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Pitch plays a crucial role in music and speech perception. Pitch perception is characterized by multiple perceptual dimensions, such as pitch height and chroma. Information provided by auditory signals that are related to these perceptual dimensions can be either congruent or incongruent. To create conflicting cues for pitch perception, we modified Shepard tones by varying the pitch height and pitch chroma dimensions in either the same or opposite directions. Our behavioral data showed that most listeners judged pitch changes based on pitch chroma, instead of pitch height, when incongruent information was provided. The reliance on pitch chroma resulted in a stable percept of upward or downward pitch shift, rather than alternating between two different percepts. Across the incongruent and congruent conditions, consistent activation was found in the bilateral superior temporal and inferior frontal areas. In addition, significantly stronger activation was observed in the inferior frontal areas during the incongruent compared to congruent conditions. Enhanced functional connectivity was found between the left temporal and bilateral frontal areas in the incongruent than congruent conditions. Increased intra-hemispheric and inter-hemispheric connectivity was also observed in the frontal areas. Our results suggest the involvement of the frontal lobe in top-down and bottom-up processes to generate a stable percept of pitch change with conflicting perceptual cues.

Historic theories of speech perception (Motor Theory and Analysis by Synthesis) invoked listeners’ knowledge of speech production to explain speech perception. Neuroimaging data show that adult listeners activate motor brain areas during speech perception. In two experiments using magnetoencephalography (MEG), we investigated motor brain activation, as well as auditory brain activation, during discrimination of native and nonnative syllables in infants at two ages that straddle the developmental transition from language-universal to language-specific speech perception. Adults are also tested in Exp. 1. MEG data revealed that 7-mo-old infants activate auditory (superior temporal) as well as motor brain areas (Broca’s area, cerebellum) in response to speech, and equivalently for native and nonnative syllables. However, in 11- and 12-mo-old infants, native speech activates auditory brain areas to a greater degree than nonnative, whereas nonnative speech activates motor brain areas to a greater degree than native speech. This double dissociation in 11- to 12-mo-old infants matches the pattern of results obtained in adult listeners. Our infant data are consistent with Analysis by Synthesis: auditory analysis of speech is coupled with synthesis of the motor plans necessary to produce the speech signal. The findings have implications for: (i) perception-action theories of speech perception, (ii) the impact of “motherese” on early language learning, and (iii) the “social-gating” hypothesis and humans’ development of social understanding.

Granger causality analysis has been suggested as a method of estimating causal modulation without specifying the direction of information flow a priori. Using BOLD-contrast functional MRI (fMRI) data, such analysis has been typically implemented in the time domain. In this study, we used magnetic resonance inverse imaging, a method of fast fMRI enabled by massively parallel detection allowing up to 10Hz sampling rate, to investigate the causal modulation at different frequencies up to 5Hz. Using a visuomotor two-choice reaction-time task, both the spectral decomposition of Granger causality and isolated effective coherence revealed that the BOLD signal at frequency up to 3Hz can still be used to estimate significant dominant directions of information flow consistent with results from the time-domain Granger causality analysis. We showed the specificity of estimated dominant directions of information flow at high frequencies by contrasting causality estimates using data collected during the visuomotor task and resting state. Our data suggest that hemodynamic responses carry physiological information related to inter-regional modulation at frequency higher than what has been commonly considered. •Causal modulation in human brain was estimated up to 5Hz using fMRI data.•The BOLD signal at 3Hz still gives consistent information flow estimates.•BOLD signals carry inter-regional modulation info at frequency higher than 1Hz.

The blood-oxygen-level-dependent (BOLD) functional MRI (fMRI) signal is a robust surrogate for local neuronal activity. However, it has been shown to vary substantially across subjects, brain regions, and repetitive measurements. This variability represents a limit to the precision of the BOLD response and the ability to reliably discriminate brain hemodynamic responses elicited by external stimuli or behavior that are nearby in time. While the temporal variability of the BOLD signal at human visual cortex has been found in the range of a few hundreds of milliseconds, the spatial distributions of the average and standard deviation of this temporal variability have not been quantitatively characterized. Here we use fMRI measurements with a high sampling rate (10Hz) to map the latency, intra- and inter-subject variability of the evoked BOLD signal in human primary (V1) visual cortices using an event-related fMRI paradigm. The latency relative to the average BOLD signal evoked by 30 stimuli was estimated to be 0.03±0.20s. Within V1, the absolute value of the relative BOLD latency was found correlated to intra- and inter-subject temporal variability. After comparing these measures to retinotopic maps, we found that locations with V1 areas sensitive to smaller eccentricity have later responses and smaller inter-subject variabilities. These correlations were found from data with either short inter-stimulus interval (ISI; average 4s) or long ISI (average 30s). Maps of the relative latency as well as inter-/intra-subject variability were found visually asymmetric between hemispheres. Our results suggest that the latency and variability of regional BOLD signal measured with high spatiotemporal resolution may be used to detect regional differences in hemodynamics to inform fMRI studies. However, the physiological origins of timing index distributions and their hemispheric asymmetry remain to be investigated. •The BOLD latency and variability was measured with 0.1s precision.•The latency of the V1 BOLD signal evoked from 30 trials was 0.03±0.20s.•Smaller eccentricity locations have larger latency•Smaller eccentricity locations have smaller inter-subject variability.

