It’s always a good feeling when I find out about a new illusion that I can share on here – this week’s Brainteaser is another about colour after-effects: The Mccullough Effect.
What makes this different to other colour after-effects is that the stimuli used in adaptation is simpler than the final illusion. This effect was discovered by Celeste McCollough in 1965, and involves alternating black and white lines (known as ‘gratings’) which are viewed as coloured after a period of adaptation. Try it for yourselves here:
First, stare at these images for a minute or so then look at the grid below
What you should notice is that these gratings now look coloured, when they are in fact black and white! The vertical lines should look red, whilst the horizontal ones look green.
What is so interesting about these after effects is that unlike others (e.g. here), this effect lasts not just for a few minutes but for hours, or even days. Some studies (e.g. Jones & Holding, 1975) have shown that adaptation for 10 minutes can lead to after effects months later!
Scientists are still not certain which part of the visual system is responsible for this effect or why it is so long-lasting. One theory is that it takes place due to neurons in V1 – the first part of the visual cortex which receives information from the optic nerve via the Lateral Geniculate Nucleus. Only neurons in early visual cortex are sensitive enough for this type of adaptation to occur. A possible reason why this effect lasts for so long could be simply that the adaptation stimulus is rare, so is not seen in the environment for us to de-adapt, whilst others believe this shows a form of associative learning. However, the exact mechanisms are still up for debate.
Another brainteaser this week, on a test which any psychology student would recognise.
First, have a look at these shapes. Which one would you call ‘bouba’ and which one would you call ‘kiki’? Once you’ve done this, scroll down to see the answer.
In fact, these shapes have not been officially named, but 95% of people asked this question name the shape on the left ‘kiki’ and the shape on the right ‘bouba’. This is amazing considering that this is a free choice, with a 50/50 answer. It seems to be that each shape is better suited to a certain name. But why?
The experiment shown above was carried out by Ramanchandran & Hubbard (2001) as part of their work on synaesthesia – a condition in which people’s senses overlap e.g. hearing sounds as viewing colours. If you’d like to read more about synaesthesia check out my blog post. Their hypothesis as to why synaesthesia occurs is that it is caused by extra connections in the brain between senses.
The authors proposed that the reason most people identify the spiky shape as ‘kiki’ and the rounded shape as ‘bouba’ because the shape of the objects mimic the phonetics of the sounds of the names when spoken. This is therefore evidence that most people, even though they do not have synaesthesia, have connections in their brain between the different senses.
Although this might just seem like a fun, but pretty trivial experiment, the results actually have profound implications for our view on how language began in the first place. As 95% of people map the same sounds to these objects, the authors suggest that there might be ‘natural constraints’ on how sounds and objects are linked. They also suggested that the representation of a word in the motor cortex (to form the shapes to speak the word) and auditory areas are linked to the visual appearance of the object, which again shows these cross-modal connections at work.