In a study to investigate the link between sound and meaning German researchers found that our emotions can change depending on the vowels we articulate. The team led by Professor Ralf Rummer and Professor Martine Grice first exposed subjects to film clips, some of which were depressing and dreary, and others bright and cheery. The subjects were then asked to make up and say aloud ten words. They discovered that when the test subjects were in a downhearted mood because they had watched the dreary clips, their made-up words included more long /o:/ sounds (as in the English word lone), whereas when they were in a positive mood, after the more uplifting film clips, their words included more long /i:/ sounds, as in the word leaf.
In a second experiment subjects watched cartoons while gripping a pen either lengthwise with their teeth, so their mouths were spread, as if pronouncing /i:/ or as if smiling or laughing, or by putting the narrow end of the pen in their mouth, as if sucking on a straw, so their mouths formed an /o:/. Those who held the pen with their teeth and had their lips spread found the cartoons funnier than the other group did. Two other groups watched the cartoons, but instead of having a pen in their mouths, were told to articulate either an /i:/ sound or an /o:/ sound every second while watching. The people producing the /i:/ sounds found the same cartoons significantly more amusing than those producing the /o:/ sounds. From these experiments the academics concluded that language users learn that the articulation of /i:/ sounds is associated with positive emotions and use words with this sound to describe positive circumstances. Conversely, the articulation of /o:/ sounds has negative associations. The research team leaders noted that many words in languages follow this pattern. Note that there is a problem with the English translation of their study on this point (eg in this article). Like is given as an example of a word containing the sound /i:/, but that is wrong (/i:/ phonetically is usually written ee or ea in English). The German example given was Liebe, love (pronounced lee-ber). The example of an /o:/ word given in the German write-up of the research was Tod, death.
For an article in English on this project see here, and for the German version see here.