The “loudness” of our thoughts–or how we imagine saying something–influences how we judge the loudness of real, external sounds, a team of researchers from NYU Shanghai and New York University has found.

Their study, titled “Imagined Speech Influences Perceived Loudness of Sound,” has been published in the journal Nature Human Behaviour, offering new insights into the nature of brain activity. The research project was conducted by Tian Xing and Bai Fan from NYU Shanghai with David Poeppel and Teng Xiangbin from New York University, and Ding Nai from Zhejiang University.

“Our ‘thoughts’ are silent to others but not to ourselves, in our own heads, such that the ‘loudness of thought’ influences the loudness of hearing,” says Poeppel, a professor of psychology and neural science.

Using an imagery-perception repetition paradigm, the team found that auditory imagery will decrease the sensitivity of actual loudness perception, with support from both behavioural loudness ratings and human electrophysiological (EEG and MEG) results.

“After imagined speaking in your mind, the actual sounds you hear will become softer–the louder the volume during imagery, the softer perception will be,” explains Tian, assistant professor of neural and cognitive sciences at NYU Shanghai. “This is because imagery and perception activate the same auditory brain areas. The preceding imagery already activates the auditory areas once, and when the same brain regions are needed for perception, they are 'tired' and will respond less.”

According to Tian, the study demonstrates that perception is a result of interaction between top-down (e.g. our cognition) and bottom-up (e.g. sensory processing of external stimulation) processes, as human beings not only receive and analyze upcoming external signals passively, but also interpret and manipulate them actively to form perception.

It is also the team’s latest piece in a series of studies using mental imagery paradigms to investigate speech monitoring and control in production process, namely, a motor-based predictive process, which can extend and predict low-level auditory attributes such as loudness.

“Combining perception and speech production monitoring and control, this study can implicate the mechanisms of mental disorders. The most relevant one is auditory hallucination mostly in schizophrenia,” he said.

The project has been supported by the National Natural Science Foundation of China and the Science and Technology Commission of Shanghai Municipality, as well as funding from the three universities.