Figure 2.

Relationships between IT, ET, and ISIs indicate sparse spiking. STRFs from four single neurons illustrate a variety of receptive field arrangements (left). Neurons can be exceedingly fast with short integration times (a and b), or can have substantially longer integration times (c and d). A variety of receptive field shapes are also observed, such as the presence of lateral inhibition (b–d), temporal inhibition (a–c), or obliquely oriented STRFs (d). In the middle panels, shuffled autocorrelograms illustrate the presence of reliable and precise spike timing (black). In all neurons studied, the shuffled autocorrelograms exhibit a sharp central peak with timing precision as low as a few hundred microseconds (a, middle) or more typically a few milliseconds (b and c). For reference, the spike train autocorrelograms are also shown (central impulse removed, gray). The relationships between interspike intervals, integration times, and encoding times are consistent with temporally sparse responses (right). The interspike interval distributions are shown with the correspond integration (dashed vertical red line) and encoding times (dashed vertical black line). As seen for all neurons, the IT is larger than the ET and most interspike intervals exceed an integration time. Thus on average, there is one precisely timed spike per integration time. In all cases, TSIs are near 1 (noted above each panel).