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Sparse Codes for Speech Predict Spectrotemporal Receptive Fields in the Inferior Colliculus

Figure 3

A half-complete, L0-sparse dictionary trained on spectrograms of speech.

This dictionary exhibits a variety of distinct shapes that capture several classes of acoustic features present in speech and other natural sounds. (a–f) Selected elements from the dictionary that are representative of different types of receptive fields: (a) a harmonic stack; (b) an onset element; (c) a harmonic stack with flanking suppression; (d) a more localized onset/termination element; (e) a formant; (f) a tight checkerboard pattern (see Fig. S1 for the full dictionary). Each rectangle represents the spectro-temporal receptive field (STRF) of a single element in the dictionary; time is plotted along the horizontal axis (from 0 to 216 msec) and log frequency is plotted along the vertical axis, with frequencies ranging from 100 Hz to 4000 Hz. (g) A graph of the usage of the dictionary elements showing that the different types of receptive field shapes separate based on usage into a series of rises and plateaus; red symbols indicate where each of the examples from panels a–f fall on the graph. The vertical axis represents the number of stimuli that required a given dictionary element in order to be represented accurately during inference.

Figure 3