Mismatch response (MMR) in neonates: beyond refractoriness.

In the adult auditory system, deviant detection and updating the representation of the environment is reflected by the event-related potential (ERP) component termed the mismatch negativity (MMN). MMN is elicited when a rare-pitch deviant stimulus is presented amongst frequent standard pitch stimuli. The same stimuli also elicit a similar discriminative ERP component in sleeping newborn infants (termed the mismatch response: MMR). Both the MMN and the MMR can be confounded by responses generated by differential refractoriness of frequency-selective neural populations. Employing a stimulus paradigm designed to minimize this confounding effect, newborns were presented with sequences of pure tones under two conditions: In the oddball block, rare deviant tones (500 Hz; 10%) were delivered amongst frequent standards (700 Hz; 90%). In the control block, a comparison tone (500 Hz) was presented with the same probability as the deviant (10%) along with the four contextual tones (700 Hz, 980 Hz, 1372 Hz, 1920.8 Hz; 22.5% each). The significant difference found between the response elicited by the deviant and the comparison tone showed that the response elicited by the deviant in the oddball sequences cannot be fully explained by frequency-specific refractoriness of the neural generators. This shows that neonates process sounds in a context-dependent manner as well as strengthens the correspondence between the adult MMN and the infant MMR

Newborn Infants Detect Cues of Concurrent Sound Segregation

Separating concurrent sounds is fundamental for a veridical perception of one's auditory surroundings. Sound components that are harmonically related and start at the same time are usually grouped into a common perceptual object, whereas components that are not in harmonic relation or have different onset times are more likely to be perceived in terms of separate objects. Here we tested whether neonates are able to pick up the cues supporting this sound organization principle. We presented newborn infants with a series of complex tones with their harmonics in tune (creating the percept of a unitary sound object) and with manipulated variants, which gave the impression of two concurrently active sound sources. The manipulated variant had either one mistuned partial (single-cue condition) or the onset of this mistuned partial was also delayed (double-cue condition). Tuned and manipulated sounds were presented in random order with equal probabilities. Recording the neonates' electroencephalographic responses allowed us to evaluate their processing of the sounds. Results show that, in both conditions, mistuned sounds elicited a negative displacement of the event-related potential (ERP) relative to tuned sounds from 360 to 400 ms after sound onset. The mistuning-related ERP component resembles the object-related negativity (ORN) component in adults, which is associated with concurrent sound segregation. Delayed onset additionally led to a negative displacement from 160 to 200 ms, which was probably more related to the physical parameters of the sounds than to their perceptual segregation. The elicitation of an ORN-like response in newborn infants suggests that neonates possess the basic capabilities of segregating concurrent sounds by detecting inharmonic relations between the co-occurring sounds

Predictive processing of pitch trends in newborn infants

The notion of predictive sound processing suggests that the auditory system prepares for upcoming sounds once it has detected regular features within a sequence. Here we investigated whether predictive processes are operating at birth in the human auditory system. Event-related potentials (ERP) were recorded from healthy newborns to occasional ascending pitch steps occurring in the 2nd or the 5th position within trains of tones with otherwise monotonously descending pitch. If the trains were processed in a predictive manner only deviant pitch steps occurring in the later train position would elicit the discriminative mismatch response (MMR). Deviants delivered in the 5th but not in the 2nd position of the tone trains elicited a significant MMR response. These results suggest that newborns represent pitch trends within sound sequences and they process them in a predictive manner

Processing of horizontal sound localization cues in newborn infants

Objectives: By measuring event-related brain potentials (ERPs), the authors tested the sensitivity of the newborn auditory cortex to sound lateralization and to the most common cues of horizontal sound localization. Design: Sixty-eight healthy full-term newborn infants were presented with auditory oddball sequences composed of frequent and rare noise segments in four experimental conditions. The authors tested in them the detection of deviations in the primary cues of sound lateralization (interaural time and level difference) and in actual sound source location (free-field and monaural sound presentation). ERP correlates of deviance detection were measured in two time windows. Results: Deviations in both primary sound localization cues and the ear of stimulation elicited a significant ERP difference in the early (90 to 140 msec) time window. Deviance in actual sound source location (the free-field condition) elicited a significant response in the late (290 to 340 msec) time window. Conclusions: The early differential response may indicate the detection of a change in the respective auditory features. The authors suggest that the late differential response, which was only elicited by actual sound source location deviation, reflects the detection of location deviance integrating the various cues of sound source location. Although the results suggest that all of the tested binaural cues are processed by the neonatal auditory cortex, utilizing the cues for locating sound sources of these cues may require maturation and learning

