Time/Room: Friday, May 17, 2019, 12:00 – 2:00 pm, Talk Room 2
Organizer(s): Laura Dugué, Paris Descartes University & Suliann Ben Hamed, Université Claude Bernard Lyon I
Presenters: Suliann Ben Hamed, Niko Busch, Laura Dugue, Ian Fiebelkorn
The phenomenological, continuous, unitary stream of our perceptual experience appears to be an illusion. Accumulating evidence suggests that what we perceive of the world and how we perceive it rises and falls rhythmically at precise temporal frequencies. Brain oscillations -rhythmic neural signals- naturally appear as key neural substrates for these perceptual rhythms. How these brain oscillations condition local neuronal processes, long-range network interactions, and perceptual performance is a central question to visual neuroscience. In this symposium, we will present an overarching review of this question, combining evidence from monkey neural and human EEG recordings, TMS interference studies, and behavioral analyses. Suliann Ben Hamed will first present monkey electrophysiology evidence for a rhythmic exploration of space by the prefrontal attentional spotlight in the alpha (8-12 Hz) frequency range and will discuss the functional coupling between this rhythmic exploration and long-range theta frequency modulations. Niko Busch will then present electro-encephalography (EEG) and psychophysics studies in humans, and argue that alpha oscillations reflect fluctuations of neuronal excitability that modulate periodically subjective perceptual experience. Laura Dugué will present a series of EEG, Transcranial Magnetic Stimulation (TMS) and psychophysics evidence in humans in favor of a functional dissociation between the alpha and the theta (3–8 Hz) rhythms underlying periodic fluctuations in perceptual and attentional performance respectively. Finally, Ian Fiebelkorn will present psychophysics studies in humans and electrophysiology evidence in macaque monkeys, and argue that the fronto-parietal theta rhythm allows for functional flexibility in large-scale networks. The multimodal approach, including human and monkey models and a large range of behavioral and neuroimaging techniques, as well as the timeliness of the question of the temporal dynamics of perceptual experience, should be of interest to cognitive neuroscientists, neurophysiologists and psychologists interested in visual perception and cognition, as well as to the broad audience of VSS.
The prefrontal attentional spotlight in time and space
Speaker: Suliann Ben Hamed, Université Claude Bernard Lyon I
Recent accumulating evidence challenges the traditional view of attention as a continuously active spotlight over which we have direct voluntary control, suggesting instead a rhythmic operation. I will present monkey electrophysiological data reconciling these two views. I will apply machine learning methods to reconstruct, at high spatial and temporal resolution, the spatial attentional spotlight from monkey prefrontal neuronal activity. I will first describe behavioral and neuronal evidence for distinct spatial filtering mechanisms, the attentional spotlight serving to filter in task relevant information while at the same time filtering out task irrelevant information. I will then provide evidence for rhythmic spatial attention exploration by this prefrontal attentional spotlight in the alpha (7-12Hz) frequency range. I will discuss this rhythmic exploration of space both from the perspective of sensory encoding and behavioral trial outcome, when processing either task relevant or task irrelevant information. While these oscillations are task-independent, I will describe how their spatial unfoldment flexibly adjusts to the ongoing behavioral demands. I will conclude by bridging the gap between this alpha rhythmic exploration by the attentional spotlight and previous reports on a contribution of long-range theta oscillations in attentional exploration and I will propose a novel integrated account of a dynamic attentional spotlight.
Neural oscillations, excitability and perceptual decisions
Speaker: Niko Busch, WWU Münster
Numerous studies have demonstrated that the power of ongoing alpha oscillations in the EEG is inversely related to neural excitability, as reflected in spike-firing rate, multi-unit activity, or the hemodynamic fMRI signal. Furthermore, alpha oscillations also affect behavioral performance in perceptual tasks. However, it is surprisingly unclear which latent perceptual or cognitive mechanisms mediate this effect. For example, an open question is whether neuronal excitability fluctuations induced by alpha oscillations affect an observer’s acuity or perceptual bias. I will present a series of experiments that aim to clarify the link between oscillatory power and perceptual performance. In short, these experiments indicate that performance during moments of weak pre-stimulus power, indicating greater excitability, is best described by a more liberal detection criterion rather than a change in detection sensitivity or discrimination accuracy. I will argue that this effect is due to an amplification of both signal and noise, and that this amplification occurs already during the first stages of visual processing.
The rhythms of visual attention
Speaker: Laura Dugué, Paris Descartes University
Despite the impression that our visual perception is seamless and continuous across time, evidence suggests that our visual experience relies on a series of discrete moments, similar to the snapshots of a video clip. My research focuses on these perceptual and attentional rhythms. Information would be processed in discrete samples; our ability to discriminate and attend to visual stimuli fluctuating between favorable and less favorable moments. I will present a series of experiments, using multimodal functional neuroimaging combined with psychophysical measurements in healthy humans that assess the mechanisms underlying psychophysical performance during and between two perceptual samples, and how these rhythmic mental representations are implemented at the neural level. I will argue that two sampling rhythms coexist, i.e. the alpha rhythm (8–12 Hz) to allow for sensory, perceptual sampling, and the theta rhythm (3–8 Hz) rather supporting rhythmic, attentional exploration of the visual environment.
Rhythmic sampling of the visual environment provides critical flexibility
Speaker: Ian Fiebelkorn, Princeton University
Environmental sampling of spatial locations is a fundamentally rhythmic process. That is, both attention-related boosts in sensory processing and the likelihood of exploratory movements (e.g., saccades in primates and whisking in rodents) are linked to theta rhythms (3–8 Hz). I will present electrophysiological data, from humans and monkeys, demonstrating that intrinsic theta rhythms in the fronto-parietal network organize neural activity into two alternating attentional states. The first state is associated with both (i) the suppression of covert and overt attentional shifts and (ii) enhanced visual processing at a behaviorally relevant location. The second state is associated with attenuated visual processing at the same location (i.e., the location that received a boost in sensory processing during the first attentional state). In this way, theta-rhythmic sampling provides critical flexibility, preventing us from becoming overly focused on any single location. Every approximately 250 ms, there is a window of opportunity when it is easier to disengage from the presently attended location and shift to another location. Based on these recent findings, we propose a rhythmic theory of environmental sampling. The fronto-parietal network is positioned at the nexus of sensory and motor functions, directing both attentional and motor aspects of environmental sampling. Theta rhythms might help to resolve potential functional conflicts in this network, by temporally isolating sensory (i.e., sampling) and motor (i.e., shifting) functions. This proposed role for theta rhythms in the fronto-parietal network could be a more general mechanism for providing functional flexibility in large-scale networks.