Cognitive Control Structures in the Imitation Learning of Spatial Sequences and Rhythms-An fMRI Study.

Imitation learning involves the acquisition of novel motor patterns based on action observation (AO). We used event-related functional magnetic resonance imaging to study the imitation learning of spatial sequences and rhythms during AO, motor imagery (MI), and imitative execution in nonmusicians and musicians. While both tasks engaged the fronto-parietal mirror circuit, the spatial sequence task recruited posterior parietal and dorsal premotor regions more strongly. The rhythm task involved an additional network for auditory working memory. This partial dissociation supports the concept of task-specific mirror mechanisms. Two regions of cognitive control were identified: 1) dorsolateral prefrontal cortex (DLPFC) was found to be more strongly activated during MI of novel spatial sequences, which allowed us to extend the 2-level model of imitation learning by Buccino et al. (2004) to spatial sequences. 2) During imitative execution of both tasks, the posterior medial frontal cortex was robustly activated, along with the DLPFC, which suggests that both regions are involved in the cognitive control of imitation learning. The musicians' selective behavioral advantage for rhythm imitation was reflected cortically in enhanced sensory-motor processing during AO and by the absence of practice-related activation differences in DLPFC during rhythm execution.

Impaired predictive timing with spared time interval production in individual with schizophrenia.

There is evidence for timing dysfunctions in schizophrenia. However, few studies have evaluated the processing of intervals in the hundreds of milliseconds range, despite their role in the timing of speech, music and movements. This study looked into the prediction and estimation mechanisms for intervals in that time range in individuals with schizophrenia and age-matched neurotypical controls. Specifically, we questioned the capacity of the patients to detect a phase shift that requires the processing of a deviation from 'what should happen when' given prior event regularity. The minimum detectable phase shift was estimated from an adaptive staircase procedure with or without the need for sensorimotor synchronization. Results revealed that patients were significantly impaired relative to controls, at each of the tested inter-onset intervals (IOI=300, 600 and 900ms). A control experiment used the method of repeated interval production to show that both groups performed similarly in the production of target intervals (T=500ms and 1000ms). We conclude that schizophrenia is associated with predictive timing deficits, which cannot be attributed directly to a faster or slower running internal clock.

Frequency discrimination duration effects for Huggins pitch and narrowband noise (L).

Frequency difference limens (FDLs) were measured for Huggins pitch (HP) stimuli, consisting of a 30-Hz wide band of interaurally decorrelated noise in a diotic low-pass noise and for 30-Hz wide bands of diotic narrowband noise presented in a diotic low-pass noise background. FDLs at a 400-ms duration for the two stimulus types were equated by adjusting the level of the narrowband noise relative to the background. The effects of duration on the FDLs were then measured for center frequencies of 300, 600, and 900 Hz. Although the results were compromised by floor effects at 900 Hz, at 300 and 600 Hz, the duration effects were very similar for the HP and narrowband noise stimuli, with a large improvement in performance between 100 and 400 ms. In contrast to previous results for pure tones, the effect of duration was independent of frequency. The results suggest that: (1) Binaural and monaural pitches may be processed using a common mechanism; (2) discrimination performance for HP and low-sensation-level narrowband noise stimuli is not determined by the number of waveform periods.

Cognitive Aging and Time Perception: Roles of Bayesian Optimization and Degeneracy.

This review outlines the basic psychological and neurobiological processes associated with age-related distortions in timing and time perception in the hundredths of milliseconds-to-minutes range. The difficulty in separating indirect effects of impairments in attention and memory from direct effects on timing mechanisms is addressed. The main premise is that normal aging is commonly associated with increased noise and temporal uncertainty as a result of impairments in attention and memory as well as the possible reduction in the accuracy and precision of a central timing mechanism supported by dopamine-glutamate interactions in cortico-striatal circuits. Pertinent to these findings, potential interventions that may reduce the likelihood of observing age-related declines in timing are discussed. Bayesian optimization models are able to account for the adaptive changes observed in time perception by assuming that older adults are more likely to base their temporal judgments on statistical inferences derived from multiple trials than on a single trial's clock reading, which is more susceptible to distortion. We propose that the timing functions assigned to the age-sensitive fronto-striatal network can be subserved by other neural networks typically associated with finely-tuned perceptuo-motor adjustments, through degeneracy principles (different structures serving a common function).

Rhythmic masking release: effects of asynchrony, temporal overlap, harmonic relations, and source separation on cross-spectral grouping.

The rhythm created by spacing a series of brief tones in a regular pattern can be disguised by interleaving identical distractors at irregular intervals. The disguised rhythm can be unmasked if the distractors are allocated to a separate stream from the rhythm by integration with temporally overlapping captors. Listeners identified which of 2 rhythms was presented, and the accuracy and rated clarity of their judgment was used to estimate the fusion of the distractors and captors. The extent of fusion depended primarily on onset asynchrony and degree of temporal overlap. Harmonic relations had some influence, but only an extreme difference in spatial location was effective (dichotic presentation). Both preattentive and attentionally driven processes governed performance.

Late onset of age-related difference in unpaced tapping with no age-related difference in phase-shift error detection and correction.

