Sensation and Perception to Awareness: Leverhulme Doctoral Scholarship Programme

Past Seminars and Events

Details of previous seminars

 Date / Room

 Speaker

 Abstract

Friday

8th October

2021

Zoom Conference

YouTube URL Coming Soon

Keynote Speakers

Dr. Emanuela Maggioni

Dr. David Plans

Prof. Miguel Nicolelis

Dr. Timothy Brown

PhD Presentations

Sensation Sussex Conference 2021 - "Perception and Consciousness: From Biological to Computational Approaches"

Beyond Seeing and Hearing: The Power of Olfaction in Multisensory Human-Computer Interaction

Finding the Corporeal: design principles for interoception-based digital therapeutics

Unable to attend due to internet issues

Sensory Feedback in Assistive Robotics: Embodiment, Agency, and Self-Trust

Itay Yaron, Kristjan Kaup, Carla Dance, Giulia Cabbai

Thursday

7th October

2021

Zoom Conference

YouTube URL Coming Soon

Keynote Speakers

Prof. Liad Mudrik

Assoc. Prof. Jaan Aru

Prof. Floris de Lange

Prof. Claire Sergent

Prof. Axel Cleeremans

Sensation Sussex Conference 2021 - "Perception and Consciousness: From Biological to Computational Approaches"

Theories of consciousness: background, predictions, and empirical testing

Cellular mechanisms of conscious processing

How does our brain use the past to predict the future in visual perception?

Distinguishing the neural mechanisms of conscious access from sensory processing and decision making

Probing conscious and unconscious perception in the microsecond range

Thursday

24th June

2021

Zoom Lecture

Prof. Bruno van Swinderen

Queensland Brain Institute

University of Queensland

Using fruit flies to understand consciousness

Although consciousness appears to be a hard problem to solve, it is likely that it evolved from adaptive brain processes already evident in insects. We study cognition in the fruit fly model Drosophila melanogaster and have developed new approaches to peer into its brain when it is sleeping or paying attention. I’ll be discussing how attention might work in the fly brain, and how flies might need distinct sleep stages to optimise cognition

Wednesday

26th May

2021

Zoom Lecture

Prof. Joel Pearson

University of New South Wales

The Human imagination: visual imagery and aphantasia

Mental imagery can be advantageous, unnecessary (aphantasia), to clinically disruptive and traumatic. It allows us to disconnect our senses from reality and test out virtual combinations of sensory experience. With methodological constraints now overcome, empirical research has shown that visual imagery can function much like a weak version of afferent perception. This talk will cover methods of objectively and reliably measuring visual imagery and the application of those methods to mapping out aphantasia (a blind mind’s eye). Further, I will cover some of the cognitive implications of having aphantasia, from memory and thoughts, to our emotions and show an overarching framework for imagery and the importance of understanding it.

Tuesday

11th May

2021

Zoom Lecture

Dr. Bevil Conway

Intramural Research Program

NIH, USA.

The neuroscience of colour and what makes primates special

Among mammals, excellent colour vision has evolved only in certain non-human primates. And yet, colour is often assumed to be just a low-level stimulus feature with a modest role in encoding and recognising objects. The rationale for this dogma is compelling: object recognition is excellent in greyscale images (consider black-and-white movies, where faces, places, objects, and story are readily apparent). In my talk I will discuss experiments in which we used colour as a tool to uncover an organisational plan in inferior temporal cortex (parallel, multistage processing for places, faces, colours, and objects) and a visual-stimulus functional representation in prefrontal cortex (PFC). The discovery of an extensive network of colour-biased domains within IT and PFC, regions implicated in high-level object vision and executive functions, compels a re-evaluation of the role of colour in behaviour. I will discuss behavioural studies prompted by the neurobiology that uncover a universal principle for colour categorization across languages, the first systematic study of the colour statistics of objects and a chromatic mechanism by which the brain may compute animacy, and a surprising paradoxical impact of memory on face colour. Taken together, my talk will put forward the argument that colour is not primarily for object recognition, but rather for the assessment of the likely behavioural relevance, or meaning, of the stuff we see.

