The way top-down and bottom-up processes interact to shape our perception and behaviour is a fundamental question and remains highly controversial. How early in a processing stream do such interactions occur, and what factors govern such interactions? The degree of abstractness of a perceptual attribute (for example, orientation versus shape in vision, or loudness versus sound identity in hearing) may determine the locus of neural processing and interaction between bottom-up and internal information. Using an imagery-perception repetition paradigm, we find that imagined speech affects subsequent auditory perception, even for a low-level attribute such as loudness. This effect is observed in early auditory responses in magnetoencephalography and electroencephalography that correlate with behavioural loudness ratings. The results suggest that the internal reconstruction of neural representations without external stimulation is flexibly regulated by task demands, and that such top-down processes can interact with bottom-up information at an early perceptual stage to modulate perception.