Dynamics of cortical contrast adaptation predict perception of signals in noise.

Neurons throughout the sensory pathway adapt their responses depending on the statistical structure of the sensory environment. Contrast gain control is a form of adaptation in the auditory cortex, but it is unclear whether the dynamics of gain control reflect efficient adaptation, and whether they shape behavioral perception. Here, we trained mice to detect a target presented in background noise shortly after a change in the contrast of the background. The observed changes in cortical gain and behavioral detection followed the dynamics of a normative model of efficient contrast gain control; specifically, target detection and sensitivity improved slowly in low contrast, but degraded rapidly in high contrast. Auditory cortex was required for this task, and cortical responses were not only similarly affected by contrast but predicted variability in behavioral performance. Combined, our results demonstrate that dynamic gain adaptation supports efficient coding in auditory cortex and predicts the perception of sounds in noise.

The effect of lexical status on prosodic processing in infants learning a fixed stress language.

In speech processing, in the first year of life, prosody and phoneme-relevant aspects serve different functions. Recent studies have assumed that the two aspects become integrated at around 9 months of age. The present study investigates the effect of lexical status on stress processing in a fixed stress language. We hypothesize that lexicality modulates stress processing, and where the stress cue is in conflict with the lexical status (legal deviant condition), we will observe differences in age indicating the stage of integration. We tested 69 6 and 10 month-old infants in an acoustic oddball event-related potential paradigm. A frequent word stimulus (baba) and a pseudoword (bebe) were used with legal versus illegal stress. We systematically swapped the standard and deviant roles of the different stress variants in two conditions. In the illegal deviant condition in the case of the word stimulus, the response pattern typical for the pseudoword (an MMR to the absence of the stress cue) was missing. This implies the suppression effect of lexicality. In the legal deviant condition, negative MMR (N-MMR) in the second time window indicated a facilitation effect of lexicality in both age groups. As only the 6-month-olds produced an N-MMR in the first time window, we concluded that in a fixed stress language, integration starts at 6 months but is only completed by the age of 10 months. Our results show that lexical status modulates stress processing at word level in a highly regularly stressed language in which stable, long-term language-specific stress representation exists from early infancy.

Orienting Attention to Auditory and Visual Short-term Memory: The Roles of Age, Hearing Loss, and Cognitive Status.

Background/Study Context: Attention can be reflectively oriented to a visual or auditory representation in short-term memory, but it is not clear how aging and hearing acuity affects reflective attention. The purpose of the present study was to examine whether performance in auditory and visual reflective attention tasks varies as a function of participants' age and hearing status.Methods: Young (19 to 33 years) and older adults with normal or mild to moderate hearing loss (62-90 years) completed a delayed match-to-sample task in which participants were first presented with a memory array of four different digits to hold in memory. Two digits were presented visually (left and right hemifield), and two were presented aurally (left and right ears simultaneously). During the retention interval, participants were presented with a cue (dubbed retro-cue), which could be either uninformative or indicated to the participants to retrospectively orient their attention to either auditory short-term memory (ASTM) or visual short-term memory (VSTM). The cue was followed by another delay, after which a single item was presented (i.e., test probe) for comparison (match or no match) with the items held in ASTM and/or VSTM.Results: Overall, informative retro-cue yielded faster response time than uninformative retro-cue. The retro-cue benefit in response time was comparable for auditory and visual-orienting retro-cue and similar in young and older adults. Regression analyses showed that only the auditory-orienting retro-cue benefit was predicted by hearing status rather than age per se.Conclusion: Both younger and older adults can benefit from visual and auditory-orienting retro-cues, but the auditory-orienting retro-cue benefit decreases with poorer hearing acuity. This finding highlights changes in cognitive processes that come with age even in those with just mild-to-moderate hearing loss, and suggest that older adults' performance in working memory tasks is sensitive to low level auditory scene analysis (i.e., concurrent sound segregation).

Does intra-uterine language experience modulate word stress processing? An ERP study.

