In experiments testing the cocktail party effect, most participants were unable to do any of the following except _____________.

In cocktail-party experiments, people generally focus on the meaning of the attended message and cannot report the content of the unattended message. They can often notice a basic physical change in it, such as the speaker’s voice changing from male to female. So the exception is detecting that voice change; the other choices involve information from the unattended stream that participants typically missed.

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