Computational Models of the Auditory System
Current modeling efforts in the laboratory are directed towards simulating neuronal activity within the spectral processing pathway in the auditory system. Psychophysical experiments in humans have established that our ability to determine the elevation of a sound source depends on the acoustic properties of the outer ear, which adds direction-dependent notches to the spectra of free-field sounds. Physiological and behavioral data suggest that the dorsal cochlear nucleus (DCN) initiates a pathway specialized to process this cue. Type O units in the inferior colliculus (IC), one of three major response types in the IC, are a main target of DCN projections and thus serve as the midbrain component of the spectral processing pathway. Over the past 30 years, a conceptual model of the neural circuitry in the deep DCN has emerged; a demonstration of a part of our corresponding computational model is shown below. In this simulation, the DCNâs principal cells (P cells or output cells) receive inputs from two sources: excitatory inputs from the auditory nerve (AN) and inhibitory inputs from vertical cells (V). The simulated acoustic input for this model is pure tones of differing frequency and stimulus level. We are now extending this model to the IC (i.e., using the output of this model as the input to an IC neuron) and performing simulations to determine if the IC model can account fully for the response properties of type O units to both simple (tones) and complex stimuli (notches).
Computer simulation of neuronal activity in the dorsal cochlear nucleus. To explore how neurons in the dorsal cochlear nucleus (DCN) respond to pure tones, click in receptive field of P cell to change the frequency and intensity of the tonal stimulus and observe the resultant activity in the model to the right. Note that when the frequency is in the middle of its range, auditory nerve (AN) fibers and DCN principal (P) cells respond to low-level stimuli, but at high levels, DCN vertical (V) cells start to fire and DCN P cells turn off.