Pseudoneglect

If you read my post on visual neglect, (or if not you can read it here), you will know that damage to the right posterior parietal cortex can cause patients to be biased to information on the right side, and ignore stimuli on the left. This is because each hemisphere processes visual information from the opposite side of space. Therefore, patients will show symptoms such as not eating the food from the left side of their plate, or moving their limbs on their left side.

One clinical test which is used to show this rightward bias in attention is the line bisection task: participants are presented with a horizontal line, and have to put a mark at the midpoint. As you can see from the example below, neglect patients will put their mark towards the right side of the line.

line bisection

However, you might not have noticed that healthy participants are biased for the left side, and will place their mark slightly towards the left of the midline. This has been termed pseudoneglect (Bowers & Heilman, 1980), as it has been suggested that healthy individuals show a weak form of neglect for the right side of space. This is the opposite deficit to that of neglect patients, who show a bias towards the right.

These findings therefore suggest a functional asymmetry between the hemispheres in controlling spatial attention (McCourt & Jewell, 1999). The right hemisphere is therefore thought to have a greater influence in directing spatial attention, as a bias is shown for the left side of space.

I hope you enjoyed this post, check back next week for a new update.

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Seeing is believing?

Another brainteaser for you!

First of all, watch this video. Make sure you pay attention to the instructions at the beginning – you’ll be asked questions about it at the end.

 

What did you think?

 

And importantly – did you see the gorilla?!

Selective attention tests like these show how focused our attention can be, to the extent that we ignore something which should be obvious. This shows that our vision can actually be quite narrow, and might not necessarily be accurate.

But this isn’t necessarily a bad thing – when there is a lot going on around us, it is useful to be able to focus on one aspect of our environment e.g. crossing a busy road, without being aware of other competing stimuli. Attention has been compared to a ‘spotlight’ or a ‘zoom lens’ in that it can be focused on a wider or more specific area of the visual field, depending on what is needed for the current task.

So, do you believe that what you see is true?

Try this test out on your family and friends – and check out my previous Brainteasers post here.