Learning in a task of complex auditory streaming and identification

Adult humans were studied for improvements in their ability to segregate natural whole speech in background noise, in 6 test sessions spaced with a very wide range of inter-session interval (ISI) ranging from minutes to weeks apart so as to examine the effect of this parameter on initial (early) and late components of perceptual learning. Improvements were found even with spacings of 3 weeks between the punctate task sessions. All subjects showed similar total learning amounts but there were sex- and ISI-dependent differences in learning patterns, which we indexed by dividing the overall exponentially-decreasing learning pattern into an early phase between the first two sessions and a later phase between the second and sixth sessions. Males tested at all ISIs and females tested at short (2, 5 and 15 min) and long (1–21 days) ISIs showed small amounts of early-phase learning and large amounts of late-phase learning. However, females tested at intermediate (30 min and 1 h) ISIs showed only early learning, i.e., faster learning given that the total learning was the same. This sex- and ISI-specific deviant pattern could be changed to the standard pattern by interposing an overnight interruption that included sleep amongst test sessions. Thus, improvement in this complex auditory streaming and identification task can occur even with very brief and widely-spaced exposure, generally through a standard pattern of slower overall learning, but also through a sex- and ISI-specific deviant pattern of very rapid early learning which can be modulated by interposed delay unlike the standard pattern.