Moving through silence in dance: A neural perspective

The word "silence" typically refers to the auditory modality, signifying an absence of sound or noise, being quiet. One may then ask: could we attribute the notion of silence to the domain of dance, e.g., when a movement is absent and the dancer stops moving? Is it at all useful to think in terms of silence when referring to dance? In this chapter, my exploration of these questions is based on recent studies in brain research, which demonstrate the remarkable facility of specific regions in the human brain to perceive visually referred biological and, in particular, human motion, leading to prediction of future movements of the human body. I will argue that merely ceasing motion is an insufficient condition for creating a perception of silence in the mind of a spectator of dance. Rather, the experience of silence in dance is a special situation where the static position of the dancer does not imply motion, and is unlikely to evoke interpretation of the intentions or the emotional expression of the dancer. For this to happen, the position of the dancer, while being still, should be held effortlessly, aimlessly, and with a minimal expression of emotion and intention. Furthermore, I suggest that dynamics, repetitive movement (such as that of Sufi whirling dervishes), can also be perceived as silence in dance because of the high level of predictability and evenness of the movement. These moments of silence in dance, which are so rare in our daily lives, invite us to experience the human body from a new, "out of the box" perspective that is the essence of all the arts.

The interaction of global motion and global form processing on the perception of implied motion: An equivalent noise approach

Global motion and global form are proposed to be processed through functionally differentiated independent channels along dorsal (motion) and ventral (form) pathways. However, more recent studies show significant interactions between these pathways by inducing the perception of motion (implied motion) from presenting the independent frames of static Glass patterns. The mechanisms behind such interaction are not adequately understood with studies showing a larger contribution of either a motion or form processing mechanism. In the current study, we adapted the equivalent noise paradigm to disentangle the effect of internal noise (local processing) and sampling efficiency (global processing) on global motion, global form, and the interaction of both on the perception of implied motion using physically equivalent stimuli. Six visually normal observers discriminated the direction or orientation of random dot kinematograms (RDK), static Glass patterns (Glass), and dynamic Glass patterns (dGlass) whose directions/orientations were determined by the means of normal distributions with a range of direction/orientation variances that served as external noise. Thresholds (τ) showed a consistent pattern across observers and external noise levels, where τ_Glass > τ_dGlass > τ_RDK. Nested model comparisons where the thresholds were related to the external noise, internal noise, and the sampling efficiency revealed that the difference in performance between the tasks was best described by the change in sampling efficiency with invariable internal noise. Our results showed that the higher thresholds for implied motion compared to real motion could be due to inefficient pooling of local dipole orientation cues at global processing stages involving motion mechanisms.

Implied motion as a possible mechanism for encoding other people's attention

Recent evidence suggests that the human brain automatically constructs a rich model of other people's attention, beyond registering low-level cues such as someone else's gaze direction. This model is not a physically accurate representation of attention, but instead appears to contain simplifying and physically incoherent features. For example, without explicitly realizing it, people treat the attentive gaze of others as though it exerts a gentle force pushing on objects. Here we specify another aspect of that implicit model of attention. People treat the attentive gaze of an agent as though it were travelling through space, with an implied motion encoded literally enough that it causes a perceptual motion adaptation effect. This implicit model of other people's attention may facilitate the process of keeping track of who is attending to what, which is essential for reading and predicting the minds and behavior of social agents. This implicit model of attention may also have shaped culturally widespread ideas about mind and spirit.