Variability in neuronal response latency has been typically considered caused by random noise. Previous studies of single cells and large neuronal populations have shown that the temporal variability tends to increase along the visual pathway. Inspired by these previous studies, we hypothesized that functional areas at later stages in the visual pathway of face processing would have larger variability in the response latency. To test this hypothesis, we used magnetoencephalographic data collected when subjects were presented with images of human faces. Faces are known to elicit a sequence of activity from the primary visual cortex to the fusiform gyrus. Our results revealed that the fusiform gyrus showed larger variability in the response latency compared to the calcarine fissure. Dynamic and spectral analyses of the latency variability indicated that the response latency in the fusiform gyrus was more variable than in the calcarine fissure between 70 ms and 200 ms after the stimulus onset and between 4 Hz and 40 Hz, respectively. The sequential processing of face information from the calcarine sulcus to the fusiform sulcus was more reliably detected based on sizes of the response variability than instants of the maximal response peaks. With two areas in the ventral visual pathway, we show that the variability in response latency across brain areas can be used to infer the sequence of cortical activity.

Frequency preference and spectral tuning are two cardinal features of information processing in the auditory cortex. However, sounds should not only be processed in separate frequency bands because information needs to be integrated to be meaningful. One way to better understand the integration of acoustic information is to examine the functional connectivity across cortical depths, as neurons are already connected differently across laminar layers. Using a tailored receiver array and surface-based cortical depth analysis, we revealed the frequency–preference as well as tuning–width dependent intrinsic functional connectivity (iFC) across cortical depths in the human auditory cortex using functional magnetic resonance imaging (fMRI). We demonstrated feature-dependent iFC in both core and noncore regions at all cortical depths. The selectivity of frequency–preference dependent iFC was higher at deeper depths than at intermediate and superficial depths in the core region. Both the selectivity of frequency–preference and tuning–width dependent iFC were stronger in the core than in the noncore region at deep cortical depths. Taken together, our findings provide evidence for a cortical depth-specific feature-dependent functional connectivity in the human auditory cortex.

This study focuses on bilingual arithmetic processing at the cortical level in an attempt to elucidate the neural sources for the performance differences observed when bilinguals use their first language (L1; the preferred language) versus their second language (L2; the non-preferred language). Previous behavioral studies on bilinguals showed a delayed response time and reduced accuracy during arithmetic processing when bilinguals were tested with their non-preferred language compared to their preferred language. One of the most widely accepted explanations of such a language effect is translation. In order to access the language-specific representation of numbers stored in the preferred language, numbers need to be translated into the preferred language, which slows down and worsens the arithmetic processing. The current study used magnetoencephalography (MEG) to examine when and where the language effect starts to emerge at the cortical level. Mental calculation tasks involving multi-digit and single-digit numbers were presented auditorally in bilinguals' L1 and L2. Behaviorally, bilinguals showed lower accuracy in the addition task in the L2 that involved two-digit numbers. At the cortical level, mental addition in both L1 and L2 engaged widely distributed cortical areas, including the frontal and temporal regions bilaterally. Comparing activation during the L1 and L2 tasks, delayed activation and stronger activation magnitude were observed during the L2 tasks. The activation in L1 addition tasks showed two pronounced activation peaks, whereas less distinct activation peaks were observed in the L2 addition tasks. This is because early activation in response to the L2 numbers was generally delayed and overlapped with the later activation, possibly indicating less sensitivity and delayed processing for verbal numbers presented in a less familiar language. The later activation showed larger amplitude in the L2 addition tasks compared to the L1 addition tasks, suggesting more neural resources and higher cognitive efforts demanded by the L2 addition tasks. These results demonstrate that the experience in learning and performing mental calculation in a specific language (e.g., L1) impacts not only arithmetic performance at the behavioral level, but also the spatiotemporal activation patterns at the cortical level.