Wednesday

24th March

2021

Zoom Lecture

Prof. Aniruddh D. Patel

Dept. of Psychology

Tufts University

Consciousness and musical beat processing

All human cultures have some form of music with a beat: a periodic underlying pulse which listeners perceive in rhythmic patterns and to which they synchronize movements when dancing. Even in the absence of movement, beat perception strongly engages motor regions of the brain, which are likely involved in predicting the timing of beats (for a recent review, see: How Beat Perception Co-opts Motor Neurophysiology: Trends in Cognitive Sciences (cell.com)). In this presentation I will explore some ideas for linking beat processing research to research on conscious content, conscious state, and conscious self. The aim is to generate discussion that could help shape future research in this area.

Wednesday

24th February

2021

Zoom Seminar

Presenters

Rhiannon Armitage

Tomasz Korbak

Mikkel Roald-Arbøl

Nadine Spychala

3rd Cohort Leverhulme Doctoral Scholar Presentations

Understanding individual differences in sweet taste

Scaling active inference

Neural underpinnings of invertebrate sleep

Measures of neural complexity and emergence related to conscious processing

Wednesday

27th January

2021

Zoom Seminar

Presenters

Jon Reus

George Kafetzis

Federico Micheli

Will Roseby

Beata Wozniak

3rd Cohort Leverhulme Doctoral Scholar Presentations

Alien Umwelts: The Perception of Otherness in the Aesthetics of Artificial Intelligence Systems

Vision at the origin of vertebrate life

Dissociating Top-Down and Bottom-Up Brain Processes in Conscious Perception

A genetic approach to sensory neuroscience

Investigating cues to colour constancy using virtual reality

Wednesday

9th December

2020

Zoom Lecture

Dr. Andrew MacAskill

University College London

Control of feeding behaviour by hippocampal ghrelin receptor signalling

His work focuses on the ventral hippocampus, an area crucial for learning and motivation, and a key node in the transition to mental illness. His team use a combination of in vivo and in vitro viral expression, two-photon microscopy, optogenetics, electrophysiology and behavioural assays to identify and characterise the neural circuitry underlying the generation of behaviour, and how this is altered in disease.

Wednesday

23rd September

2020

Zoom Lecture

Prof. Charles Spence

Crossmodal Research Lab

Oxford University

Gastrophysics: The New Science of Eating

Gastrophysics, the new science of eating, focuses attention on ‘the everything else’ apart from the food that nevertheless still influences the tasting experience, be it in the high-end restaurant or the home: Everything from the colour of the plate on which the food is served (and the gastroporn thereon), through the weight of the cutlery that is used to consume it (assuming that there is any, which can’t always be guaranteed these days), not to mention the music that happens to be playing in the background (sonic seasoning). Gastrophysics aims to bring the scientific approach, inspired by the latest insights from multisensory perception research concerning the roles of taste, smell, touch, sight and sound, together with the best in culinary artistry, in order to help design more engaging, more enjoyable, and more memorable experiences for diners in the future. I will describe a number of our recent attempts, using magic, visual illusions, and ASMR to deliver extraordinary tasting experiences to drinkers and diners.

Wednesday

22nd July

2020

Zoom Lecture

Assistant Prof. Caroline E. Robertson

Psychological and Brain Science

Dartmouth College, USA.

The limits of color awareness during active, real-world vision

Color is a foundational aspect of visual experience that aids in segmenting objects, identifying food sources, and signaling emotions. Intuitively, it feels that we are immersed in a colorful world that extends to the farthest limits of our periphery. How accurate is our intuition? Here, we used gaze-contingent rendering in immersive VR to reveal the limits of color awareness during naturalistic viewing. Observers explored 360° real-world environments, which we altered so that only the regions where observers looked were in color, while their periphery was black-and-white. Overall, we found that observers routinely failed to notice when color vanished from the majority of their visual world. These results show that our intuitive sense of a rich, colorful world is largely incorrect.

Wednesday

20th May

2020

Zoom Lecture

Dr. Annika Boldt

Cognitive Neuroscience

University College London

Distinct and overlapping neural correlates of metacognitive monitoring and metacognitive control

Metacognition is the act of reflecting on one’s own mental states, often for the purpose of cognitive control. Previous research has shown that people can accurately report their confidence in their decisions and memories. Research has also investigated how these metacognitive signals are generated and which brain networks encode them. However, we are only just beginning to understand how metacognitive knowledge gets selected to optimise behaviour (metacognitive control). I will present data from studies in which I investigate how metacognition can guide people's decisions to cognitively offload, that is using external aids to reduce the demands of a task. In this context, I then show that metacognitive monitoring and metacognitive control share overlapping brain patterns using a multivariate analysis approach.

