Upshot: Despite decades of research, a functional understanding of the neuronal mechanisms of Auditory Scene Analysis (ASA) remains elusive. Most studies had focused on the instant processing of simple sounds in passive settings and a head-centered (egocentric) reference frame. During realistic ASA, however, the continuous modulation of sensory input resulting from self-motion fundamentally impacts the processing of the sound source of interest, particularly the representation of its egocentric relative to the absolute (i.e. allocentric) location in space. Moreover, identification of a particular sound source critically depends on its behavioral relevance. To overcome current methodological limitations, we developed an new paradigm for selective listening iin environments with multiple sound source called SIT (Sensory Island Task, Ferreiro et al., 2020, see also lab news and below for more info). SIT allows us to study context-dependent sound source localization during chronic recording of neuronal activity.
A central function of sensory systems is the gathering of information about dynamic interactions with the environment during active exploration. To determine whether modulation of a sensory cue was externally caused or a result of self-motion is fundamental to perceptual invariance and requires the continuous update of sensory processing about recent movements. This process is highly context-dependent and crucial for perceptual performances such as decision-making and sensory object formation. Yet despite its fundamental ecological role, active sensing is rarely incorporated in perceptual or neurophysiological investigations of sensory processing in animals. We developed the Sensory Island Task (SIT), a new freely moving search paradigm to study sensory processing and perception.In SIT, animals explore an open-field arena to find a sensory target relying solely on changes in the presented stimulus, which is controlled by closed-loop position tracking in real-time. Within a few sessions, animals are trained via positive reinforcement to search for a particular area in the arena (“target island”), which triggers the presentation of the target stimulus. The location of the target island is randomized across trials, making the modulated stimulus feature the only informative cue for task completion. Animals report detection of the target stimulus by remaining within the island for a defined time (“sit-time”). Multiple “non-target” islands can be incorporated to test psychometric discrimination and identification performance. We exemplify the suitability of SIT for rodents (Mongolian gerbil, Meriones unguiculatus) and small primates (mouse lemur, Microcebus murinus) and for studying various sensory perceptual performances (auditory frequency discrimination, sound source localization, visual orientation discrimination). Furthermore, we show that pairing SIT with chronic electrophysiological recordings allows revealing neuronal signatures of sensory processing under ecologically relevant conditions during goal-oriented behavior. In conclusion, SIT represents a flexible and easily implementable behavioral paradigm for mammals that combines self-motion and natural exploratory behavior to study sensory sensitivity and decision-making and their underlying neuronal processing.
Similar as with non-human animals (Ferreiro, Amaro et al., 2020), we've developed an application to perform auditory discrimiation experiments involving active exploration with humans. With small differences, such as a square arena (instead of circular) and auditory stimuli delivered via bluetooth headphones (instead of free-field), we have essentially replicated the SIT paradigm in humans. Together, the human and non-human animal SIT should complement each other in the quest to further our understanding of naturalistic behaviour and sensory processing.
Upshot: Hearing impairment, which is the most frequent sensory deficit today, deprives many – especially elderly – people of acoustic orientation and communication in complex environments and highlights the translational significance for an in-depth understanding of the underlying mechanisms (see also next section). A complementary line of my research is therefore dedicated to advance our understanding how neural processing of spatial information in the brainstem differs between normal acoustic and neuro-prosthetic stimulation by the use of cochlear implants (Müller et al., 2018 ASA). The lab formed collaborations with the two largest cochlear implants manufacturers that allow performing translational research in an animal model for human hearing loss and presbycusia.