People make judgements on others' trustworthiness in just half a second by hearing their voice, an international research team revealed on Thursday.

In their new study, British researchers from University of Glasgow, together with US researchers, have shown that a simple "Hello" is enough to allow most people to draw conclusions about personality type. And people can make these judgements even without seeing the person they are speaking to.

The researchers played recordings of people saying hello, and asked participants to rank them according to 10 pre-defined personality traits, including trustworthiness, dominance, attractiveness and warmth.

They found that most of the recorded voices elicited the same response from participants and that these opinions were formed rapidly, after hearing the voices for only 300-500 msecs, which is 0.3-0.5 seconds. This suggests the tone of voice when saying hello directly and immediately informs the first impression of the person to whom you are speaking.

"It is amazing that from such short bursts of speech you can get such a definite impression of a person," said Dr Phil McAleer, who led the study, adding "Irrespective of whether it is accurate, your impression is the same as what the other listeners get."

He added that this research promises to help in the drive to improve the efficiency of voice-operated systems and learning aids.