Ghost Condition Research Articles

Are there dedicated neural mechanisms for imitation? A study of grist and mills.

Are there brain regions that are specialized for the execution of imitative actions? We compared two hypotheses of imitation: the mirror neuron system (MNS) hypothesis predicts frontal and parietal engagement which is specific to imitation, while the Grist-Mills hypothesis predicts no difference in brain activation between imitative and matched non-imitative actions. Our delayed imitation fMRI paradigm included two tasks, one where correct performance was defined by a spatial rule and another where it was defined by an item-based rule. For each task, participants could learn a sequence from a video of a human hand performing the task, from a matched "Ghost" condition, or from text instructions. When participants executed actions after seeing the Hand demonstration (compared to Ghost and Text demonstrations), no activation differences occurred in frontal or parietal regions; rather, activation was localized primarily to occipital cortex. This adds to a growing body of evidence which indicates that imitation-specific responses during action execution do not occur in canonical mirror regions, contradicting the mirror neuron system hypothesis. However, activation differences did occur between action execution in the Hand and Ghost conditions outside MNS regions, which runs counter to the Grist-Mills hypothesis. We conclude that researchers should look beyond these hypotheses as well as classical MNS regions to describe the ways in which imitative actions are implemented by the brain.

Varieties of social learning in children: Characterizing the development of imitation, goal emulation and affordance learning within subjects and tasks

Children’s social learning (SL) is characterized by significant variation. Explaining when and why children excel in some SL problems but not others is an unappreciated but significant problem in the developmental sciences. Here, two studies explore different forms of SL in preschoolers (3–6 years) using two tablet-based tasks, Cognitive and Spatial. These tasks involve sequencing items by their identity (e.g., Apple→Boy→Cat) or spatial location (e.g., Top→Bottom→Right). Experiment 1 (n = 189) explored children’s ability to learn different sequences by individual—trial-and-error—learning (baseline), recalling these individually learned sequences after a brief delay (recall), copying a novel sequence following a demonstration (novel imitation), and copying a familiar sequence that had been previously learned by trial and error (familiar imitation). Experiment 2 (n = 99) measured novel imitation and individual recall in addition to children’s ability to learn different sequences from a model’s mistake (goal emulation) and from physical/symbolic feedback provided automatically by a tablet (i.e., ghost condition). Results showed that familiar imitation and goal emulation developed early across tasks. Whereas novel imitation and ghost (affordance) learning developed late. An exploration of the dimensionality of these skills showed that imitation (Exp. 1), whether familiar or novel, was domain-specific. In contrast, emulation (Exp. 2) was multi-dimensional in the Spatial Task but unidimensional in the Cognitive Task. These results highlight the mosaic nature of children’s SL development. Results provide a model for explaining some of the observed variation in children’s performance across task and research paradigms. This information can be used to better predict when and why children are likely to succeed (or fail) in SL tasks.

Translating visual information into action predictions: Statistical learning in action and nonaction contexts.

Humans are sensitive to the statistical regularities in action sequences carried out by others. In the present eyetracking study, we investigated whether this sensitivity can support the prediction of upcoming actions when observing unfamiliar action sequences. In two between-subjects conditions, we examined whether observers would be more sensitive to statistical regularities in sequences performed by a human agent versus self-propelled 'ghost' events. Secondly, we investigated whether regularities are learned better when they are associated with contingent effects. Both implicit and explicit measures of learning were compared between agent and ghost conditions. Implicit learning was measured via predictive eye movements to upcoming actions or events, and explicit learning was measured via both uninstructed reproduction of the action sequences and verbal reports of the regularities. The findings revealed that participants, regardless of condition, readily learned the regularities and made correct predictive eye movements to upcoming events during online observation. However, different patterns of explicit-learning outcomes emerged following observation: Participants were most likely to re-create the sequence regularities and to verbally report them when they had observed an actor create a contingent effect. These results suggest that the shift from implicit predictions to explicit knowledge of what has been learned is facilitated when observers perceive another agent's actions and when these actions cause effects. These findings are discussed with respect to the potential role of the motor system in modulating how statistical regularities are learned and used to modify behavior.

Stability of singularity-free cosmological solutions in Hořava-Lifshitz gravity

We study stability of singularity-free cosmological solutions with positive cosmological constant based on projectable Ho\v{r}ava-Lifshitz (HL) theory. In HL theory, the isotropic and homogeneous cosmological solutions with bounce can be realized if spacial curvature is non-zero. By performing perturbation analysis around non-flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime, we derive a quadratic action and discuss the stability, i.e, ghost and tachyon-free conditions. Although the squared effective mass of scalar perturbation must be negative in infrared regime, we can avoid tachyon instability by considering strong Hubble friction. Additionally, we estimate the backreaction from the perturbations on background geometry, especially, against anisotropic perturbation in closed FLRW spacetime. It turns out that certain types of bouncing solution may be spoiled even if all perturbation modes are stable.