BACKGROUND: Preterm birth is associated with various risks, including delayed or atypical language development. The prenatal start of prosodic tuning may affect the processing of word stress, an important suprasegmental feature of spoken utterances. AIM: Our study focused on the expected contribution of intra-uterine experience to word stress processing. We aimed to demonstrate the hypothesized effect of intra-uterine sound exposition on stress sensitivity. METHOD: We recorded ERP responses of 34 preterm infants elicited by bisyllabic pseudo-words in two oddball conditions by switching the stress pattern (legal vs. illegal) and role (standard vs. deviant). RESULTS: The mismatch responses found were synchronized to each syllable of the illegally stressed stimuli with no difference between pre- and full-term infants. However, the clear role of the preterm status was demonstrated by the exaggerated processing of the native stress information. The impact of intra-uterine exposure to prosody was confirmed by our finding that moderate-late preterm infants outperformed the very preterm ones. CONCLUSION: Intra-uterine exposition to prosodic features appears to contribute to the emergence of stable long-term stress representation. When this tuning is missing it is considered a risk for the language acquisition process.

Age-related differences in orienting attention to sound object representations.

We examined the effect of age on listeners' ability to orient attention to an item in auditory short-term memory (ASTM) using high-density electroencephalography, while participants completed a delayed match-to-sample task. During the retention interval, an uninformative or an informative visual retro-cue guided attention to an item in ASTM. Informative cues speeded response times, but only for young adults. In young adults, informative retro-cues generated greater event-related potential amplitude between 450 and 650 ms at parietal sites, and an increased sustained potential over the left central scalp region, thought to index the deployment of attention and maintenance of the cued item in ASTM, respectively. Both modulations were reduced in older adults. Alpha and low beta oscillatory power suppression was greater when the retro-cue was informative than uninformative, especially in young adults. Our results point toward an age-related decline in orienting attention to the cued item in ASTM. Older adults may be dividing their attention between all items in working memory rather than selectively focusing attention on a single cued item.

Lexical influence on stress processing in a fixed-stress language.

In the present study, we investigate how lexicality affects the processing of suprasegmental features at the word level. In contrast to earlier studies which analyzed the role of either segmental or suprasegmental feature in language processing our aim was to investigate the effect of the lexical status on the processing of violated stress pattern defined by linguistic rules. We have conducted a passive oddball ERP experiment, presenting a frequent CVCV word with legal (familiar) and illegal (unfamiliar) stress patterns. Former results obtained with pseudo-words in a similar paradigm enabled to assess the influence of lexical information on stress processing. The presence of lexically relevant information resulted in different ERP patterns compared to those obtained with pseudo-words. We obtained two consecutive MMN responses to the illegally stressed words while violating the illegal stress pattern with a legal one the deviant stimulus elicited two consecutive MMN responses as well. In the latter condition lexicality clearly enhanced the comparison of prosodic information between standard and deviant stimuli, as these components very completely missing when presenting pseudo-words. We interpret the results that lexicality acts as a filter since in the absence of lexical familiarity unfamiliar stress patterns are discriminated better. Our results highlight that even when stress is fully predictable, it is taken into account during pre-attentive processing of linguistic input.

Neural Correlates of Speech Segregation Based on Formant Frequencies of Adjacent Vowels.

The neural substrates by which speech sounds are perceptually segregated into distinct streams are poorly understood. Here, we recorded high-density scalp event-related potentials (ERPs) while participants were presented with a cyclic pattern of three vowel sounds (/ee/-/ae/-/ee/). Each trial consisted of an adaptation sequence, which could have either a small, intermediate, or large difference in first formant (Δf1) as well as a test sequence, in which Δf1 was always intermediate. For the adaptation sequence, participants tended to hear two streams ("streaming") when Δf1 was intermediate or large compared to when it was small. For the test sequence, in which Δf1 was always intermediate, the pattern was usually reversed, with participants hearing a single stream with increasing Δf1 in the adaptation sequences. During the adaptation sequence, Δf1-related brain activity was found between 100-250 ms after the /ae/ vowel over fronto-central and left temporal areas, consistent with generation in auditory cortex. For the test sequence, prior stimulus modulated ERP amplitude between 20-150 ms over left fronto-central scalp region. Our results demonstrate that the proximity of formants between adjacent vowels is an important factor in the perceptual organization of speech, and reveal a widely distributed neural network supporting perceptual grouping of speech sounds.