Sensitivity to temporal structure facilitates perceptual analysis of complex auditory scenes.

The notion that sensitivity to the statistical structure of the environment is pivotal to perception has recently garnered considerable attention. Here we investigated this issue in the context of hearing. Building on previous work (Sohoglu and Chait, 2016a; elife), stimuli were artificial 'soundscapes' populated by multiple (up to 14) simultaneous streams ('auditory objects') comprised of tone-pip sequences, each with a distinct frequency and pattern of amplitude modulation. Sequences were either temporally regular or random. We show that listeners' ability to detect abrupt appearance or disappearance of a stream is facilitated when scene streams were characterized by a temporally regular fluctuation pattern. The regularity of the changing stream as well as that of the background (non-changing) streams contribute independently to this effect. Remarkably, listeners benefit from regularity even when they are not consciously aware of it. These findings establish that perception of complex acoustic scenes relies on the availability of detailed representations of the regularities automatically extracted from multiple concurrent streams.

Sensitivity to the temporal structure of rapid sound sequences - An MEG study.

To probe sensitivity to the time structure of ongoing sound sequences, we measured MEG responses, in human listeners, to the offset of long tone-pip sequences containing various forms of temporal regularity. If listeners learn sequence temporal properties and form expectancies about the arrival time of an upcoming tone, sequence offset should be detectable as soon as an expected tone fails to arrive. Therefore, latencies of offset responses are indicative of the extent to which the temporal pattern has been acquired. In Exp1, sequences were isochronous with tone inter-onset-interval (IOI) set to 75, 125 or 225ms. Exp2 comprised of non-isochronous, temporally regular sequences, comprised of the IOIs above. Exp3 used the same sequences as Exp2 but listeners were required to monitor them for occasional frequency deviants. Analysis of the latency of offset responses revealed that the temporal structure of (even rather simple) regular sequences is not learnt precisely when the sequences are ignored. Pattern coding, supported by a network of temporal, parietal and frontal sources, improved considerably when the signals were made behaviourally pertinent. Thus, contrary to what might be expected in the context of an 'early warning system' framework, learning of temporal structure is not automatic, but affected by the signal's behavioural relevance.

Analysis of DNA by Southern blotting.

The purpose of this protocol is to detect specific DNA sequences in a complex sample by hybridization to a labeled probe.

Isolation of plasmid DNA from bacteria.

The purpose of this protocol is the isolation of plasmid DNA from bacteria. The boiling method for isolating plasmids by Holmes and Quigley (1981) is presented here. This method is rapid and simple and it allows for a large number of samples to be processed simultaneously (up to 40 samples). Thus, it is appropriate for the preparation of bacterial plasmids in order to screen a large number of colonies or small cultures for the presence of recombinant DNA inserts. The protocol can be effectively scaled up for the preparation of plasmids from liter cultures.

Preparation of genomic DNA from bacteria.

The purpose of this protocol is the isolation of bulk cellular DNA from bacteria (alternatively see Preparation of genomic DNA from Saccharomyces cerevisiae or Isolation of Genomic DNA from Mammalian Cells protocols).

The role of temporal regularity in auditory segregation.

The idea that predictive modelling and extraction of regularities plays a pivotal role in auditory segregation has recently attracted considerable attention. The present study investigated the effect of one basic form of regularity, rhythmic regularity, on auditory stream segregation. We departed from the classic streaming paradigm and developed a new stimulus, Rand-AB, consisting of two, concurrently presented, temporally uncorrelated, tone sequences (with frequencies A and B). To evaluate segregation, we used an objective measure of the extent to which listeners are able to selectively attend to one of the sequences in the presence of the other. Performance was quantified on a difficult pattern detection task which involves detecting a rarely occurring pattern of amplitude modulation applied to three consecutive A or B tones. In all cases the attended sequence was temporally irregular (with a random inter-tone-interval (ITI) between 100 and 400 ms) and the regularity status of the competing sequence was set to one of four conditions: (1) random ITI between 100 and 400 ms (2) isochronous with ITI = 400 ms. (3) isochronous with ITI = 250 ms (equal to the mean rate of the attended sequence) (4) isochronous with ITI = 100 ms. For a frequency separation of 2 (but not 4) semi tones we observed improved performance in conditions (3) and (4) relative to (1), suggesting that stream segregation is facilitated when the distracter sequence is temporally regular, but that the effect of temporal regularity as a cue for segregation is limited to relatively fast rates and to situations where frequency separation is insufficient for segregation. These findings provide new evidence to support models of streaming that involve segregation based on the formation of predictive models.