Split Brain Research Fails to Replicate Different Hemisphere Awareness After Corpus Callosotomy

According to the Nobel-prize-winning work in the 1960's by Sperry and Gazzaniga, after the two cerebral hemisphere are cut by callosotomy (a surgery sometimes done for intractable epilepsy), a person seeing an object in one visual field can signal seeing it with the hand on that side, but not with the hand on the other side, which will respond as if no object was seen.

I'd heard several tales in more recent years from neuropsychologists just out of university training of how researchers at their institutions were failing to replicate those classic results. This was usually attributed to variations in the surgery performed, as well as the fact the posterior commissure was usually left intact.

However, in a recent issue of Brain, Pinto and colleagues below report they have systematically re-studied many of the patients from these surgeries and are showing that a single awareness persists in such subjects-- exactly as the persons who had the surgery (I've seen three since the 1990's) themselves will tell you, if you ask them :).

What improved over the decades? Perhaps they got better at re-routing the interrupted communications. Did the subjects ever have more than one center of consciousness? Probably no more than we do when we split our attention between simultaneous tasks.

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ABSTRACT

Split brain: divided perception but undivided consciousness

Yair Pinto David A. Neville Marte Otten Paul M. Corballis Victor A. F. Lamme Edward H. F de Haan Nicoletta Foschi Mara Fabri

Brain (2017) aww358. DOI: https://doi.org/10.1093/brain/aww358

Published: 24 January 2017

In extensive studies with two split-brain patients we replicate the standard finding that stimuli cannot be compared across visual half-fields, indicating that each hemisphere processes information independently of the other. Yet, crucially, we show that the canonical textbook findings that a split-brain patient can only respond to stimuli in the left visual half-field with the left hand, and to stimuli in the right visual half-field with the right hand and verbally, are not universally true. Across a wide variety of tasks, split-brain patients with a complete and radiologically confirmed transection of the corpus callosum showed full awareness of presence, and well above chance-level recognition of location, orientation and identity of stimuli throughout the entire visual field, irrespective of response type (left hand, right hand, or verbally). Crucially, we used confidence ratings to assess conscious awareness. This revealed that also on high confidence trials, indicative of conscious perception, response type did not affect performance. These findings suggest that severing the cortical connections between hemispheres splits visual perception, but does not create two independent conscious perceivers within one brain.

On the Vagueness of Species, Part 5: Excluding Some Higher Order Vagueness

In several earlier entries in this blog, I’ve discussed the vagueness of species, the idea that our identification of an individual life form with one species and not another can be vague. I’ve suggested that the concept of rough sets can be usefully applied to Darwin’s species concept.

Epistemic concepts of vagueness say that there really is an exact count of grains where a group of grains are a heap, or an exact count of hairs where a head becomes bald, but that we do not know what that number is. This differs from the more common idea that our terms themselves are vague in application to an exact world.

Where does the rough set concept come in in those differing ideas of vagueness? Is it a vagueness of our concept or of our knowledge of the concept? It is both.

First, as applied to whether a given individual is definitely a species member, definitely not a species member, or vaguely a member, the vagueness is either in our terms or in the members themselves: if an individual life form is only vaguely an orange tree, that is either that we do not have sufficient precision in the orange tree definition to decide, or the tree is the kind of hybrid which is vaguely an orange tree by its nature. In these cases we don’t generally think there are any further unknown facts which would decide the matter.

Second, the rough set concept is without any need for secondary, higher-order vagueness. Such higher-order vagueness is said to be when

in addition to the unclarity of the borderline case, there is normally unclarity as to where the unclarity begins. In other words ‘borderline case’ has borderline cases. This higher order vagueness seems to show that ‘vague’ is vague”

according to the Stanford Encyclopedia of Philosophy. However, with rough set theory, there should be no question regarding whether an individual is definitely a species member or vaguely a species member. If there remains a question of species membership at all, this puts the member entirely into the vague category, which removes the question of whether the member is vaguely vaguely a member: all such border cases are vague ones. The rough set concept thus collapses all secondary vagueness of that sort into the primary vagueness portion of the rough set.

How is this an epistemic view of higher-order vagueness? Between the life forms that are definitely in the species and those that are vaguely so there is a definite boundary. More than this, it is one we should be able to know.

Winter Soursop

Pictures taken today from the waterlogged front lawn: two immature soursop fruit (Annona muricata) on a tree planted in the front bed just a year ago. This tree has grown quickly. Supposedly, when the fruit is mature it will yellow slightly and blur the lines defining segments around each spine in the rind.

Soursop is touted on the web for anti-cancer properties of a tea made from its leaves. Although a category of plant extracts classified as annonaceous acetogenins, which are found only in the soursop (graviola or guanabana) family of trees, do kill cancer cells in vitro (cell cultures in test tubes), there is no evidence beyond hearsay of anti-cancer properties in live humans. But the leaf tea and fruit are both tasty.