Single trial time–frequency domain analysis of error processing in post-traumatic stress disorder

Error processing studies in psychology and psychiatry are relatively common. Event-related potentials (ERPs) are often used as measures of error processing, two such response-locked ERPs being the error-related negativity (ERN) and the error-related positivity (Pe). The ERN and Pe occur following committed error in reaction time tasks as low frequency (4–8 Hz) electroencephalographic (EEG) oscillations registered at the midline fronto-central sites. We created an alternative method for analyzing error processing using time–frequency analysis in the form of a wavelet transform. A study was conducted in which subjects with PTSD and healthy control completed a forced-choice task. Single trial EEG data from errors in the task were processed using a continuous wavelet transform. Coefficients from the transform that corresponded to the theta range were averaged to isolate a theta waveform in the time–frequency domain. Measures called the time–frequency ERN and Pe were obtained from these waveforms for five different channels and then averaged to obtain a single time–frequency ERN and Pe for each error trial. A comparison of the amplitude and latency for the time–frequency ERN and Pe between the PTSD and control group was performed. A significant group effect was found on the amplitude of both measures. These results indicate that the developed single trial time–frequency error analysis method is suitable for examining error processing in PTSD and possibly other psychiatric disorders.

► A continuous wavelet transform was used on single trial EEG recordings.
► A theta (4–8 Hz) waveform was constructed from the wavelet coefficients.
► Comparisons in error processing were made between PTSD and control subjects.
► Measures from the PTSD subjects were deficient when compared to that of the controls.
► Single trial time–frequency error measures were shown to be possible in PTSD.