Rhythmic priming of phonetic perception with a chirp that compensates for cochlear delay

The frequency-dependent transmission delay in the auditory pathway, which occurs in the cochlea, can be counteracted with chirps. These rapid upward frequency sweeps maximally stimulate auditory brainstem structures due to neural synchrony. This study investigated whether improved neural synchrony from priming with chirps could benefit phonetic perception. Priming conditions were 1) regular isochronous presentation with a chirp onset asynchrony of 45 ms, 2) randomly presented chirps, and 3) pink noise only. After a 2.6 s priming window a vowel discrimination task was performed where syllable pairs were either of the same duration, or the second member of the pair was 45 ms longer. EEG data was acquired from participants (N=14) and behavioral, sensor- (electrode) and source-level (auditory α clusters) measures were analyzed. Behavioral results showed no effect of priming but significantly lower discrimination accuracy when the syllables were different in duration. Sensor-level analyses, from FCz and Global Field Potentials, showed no effect of priming or syllable pair. An auditory α cluster localized to the left Medial Temporal Gyrus showed a divergence in event-related spectral perturbation results whereby there was synchronization in the noise only condition and desynchronization for both chirp conditions. These results are not consistent with operational descriptions of priming involving temporal expectancy and anticipatory attending. They indicate that perceptual priming, based on chirps that compensate for cochlear temporal dispersion, influences the cortical processing involved in the maintenance of a speech discrimination task, possibly by introducing a perceptual background or by upregulating subcortical instances of the auditory pathway.