Temporal Perception and Attention in Trained Musicians

Considerable evidence converges on the plasticity of attention and the possibility that it can be modulated through regular training. Music training, for instance, has been correlated with modulations of early perceptual and attentional processes. However, the extent to which music training can modulate mechanisms involved in processing information (i.e., perception and attention) is still widely unknown, particularly between sensory modalities. If training in one sensory modality can lead to concomitant enhancements in different sensory modalities, then this could be taken as evidence of a supramodal attentional system. Additionally, if trained musicians exhibit improved perceptual skills outside of the domain of music, this could be taken as evidence for the notion of far-transfer, where training in one domain can lead to improvements in another. To investigate this further, we evaluated the effects of music training using tasks designed to measure simultaneity perception and temporal acuity, and how these are influenced by music training in auditory, visual, and audio-visual conditions. Trained musicians showed significant enhancements for simultaneity perception in the visual modality, as well as generally improved temporal acuity, although not in all conditions. Visual cues directing attention influenced simultaneity perception for musicians for visual discrimination and temporal accuracy in auditory discrimination, suggesting that musicians have selective enhancements in temporal discrimination, arguably due to increased attentional efficiency when compared to nonmusicians. Implications for theory and future training studies are discussed.

Auditory Brainstem Responses to Successive Sounds: Effects of Gap Duration and Depth

Temporal acuity is the ability to differentiate between sounds based on fluctuations in the waveform envelope. The proximity of successive sounds and background noise diminishes the ability to track rapid changes between consecutive sounds. We determined whether a physiological correlate of temporal acuity is also affected by these factors. We recorded the auditory brainstem response (ABR) from human listeners using a harmonic complex (S1) followed by a brief tone burst (S2) with the latter serving as the evoking signal. The duration and depth of the silent gap between S1 and S2 were manipulated, and the peak latency and amplitude of wave V were measured. The latency of the responses decreased significantly as the duration or depth of the gap increased. The amplitude of the responses was not affected by the duration or depth of the gap. These findings suggest that changing the physical parameters of the gap affects the auditory system’s ability to encode successive sounds.

A role of oligodendrocytes in information processing

Myelinating oligodendrocytes enable fast propagation of action potentials along the ensheathed axons. In addition, oligodendrocytes play diverse non-canonical roles including axonal metabolic support and activity-dependent myelination. An open question remains whether myelination also contributes to information processing in addition to speeding up conduction velocity. Here, we analyze the role of myelin in auditory information processing using paradigms that are also good predictors of speech understanding in humans. We compare mice with different degrees of dysmyelination using acute multiunit recordings in the auditory cortex, in combination with behavioral readouts. We find complex alterations of neuronal responses that reflect fatigue and temporal acuity deficits. We observe partially discriminable but similar deficits in well myelinated mice in which glial cells cannot fully support axons metabolically. We suggest a model in which myelination contributes to sustained stimulus perception in temporally complex paradigms, with a role of metabolically active oligodendrocytes in cortical information processing.

The Effect of Phantom Stimulation and Pseudomonophasic Pulse Shapes on Pitch Perception by Cochlear Implant Listeners

It has been suggested that a specialized high-temporal-acuity brainstem pathway can be activated by stimulating more apically in the cochlea than is achieved by cochlear implants (CIs) when programmed with contemporary clinical settings. We performed multiple experiments to test the effect on pitch perception of phantom stimulation and asymmetric current pulses, both supposedly stimulating beyond the most apical electrode of a CI. The two stimulus types were generated using a bipolar electrode pair, composed of the most apical electrode of the array and a neighboring, more basal electrode. Experiment 1 used a pitch-ranking procedure where neural excitation was shifted apically or basally using so-called phantom stimulation. No benefit of apical phantom stimulation was found on the highest rate up to which pitch ranks increased (upper limit), nor on the slopes of the pitch-ranking function above 300 pulses per second (pps). Experiment 2 used the same procedure to study the effects of apical pseudomonophasic pulses, where the locus of excitation was manipulated by changing stimulus polarity. A benefit of apical stimulation was obtained for the slopes above 300 pps. Experiment 3 used an adaptive rate discrimination procedure and found a small but significant benefit of both types of apical stimulation. Overall, the results show some benefit for apical stimulation on temporal pitch processing at high pulse rates but reveal that the effect is smaller and more variable across listeners than suggested by previous research. The results also provide some indication that the benefit of apical stimulation may decline over time since implantation.

