We're used to thinking of neglect as a lack of appropriate care, but to a neuroscientist, it has a very different meaning. "Spatial neglect" is a neurological condition caused by damage to one half of the brain (usually the right), where patients find it difficult to pay attention to one half of their visual space (usually the left).
This bias can affect their mental images too. If neglect patients are asked to draw clocks, many only include the numbers from 12 to 6, while some shunt all the numbers to the right side. When two famous neglect patients were asked to describe a familiar square in Milan, the city they grew up in, the landmarks they reported shifted depending on where they pictured themselves standing in the square. They would only report buildings to the right of their imagined position - swap the location and new buildings would suddenly come into mental view.
Patients tend to be particularly unaware of things on the left if other objects on the right are vying for their attention - this phenomenon, where only one of two simultaneously presented objects is seen, is called "visual extinction".
Neglect is clearly a fascinating condition but also a debilitating and underappreciated one. It affects up to 60% of patients who suffer strokes on the right side of their brain, and it can hamper recovery and deny patients their independence. As such, there are plenty of researchers interested in finding ways of improving its symptoms. David Soto from Imperial College London is one of them, and he has discovered a deceptively simple way of helping neglect patients to regain their lost awareness - listen to their favourite music.
Soto was encouraged by a recent study, which found that stroke victims showed greater improvements in both memory and attention when they tuned into music than when they listened to audiobooks or worked in silence. And other studies have suggested that emotional faces are less likely to fall prey to visual extinction than less compelling images. But Soto wanted to see if the patient's own emotional state had anything to do with their awareness. Would it be possible to reduce the symptoms of neglect simply by making patients feel happier through the medium of pleasant melodies?
Soto worked with three neglect patients, known by their initials MP, RH and AS - two of whom had damage to the right side of their brain, and one who had suffered damage to his left. Each of them chose happy music that they liked (Kenny Rogers, the Flying Burrito Brothers Band, and Frank Sinatra respectively) and music that they didn't (Sonic Youth, the Ramones and Rakim). Music chosen, the patients had to identify differently coloured shapes that appeared on the left or right of a computer screen, either alone or in pairs.
On the whole, the three of them were better at identifying shapes when their favoured tracks were playing than when they were listening to the disliked tunes or silence. The pleasant music has the most dramatic effect when the patients had to identify pairs of shapes - under normal circumstances, this extra drain on their attention meant that they only answered correctly on about 30% of trials. With the pleasant music around, this increased to 50%, and with the rejected music, it fell to just 15%.
For their second challenge, the trio had to hold down a button when a red target appearing in their visual field, while ignoring green ones. As you'd expect, they made more mistakes if the objects appeared on the opposite side to their brain damage, but the happy music compensated for that somewhat. Their neglect was much less when they listened to tunes they liked rather than those they didn't. MP, in particular, went on to perform well in a variety of tasks with his music of choice on play, including reading nonsense-words on the neglected side of his field of view, or accurately dividing a line in two down the middle.
It's possible that the music simply made the patients more alert, but the evidence for this was shaky. When Soto measured the patients' heart rates and the ability of their skin to conduct electricity (an indicator of how moist it is), he found few consistent differences between the two types of music or even between either one and no music at all.
Nor does Soto think that any specific property of the music he used was responsible - after all, the tracks included a large variety of pitch, tempo, lyrics and so on. The critical factor in the tunes was nothing to do with their acoustics and everything to do with how much the patients enjoyed them.
Soto thinks that it's more likely that the good mood induced by the music was responsible for the boost in performance. Indeed, previous studies have found that good moods make people better at paying attention to a larger visual field - they broaden the area our mental spotlights shine onto.
To test that idea, Soto worked with MP and played him his favourite artist before the target-spotting test, and showed him happy, positive pictures to sustain his good vibrations. His performance was flawless - in every trial, no matter where the target appeared, he spotted it correctly. When Soto killed the buzz of the music by talking about the current financial crisis and showing MP some bleak, unhappy pictures, his performance fell again. He spotted 88% of targets on the same side as his injury but only 9% of those on the other.
Scans of MP's brain supported the link between music, mood and loss of neglect. Soto found that his favourite tunes stimulated a unison of brain activity in parts of the brain involved in emotion and visual processing. He used functional magnetic resonance imaging to study MP's brain as he carried out the target-spotting task.
Compared to the tracks he hated, the pleasant music was associated with greater activity in his left orbitofrontal cortex (OFC). This part of the brain involved in emotion and pleasurable feelings and that's known to be activated in response to beloved music. Soto also found greater activity in areas on the right side of his brain involved in visual processing and he saw that these areas were more strongly connected to the left OFC.
Obviously, this is a fairly small study with only three patients (and many of the experiments were done with just MP). Nonetheless, it suggests an interesting line of research to pursue, and perhaps something else for doctors to try when working with recovering stroke patients. And in many ways, the music is a red herring - in Soto's work, it was just a tool for generating a good mood. That, it seems, was the key to reducing visual neglect.
[NB To my knowledge, in most cases of visual neglect, patients aren't
aware of half of their visual field. That doesn't mean that they can't physically see it. It seems to me therefore that headlines like "Music therapy restores vision" and "Listening to music could save stroke victims' sight" are just wrong. Neuroscientists - am I right or am I being too critical? - Ed]
Reference: Soto, D., Funes, M., Guzman-Garcia, A., Warbrick, T., Rotshtein, P., & Humphreys, G. (2009). Pleasant music overcomes the loss of awareness in patients with visual neglect Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0811681106
More on visual awareness:
Blind man navigates obstacle course perfectly with no visual awareness
'Talking face' simulations in the brain help us work out what's being said