p013fig01.09 A sigmoid signal function generates a quenching threshold below which cell activities are treated like noise and suppressed. Activities that are larger than the quenching threshold are contrast enhanced and stored in short-term memory.<BR>||  Quenching threshold xi(o) vs i.<BR><TABLE border="1"><TR><TD><B>f</b></td><TD><B>Xi(∞)= xi(∞)/sum[j: xj(∞)]</b></td><TD><B>x(∞)</b></td></tr><TR><TD>sigmoid</td><TD>tunable filter<BR>stores infinitely many contrast-enhanced patterns</td><TD>suppresses noise</td></tr></table>