The progress in the field of tinnitus largely depends on the development of a reliable tinnitus animal model. Recently, a new method based on the acoustic startle reflex modification was introduced for tinnitus screening in laboratory animals. This method was enthusiastically adopted and now widely used by many scientists in the field due to its seeming simplicity and a number of advantages over the other methods of tinnitus assessment. Furthermore, this method opened an opportunity for tinnitus assessment in humans as well. Unfortunately, multiple modifications of data collection and interpretation implemented in different labs make comparisons across studies very difficult. In addition, recent animal and human studies have challenged the original "filling-in" interpretation of the paradigm. Here, we review the current literature to emphasize on the commonalities and differences in data collection and interpretation across laboratories that are using this method for tinnitus assessment. We also propose future research directions that could be taken in order to establish whether or not this method is warranted as an indicator of the presence of tinnitus.

Averaged responses to loud clicks were recorded in the unrectified and rectified masseter electromyogram (EMG) of 18 healthy subjects. Unilateral clicks (0.1 ms, 3 Hz, 70–100 dB NHL), delivered during a steady masseter contraction, evoked bilateral responses that appeared to consist of 2 components on the basis of threshold, latency, and their appearance in rectified EMG. The lowest threshold response appeared as a p16 wave (onset 11–13 ms) in the unrectified EMG and corresponded with a 10- to 12-ms period of inhibition in the rectified EMG. Higher-intensity clicks recruited an earlier p11 response in the unrectified EMG (onset 7.0–9.2 ms) that sometimes appeared as an initial increase in the rectified EMG before suppression. The amplitude of the p11 wave scaled with background EMG level and was asymmetrically modulated by 30° tilt of the whole body. The threshold of the early p11/n15 wave in masseter was the same as the threshold for click-induced vestibulocollic reflexes. Single motor unit recordings demonstrated that responses in masseters corresponded to a silent period in unit firing that began earlier and lasted longer at 100 dB than at 80 dB. We propose that loud clicks induce 2 partially overlapping short-latency reflexes in masseter muscle EMG: a p11/n15 response, which we suggest is of vestibular origin, and a p16/n21 response, which we suggest is equivalent to the previously described jaw–acoustic reflex.

Objective: The development of a new non-intrusive optical system for remotely measuring acoustic startle reflex (ASR) in humans. Approach: The eye reflex movement during an acoustic stimulation session is recorded through a high-speed digital camera. The eyes region is isolated by the rest of the face by an advanced pyramid-like feature detection algorithm, which greatly reduces the number of false positives. A separate Lucas–Kanade optical flow routine is designed for the eyeblink movement detection and the startle eyeblink reflex (SEBR) curve extraction. Image masking is implemented for the elimination of unwanted artifacts caused mainly by voluntary eye movement. The proposed system was tested along with a valid EMG system on a sample of 32 healthy randomly selected adults, and the results were compared in order to measure the system’s degree of reliability. Main results: To assess the proposed method’s validity the EMG data was used as a benchmark. The results showed strong correlation between EMG and Camera acquired results, which proves the validity of the proposed method. Furthermore, by comparing the response probability and the signal to noise ratio (SNR) for the two techniques, we proved that the proposed method can surpass the traditional EMG system in terms of accuracy and reliability. Significance: The proposed technique presents a simple, robust and reliable non-intrusive means of measuring ASR in humans, with the potential of future implementation on various ASR psychophysiology experiments, such as the study of PPI.

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