Previous behavioral research has shown memory for visually presented material to be impaired by auditory stimuli irrelevant to the memory task. Although under debate, a prevailing theoretical account of the irrelevant sound effect assumes that speech sounds receive special treatment in the human brain. We measured MEG from subjects memorizing a sequence of visually presented digits. During the memory task, the subjects were exposed to semisynthetically generated (SSG) speech sounds and sinusoidal tones, both controlled for acoustic structure. These conditions were contrasted with a silent control condition and no-task conditions in which the same auditory and visual stimuli were presented without a memory task. Sensory processing of the irrelevant auditory stimuli was investigated as indexed by the cortically generated N1m response. The results corroborated our previous findings showing that a short-term memory load enhances the sensory processing of irrelevant auditory stimuli, and that this enhancement is greater during the encoding than the retention phase of the memory task. This top-down modulation of sensory processing seems to affect both speech and non-speech sounds in a similar manner, although speech sounds seem to elicit larger responses in human auditory cortex.
展开▼
