The perceptual salience of a target tone presented in a multitone background is increased by the presentation of a precursor sound consisting of the multitone background alone. It has been proposed that this "enhancement" phenomenon results from an effective amplification of the neural response to the target tone. In this study, we tested this hypothesis in humans, by comparing the auditory steady-state response (ASSR) to a target tone that was enhanced by a precursor sound with the ASSR to a target tone that was not enhanced. In order to record neural responses originating in the brainstem, the ASSR was elicited by amplitude modulating the target tone at a frequency close to 80 Hz. The results did not show evidence of an amplified neural response to enhanced tones. In a control condition, we measured the ASSR to a target tone that, instead of being perceptually enhanced by a precursor sound, was acoustically increased in level. This level increase matched the magnitude of enhancement estimated psychophysically with a forward masking paradigm in a previous experimental phase. We found that the ASSR to the tone acoustically increased in level was significantly greater than the ASSR to the tone enhanced by the precursor sound. Overall, our results suggest that the enhancement effect cannot be explained by an amplified neural response at the level of the brainstem. However, an alternative possibility is that brainstem neurons with enhanced responses do not contribute to the scalp-recorded ASSR.

As eye movements are mostly automatic and overtly generated to attain visual goals, individuals have a poor metacognitive knowledge of their own eye movements. We present an exploratory study on the effects of real-time continuous auditory feedback generated by eye movements. We considered both a tracking task and a production task where smooth pursuit eye movements (SPEM) can be endogenously generated. In particular, we used a visual paradigm which enables to generate and control SPEM in the absence of a moving visual target. We investigated whether real-time auditory feedback of eye movement dynamics might improve learning in both tasks, through a training protocol over 8 days. The results indicate that real-time sonification of eye movements can actually modify the oculomotor behavior, and reinforce intrinsic oculomotor perception. Nevertheless, large inter-individual differences were observed preventing us from reaching a strong conclusion on sensorimotor learning improvements.

The gain and speed of smooth pursuit eye movements quickly drop whenever a moving tracked target disappears behind an occluder. The present study tests to what extent pursuit maintenance after target disappearance depends on the occluder's characteristics. In all experiments, a target moving for 2500 ms, (or 1250 ms) at 13.3°/s (or 26.6°/s), disappears behind an occluder for 700 ms (or 350 ms). Participants are asked to maintain their pursuit eye movements as long as possible after target disappearance. Experiment 1 compares smooth pursuit with four types of occluders and shows that a texture of flickering disks allows maintaining pursuit for long durations. Experiment 2 investigates the capability to maintain pursuit with occluders of varying flickering frequencies (3, 5, 10, 20, and 30 Hz). It is found that after target disappearance, smooth pursuit is maintained for longer durations with flicker at 10 and 20 Hz, relative to other flickering frequencies (3, 5, and 30 Hz). Experiment 3 tests whether disk size and disk density of a flickering occluding texture influence smooth pursuit maintenance. Finally, Experiment 4 tests the influence of the contrast distribution of the flickering disks on pursuit maintenance. Altogether, the results show that individuals can maintain smooth pursuit for long durations after target disappearance behind an occluding texture of disks flickering at temporal frequency above 5 Hz with balanced contrast. It is suggested that eye-induced reverse-phi motion responses in MT/MST neurons provide a positive visual feedback to the pursuit system, allowing generating smooth pursuit in the absence of explicit stimulus motion.