Wednesday

19th February

2020

Pevensey 1A6

Prof. Tony Prescott

Cognitive Robotics

University of Sheffield

The Synthetic Psychology of the Self

Synthetic psychology describes the approach of “understanding through building” applied to the brain and behaviour. In this talk I will illustrate the interplay between the synthetic and empirical traditions in psychology by considering the specific challenge of synthesizing a “sense of self” for a humanoid robot using biomimetic artificial intelligence. The starting hypothesis is that the human self is brought into being by the activity of a set of transient self-processes instantiated by the brain and body. I propose that we can synthesize a robot self by developing equivalent sub-systems within an integrated cognitive architecture for a humanoid robot. The talk will be illustrated using ongoing work to create a sense of self for a humanoid robot that has physical, temporal, interpersonal and narrative components set within a multi-layered model of mind.

Wednesday

22nd January

2020

Silverstone SB211 - Sussex Humanities Lab

Presenters

Sam Bilbow

 

Clémence Compain

Sina Dominiak

Jacapo Modoni

2nd Cohort Leverhulme Doctoral Scholar Presentations

Impact on human perception and expression, using augmented-reality technology as a medium for computational art                                                                                                                                            

Perceptual biases and metacognition during visual decision-making

Plasticity of visual processing in primary visual cortex

Putting the spotlight on taste: behavioural and optical interrogation of the neural mechanism of hedonic taste perception

Wednesday

11th December

2019

Silverstone SB211 - Sussex Humanities Lab

Presenters

Tessa Herzog

Fiona Miller
 

Isabel Maranhão

2nd Cohort Leverhulme Doctoral Scholar Presentations

Information encoding at the first visual synapse in the visual pathway

Towards a therapeutic compositional model: can attributes of sound and music be isolated and composed to induce optimum HRV in PTSD sufferers?                                

Sequence processing in dyslexic and non dyslexic groups

Wednesday

20th November

2019

Pevensey 1A6

Dr Peggy Seriès

Computational Cognitive Neuroscience and Psychiatry

University of Edinburgh

Are Schizophrenia and Autism Disorders of Prediction?

A growing idea in computational neuroscience is that perception and cognition can be successfully described in terms of predictive processing or Bayesian inference:  the nervous system would maintain and update internal probabilistic models that serve to interpret the world and guide our actions. This approach is increasingly recognised to also be of interest to Psychiatry. Mental illness could correspond to the brain trying to interpret the world through distorted internal models, or incorrectly combining such internal models with sensory information. These ideas have become dominant in trying to understand autism and schizophrenia in particular.

I will describe work pursued in my lab that aims at uncovering such internal models, using behavioural experiments and computational methods.

In health, we are particularly interested in clarifying how prior beliefs affect perception and decision-making, how long they take to build up or be unlearned, how complex they can be, and how they can inform us on the type of computations and learning that the brain performs. In mental illness, we are interested in understanding whether/how the machinery of probabilistic inference could be impaired, and/or relies on the use of distorted priors.

I will introduce the emerging field of Computational Psychiatry and describe recent results relevant to the study of schizophrenia and autism where we directly and quantitatively test the current theories according to which perceptual inference,  perceptual priors integration or the relative precision of priors vs likelihood would differ in these disorders, as compared to controls.

Wednesday

23rd October

2019

Pevensey 1A6

Professor Adam Zeman

Cognitive and Behavioural Neurology

University of Edinburgh

Eye's Mind Project

 

The Eye’s Mind – perspectives on visual imagery

For most of us visual imagery is a conspicuous ingredient of the imaginative experience which allows us to escape from the here and now into the past, the future and the worlds conceived by science and art. There appears to be wide inter-individual variation in the vividness of visual imagery. Although Galton, in the 1880s, recognised that some individuals may lack wakeful imagery entirely, the existence of ‘extreme imagery’ has been oddly neglected since his early work.


In 2015 we coined the term ‘aphantasia’ to describe the lack of the mind’s eye, describing 21 individuals who reported a lifelong inability to visualise (Cortex, 2015;73:378-80). Since then we have heard from over 13,000 people, most reporting lifelong aphantasia, or its converse hyperphantasia, but also less common ‘acquired’ imagery loss resulting from brain injury or psychological disorder. Preliminary analyses suggests association between vividness extremes, occupational preference and reported abilities in face recognition and autobiographical memory.


