Final answer:
Alan's inability to communicate between his brain's hemispheres is due to the severing of the corpus callosum. This condition, known as split-brain, leads to certain cognitive challenges, like the inability to verbally identify objects presented to the left visual field while still being able to select them with the left hand.
Step-by-step explanation:
Alan is a split-brain patient, which indicates that his cerebral hemispheres cannot communicate effectively with each other. This condition is most commonly a result of severing the corpus callosum, which is the major structure that connects the two hemispheres and enables interhemispheric communication.
Split-brain patients exhibit unique cognitive phenomena. For instance, when an object is shown to the left visual field, the patient may not be able to verbally identify it because the right hemisphere, which processes this visual input, cannot communicate with the language centers typically located in the left hemisphere. However, the patient may still be able to select the object with their left hand, which is controlled by the right hemisphere, demonstrating that some processing can occur without interhemispheric communication.
In summary, Alan's condition of having a split-brain is due to the corpus callosum being cut, which prevents the left and right brain hemispheres from communicating with each other and results in the aforementioned cognitive effects.