Dr. Ross Williamson

PhD Title:
The influence of statistical context on the neural representation of sound

PhD Abstract:
Models of stimulus-response functions have been used for decades in an attempt to understand the complex relationship between a sensory stimu- lus and the neural response that it elicits. A popular model for character- ising auditory function is the spectrotemporal receptive field (STRF), originally due to Aertsen and Johannesma (1980); Aertsen et al. (1980, 1981). However, the STRF model predicts auditory cortical responses to complex sounds very poorly, presumably because the model is linear in the stimulus spectrogram and thus incapable of capturing spectrotemporal nonlineari- ties in auditory responses.

Ahrens et al. (2008a) introduced a multilinear framework, which captures neuron-specific nonlinear effects of stimulus context on spiking responses to complex sounds. In such a framework, contextual effects are interpreted as non-linear stimulus interactions that modulate the input to a subsequent STRF-like linear filter. We derive various extensions to this framework, and demonstrate that the nonlinear effects of stimulus context are largely in- separable, and fundamentally different for near-simultaneous and delayed non-simultaneous sound energy. In two populations of neurons, recorded from the mouse auditory cortex and thalamus, we show that simultane- ous sound energy provides a nonlinear positive (amplifying) gain to the subsequent linear filter, while non-simultaneous sound energy provides a negative (dampening) gain. We demonstrate that this structure is largely responsible for providing a significant increase in the predicitve capabili- ties of the model.

Using this framework, we show that nonlinear context dependence dif- fers between cortical fields, consistent with previous studies (Linden et al., 2003). Furthermore, we illustrate how such a model can be used to probe the nonlinear mechanisms that underly the ability of the auditory system to operate in diverse acoustic environements. These results provide a novel extension to the study of receptive fields in multiple brain areas, and ex- tend existing understanding of the way in which stimulus context drives complex auditory responses.

Next employment after CoMPLEX:
Post-Doc at Harvard Medical School, Boston MA, USA


Ross Williamson

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