AbstractHow we distinguish multiple simultaneous stimuli is uncertain, particularly given that such stimuli sometimes recruit largely overlapping populations of neurons. One hypothesis is that tuning curves might change to limit the number of stimuli driving any given neuron when multiple stimuli are present. To test this hypothesis, we recorded the activity of neurons in the inferior colliculus while monkeys localized either one or two simultaneous sounds differing in frequency. Although monkeys easily distinguished simultaneous sounds (∼90% correct performance), the frequency tuning of inferior colliculus neurons on dual sound trials did not improve in any obvious way. Frequency selectivity was degraded on dual sound trials compared to single sound trials: tuning curves broadened, and frequency accounted for less of the variance in firing rate. These tuning curve changes led a maximum-likelihood decoder to perform worse on dual sound trials than on single sound trials. These results fail to support the hypothesis that changes in frequency response functions serve to reduce the overlap in the representation of simultaneous sounds. Instead these results suggest alternative theories, such as recent evidence of alternations in firing rate between the rates corresponding to each of the two stimuli, offer a more promising approach.
Multiple sounds degrade the frequency representation in monkey inferior colliculus
