Split-brain syndrome is caused when the corpus callosum is cut to prevent epileptic seizures from spreading from one side of the brain to the other. After some time passes from the procedure most patients are indistinguishable from a "normal" person because they adapt.
In a typical split-brain experiment, two stimuli are presented to the patient in such a way that one will be processed by the left hemisphere and the other by the right hemisphere. For example, the word ‘key-ring’ might be projected such that ‘key’ is restricted to the patient’s left visual field (LVF) and ‘ring’ is restricted to the patient’s right visual field (RVF). The contralateral structure of the visual system ensures that stimuli projected to the LVF are processed in the right hemisphere and vice-versa. Other perceptual systems can be studied in a similar manner. For example, tactile perception is examined by asking the patient to compare, either by verbal report or by pointing, objects presented to each hand.
Such studies have revealed two kinds of disunities in the split-brain: behavioral disunities and representational disunities. Behavioral disunities are most striking. When asked to report what she sees the patient in the key-ring experiment will typically say that she sees only the word ‘ring’; yet, with her left hand, the patient may select a picture of a key and ignore pictures of both a ring and a key-ring. Generally speaking, visual information projected to the RVF cannot be verbally reported, and visual information projected to the LVF is unavailable for behavior involving the right hand. In the tactile modality, the patient cannot describe, or use her right hand to respond to, objects palpitated by her left hand, and objects palpitated by the right hand cannot be reported via left-handed actions.
Representational disunities involve a lack of integration between the contents of the
patient’s conscious states. These states do not enjoy the inferential promiscuity that
conscious states typically enjoy. The patient in the key-ring experiment appears to have
representations of the words ‘key’ and ‘ring’ without having a representation of the word ‘key-ring’. Similarly, a patient might appear to be conscious of the identity of the objects palpitated by each hand but have no conjoint awareness of both objects. As we shall see, the precise nature of behavioral and representational disunities differs from patient to patient, but the foregoing description captures the core features of the split-brain syndrome.
-The Unity of Consciousness and the Split-Brain Syndrome
Your question specifically asks about what happens when there is conflict between the hemispheres. One side being pleasured and another side being tortured. In general the response mode will determine which action is taken. The right typically responding to visuo-structural similarities between two stimuli and the left functional-conceptual similarities according to Levy J (1976). However the left side of the brain tends to remain dominate in determining what the end result is during conflicting stimuli.
In general, not only partially but also fully split-brain patients behave in a coordinated, purposeful and consistent manner, belying the independent, parallel, usually different and occasionally conflicting processing of the same information from the environment by the two disconnected hemispheres. Free field performance often resembles that of the superior hemisphere (horse race), especially when the task is linguistic and performed better in the disconnected LH. Occasionally the LH dominates free field responses even when it is inferior to the RH. On rare occasions the RH dominates in spite of being inferior, particularly when the task has prominent visuospatial components. Thus, hemispheric dominance in responding is not al ways the same as the superior unilateral competence (Levy and Trevarthen, 1976).
When the two hemispheres receive competing stimuli at the same time, the response mode tends to determine which hemisphere controls behavior: Lh responses reflect RH decisions and Rh responses reflect LH decisions, even when these decisions are in mutual conflict. A variant of this technique presents brief chimeras consisting of competing half stimuli around fixation, divided along the vertical meridian (Levy and Trevarthen 2). In this case, both the nature of the task and the response mode interact to select a behaviorally dominant hemisphere.
Bimanual responses facilitate interhemispheric cooperation for compatible stimuli in the two VFs even in the split brain. It seems that motor responses tend to be unified so that in the chronic condition the two hands do not respond in conflict with each other even when the two hemispheres make conflicting decisions.
The disconnected LH can be said to be generally dominant for several reasons. First, it is more likely than the RH to assume control over behavior in unlateralized situations. Second, it has better ipsilateral visual and tactile-kinesthetic sensory motor control than the RH. Third, LH performance is more stable and less sensitive to small task differences. Fourth, although each disconnected hemisphere is hemianopic with respect to ipsilateral half space and does not deny ipsilateral perceptual experience, the disconnected LH does routinely express disbelief of correct RH responses to left sensory field stimuli.
-The Split brain
