Abstract
Our ability to detect target sounds in complex acoustic backgrounds is often limited not by the ear's resolution, but by the brain's information-processing capacity. The neural mechanisms and loci of this “informational masking” are unknown. We combined magnetoencephalography with simultaneous behavioral measures in humans to investigate neural correlates of informational masking and auditory perceptual awareness in the auditory cortex. Cortical responses were sorted according to whether or not target sounds were detected by the listener in a complex, randomly varying multi-tone background known to produce informational masking. Detected target sounds elicited a prominent, long-latency response (50–250 ms), whereas undetected targets did not. In contrast, both detected and undetected targets produced equally robust auditory middle-latency, steady-state responses, presumably from the primary auditory cortex. These findings indicate that neural correlates of auditory awareness in informational masking emerge between early and late stages of processing within the auditory cortex.
Highlights
On a busy street corner, in a crowded restaurant, or in a rainforest at twilight, the sounds emitted from multiple sources mix together to form a highly convoluted and complex acoustic environment
Sounds that are well above the sensory threshold may sometimes fail to be perceived when they occur amid competing sounds, as often happens in everyday life
Human listeners performed an auditory detection task in which they had to indicate when they heard a stream of repeating tones embedded in a stochastic tone background
Summary
On a busy street corner, in a crowded restaurant, or in a rainforest at twilight, the sounds emitted from multiple sources mix together to form a highly convoluted and complex acoustic environment. The background or masking sound produces a pattern of excitation in the cochlea that either swamps or suppresses the activity due to the target sound, so that the target is no longer accurately represented in the auditory nerve [2]. This form of masking, traditionally known as ‘‘energetic masking,’’ has been the subject of most formal psychophysical studies of masking dating back nearly 100 years [3]. The maskers and targets used in such experiments are typically predictable (i.e., the same sounds are presented over many repetitions), and are distinguished from one another
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