Katy Perry likes her music to pass the ''goose bump test''.

The 'Roar' hitmaker chooses the tracks for her album by seeing if it makes the hairs on her arms stand on end every time she listens to it because that means it will emotionally reach out to her fans.

She said: ''There's this test that I do in the studio, after a song's complete and you've tracked some vocals. It's kind of like the goose bump test. If, every time you hear it, it gives you goose bumps, it's hitting a chord inside of you that's really important.

Meanwhile, the 29-year-old singer admits she was inspired to write her new single 'Unconditionally' after visiting Madagascar with UNICEF.

Speaking to MTV, she explained: ''We live in such a world that is run by social status and material possession, and it can get really overwhelming and tiring to keep up with that - people are actually turned on by the amount of likes they have; it's crazy that our minds think that way these days.

''And so I went to the top of this mountain, I saw all these children, and the love that they had towards each other, they had no idea what Twitter or Facebook or any of that stuff was, they didn't care about it. It was this unconditional love between all of them. It was that kind of pure love that's unaffected by the trends of the world.''