An age-related difference in accuracy and variability of unpaced timing tasks suggests that the internal clock for the processing of intervals of hundreds of milliseconds slows down with age. However, we recently found that sensorimotor synchronization (SMS) error detection and correction abilities are preserved into the ninth and tenth decades, although fastest tapping rate decreases (Turgeon, Wing, & Taylor, 2011). Further testing with the same sample of participants in the present study provides evidence for slowing of the internal clock with age. We report an age-related decrease in spontaneous motor tempo (SMT), an age-related increase in produced period when estimating target durations of 500 ms and 1000 ms, and an age-related increase in "clock variance" in continuing tapping intervals ranging from 300 ms to 900 ms. The profile of age-related difference across the 2 studies suggests a late onset, starting in the ninth decade, of clock slowing without age-related difference in timing error monitoring. The finding that unpaced timing is affected by age, whereas paced timing involved in SMS is not, suggests separate underlying mechanisms for internally generated intervals and monitoring of external timing errors.

Automatic imitation in rhythmical actions: kinematic fidelity and the effects of compatibility, delay, and visual monitoring.

We demonstrate that observation of everyday rhythmical actions biases subsequent motor execution of the same and of different actions, using a paradigm where the observed actions were irrelevant for action execution. The cycle time of the distractor actions was subtly manipulated across trials, and the cycle time of motor responses served as the main dependent measure. Although distractor frequencies reliably biased response cycle times, this imitation bias was only a small fraction of the modulations in distractor speed, as well as of the modulations produced when participants intentionally imitated the observed rhythms. Importantly, this bias was not only present for compatible actions, but was also found, though numerically reduced, when distractor and executed actions were different (e.g., tooth brushing vs. window wiping), or when the dominant plane of movement was different (horizontal vs. vertical). In addition, these effects were equally pronounced for execution at 0, 4, and 8 s after action observation, a finding that contrasts with the more short-lived effects reported in earlier studies. The imitation bias was also unaffected when vision of the hand was occluded during execution, indicating that this effect most likely resulted from visuomotor interactions during distractor observation, rather than from visual monitoring and guidance during execution. Finally, when the distractor was incompatible in both dimensions (action type and plane) the imitation bias was not reduced further, in an additive way, relative to the single-incompatible conditions. This points to a mechanism whereby the observed action's impact on motor processing is generally reduced whenever this is not useful for motor planning. We interpret these findings in the framework of biased competition, where intended and distractor actions can be represented as competing and quasi-encapsulated sensorimotor streams.

Timing and aging: slowing of fastest regular tapping rate with preserved timing error detection and correction.

This study assessed motor limits of regular tapping, timing error detection, and correction in 60 participants aged from 19 to 98 years. Rate limitations on motor production were estimated from the average inter-tap interval when tapping as fast as possible for 30 s. Timing error detection required participants to judge whether a sound sequence presented at a slow, intermediate, or fast speed contained an irregularity because of phase shift. This was performed with or without synchronizing to the sounds. On the basis of the just-detectable positive phase shift (JND), participants synchronized with sequences containing phase shifts that were subliminal, just detectable or supraliminal. On average, JNDs were 9% of the inter-onset interval and by and large were not affected by synchronization tapping. Speed of error correction was estimated from the number of tones to return within 20% of the preshift synchronization error. Consistent with previous findings of motor slowing with aging, the fastest inter-tap interval increased with age. However, there was no age-related decline in JNDs or speed of error correction, both of which reflect predictive abilities for intervals within the motor repertoire of human adults. These results point towards intact timing error processing up to an advanced age. In assessing timing abilities in the brain of older adults, it is important to differentiate between motor slowing and its impact on rhythmic behavior (e.g., walking pace) from anticipatory mechanisms ('what to expect when') and how these are used to adjust the timing of actions ('what to do when').

Rhythmic masking release: contribution of cues for perceptual organization to the cross-spectral fusion of concurrent narrow-band noises.

The contribution of temporal asynchrony, spatial separation, and frequency separation to the cross-spectral fusion of temporally contiguous brief narrow-band noise bursts was studied using the Rhythmic Masking Release paradigm (RMR). RMR involves the discrimination of one of two possible rhythms, despite perceptual masking of the rhythm by an irregular sequence of sounds identical to the rhythmic bursts, interleaved among them. The release of the rhythm from masking can be induced by causing the fusion of the irregular interfering sounds with concurrent "flanking" sounds situated in different frequency regions. The accuracy and the rated clarity of the identified rhythm in a 2-AFC procedure were employed to estimate the degree of fusion of the interferring sounds with flanking sounds. The results suggest that while synchrony fully fuses short-duration noise bursts across frequency and across space (i.e., across ears and loudspeakers), an asynchrony of 20-40 ms produces no fusion. Intermediate asynchronies of 10-20 ms produce partial fusion, where the presence of other cues is critical for unambiguous grouping. Though frequency and spatial separation reduced fusion, neither of these manipulations was sufficient to abolish it. For the parameters varied in this study, stimulus onset asynchrony was the dominant cue determining fusion, but there were additive effects of the other cues. Temporal synchrony appears to be critical in determining whether brief sounds with abrupt onsets and offsets are heard as one event or more than one.