Silvia Spadacenta

Bio: Silvia Spadacenta is an academic researcher from University of Tübingen. The author has contributed to research in topics: Facial expression & Gaze. The author has an hindex of 2, co-authored 8 publications receiving 11 citations.

A Naturalistic Dynamic Monkey Head Avatar Elicits Species-Typical Reactions and Overcomes the Uncanny Valley

Abstract: Research on social perception in monkeys may benefit from standardized, controllable, and ethologically valid renditions of conspecifics offered by monkey avatars. However, previous work has cautioned that monkeys, like humans, show an adverse reaction toward realistic synthetic stimuli, known as the “uncanny valley” effect. We developed an improved naturalistic rhesus monkey face avatar capable of producing facial expressions (fear grin, lip smack and threat), animated by motion capture data of real monkeys. For validation, we additionally created decreasingly naturalistic avatar variants. Eight rhesus macaques were tested on the various videos and avoided looking at less naturalistic avatar variants, but not at the most naturalistic or the most unnaturalistic avatar, indicating an uncanny valley effect for the less naturalistic avatar versions. The avoidance was deepened by motion and accompanied by physiological arousal. Only the most naturalistic avatar evoked facial expressions comparable to those toward the real monkey videos. Hence, our findings demonstrate that the uncanny valley reaction in monkeys can be overcome by a highly naturalistic avatar. SIGNIFICANCE STATEMENTWe introduce a new, naturalistic monkey avatar and validate it as an appropriate stimulus for studying primate social cognition by demonstrating that it elicits natural looking patterns and facial reactions in macaque monkeys rather than evoking an “uncanny” avoidance reaction. The fact that a degraded version of the avatar is able to evoke an uncanniness reaction confirms its existence in monkeys, supporting an evolutionary old behavioral commonality shared by monkeys and man. However, as this reaction can be overcome by a very naturalistic avatar, the uncanny valley is clearly not an inevitable consequence of high degrees of realism.

Reflexive gaze following in common marmoset monkeys.

Abstract: The ability to extract the direction of the other’s gaze allows us to shift our attention to an object of interest to the other and to establish joint attention. By mapping one’s own intentions on the object of joint attention, humans develop a Theory of (the other’s) Mind (TOM), a functional sequence possibly disrupted in autism. Gaze following of both humans and old world monkeys is orchestrated by very similar cortical architectures, strongly suggesting homology. Also new world monkeys, a primate suborder that split from the old world monkey line about 35 million years ago, have complex social structures and one member of this group, the common marmosets (Callithrix jacchus) are known to follow human head-gaze. However, the question is if they use gaze following to establish joint attention with conspecifics. Here we show that this is indeed the case. In a free choice task, head-restrained marmosets prefer objects gazed at by a conspecific and, moreover, they exhibit considerably shorter choice reaction times for the same objects. These findings support the assumption of an evolutionarily old domain specific faculty shared within the primate order and they underline the potential value of marmosets in studies of normal and disturbed joint attention.

Reflexive gaze following in common marmoset monkeys

Abstract: The ability to extract the direction of the others gaze allows us to shift our attention to an object of interest to the other and to establish joint attention. By mapping ones own expectations, desires and intentions on the object of joint attention, humans develop a Theory of (the others) Mind (TOM), a functional sequence possibly disrupted in autism. Although old world monkeys probably do not possess a TOM, they follow the others gaze and they establish joint attention. Gaze following of both humans and old world monkeys fulfills Fodors criteria of a domain specific function and is orchestrated by very similar cortical architectures, strongly suggesting homology. Also new world monkeys, a primate suborder that split from the old world monkey line about 35 million years ago, have complex social structures. One member of this group, the common marmoset (Callithrix jacchus), has received increasing interest as a potential model in studies of normal and disturbed human social cognition. Marmosets are known to follow human head-gaze. However, the question is if they use gaze following to establish joint attention with conspecifics. Here we show that this is indeed the case. In a free choice task, head-restrained marmosets prefer objects gazed at by a conspecific and, moreover, they exhibit considerably shorter choice reaction times for the same objects. These findings support the assumption of an evolutionary old domain specific faculty shared within the primate order and they underline the potential value of marmosets in studies of normal and disturbed joint attention.nnHIGHLIGHTSO_LICommon marmosets follow the head gaze of conspecifics in order to establish joint attention.nC_LIO_LIBrief exposures to head gaze are sufficient to reallocate an animals attention.nC_LIO_LIThe tendency to follow the others gaze competes with the attractional binding of the conspecifics facenC_LI