Many people with lifelong aphantasia nevertheless dream visually. Imagery in other modalities is variably affected. Extreme imagery appears to run in families more often than would be expected by chance. I will describe our studies of a- and hyper-phantasia in the context of the Eye’s Mind project, an interdisciplinary collaboration funded by the AHRC. In addition to our work on extreme imagery, members of the Eye’s Mind team have reviewed the intellectual history of visual imagery (MacKisack et al, Frontiers in Psychology, 2016) and undertaken a recent ALE meta-analysis of functional imaging studies of visualisation (Winlove et al, Cortex, 2018).

Wednesday

25th September

2019

Pevensey 1A6

Dr Romy Lorenz

Cognitive Science

Postdoctoral Fellow, Cambridge, Stanford, Max Planck Institute

Towards a neurobiologically-derived cognitive taxonomy

The classic taxonomy of cognitive processes was developed largely blind to the functional organization of the brain; therefore, classic cognitive tasks tend to tap multiple cognitive processes that involve multiple brain networks. Resolving this many-to-many mapping problem between cognitive tasks and brain networks is practically intractable with standard fMRI methodology as only a small subset of all possible cognitive tasks can be tested. This is problematic, as studying only a fraction from the large space of cognition can result in over-specified inferences about functional-anatomical mappings with a misleadingly narrow function being proposed as the definitive role of a network, concealing the broader role each network may play in cognition. 

In this talk, I present an alternative approach that resolves these problems by combining real-time fMRI with a branch of machine learning, Bayesian optimization. Neuroadaptive Bayesian optimization is a powerful strategy to efficiently explore more experimental conditions than is currently possible with standard methodology. I will present results from a study where we used this method to identify the exact cognitive task conditions that optimally dissociate frontoparietal brain networks. Our findings deviate from previous meta-analyses and hypothesized functional labels for these frontoparietal brain networks. Taken together the results form the starting point for a neurobiologically-derived cognitive taxonomy. 

In addition, I will touch on the potential of the approach in combination with non-invasive brain stimulation (e.g., tACS) and for accelerated biomarker discovery. Interestingly, Bayesian optimization can also be combined with preregistration to cover exploration, mitigating researcher bias more broadly and improving reproducibility. 

As I have started my Sir Henry Wellcome Postdoctoral Fellowship in September last year, I will also share my research vision going forward and will illustrate how automated meta-analytic and text mining techniques can help me in my endeavour to map associations between cognitive processes and brain networks as well as how deep learning methods could help us to move beyond descriptive mappings and advance mechanistic discovery in network neuroscience.

Tuesday

16th July

2019

Arts A01, Arts Hallway, Quiet Room (Meeting House)

Keynote Speakers

Prof. Andy Clark

Dr. Katerina Fotopoulou

Dr. Ryota Kanai

Dr. Rosalyn Moran

Sensation Sussex Conference 2019 - "The Predictive Brain: From Perception to Awareness"

Bayesing Qualia: Consciousness as Inference, not Raw Datum                                                                                

Mentalising Homeostasis: The Social Origins of Interoceptive Active Inference                                                                                

Information Generation as a Core Function of Consciousness

Active Inference in Gaming Environments for Computational Psychiatry.

Wednesday

12th June

2019

Pevensey 1A6

 

 

Dr Jörg Fachner

Anglia Ruskin University,

Professor of Music, Health and the Brain,

Cambridge Institute for Music Therapy

Hyperscanning during music therapy, spontaneously emerging imagery and altered states of consciousness

In Guided imagery and music (GIM) a therapist accompanies and guides the imagery of a client in order ‘to work on challenging life issues, for instance, disturbing old memories, losses, traumata, bothering health conditions, and relationship issues. The client (Traveler) reclines with closed eyes while the therapist initiates an altered state of consciousness (ASC) induction. The therapist (Guide) then chooses a pre-determined music program, or spontaneously chooses music to match the client’s imagery. As the music plays, the client describes any imagery, feelings, or thoughts. To analyse how emotions and imagery are processed and recognized, we employed a hypserscanning EEG, in which the brain activity during a real therapy session was synchronously recorded and identified moments of interest and Interrater overlaps of video ratings were then transcribed and submitted to an analysis of frontal brain activity over time.

