The nature of sensory time perception – centralised or distributed?

Using psychophysical methods and human subjects, this work aims to investigate the role of human sensory systems in the perception and passage of time. Specifically, I question the centralised nature of timing and whether a central clock exists to mediate incoming timing signals across the different sensory modalities. The alternative is that our timing mechanisms are embodied within distributed, modality-specific networks, each operating in a dedicated and independent manner. In my first experiment subjects were exposed to a range of rhythms presented to audio, visual and tactile sensory modalities, and were asked to reproduce a test rhythm via a tapping device. Subjects were able to adapt to a range of rhythms; however, the resulting after-effects were only evidenced when the adapting and test sensory modalities matched. My second experiment questioned how we construct sensory rhythms and, using the same method of rhythm adaptation, I used a single empty interval as a test stimulus. Results show that adapting to a given rhythmic rate strongly influences the temporal perception of a single empty interval. This questions the seemingly unique nature of rhythm, suggesting that adaptive distortions in perceived rate of signals within a sequence are, at least in part, a consequence of distortions in the perception of the inter-stimulus interval between the sequence’s component signals. My third experiment focused on more complicated rhythms in the form of anisochrony. I found limited observable after-effects as a result of exposing subjects to patterned rhythms across auditory, visual and tactile sensory modalities. The final experiment demonstrated significant after-effects following exposure to perfectly interleaved auditory and visual rhythms. These results collectively demonstrate mechanisms actively underpinning human perception of time and importantly, present evidence of dynamically distributed mechanisms linked to each sensory modality and processing incoming timing signals in a dedicated manner

Disentangling Neural Synchronization and Sustained Neural Activity in the Processing of Auditory Temporal Patterns

First paragraph: Temporal regularity within sensory input, can be defined as a uniformly structured and recurring stimulation. Perceiving temporal regularity is integral to effectively perceiving the world around us, such as in speech and music perception. Indeed, natural environments constantly present our perceptual systems with different forms of temporal regularities and rhythms. Efficient sensitivity to temporal changes not only allows us to maintain a coherent perception of our experiences, but importantly, also allows us to build expectations and predict future events (Gutschalk et al., 2002; Nobre and van Ede, 2017). Previous work investigating the underlying neural mechanisms of temporal pattern perception have focused on neural synchronization (NS). This is defined as the ability of neural oscillations to synchronize with temporal regularity in external stimuli (Lakatos et al., 2008; Henry and Obleser, 2012), further suggesting that temporal regularity boosts neural activity at the same frequency as that of the external stimulus. This externally-synchronized neural activity can then be used to predict future auditory activity (Nobre and van Ede, 2017). More recently, the role of sustained activity (SA) has also been investigated in temporal regularity perception, using electroencephalography (EEG) and magnetoencephalography (Barascud et al., 2016; Southwell and Chait, 2018). For instance, detection of regularity in short auditory sequences is demarcated by increased sustained low-frequency evoked magnetoencephalographic activity, which occurs irrespective of the temporal structure (Barascud et al., 2016). The precise relationship between NS and SA is not fully understood. One suggestion is that NS allows the recognition of auditory patterns, while SA subsequently allows the processing of this information in the higher order brain regions. A recently published study by Herrmann and Johnsrude (2018) examined the relationship between NS and SA in the processing of auditory temporal patterns using EEG

Auditory Rate Perception Displays a Positive Serial Dependence

We investigated perceived timing in auditory rate perception using a reproduction task. The study aimed to test (a) whether central tendency occurs in rate perception, as shown for interval timing, and (b) whether rate is perceived independently on each trial or shows a serial dependence, as shown for other perceptual attributes. Participants were well able to indicate perceived rate as reproduced and presented rates were linearly related with a slope that approached unity, although tapping significantly overestimated presented rates. While the slopes approached unity, they were significantly less than 1, indicating a central tendency in which reproduced rates tended towards the mean of the presented range. We tested for serial dependency by seeing if current trial rate reproductions depended on the preceding rate. In two conditions, a positive dependence was observed. A third condition in which participants withheld responses on every second trial produced a negative dependency. These results suggest separate components of serial dependence linked to stimulus and response: Withholding responses reveals a negative perceptual effect, whereas making responses adds a stronger positive effect that is postperceptual and makes the combined effect positive. Together, these data show that auditory rate perception exhibits both central tendency and serial dependence effects

A longitudinal framework to describe the relation between age-related hearing loss and social isolation

Many older adults live with some form of hearing loss and have difficulty understanding speech in the presence of background sound. Experiences resulting from such difficulties include increased listening effort and fatigue. Social interactions may become less appealing in the context of such experiences, and age-related hearing loss is associated with an increased risk of social isolation and associated negative psychosocial health outcomes. However, the precise relationship between age-related hearing loss and social isolation is not well described. Here, we review the literature and synthesize existing work from different domains to propose a framework with three conceptual anchor stages to describe the relation between hearing loss and social isolation: within-situation disengagement from listening, social withdrawal, and social isolation. We describe the distinct characteristics of each stage and suggest potential interventions to mitigate negative impacts of hearing loss on social lives and health. We close by outlining potential implications for researchers and clinicians

Cortical activation during imagined walking for people with lower limb loss: a pilot study

Each year in Canada, a substantial number of adults undergo limb amputation, with lower limb amputation (LLA) the most prevalent. Enhancing walking ability is crucial for optimizing rehabilitation outcomes, promoting participation, and facilitating community reintegration. Overcoming challenges during the acute post-amputation phase and sub-acute rehabilitation necessitates alternative approaches, such as motor imagery and mental practice, to maximize rehabilitation success. However, the current evidence on activation patterns using motor imagery in individuals with LLA is limited. The primary objective was to assess the feasibility of observing brain activation during imagined walking in individuals with LLA utilizing 3T functional magnetic resonance imaging (fMRI). Eight individuals with LLA and 11 control subjects participated. Consistent with representations of the lower limbs, both control and amputee groups demonstrated bilateral activation in the medial surface of the primary motor and somatosensory cortices. However, individuals with lower limb amputations exhibited significantly greater activation during imagined walking, particularly in frontal regions and the medial surface of the primary motor and supplementary motor cortices. Furthermore, the volume of activation in the bilateral primary motor cortices was higher for participants with amputations compared to controls. The protocol developed in this study establishes a foundation for evaluating the effects of a gait training program that incorporates mental imagery alongside conventional rehabilitation practices, in contrast to standard care alone. This pilot investigation holds potential to enhance our understanding of brain plasticity in individuals with LLA and pave the way for more effective rehabilitation strategies to optimize functional recovery and community reintegration

Brainhack: Developing a culture of open, inclusive, community-driven neuroscience

Brainhack is an innovative meeting format that promotes scientific collaboration and education in an open, inclusive environment. This NeuroView describes the myriad benefits for participants and the research community and how Brainhacks complement conventional formats to augment scientific progress