Time changes: Temporal contexts support event segmentation in associative memory

We tend to mentally segment a series of events according to perceptual contextual changes, such that items from a shared context are more strongly associated in memory than items from different contexts. It is also known that temporal context provides a scaffold to structure experiences in memory, but its role in event segmentation has not been investigated. We adapted a previous paradigm, which was used to investigate event segmentation using visual contexts, to study the effects of changes in temporal contexts on event segmentation in associative memory. We presented lists of items in which the inter-stimulus intervals (ISIs) ranged across lists between 0.5 and 4 s in 0.5 s steps. After each set of six lists, participants judged which one of two test items were shown first (temporal order judgment) for items that were either drawn from the same list or from consecutive lists. Further, participants judged from memory whether the ISI associated to an item lasted longer than a standard interval (2.25s) that was not previously shown. Results showed faster responses for temporal order judgments when items were drawn from the same context, as opposed to items drawn from different contexts. Further, we found that participants were well able to provide temporal duration judgments based on recalled durations. Finally, we found temporal acuity, as estimated by psychometric curve fitting parameters of the recalled durations, correlated inversely with within-list temporal order judgments. These findings show that changes in temporal context support event segmentation in associative memory.

Perceptual timing precision with vibrotactile, auditory, and multisensory stimuli

It is important to understand the perceptual limits on vibrotactile information-processing because of the increasing use of vibrotactile signals in common technologies like cell phones. To advance such an understanding, we examined vibrotactile temporal acuity and compared it to auditory and bimodal (synchronous vibrotactile and auditory) temporal acuity. In a pair of experiments, subjects experienced a series of empty intervals, demarcated by stimulus pulses from one of the three modalities. One trial contained up to 5 intervals, where the first intervals were isochronous at 400 ms, and the last interval varied from 400 by ±1-80 ms. If the final interval was < 400 ms, the last pulse seemed “early”, and if the final interval was > 400 ms, the last pulse seemed “late”. In Experiment One, each trial contained four intervals, where the first three were isochronous. Subjects judged the timing of the last interval by describing the final pulse as either “early” or “late”. In Experiment Two, the number of isochronous intervals in a trial varied from one to four. Psychometric modeling revealed that vibrotactile temporal processing was less acute than auditory or bimodal temporal processing, and that auditory inputs dominated bimodal perception. Additionally, varying the number of isochronous intervals did not affect temporal sensitivity in either modality, suggesting the formation of memory traces. Overall, these results suggest that vibrotactile temporal processing is worse than auditory or bimodal temporal processing, which are similar. Also, subjects need no more than one isochronous reminder per trial for optimal performance.

The effect of phantom stimulation and pseudomonophasic pulse shapes on pitch perception by cochlear implant listeners

It has been suggested that a specialised high-temporal-acuity brainstem pathway can be activated by stimulating more apically in the cochlea than is achieved by cochlear implants (CIs) when programmed with contemporary clinical settings. Muliple experiments were carried out to test the effect of phantom stimulation and asymmetric current pulses, both supposedly stimulating beyond the most apical electrode of a CI, on pitch perception. The two stimulus types were generated using a bipolar electrode pair, composed of the most apical electrode of the array and a neighbouring, more basal electrode. Experiment 1 used a pitch-ranking procedure where neural excitation was shifted apically or basally using so-called phantom stimulation. No benefit of apical stimulation was found on the highest rate up to which pitch ranks increased, nor on the slopes of the pitch-ranking function above 300 pulses per second (pps). Experiment 2 used the same procedure to study the effects of asymmetric pseudomonophasic pulses, where the locus of excitation was manipulated by changing stimulus polarity. A benefit of apical stimulation was obtained only for the slopes above 300 pps. Experiment 3 used an adaptive rate discrimination procedure and a small but significant benefit of apical stimulation was found. Overall the results show some benefit for apical stimulation on temporal pitch processing at high pulse rates but reveal that the effect is rather small and highly variable across listeners. The results also provide some indication that the benefit of apical stimulation may decline over time since implantation.

Using spectral blurring to assess effects of channel interaction on speech-in-noise perception with cochlear implants

Cochlear implant (CI) listeners struggle to understand speech in background noise. Interactions between electrode channels due to current spread increase the masking of speech by noise and lead to difficulties with speech perception. Strategies that reduce channel interaction therefore have the potential to improve speech-in-noise perception by CI listeners, but previous results have been mixed. We investigated the effects of channel interaction on speech-in-noise perception and its association with spectro-temporal acuity in a listening study with 12 CI users. Instead of attempting to reduce channel interaction, we introduced spectral blurring to simulate some of the effects of channel interaction by adjusting the overlap between electrode channels at the input level of the analysis filters or at the output by using several simultaneously-stimulated electrodes per channel. We measured speech reception thresholds in noise as a function of the amount of blurring applied to either all 15 electrode channels or to 5 evenly spaced channels. Performance remained roughly constant as the amount of blurring applied to all channels increased up to some knee point, above which it deteriorated. This knee point differed across listeners in a way that correlated with performance on a non-speech spectro-temporal task, and is proposed here as an individual measure of channel interaction. Surprisingly, even extreme amounts of blurring applied to 5 channels did not affect performance. The effects on speech perception in noise were similar for blurring at the input and at the output of the CI. These results confirm the assumption that CI users make use of a limited number of effective channels, are highly resilient against spectral distortions and can tolerate substantial deviations from their everyday settings without harming their speech perception. These findings may explain the mixed results by strategies that optimized or deactivated a small number of electrodes evenly distributed along the array.