About 200 cells were sampled, though not all tests were available from every cell. Here we show distributions of parameters measured from the flashing spot (on the left) and the sinusoidally modulated spot (on the right) tests. Green squares represent subjectively categorized nonlagged cells, red circles represent lagged cells, and blue crosses represent cells for which I could not find any basis for categorization.
Halfrise and halffall latencies are useful in adult data for distinguishing lagged from nonlagged cells [Humphrey and Weller 88; Saul and Humphrey 90] because lagged cells tend to have long halfrise latencies due to the early inhibition and slow buildup of the excitatory response, and long halffall latencies due to the anomalous offset discharge.
Latency and absolute phase are measured from the phase vs. temporal frequency data by fitting a line (weighted by amplitude and the reciprocal of the standard error of the phase means). Latency is the slope and absolute phase the intercept of this line, so that latency is related to the behavior at high frequency and absolute phase the behavior at low frequency, roughly speaking. Lagged cells in adult cats have latencies longer than 100ms and absolute phase lags (above 0 cycles), nonlagged cells have latencies less than 100ms and absolute phase leads (below 0 cycles) [Saul and Humphrey 90].
In young kittens, halfrise and halffall latencies are much longer, and don't distinguish apparent lagged and nonlagged cells. Similarly, phase latencies (also known as integration time) are long and similar across cell types. One of the novel findings here is that lagged cells in young kittens have absolue phase leads. This presumably reflects the weakness of the inhibition at these ages, since it is that inhibition in "mature" lagged cells that is responsible for the absolute phase lag according to our current model.
So, in summary, there are two general findings:
|Latency decreases, primarily between 5 and 6 weeks, but long-latency cells remain until at least 8 weeks||Lagged cells don't show absolute phase lags or clear inhibition in young kittens. These appear to strengthen primarily after about 8 weeks|
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Date created: November 5, 1997 Last modified: November 5, 1997 Copyright © 1997, Alan Saul Maintained by: Alan Saul Alan Saul