Detecting the temporal structure of sound sequences in newborn infants

Most high-level auditory functions require one to detect the onset and offset of sound sequences as well as registering the rate at which sounds are presented within the sound trains. By recording event-related brain potentials to onsets and offsets of tone trains as well as to changes in the presentation rate, we tested whether these fundamental auditory capabilities are functional at birth. Each of these events elicited significant event-related potential components in sleeping healthy neonates. The data thus demonstrate that the newborn brain is sensitive to these acoustic features suggesting that infants are geared towards the temporal aspects of segregating sound sources, speech and music perception already at birth

EEG signatures accompanying auditory figure-ground segregation

In everyday acoustic scenes, figure-ground segregation typically requires one to group together sound elements over both time and frequency. Electroencephalogram was recorded while listeners detected repeating tonal complexes composed of a random set of pure tones within stimuli consisting of randomly varying tonal elements. The repeating pattern was perceived as a figure over the randomly changing background. It was found that detection performance improved both as the number of pure tones making up each repeated complex (figure coherence) increased, and as the number of repeated complexes (duration) increased – i.e., detection was easier when either the spectral or temporal structure of the figure was enhanced. Figure detection was accompanied by the elicitation of the object related negativity (ORN) and the P400 event-related potentials (ERPs), which have been previously shown to be evoked by the presence of two concurrent sounds. Both ERP components had generators within and outside of auditory cortex. The amplitudes of the ORN and the P400 increased with both figure coherence and figure duration. However, only the P400 amplitude correlated with detection performance. These results suggest that 1) the ORN and P400 reflect processes involved in detecting the emergence of a new auditory object in the presence of other concurrent auditory objects; 2) the ORN corresponds to the likelihood of the presence of two or more concurrent sound objects, whereas the P400 reflects the perceptual recognition of the presence of multiple auditory objects and/or preparation for reporting the detection of a target object

Do newborn infants sense the beat?

ABSTRACT I. BACKGROUND Music is present in some form in all human cultures. Sensitivity to various elements of music appears quite early on in infancy with understanding and appreciation of music emerging later through interaction between developing perceptual capabilities and cultural influence. Whereas there is already some information regarding spectral processing abilities of newborn infants, little is known about how they process rhythm. The ability to sense beat (a regular pulse in an auditory signal; termed 'tactus' in music theory); helps individuals to synchronize their movements with each other, such as necessary for dancing or producing music together. While beat induction would be very difficult to assess in newborns using behavioral techniques, it is possible to measure electrical brain responses to sounds (auditory event related brain potentials, ERP), even in sleeping babies. II. AIMS In order to understand how humans can learn to understand music, we need to discover what perceptual capabilities infants are born with. Theorists are divided on the issue whether the processing of beat is innate or learned. The goal of the current study was to test beat induction in sleeping newborn babies, by assessing whether or not the neonate auditory system forms expectation for the onset (downbeat) of the cycle in a regular rhythmic sound sequence. III. METHODS We presented 14 healthy sleeping neonates with sound sequences based on a typical two-measure rock drum accompaniment pattern (S1) composed of snare, bass and hi-hat spanning eight equally spaced (isochronous) positions. Four further variants of the S1 pattern (S2-S4 and D) were created by omitting sounds in different positions. The omissions in S2, S3, and S4 do not break the rhythm when presented in random sequences of S1-S4 linked together, because the omitted sounds are at the lowest level of the metrical hierarchy of this rhythm and, therefore, perceptually less salient. The four strictly metrical sound patterns (S1-S4; standard) made up the majority of the patterns in the sequences. Occasionally, the D pattern was delivered in which the downbeat was omitted. A control sequence repeating the D pattern 100% of the time was also delivered ("deviant-control"). Sleeping newborn infant participating in the experiment. The rhythm was delivered to the baby through self-adhesive ear-couplers at a low volume while electrical brain activity was measured with electrodes attached to the scalp and the face. Measurements followed feeding and lasted for about 20 minutes. The mother of the baby was present during the procedure (Photo courtesy of Gabor Stefanics, MTAPI, Budapest)

Newborn infants differently process adult directed and infant directed speech

Infant directed speech (IDS) may serve important functions in language acquisition and in adult-infant communication. The processing of IDS evolves during the first years of life. In order to serve as an effective tool of language acquisition, already very young infants should be able to distinguish IDS from adult directed speech (ADS). We tested whether the ability to discriminate these two speech registers is functional in neonates, by recording EEG from 98 newborn infants in response to Hungarian words naturally spoken in the IDS and the ADS register. Words presented in the ADS register elicited a centro-parietal slow positivity in the 200–600 ms time window whereas words in IDS register elicited a small frontal negativity in the 700–900 ms time window. We conclude that newborn infants differentiate natural speech sounds based on speech register