Here we were interested how the temporal dynamics of brain activity changed according to the emotional impact of the emerging imagery and how this was related to the therapy process.  During the emergence of important personal visual imagery and dialogue with a significant person in the therapy, a shift of the frontal asymmetry indicated a strong emotional response in the therapist-client interaction. Peaks in Frontal Alpha Asymmetry (FAA) dynamics represented emotional peaks of intensity during selected moments. The shared emotional processing during therapy is fluctuating between negative and positive emotions, while challenging, negative emotions are related to therapeutic work on fear, anxiety and hopelessness. Directionality of FAA Peak dynamics represented shared emotional valence. Being in an ASC allowed associating more freely and gaining access to important imagery, however is not necessary related to positive emotions.

Wednesday

15th May

2019  

Pevensey 1A6

Professor Marc Buehner

Cardiff University,

School of Psychology

Temporal Binding of Actions and Effects: A measure of Sense of Agency?

Temporal Binding (TB) refers to the mutual attraction in subjective time between a cause and its effect: Relative to single-event baseline judgments, people’s perception of causal actions and their outcomes systematically shifts in subjective awareness.  Specifically, causal actions are perceived relatively later, while their outcomes are perceived relatively earlier – action and outcome attract each other in subjective experience (cf. Haggard, Clark, & Kalogeras, 2002).  Because the majority of demonstrations of TB deployed intentional action as the critical cause, TB is now increasingly deployed as a convenient proxy measure for Sense of Agency (SoA). Moreover, reduced TB for negative outcomes has been interpreted to reflect reduced SoA for actions that bring about negative consequences: For example, reduced TB for penalties delivered to a peer when following an experimenter’s instruction (as opposed to under free will) is taken to show that coercion reduces one’s SoA for self-action along the lines of the Nuremberg defense (Caspar, Christensen, Cleeremans, & Haggard, 2016).  In this talk I will caution against overinterpreting binding as tracking SoA with three arguments: a) Agency is confounded with causality and there is now ample evidence to show that TB is in fact driven by causality – Intentional action is neither necessary nor sufficient to produce TB; b) preparations such as Caspar et al. actually deployed causal structures where the coerced action would be expected to be temporally bound to the preceding command, thus reducing TB in any case; c) attempts to replicate reductions in TB for negative outcomes have failed. Binding is still an interesting phenomenon, however, and might be useful in offering deeper insights into temporal processing more generally.

Friday

3rd May

2019

Pevensey 1A6

Dr Liz Irvine

Cardiff University

Lecturer in Philosophy

How (not) to measure consciousness

Consciousness science presents an interesting example of the way that theory development is deeply entwined with the problem of how to measure or detect the phenomenon of interest. Different theories of consciousness often rely on different measurement procedures for consciousness and there is, as yet, no consensus about what the appropriate measurement procedures are. It is often suggested that better measures can be developed by rigorous comparison of multiple measurement procedures. In this talk I evaluate two comparative approaches, measurement robustness and calibration techniques, and argue that they are in fact of limited use here, and highlight general problems in applying comparative methods to develop psychological measures.

Wednesday

20th March

2019

Pevensey 1A6

Dr Tristan Bekinschtein 

Cambridge University

Department of Psychology

Meditation, hypnagogia and the stability of consciousness

Seems limiting that we talk about phenomenology and experiences but then we measure reaction times and errors. Can we study the contents of our mind? I would argue that we are always studying content in psychology but not caring or not willing to engage in the question. I will present two main methods to capture what we think -direct and indirect- that may allow us to formalize the questions about content. I would also like to discuss two methods in cognitive neuroscience to map the underpinnings of the contents: neural decoding and intensity tracking. I will illustrate the results and discussion with EEG and fMRI experiments during pharmacologically induced states, sleep transitions and meditative techniques.

