Evaluating signal-correlated noise as a control task with language-related gamma activity on electrocorticography

Our recent electrocorticography (ECoG) study suggested reverse speech, a widely used control task, to be a poor control for non-language-related auditory activity. We hypothesized that this may be due to retained perception as a human voice. We report a follow-up ECoG study in which we contrast forward and reverse speech with a signal-correlated noise (SCN) control task that cannot be perceived as a human voice.

Ten patients were presented 90 audible stimuli, including 30 each of corresponding forward speech, reverse speech, and SCN trials, during ECoG recording with evaluation of gamma activity between 50 and 150 Hz.

Sites of the lateral temporal gyri activated throughout speech stimuli were generally less activated by SCN, while some temporal sites seemed to process both human and non-human sounds. Reverse speech trials were associated with activities across the temporal lobe similar to those associated with forward speech.

Findings herein externally validate functional neuroimaging studies utilizing SCN as a control for non-language-specific auditory function. Our findings are consistent with the notion that stimuli perceived as originating from a human voice are poor controls for non-language auditory function.

Our findings have implications in functional neuroimaging research as well as improved clinical mapping of auditory functions.