However, there was no constraint forcing the envelope adjustment to remain consistent with the subband fine structure (Ghitza, 2001), or to produce new subbands that were mutually consistent (in the sense that combining them would produce a signal that would yield the same subbands when decomposed again). It was thus generally the case that during the first few iterations, the envelopes measured at the beginning of cycle n + 1 did not completely retain the adjustment imposed www.selleckchem.com/products/Everolimus(RAD001).html at

cycle n, because combining envelope and fine structure, and summing up the subbands, tended to change the envelopes in ways that altered their statistics. However, we found that with iteration, the envelopes generally converged to a state with the desired statistics. The fine structure was not directly constrained, and relaxed to a state consistent with the envelope constraints. Convergence was monitored by computing the error in each statistic at the start of each iteration and measuring the signal-to-noise ratio (SNR) as the ratio of the squared error of a statistic class, summed across all statistics in the class, to the sum of the squared statistic values of that class. The procedure was halted once all MEK inhibitor classes of statistics were imposed with an SNR of 30 dB or higher or when 60 iterations were reached. The procedure was considered to have converged if the

average SNR of all statistic classes was 20 dB second or higher. Occasionally the synthesis process converged to a local minimum in which it failed to produce a signal matching

the statistics of an original sound according to our criterion. This was relatively rare, and such failures of convergence were not used in experiments. Although the statistics in our model constrain the distribution of the sound signal, we have no explicit probabilistic formulation and as such are not guaranteed to be drawing samples from an explicit distribution. Instead, we qualitatively mimic the effect of sampling by initializing the synthesis with different samples of noise (as in some visual texture synthesis methods) (Heeger and Bergen, 1995 and Portilla and Simoncelli, 2000). An explicit probabilistic model could be developed via maximum entropy formulations (Zhu et al., 1997), but sampling from such a distribution is generally computationally prohibitive. We thank Dan Ellis for helpful discussions and Mark Bee, Mike Landy, Gary Marcus, and Sam Norman-Haignere for comments on drafts of the manuscript. “
“During successful reading, the visual system efficiently transforms a complex input of contrast-defined strokes of ink into phonological and semantic word representations. After entering primary visual cortex (V1), visual information about words undergoes several transformations in extrastriate cortex, including regions localized to ventral occipitotemporal (VOT) cortex (Dehaene et al., 2005 and DiCarlo and Cox, 2007).