A pitch glide activates an intermediate response between auditory N1 and mismatch negativity

Auditory representations for long lasting sounds: Insights from event-related brain potentials and neural oscillations

The basic features of short sounds, such as frequency and intensity including their temporal dynamics, are integrated in a unitary representation. Knowledge on how our brain processes long lasting sounds is scarce. We review research utilizing the Mismatch Negativity event-related potential and neural oscillatory activity for studying representations for long lasting simple versus complex sounds such as sinusoidal tones versus speech. There is evidence for a temporal constraint in the formation of auditory representations: Auditory edges like sound onsets within long lasting sounds open a temporal window of about 350 ms in which the sounds' dynamics are integrated into a representation, while information beyond that window contributes less to that representation. This integration window segments the auditory input into short chunks. We argue that the representations established in adjacent integration windows can be concatenated into an auditory representation of a long sound, thus, overcoming the temporal constraint.

Sound Change Integration Error: An Explanatory Model of Tinnitus

A growing body of research is focused on identifying and understanding the neurophysiological mechanisms that underlie tinnitus. Unfortunately, however, most current models cannot adequately explain the majority of tinnitus features. For instance, although tinnitus generally appears within minutes after entering a silent environment, most models postulate that tinnitus emerges over a much larger timescale (days). Similarly, there is a limited understanding of how the severity of tinnitus can differ in patients with a similar degree of hearing loss. To address this critical knowledge gap, we have formulated a novel explanatory model of tinnitus, the perception-update (PU) model, which rests on a theory of information processing and can explain several key characteristics of tinnitus onset. The PU model posits that the brain continuously updates the information received from the inner ear by comparing it to the received information immediately before. That is, the auditory system processes the relative change in sensory input, as opposed to the absolute value of the auditory input. This is analogous to the functioning of data compression technology used for music and images called differential pulse code modulation (differential PCM). The PU model proposes that the inner ear transmits sound change to the auditory cortex via an auditory N1 response, an event-related potential component that constitutes is a prime signaler of auditory input change. In cases of hearing impairment, the PU model posits that the auditory system finds itself in a state of uncertainty where perception has to be predicted based on previous stimulation parameters, which can lead to the emergence of tinnitus.

Spatiotemporal characteristics of the neural activities processing consonant/dissonant tones in melody

To identify neural correlates underlying melody processing, we measured MEG responses elicited by keynote and out-of-key tones at the end of musical phrases. These melodies were newly composed and unknown to the subjects. Significant enlargements of N1m/P2m peaks at about 120-160 ms were observed in response to dissonant (out-of-key) tones compared to those in response to consonant (keynote) tones. The equivalent current dipoles (ECD) of the N1m were localized in areas centered at bilateral primary auditory cortices in the superior surface of the temporal lobe. Following the N1m/P2m, a late component occurring at 280-530 ms was observed. As the latency proceeded, the location of ECD sources of the late component shifted in the right hemisphere, but not in the left hemisphere, from the supratemporal auditory cortex to a posterior inferior auditory association cortex around the superior temporal sulcus (STS). The grand mean locations of the ECDs for consonant and dissonant tones were separated at a peak period of 380-410 ms of the late component but converged to the same region around the STS in the last period of 440-530 ms. These observations suggest that the neural activities generating the N1m component in the bilateral auditory cortices may play a role in automatic detection of tonality mismatch based on the pitch analysis. The activities of the late component around the posterior part of the right STS are thought to be involved in the analysis of pitch-sequence, such as how the pitch changes temporally, as a pre-process of melody perception.