A New Approach to Model Pitch Perception Using Sparse Coding
Fig 2
Different complex harmonic stimuli with the same pitch.
(A) The Fourier transform (FT) of three complex harmonics stimuli with a fundamental frequency of f0 = 240 Hz. The three signals have different spectral components: Sin,1(f) is composed of the first harmonic component of f0; Sin,2(f) consists of the first four successive harmonics of f0; and Sin,3(f) is formed from of the 10–13 harmonics. (B) The corresponding output of the cochlear model [26], i.e., the AN population responses for the three stimuli. The y-axis represents the normalized characteristic frequencies (CFs), which is CF divided by f0, on a linear scale, and the x-axis shows the post-stimulus time in milliseconds. The cochlear input is a 15ms long stimulus, and the resulting output is taken from the last 5ms. Note the different patterns of the AN activities that correspond to the three different cases: a stimulus with low frequencies excites the apical parts of the cochlea (lower part in the images), while a stimulus with higher frequencies excites the basal parts. Note also that the AN population responses define unique spatiotemporal patterns of activities for each of the stimuli. All the three stimuli have relatively low sound levels (30 dB SPL), which means that the cochlea response is linear.