; the Left Hemisphere, by contrast, is hypothesized to show the reverse pattern in performance.

Method – Example of narrative condition

Since a split brain patient has no Since a split brain patient has no connection between their two connection between their two hemispheres, information cannot be hemispheres, information cannot be sent between them. Thus we are able sent between them. Thus we are able to test each hemisphere in isolation to test each hemisphere in isolation and explore their individual and explore their individual specializations and idiosyncratic specializations and idiosyncratic characteristics. characteristics. The Left hemisphere is dominant in The Left hemisphere is dominant in terms of language. The Right terms of language. The Right hemisphere has very little language hemisphere has very little language ability. We expect the RH to fail at the ability. We expect the RH to fail at the inferential tasks which involve inferential tasks which involve narrative situations and to succeed at narrative situations and to succeed at inferential tasks that involve spatial inferential tasks that involve spatial situations. This is because the RH situations. This is because the RH cannot create narratives to string cannot create narratives to string events together and a narrative is events together and a narrative is essentially a set of inferences and essentially a set of inferences and counterfactuals. This experiment is counterfactuals. This experiment is designed to show the dissociation designed to show the dissociation between inferences implicated in the between inferences implicated in the process of narrative formation and process of narrative formation and inferences in other tasks (viz., spatial) inferences in other tasks (viz., spatial) to demonstrate that inference is not a to demonstrate that inference is not a unitary ability but one that is particular unitary ability but one that is particular to certain levels of practice and use in to certain levels of practice and use in specialized processes, specifically the specialized processes, specifically the Left hemisphere Interpreter.Left hemisphere Interpreter.

This experiment joins the debate on how narrative, and thus interpretation, within consciousness is represented in the mind of a Split Brain patient. It helps clarify the nature of the Left Hemisphere Interpreter through identifying its specific type of content, namely, narrative events. Further work will focus on the nature of the relationship between interpretation and conscious experience.

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Method - Example of spatial control condition

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