Neuropsychology

Split-Brain Laboratory

Set up a lateralised trial, predict whether the answer can get out, and then find the conditions the classic result quietly depends on.

Simulated - a deliberately simplified model, original items, no published stimuli and no real participants

Learning objective

By the end you should be able to work out what a split-brain trial shows about routing, rather than about what each hemisphere is for.

About 20 minutes, in two experiments. Nothing you do here is saved or sent anywhere.

Read this before you start

Nothing on this page is flashed to one visual field. A web page cannot control where your eyes are, and lateralised presentation needs fixation control and timing that a browser cannot provide. You build a trial and the tool reports what a simplified model predicts. The model is an argument about routing, not a measurement.

The findings behind it come from a very small number of people who had surgery for severe epilepsy, whose brains differed from typical brains in other ways too. Results varied between them and between tasks.

Experiment 1. Choose where the item appears and how you ask for a response. Predict the outcome, then run the trial. Then open Cut the corpus callosum and run the same trial again.
Keep going until you have found a trial where cutting the callosum changes the outcome and one where it changes nothing.
Experiment 2. Take the one trial that classically fails and switch off, one at a time, the conditions it depends on.

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The trials are computed and drawn in your browser, so this section cannot run with JavaScript switched off. The rest of this page is readable without it.

What is the best account of that? The right hemisphere saw it but the person was not conscious of it The hemisphere that saw it is not the hemisphere that speaks, and the two can no longer pass the information between them The left hemisphere is dominant, so it overrode the right The right hemisphere is the visual hemisphere and the left is the verbal one

1 Building a trial
2 What the result depends on

Need a hand?

Key terms

Corpus callosum: The band of fibres carrying information between the hemispheres. Cutting it is the manipulation here.
Visual field: Which side of the fixation point something appears on. It decides which hemisphere receives it first, whichever eye is open.
Response channel: How the answer is given — speech, left hand or right hand. Each one is reachable from different parts of the system.
Lateralisation: A function being handled more by one hemisphere than by the other. It is a tendency across people, not a switch inside one.

The trial

How we ask for a response

Your prediction, before you run it

Cut the corpus callosum, and run the same trial again

The corpus callosum

Show a different item

What is presented

When the goal is met

Where the information can and cannot go

Trials you have run

Every combination at once

All six combinations of visual field and response channel, with the model's outcome for both an intact and a sectioned callosum
Item appears in	Response channel	Callosum intact	Callosum sectioned

With the callosum intact every cell succeeds, because both hemispheres receive the item within a few tens of milliseconds. After a complete section, a response succeeds only when the hemisphere that received the item also controls the channel you asked with. That is the whole model.

1. A magazine article says some people are "right-brained" - creative, intuitive, visual - and others are "left-brained". What is the strongest objection from this material? The studies involved very few people The findings describe which hemisphere can act on an item in a given moment in people whose hemispheres were surgically disconnected; in a connected brain both hemispheres receive everything almost at once Both hemispheres do all the same things equally well The operation is hardly ever performed now

2. A fictional participant with a complete section names a word shown in the left visual field on 8 trials out of 10. Which conclusion is safest? Their right hemisphere must produce speech The contralateral routing account is wrong Something let the information reach the left hemisphere, and the method has to be checked before anything is concluded about the brain The section must have been incomplete

What the patient can report depends on which hemisphere received the stimulus and which one controls the channel you ask through. The same item is available or unavailable depending on the route, not on which hemisphere is cleverer. Cut the callosum and the two halves stop sharing; leave it intact and the difference disappears. Lateralisation is a tendency in a connected brain, which is why “left-brained people” does not follow.

Split-Brain Laboratory

Learning objective

Read this before you start

First, a judgement

The laboratory

Experiment 1 - building a trial

Where the information can and cannot go

The trial that is supposed to fail

Why, condition by condition

Trials you have run

Challenge - two claims to weigh

What this demonstrates