Daniel J. Cameron

The Effect of Dopaminergic Medication on Beat-Based Auditory Timing in Parkinson's Disease.

Parkinson’s disease (PD) adversely affects timing abilities. Beat-based timing is a mechanism that times events relative to a regular interval, such as the “beat” in musical rhythm, and is impaired in PD. It is unknown if dopaminergic medication influences beat-based timing in PD. Here, we tested beat-based timing over two sessions in participants with PD (OFF then ON dopaminergic medication) and in unmedicated control participants. People with PD and control participants completed two tasks. The first was a discrimination task in which participants compared two rhythms and determined whether they were the same or different. Rhythms either had a beat structure (metric simple rhythms) or did not (metric complex rhythms), as in previous studies. Discrimination accuracy was analyzed to test for the effects of beat structure, as well as differences between participants with PD and controls, and effects of medication (PD group only). The second task was the Beat Alignment Test (BAT), in which participants listened to music with regular tones superimposed, and responded as to whether the tones were “ON” or “OFF” the beat of the music. Accuracy was analyzed to test for differences between participants with PD and controls, and for an effect of medication in patients. Both patients and controls discriminated metric simple rhythms better than metric complex rhythms. Controls also improved at the discrimination task in the second vs. first session, whereas people with PD did not. For participants with PD, the difference in performance between metric simple and metric complex rhythms was greater (sensitivity to changes in simple rhythms increased and sensitivity to changes in complex rhythms decreased) when ON vs. OFF medication. Performance also worsened with disease severity. For the BAT, no group differences or effects of medication were found. Overall, these findings suggest that timing is impaired in PD, and that dopaminergic medication influences beat-based and non-beat-based timing differently. Judging the beat in music does not appear to be affected by PD or by dopaminergic medication.

Cross-cultural influences on rhythm processing: reproduction, discrimination, and beat tapping

The structures of musical rhythm differ between cultures, despite the fact that the ability to entrain movement to musical rhythm occurs in virtually all individuals across cultures. To measure the influence of culture on rhythm processing, we tested East African and North American adults on perception, production, and beat tapping for rhythms derived from East African and Western music. To assess rhythm perception, participants identified whether pairs of rhythms were the same or different. To assess rhythm production, participants reproduced rhythms after hearing them. To assess beat tapping, participants tapped the beat along with repeated rhythms. We expected that performance in all three tasks would be influenced by the culture of the participant and the culture of the rhythm. Specifically, we predicted that a participant’s ability to discriminate, reproduce, and accurately tap the beat would be better for rhythms from their own culture than for rhythms from another culture. In the rhythm discrimination task, there were no differences in discriminating culturally familiar and unfamiliar rhythms. In the rhythm reproduction task, both groups reproduced East African rhythms more accurately than Western rhythms, but East African participants also showed an effect of cultural familiarity, leading to a significant interaction. In the beat tapping task, participants in both groups tapped the beat more accurately for culturally familiar than for unfamiliar rhythms. Moreover, there were differences between the two participant groups, and between the two types of rhythms, in the metrical level selected for beat tapping. The results demonstrate that culture does influence the processing of musical rhythm. In terms of the function of musical rhythm, our results are consistent with theories that musical rhythm enables synchronization. Musical rhythm may foster musical cultural identity by enabling within-group synchronization to music, perhaps supporting social cohesion.

Perception of Rhythmic Similarity is Asymmetrical, and Is Influenced by Musical Training, Expressive Performance, and Musical Context

Rhythm is an essential part of the structure, behaviour, and aesthetics of music. However, the cognitive processing that underlies the perception of musical rhythm is not fully understood. In this study, we tested whether rhythm perception is influenced by three factors: musical training, the presence of expressive performance cues in human-performed music, and the broader musical context. We compared musicians and nonmusicians’ similarity ratings for pairs of rhythms taken from Steve Reich’s Clapping Music. The rhythms were heard both in isolation and in musical context and both with and without expressive performance cues. The results revealed that rhythm perception is influenced by the experimental conditions: rhythms heard in musical context were rated as less similar than those heard in isolation; musicians’ ratings were unaffected by expressive performance, but nonmusicians rated expressively performed rhythms as less similar than those with exact timing; and expressively-performed rhythms were rated as less similar compared to rhythms with exact timing when heard in isolation but not when heard in musical context. The results also showed asymmetrical perception: the order in which two rhythms were heard influenced their perceived similarity. Analyses suggest that this asymmetry was driven by the internal coherence of rhythms, as measured by normalized Pairwise Variability Index (nPVI). As predicted, rhythms were perceived as less similar when the first rhythm in a pair had greater coherence (lower nPVI) than the second rhythm, compared to when the rhythms were heard in the opposite order.

Evaluating Affordable Cranial Ultrasonography in East African Neonatal Intensive Care Units

Neuroimaging is a valuable diagnostic tool for the early detection of neonatal brain injury, but equipment and radiologic staff are expensive and unavailable to most hospitals in developing countries. We evaluated an affordable, portable ultrasound machine as a quantitative and qualitative diagnostic tool and to establish whether a novice sonographer could effectively operate the equipment and obtain clinically important information. Cranial ultrasonography was performed on term healthy, pre-term and term asphyxiated neonates in Rwandan and Kenyan hospitals. To evaluate the detection of ventriculomegaly and compression injuries, we measured the size of the lateral ventricles and corpus callosum. The images were also assessed for the presence of other cerebral abnormalities. Measurements were reliable across images, and cases of clinically relevant ventriculomegaly were detected. A novice sonographer had good-to-excellent agreement with an expert. This study demonstrates that affordable equipment and cranial ultrasound protocols can be used in low-resource settings to assess the newborn brain.

Does the beat go on?: identifying rhythms from brain waves recorded after their auditory presentation

Music imagery information retrieval (MIIR) systems may one day be able to recognize a song just as we think of it. As one step towards such technology, we investigate whether rhythms can be identified from an electroencephalography (EEG) recording taken directly after their auditory presentation. The EEG data has been collected during a rhythm perception study in Kigali, Rwanda and comprises 12 East African and 12 Western rhythmic stimuli presented to 13 participants. Each stimulus was presented as a loop for 32 seconds followed by a break of four seconds before the next one started. Using convolutional neural networks (CNNs), we are able to recognize individual rhythms with a mean accuracy of 22.9% over all subjects by just looking at the EEG recorded during the silence between the stimuli.