Wednesday

20th February

2019

Pevensey 1A6

Professor Sarah Garfinkel

University of Sussex

Professor in Psychiatry, Neuroscience and Imaging

Hearts and Minds: Interoceptive signals guide emotion and cognition

There is increasing recognition that cognitive and emotional processes are shaped by the dynamic integration of brain and body. A major channel of interoceptive information comes from the heart, where phasic signals are conveyed to the brain to indicate how fast and strong the heart is beating. This talk will detail how cardiac afferent signals can alter emotion processing and guide intuitive decision-making. Moreover, this interoceptive channel is disrupted in distinct ways in first episode psychosis, schizophrenia, autism and anxiety. This talk will provide empirical examples and suggest how specific interoceptive disturbances may contribute to our understanding of distinct symptoms, including dissociation and altered affective processing. Finally, new work will be presented on interoceptive training to demonstrate enhanced interoceptive precision following targeted feedback. The discrete cardiac effects on emotion and cognition have broad relevance to clinical neuroscience, with implications for peripheral treatment targets and behavioural interventions.

Wednesday

23rd January

2019

Pevensey 1A6

Professor Jamie Ward

University of Sussex

Co-Director of Leverhulme Doctoral Scholarship Programme

Unusual perceptual experiences as a window into individual differences in the brain and cognition

In this seminar, I will present the current state of knowledge about anomalous perceptual experiences in synaesthesia (e.g. experiencing colours for letters, tastes for words) that links together various levels of understanding from genetics through to brain structure, cognition, and perceptual experiences.  Whereas other kinds of anomalous perceptual experiences (e.g. visual hallucinations in people going blind) are triggered via compensatory plasticity changes in the brain, due to unreliable sensory inputs, this is not the case in developmental forms of synaesthesia.  If anything, their perceptual abilities are atypically good (on objective measures) and, moreover, they subjectively report higher sensitivity/aversion to sensory stimuli.  The latter closely resembles a defining symptom of autism, and I present evidence that the two conditions are related.  Enhanced perceptual functioning is one of several cognitive features that appear to be enhanced in synaesthesia (the others include memory and mental imagery).  Finally, I will discuss why these anomalous experiences exist.  I will argue that they do not convey any new information about the world (and, hence, have limited functionality) but are, instead, an emergent property of other adaptive design features.  In effect, synaesthesia is not functional in itself but the underlying disposition towards developing synaesthesia may well be.

Wednesday

12th December

2018

Pevensey 1A6

Warrick Roseboom

University of Sussex

Sackler Centre for Consciousness Science & Dept of Informatics

Why “intentional binding” is a poor measure of sense of agency – and how it might be redeemed

Sense of agency describes the feeling that you are the author of your own actions. The academic literature on sense of agency has exploded in the past two decades following the discovery of an apparently implicit measure of agency called intentional binding (IB). IB refers to the subjective contraction of the temporal interval between an action (e.g. pressing a light switch) and its putative outcome (the light coming on), compared to non-self-intentional event pairings (e.g. observing someone else switch on a light). Recent work from our group demonstrates several key challenges to using IB to measure agency. First, IB dissociates from explicit judgments of agency at least as often as it doesn’t - including important cases such as sense of agency for group actions. Second, when appropriate non-intentional event baseline conditions are used, such as watching your own movements replayed from a first-person perspective in virtual reality without making any action, evidence for IB disappears entirely. Third, taking the differential sensory precision of action and outcome events into account in simple multisensory causal-binding models fully explains IB effects without appealing to intention whatsoever. However, other recent findings using IB in the context of post-hypnotic suggestion of involuntariness provide the strongest evidence yet that the experience of agency is reflected in IB. In sum, these cases demonstrate that the instances in which IB appropriately indexes agency are much more limited than previously assumed and provide clear direction on where future investigations of the phenomenology of agency should be conducted.

Wednesday

21st November

2018

Pevensey 1A6

Presenters

Dennis Larsson

Magdalena del Río Forster

Filippo Torresan

1st Cohort Leverhulme Doctoral Scholar Presentations

Brain-body interaction underlying interoceptive awareness

Individual differences in sensory sensitivity - links to autism and synaesthesia                                                                                    

The Predictive Brain: From Presence to Agency via Counterfactuals?

Wednesday

17th October

2018

Pevensey 1A6

Presenters

Philipp Kaniuth

Carla Dance

Joshua Hargreaves

1st Cohort Leverhulme Doctoral Scholar Presentations

The Sense of Agency - A closer look at Consciousness and Causality

A ‘blind mind’s eye’: Visual knowledge in Aphantasia

Exploring the role 'influential' behaviours which facilitate socio-temporal synchrony during musical joint action