Figure 4.

FC class-specific responses to task-relevant sounds. (a) A single unit's response to two randomly alternating target tones in a tone detection task, plotted as in Fig. 2. This cell responded equally well to either of the two target tones (550 or 2200 Hz) but not to any of the 30 different reference noise stimuli. (b) During two-tone discrimination the 550 Hz (low) tone became a reference sound, and the unit now stopped responding to this tone, while maintaining its response to the 2200 Hz (high) tone, which remained a target. (c) Each point indicates the response of a neuron (n=66/115 responsive neurons) to the same target tone during tone detection (vertical axis) and discrimination (horizontal axis). Responses to the target tone were strongly correlated between behavior conditions (r=0.51, p<0.001). The dashed ellipse indicates the first (major axis) and second (minor axis) principal components of the covariance matrix of target responses under the two task conditions. The regression line (black) has a slope of 0.9, indicating that response magnitude was similar in both conditions. (d) Responses of the same neurons to the tone whose task-related ‘stimulus class’ or ‘meaning’ switched from target during tone detection to reference during the two-tone discrimination task, plotted as in c. Responses were much weaker when the tone acted as a reference in the two-tone discrimination task, and the responses were not correlated between behavior conditions (r=0.16, p>0.2).