Neuroscience
-
In everyday listening environments, a main task for our auditory system is to follow one out of multiple speakers talking simultaneously. The present study was designed to find electrophysiological indicators of two central processes involved - segregating the speech mixture into distinct speech sequences corresponding to the two speakers, and then attending to one of the speech sequences. We generated multistable speech stimuli that were set up to create ambiguity as to whether only one or two speakers are talking. ⋯ In the latter case, they distinguished which speaker was in their attentional foreground. Our data show a long-lasting event-related potential (ERP) modulation starting at 130ms after stimulus onset, which can be explained by the perceptual organization of the two speech sequences into attended foreground and ignored background streams. Our paradigm extends previous work with pure-tone sequences toward speech stimuli and adds the possibility to obtain neural correlates of the difficulty to segregate a speech mixture into distinct streams.
-
Repeating spatiotemporal spike patterns exist and carry information. How this information is extracted by downstream neurons is unclear. Here we theoretically investigate to what extent a single cell could detect a given spike pattern and what the optimal parameters to do so are, in particular the membrane time constant τ. ⋯ Long sequences could be recognized thanks to coincidence detectors working at a much shorter timescale. This is consistent with the fact that recognition is still possible if a sound sequence is compressed, played backward, or scrambled using 10-ms bins. Coincidence detection is a simple yet powerful mechanism, which could be the main function of neurons in the brain.
-
Music is a curious example of a temporally patterned acoustic stimulus, and a compelling pan-cultural phenomenon. This review strives to bring some insights from decades of music psychology and sensorimotor synchronization (SMS) literature into the mainstream auditory domain, arguing that musical rhythm perception is shaped in important ways by temporal processing mechanisms in the brain. The feature that unites these disparate disciplines is an appreciation of the central importance of timing, sequencing, and anticipation. ⋯ We then move away from music to explore the perceptual effects of rhythmic timing in pattern detection, auditory scene analysis, and speech perception. Finally, we review the neurophysiology of general timing processes that may underlie aspects of the perception of rhythmic patterns. We conclude with a brief summary and outlook for future research.
-
Predictive coding is possibly one of the most influential, comprehensive, and controversial theories of neural function. While proponents praise its explanatory potential, critics object that key tenets of the theory are untested or even untestable. The present article critically examines existing evidence for predictive coding in the auditory modality. ⋯ More work exists on the proposed oscillatory signatures of predictive coding, and on the relation between attention and precision. However, results on these latter two assumptions are mixed or contradictory. Looking to the future, more collaboration between human and animal studies, aided by model-based analyses will be needed to test specific assumptions and implementations of predictive coding - and, as such, help determine whether this popular grand theory can fulfill its expectations.
-
Review
Automatic frequency-shift detection in the auditory system: A review of psychophysical findings.
The human brain has the task of binding successive sounds produced by the same acoustic source into a coherent perceptual stream, and binding must be selective when several sources are concurrently active. Binding appears to obey a principle of spectral proximity: pure tones close in frequency are more likely to be bound than pure tones with remote frequencies. It has been hypothesized that the binding process is realized by automatic "frequency-shift detectors" (FSDs), comparable to the detectors of spatial motion in the visual system. ⋯ A number of variants of this study have been performed since 2005, in order to confirm the existence of FSDs, to characterize their properties, and to clarify as far as possible their neural underpinnings. The results obtained up to now suggest that the working of the FSDs exploits an implicit sensory memory which is powerful with respect to both capacity and retention time. Tones within chords can be perceptually enhanced by small frequency shifts, in a manner suggesting that the FSDs can serve in auditory scene analysis not only as binding tools but also, to a limited extent, as segregation tools.