Neurophysiological and Behavioral Responses of Mandarin Lexical Tone Processing

Language experience enhances discrimination of speech contrasts at a behavioral- perceptual level, as well as at a pre-attentive level, as indexed by event-related potential (ERP) mismatch negativity (MMN) responses. The enhanced sensitivity could be the result of changes in acoustic resolution and/or long-term memory representations of the relevant information in the auditory cortex. To examine these possibilities, we used a short (ca. 600 ms) vs. long (ca. 2,600 ms) interstimulus interval (ISI) in a passive, oddball discrimination task while obtaining ERPs. These ISI differences were used to test whether cross-linguistic differences in processing Mandarin lexical tone are a function of differences in acoustic resolution and/or differences in long-term memory representations. Bisyllabic nonword tokens that differed in lexical tone categories were presented using a passive listening multiple oddball paradigm. Behavioral discrimination and identification data were also collected. The ERP results revealed robust MMNs to both easy and difficult lexical tone differences for both groups at short ISIs. At long ISIs, there was either no change or an enhanced MMN amplitude for the Mandarin group, but reduced MMN amplitude for the English group. In addition, the Mandarin listeners showed a larger late negativity (LN) discriminative response than the English listeners for lexical tone contrasts in the long ISI condition. Mandarin speakers outperformed English speakers in the behavioral tasks, especially under the long ISI conditions with the more similar lexical tone pair. These results suggest that the acoustic correlates of lexical tone are fairly robust and easily discriminated at short ISIs, when the auditory sensory memory trace is strong. At longer ISIs beyond 2.5 s language-specific experience is necessary for robust discrimination

Attentional Resources Are Needed for Auditory Stream Segregation in Aging

The ability to select sound streams from background noise becomes challenging with age, even with normal peripheral auditory functioning. Reduced stream segregation ability has been reported in older compared to younger adults. However, the reason why there is a difference is still unknown. The current study investigated the hypothesis that automatic sound processing is impaired with aging, which then contributes to difficulty actively selecting subsets of sounds in noisy environments. We presented a simple intensity oddball sequence in various conditions with irrelevant background sounds while recording EEG. The ability to detect the oddball tones was dependent on the ability to automatically or actively segregate the sounds to frequency streams. Listeners were able to actively segregate sounds to perform the loudness detection task, but there was no indication of automatic segregation of background sounds while watching a movie. Thus, our results indicate impaired automatic processes in aging that may explain more effortful listening, and that tax attentional systems when selecting sound streams in noisy environments

Statistical Learning of Melodic Patterns Influences the Brain's Response to Wrong Notes

The theory of statistical learning has been influential in providing a framework for how humans learn to segment patterns of regularities from continuous sensory inputs, such as speech and music. This form of learning is based on statistical cues and is thought to underlie the ability to learn to segment patterns of regularities from continuous sensory inputs, such as the transition probabilities in speech and music. However, the connection between statistical learning and brain measurements is not well understood. Here we focus on ERPs in the context of tone sequences that contain statistically cohesive melodic patterns. We hypothesized that implicit learning of statistical regularities would influence what was held in auditory working memory. We predicted that a wrong note occurring within a cohesive pat tern (within-pattern deviant) would lead to a significantly larger brain signal than a wrong note occurring between cohesive patterns (between-pattern deviant), even though both deviant types were equally likely to occur with respect to the global tone sequence. We discuss this prediction within a simple Markov model framework that learns the transition probability regularities within the tone sequence. Results show that signal strength was stronger when cohesive patterns were violated and demonstrate that the transitional probability of the sequence influences the memory basis for melodic patterns. Our results thus characterize how informational units are stored in auditory memory trace for deviance detection and provide new evidence about how the brain organizes sequential sound input that is useful for perception

The Duration of Auditory Sensory Memory for Vowel Processing: Neurophysiological and Behavioral Measures

Speech perception behavioral research suggests that rates of sensory memory decay are dependent on stimulus properties at more than one level (e.g., acoustic level, phonemic level). The neurophysiology of sensory memory decay rate has rarely been examined in the context of speech processing. In a lexical tone study, we showed that long-term memory representation of lexical tone slows the decay rate of sensory memory for these tones. Here, we tested the hypothesis that long-term memory representation of vowels slows the rate of auditory sensory memory decay in a similar way to that of lexical tone. Event-related potential (ERP) responses were recorded to Mandarin non-words contrasting the vowels /i/ vs. /u/ and /y/ vs. /u/ from first-language (L1) Mandarin and L1 American English participants under short and long interstimulus interval (ISI) conditions (short ISI: an average of 575 ms, long ISI: an average of 2675 ms). Results revealed poorer discrimination of the vowel contrasts for English listeners than Mandarin listeners, but with different patterns for behavioral perception and neural discrimination. As predicted, English listeners showed the poorest discrimination and identification for the vowel contrast /y/ vs. /u/, and poorer performance in the long ISI condition. In contrast to Yu et al. (2017), however, we found no effect of ISI reflected in the neural responses, specifically the mismatch negativity (MMN), P3a and late negativity ERP amplitudes. We did see a language group effect, with Mandarin listeners generally showing larger MMN and English listeners showing larger P3a. The behavioral results revealed that native language experience plays a role in echoic sensory memory trace maintenance, but the failure to find an effect of ISI on the ERP results suggests that vowel and lexical tone memory traces decay at different rates.Highlights:We examined the interaction between auditory sensory memory decay and language experience.We compared MMN, P3a, LN and behavioral responses in short vs. long interstimulus intervals.We found that different from lexical tone contrast, MMN, P3a, and LN changes to vowel contrasts are not influenced by lengthening the ISI to 2.6 s.We also found that the English listeners discriminated the non-native vowel contrast with lower accuracy under the long ISI condition