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要旨:
Natural auditory objects are complex and often composed of more than one defining acoustic feature. However, not all features are usually essential for the spontaneous identification of a given object and a given object can often be detected or discriminated using several of its features. For example, a dynamically moving sound might be localized by its immediate intensity difference between the ears or by slower changes in amplitude over time. How different stimulus features for object discrimination are selected in the brain is not well understood. In addition, it remains unclear how the fidelity of cue selection may be dynamically altered in a given task context. The goal of this project is to explore a rodent model to study the neural basis of sound feature selection in acoustic discrimination.
We tested rats in an acoustic motion discrimination task, where the animals had to discriminate right- and left-ward moving sounds. The two stimuli consisted of white noise pulses that were simultaneously presented from each side of the operant conditioning box. The percept of horizontal motion was then imposed by modulating the amplitude of these two streams in opposite directions over time and by a difference in the initial amplitude of the left and right streams. This provided two potential cues to solve the task, the relative weighting of which could also be manipulated by changing the level of amplitude difference between both streams. Using reaction time and correct percept identification as behavioral metrics, we found that rats spontaneously developed a preference for one of the two stimulus features for discrimination, mainly for stimulus onset. Interestingly, however, individual animals sometimes relied on different features to identify each stimulus (leftward or rightward moving). These results provide the grounds to study the neural mechanism of this stimulus selection and encoding, and pave the way for a more detailed analysis of the spontaneous selection of features for auditory identification tasks. Specifically, our results highlight the heterogeneity in the strategies developed by animals to solve sensory tasks and parallel previous results found by studies in the visual system.