Physiologically-Inspired Neural Circuits for the Recognition of Dynamic Faces

Abstract: Dynamic faces are essential for the communication of humans and non-human primates. However, the exact neural circuits of their processing remain unclear. Based on previous models for cortical neural processes involved for social recognition (of static faces and dynamic bodies), we propose two alternative neural models for the recognition of dynamic faces: (i) an example-based mechanism that encodes dynamic facial expressions as sequences of learned keyframes using a recurrent neural network (RNN), and (ii) a norm-based mechanism, relying on neurons that represent differences between the actual facial shape and the neutral facial pose. We tested both models exploiting highly controlled facial monkey expressions, generated using a photo-realistic monkey avatar that was controlled by motion capture data from monkeys. We found that both models account for the recognition of normal and temporally reversed facial expressions from videos. However, if tested with expression morphs, and with expressions of reduced strength, both models made quite different prediction, the norm-based model showing an almost linear variation of the neuron activities with the expression strength and the morphing level for cross-expression morphs, while the example based model did not generalize well to such stimuli. These predictions can be tested easily in electrophysiological experiments, exploiting the developed stimulus set.

Representation of the observer's predicted outcome value in mirror and nonmirror neurons of macaque F5 ventral premotor cortex.

Abstract: In the search for the function of mirror neurons, a previous study reported that F5 mirror neuron responses are modulated by the value that the observing monkey associates with the grasped object. Yet we do not know whether mirror neurons are modulated by the expected reward value for the observer or also by other variables, which are causally dependent on value (e.g., motivation, attention directed at the observed action, arousal). To clarify this, we trained two rhesus macaques to observe a grasping action on an object kept constant, followed by four fully predictable outcomes of different values (2 outcomes with positive and 2 with negative emotional valence). We found a consistent order in population activity of both mirror and nonmirror neurons that matches the order of the value of this predicted outcome but that does not match the order of the above-mentioned value-dependent variables. These variables were inferred from the probability not to abort a trial, saccade latency, modulation of eye position during action observation, heart rate, and pupil size. Moreover, we found subpopulations of neurons tuned to each of the four predicted outcome values. Multidimensional scaling revealed equal normalized distances of 0.25 between the two positive and between the two negative outcomes suggesting the representation of a relative value, scaled to the task setting. We conclude that F5 mirror neurons and nonmirror neurons represent the observer's predicted outcome value, which in the case of mirror neurons may be transferred to the observed object or action.NEW & NOTEWORTHY Both the populations of F5 mirror neurons and nonmirror neurons represent the predicted value of an outcome resulting from the observation of a grasping action. Value-dependent motivation, arousal, and attention directed at the observed action do not provide a better explanation for this representation. The population activity's metric suggests an optimal scaling of value representation to task setting.

