Fig. 5.

Dependence of STG activity on the reference and test stimuli. Firing rates of STG neurons were modeled as a linear function of both the reference stimulus and the test stimulus. The model took the following form: Firing_Rate = a₁(t) * Morph_value_{Reference stimulus} + a₂(t) * Morph_value_{Test stimulus} + a₃(t). The a₁, a₂, and a₃ are regression coefficients, as a function of time. The a₁ and a₂ represent the effects of the reference and test stimulus, respectively, on a neuron's firing rate. A: a single neuron example of the linear relationship between test-stimulus activity and the reference and test stimulus. Solid lines indicate the mean value for each regression coefficient, and the shaded areas indicate the 95% confidence intervals of mean. Data in grey indicate the time-varying coefficient values for the reference stimulus (a₁), whereas the data in black indicate the time-varying coefficient values for the test stimulus (a₂). Thick bars at the top of the plot indicate those time points when a₁ (gray bar) or a₂ (black bars) were reliably different (P < 0.05) from 0. The 2 vertical lines indicate stimulus onset and offset, respectively. B: population analysis of the linear-regression model. Distribution of index values based on the difference between the absolute values of the a₁ and a₂ coefficients. If the index value was >0, it indicated that the absolute value of the a₂ coefficient was greater than that of the a₁ coefficient. If the index value was <0, it indicated that absolute value of the a₁ coefficient was greater than that of the a₂ coefficient.