A、Because those women’s voices sound like men’s. B、Because a woman would compare her voice to that of the other female speakers.

The human brain processes male and female voices differently, according to a recent study, which explains why most of us hear female voices more clearly. The study also explains how we form mental images of people based only on the sound of their voices. The findings, published in the journal NeuroImage, might also give insight into why many men tire of hearing women speak. It seems the complexity of female voices requires a lot of brain activity.
    "’It is females’ increased use of prosody, or the natural ’melody’ of speech, that makes their voices more complex," says author Professor Michael Hunter. Hunter, professor of medicine and biomedical sciences at the University of Sheffield’s Cognition and Neuroimaging Laboratory, says these qualities are not related to pitch, but rather to the vibration and number of sound waves.
    For the study Hunter and his colleagues played recordings of male and female voices to 12 men while they underwent MRI, or magnetic resonance imaging, brain scans. Test subjects assigned a gender to the voices they heard while the scans took place, and were 98% to 99% accurate. Researchers monitored the areas of the brain that showed activity during the scans.
    The scientists found that female voices activated the brain’s auditory section. But male voices activated the area at the back of the brain called the mind’s eye, where people compare other individuals and things to themselves. While the researchers only analysed how a male brain works, they theorized that female voices are always processed in the brain’s auditory region, even when women are listening to other women.
    But Hunter thinks female voices may also activate the mind’s eye in females, since a woman would compare her voice to that of the other female speaker. Since humans process female voices in an area of the brain that’s geared for sound, we tend to hear female voices more clearly. While Hunter believes female voices are complex, he says that once they are interpreted in the auditory part of the brain, they are more fully and readily decoded.