Creepy cats and strange high houses: Support for configural processing in testing predictions of nine uncanny valley theories

Abstract: In 1970, Masahiro Mori proposed the uncanny valley (UV), a region in a human-likeness continuum where an entity risks eliciting a cold, eerie, repellent feeling Recent studies have shown that this feeling can be elicited by entities modeled not only on humans but also nonhuman animals The perceptual and cognitive mechanisms underlying the UV effect are not well understood, although many theories have been proposed to explain them To test the predictions of nine classes of theories, a within-subjects experiment was conducted with 136 participants The theories' predictions were compared with ratings of 10 classes of stimuli on eeriness and coldness indices One type of theory, configural processing, predicted eight out of nine significant effects Atypicality, in its extended form, in which the uncanny valley effect is amplified by the stimulus appearing more human, also predicted eight Threat avoidance predicted seven; atypicality, perceptual mismatch, and mismatch+ predicted six; category+, novelty avoidance, mate selection, and psychopathy avoidance predicted five; and category uncertainty predicted three Empathy's main prediction was not supported Given that the number of significant effects predicted depends partly on our choice of hypotheses, a detailed consideration of each result is advised We do, however, note the methodological value of examining many competing theories in the same experiment

Categorization-based stranger avoidance does not explain the uncanny valley effect

Abstract: The uncanny valley hypothesis predicts that an entity appearing almost human risks eliciting cold, eerie feelings in viewers. Categorization-based stranger avoidance theory identifies the cause of this feeling as categorizing the entity into a novel category. This explanation is doubtful because stranger is not a novel category in adults; infants do not avoid strangers while the category stranger remains novel; infants old enough to fear strangers prefer photographs of strangers to those more closely resembling a familiar person; and the uncanny valley’s characteristic eeriness is seldom felt when meeting strangers. We repeated our original experiment with a more realistic 3D computer model and found no support for categorization-based stranger avoidance theory. By contrast, realism inconsistency theory explains cold, eerie feelings elicited by transitions between instances of two different, mutually exclusive categories, given that at least one category is anthropomorphic: Cold, eerie feelings are caused by prediction error from perceiving some features as features of the first category and other features as features of the second category. In principle, realism inconsistency theory can explain not only negative evaluations of transitions between real and computer modeled humans but also between different vertebrate species.

Marmosets: a promising model for probing the neural mechanisms underlying complex visual networks such as the frontal-parietal network.

Abstract: The technology, methodology and models used by visual neuroscientists have provided great insights into the structure and function of individual brain areas. However, complex cognitive functions arise in the brain due to networks comprising multiple interacting cortical areas that are wired together with precise anatomical connections. A prime example of this phenomenon is the frontal-parietal network and two key regions within it: the frontal eye fields (FEF) and lateral intraparietal area (area LIP). Activity in these cortical areas has independently been tied to oculomotor control, motor preparation, visual attention and decision-making. Strong, bidirectional anatomical connections have also been traced between FEF and area LIP, suggesting that the aforementioned visual functions depend on these inter-area interactions. However, advancements in our knowledge about the interactions between area LIP and FEF are limited with the main animal model, the rhesus macaque, because these key regions are buried in the sulci of the brain. In this review, we propose that the common marmoset is the ideal model for investigating how anatomical connections give rise to functionally-complex cognitive visual behaviours, such as those modulated by the frontal-parietal network, because of the homology of their cortical networks with humans and macaques, amenability to transgenic technology, and rich behavioural repertoire. Furthermore, the lissencephalic structure of the marmoset brain enables application of powerful techniques, such as array-based electrophysiology and optogenetics, which are critical to bridge the gaps in our knowledge about structure and function in the brain.

Gaze following requires early visual experience

Abstract: Significance Early in life, humans spontaneously learn to extract complex visual information without external guidance. Current vision models fail to replicate such learning, relying instead on extensive supervision. A classic example is gaze understanding, an early-learned skill useful for joint attention and social interaction. We studied gaze understanding in children who recovered from early-onset near-complete blindness through late cataract surgery. Following treatment, they acquired sufficient visual acuity for detailed pattern recognition, but they failed to develop automatic gaze following. Our computational modeling suggests that their learning is severely limited due to reduced availability of internal self-supervision mechanisms, which guide learning in normal development. The results have implications to understanding natural visual learning, potential rehabilitation, and obtaining unsupervised learning in vision models.