Speech understanding is known to become more difficult with increasing amounts of background noise even in the absence of hearing impairment. Some of these difficulties may be attributed to degraded neural representation of speech-related temporal cues. The envelope following response (EFR) is a far-field EEG response that can indicate how well a population of auditory nerve fibres phase-locks to the stimulus envelope, and thereby provide an indication of the robustness of temporal cue processing. The quality of the acquired response is affected by whether the eliciting stimulus is sinusoidally amplitude-modulated (the stimuli used most often to elicit and EFR; SAM-EFR) or rectangularly amplitude-modulated (RAM-EFR), which has also been used in recent studies. Robustness of the EFR (SAM or RAM) can be affected by background noise.

This study investigated characteristics of SAM-EFR or RAM-EFR in noise, and relevance to speech processing in noise. Characteristics of SAM-EFR and RAM-EFR were obtained for a signal of 110 Hz and carrier frequency of 2 kHz in the same participants for a range of modulators (80-200 Hz) and as a function of modulator cycles (2-10). Robustness was assessed by comparing the EFR responses in the absence or presence of noise. The EFR magnitude was derived and compared across stimulus modulator frequency and number of cycles, as well as with, and without the presence of noise. Results of SAM-EFR and RAM-EFR are discussed with regards to temporal processing degradation in noise and relevance to speech envelope coding in noise.