Motor facilitation during observation of implied motion: Evidence for a role of the left dorsolateral prefrontal cortex

The phenomenon of motor resonance (the increase in motor cortex excitability during observation of actions) has been previously described. Transcranial magnetic stimulation (TMS) studies have demonstrated a similar effect during perception of implied motion (IM). The left dorsolateral prefrontal cortex (DLPFC) seems to be activated during action observation. Furthermore, the role of this brain area in motor resonance to IM is yet to be investigated. Fourteen healthy volunteers were enrolled into the study. We used transcranial direct current stimulation (tDCS) to stimulate DLPFC aiming to investigate whether stimulation with different polarities would affect the amplitude of motor evoked potential collected during observation of images with and without IM. The results of our experiment indicated that Cathodal tDCS over the left DLPFC prevented motor resonance during observation of IM. On the contrary, anodal and sham tDCS did not significantly modulate motor resonance to IM. The current study expands the understanding of the neural circuits engaged during observation of IM. Our results are consistent with the hypothesis that action understanding requires the interaction of large networks and that the left DLPFC plays a crucial role in generating motor resonance to IM.

Evaluating the influence of a fixated object's spatio-temporal properties on gaze control

Despite recent progress in understanding the factors that determine where an observer will eventually look in a scene, we know very little about what determines how an observer decides where he or she will look next. We investigated the potential roles of object-level representations in the direction of subsequent shifts of gaze. In five experiments, we considered whether a fixated object's spatial orientation, implied motion, and perceived animacy affect gaze direction when shifting overt attention to another object. Eye movements directed away from a fixated object were biased in the direction it faced. This effect was not modified by implying a particular direction of inanimate or animate motion. Together, these results suggest that decisions regarding where one should look next are in part determined by the spatial, but not by the implied temporal, properties of the object at the current locus of fixation.

Implied motion language can influence visual spatial memory

How do language and vision interact? Specifically, what impact can language have on visual processing, especially related to spatial memory? What are typically considered errors in visual processing, such as remembering the location of an object to be farther along its motion trajectory than it actually is, can be explained as perceptual achievements that are driven by our ability to anticipate future events. In two experiments, we tested whether the prior presentation of motion language influences visual spatial memory in ways that afford greater perceptual prediction. Experiment 1 showed that motion language influenced judgments for the spatial memory of an object beyond the known effects of implied motion present in the image itself. Experiment 2 replicated this finding. Our findings support a theory of perception as prediction.

Encodings of implied motion for animate and inanimate object categories in the two visual pathways

Previous research has proposed two separate pathways for visual processing: the dorsal pathway for "where" information vs. the ventral pathway for "what" information. Interestingly, the middle temporal cortex (MT) in the dorsal pathway is involved in representing implied motion from still pictures, suggesting an interaction between motion and object related processing. However, the relationship between how the brain encodes implied motion and how the brain encodes object/scene categories is unclear. To address this question, fMRI was used to measure activity along the two pathways corresponding to different animate and inanimate categories of still pictures with different levels of implied motion speed. In the visual areas of both pathways, activity induced by pictures of humans and animals was hardly modulated by the implied motion speed. By contrast, activity in these areas correlated with the implied motion speed for pictures of inanimate objects and scenes. The interaction between implied motion speed and stimuli category was significant, suggesting different encoding mechanisms of implied motion for animate-inanimate distinction. Further multivariate pattern analysis of activity in the dorsal pathway revealed significant effects of stimulus category that are comparable to the ventral pathway. Moreover, still pictures of inanimate objects/scenes with higher implied motion speed evoked activation patterns that were difficult to differentiate from those evoked by pictures of humans and animals, indicating a functional role of implied motion in the representation of object categories. These results provide novel evidence to support integrated encoding of motion and object categories, suggesting a rethink of the relationship between the two visual pathways.

Neural circuits underlying motor facilitation during observation of implied motion

In the present study we used single and paired-pulse Transcranial Magnetic Stimulation (TMS) to evaluate the effect of implied motion on primary motor cortex microcircuits. We found that observation of the implied motion of a static image increases MEP amplitude and reduces short-interval intracortical inhibition (SICI), without significant modulation of intracortical facilitation and sensory-motor integration. Our results add to the existing literature on the activation of the observation-execution matching system and describe a selective modulation of GABAergic cortical microcircuits during observation of implied motion.