Toddlers’ action prediction: Statistical learning of continuous action sequences

The current eye-tracking study investigated whether toddlers use statistical information to make anticipatory eye movements while observing continuous action sequences. In two conditions, 19-month-old participants watched either a person performing an action sequence (Agent condition) or a self-propelled visual event sequence (Ghost condition). Both sequences featured a statistical structure in which certain action pairs occurred with deterministic transitional probabilities. Toddlers learned the transitional probabilities between the action steps of the deterministic action pairs and made predictive fixations to the location of the next action in the Agent condition but not in the Ghost condition. These findings suggest that young toddlers gain unique information from the statistical structure contained within action sequences and are able to successfully predict upcoming action steps based on this acquired knowledge. Furthermore, predictive gaze behavior was correlated with reproduction of sequential actions following exposure to statistical regularities. This study extends previous developmental work by showing that statistical learning can guide the emergence of anticipatory eye movements during observation of continuous action sequences.

The Ghost in the Touchscreen: Social Scaffolds Promote Learning by Toddlers.

This study examined the effect of a "ghost" demonstration on toddlers' imitation. In the ghost condition, virtual pieces moved to make a fish or boat puzzle. Fifty-two 2.5- and 3-year-olds were tested on a touchscreen (no transfer) or with 3D pieces (transfer); children tested with 3D pieces scored above a no demonstration baseline, but children tested on the touchscreen did not. Practice on the touchscreen (n=23) by 2.5- and 3-year-olds prior to the ghost demonstration did not improve performance. Finally, children who learned the puzzle task via a social demonstration and were tested on the touchscreen (n=26) performed better than the ghost conditions. Taken together, these studies demonstrate that social demonstrations enhance learning from novel touchscreen tools during early childhood.

Competition and cooperation with virtual players in an exergame

Two cross-sectional studies investigated the effects of competition and cooperation with virtual players on exercise performance in an immersive Virtual reality (VR) cycle exergame. Study 1 examined the effects of: (1) self-competition whereby participants played the exergame while competing against a replay of their previous exergame session (Ghost condition), and (2) playing the exergame with a virtual trainer present (Trainer condition) on distance travelled and calories expended while cycling. Study 2 examined the effects of (1) competition with a virtual trainer system (Competitive condition) and (2) cooperation with a virtual trainer system (Cooperative condition). Post exergame enjoyment and motivation were also assessed.The results of Study 1 showed that the trainer system elicited a lesser distance travelled than when playing with a ghost or on one’s own. These results also showed that competing against a ghost was more enjoyable than playing on one’s own or with the virtual trainer. There was no significant difference between the participants’ rated enjoyment and motivation and their distance travelled or calories burned. The findings of Study 2 showed that the competitive trainer elicited a greater distance travelled and caloric expenditure, and was rated as more motivating. As in Study 1, enjoyment and motivation were not correlated with distance travelled and calories burned.ConclusionTaken together, these results demonstrate that a competitive experience in exergaming is an effective tool to elicit higher levels of exercise from the user, and can be achieved through virtual substitutes for another human player.

Observational learning of tool use in children: Investigating cultural spread through diffusion chains and learning mechanisms through ghost displays

In the first of two experiments, we demonstrate the spread of a novel form of tool use across 20 “cultural generations” of child-to-child transmission. An experimentally seeded technique spread with 100% fidelity along twice as many “generations” as has been investigated in recent exploratory “diffusion” experiments of this type. This contrasted with only a single child discovering the technique spontaneously in a comparable group tested individually without any model. This study accordingly documents children’s social learning of tool use on a new, population-level scale that characterizes real-world cultural phenomena. In a second experiment, underlying social learning processes were investigated with a focus on the contrast between imitation (defined as copying actions) and emulation (defined as learning from the results of actions only). In two different “ghost” conditions, children were presented with the task used in the first experiment but now operated without sight of an agent performing the task, thereby presenting only the information used in emulation. Children in ghost conditions were less successful than those who had watched a model in action and showed variable matching to what they had seen. These findings suggest the importance of observational learning of complex tool use through imitation rather than only through emulation. Results of the two experiments are compared with those of similar experiments conducted previously with chimpanzees and are discussed in relation to the wider perspective of human culture and the influence of task complexity on social learning.

Newtonian limit of nonlocal cosmology

We study the consequences of the $f(R/\ensuremath{\square})$ gravity models for the Solar System and the large-scale structure of the Universe. The spherically symmetric solutions can be used to obtain bounds on the constant and the linear parts of the correction terms. The evolution of cosmological matter structures is shown to be governed by an effectively time-dependent Newton's constant. We also analyze the propagation of the perturbation modes. Tensor and vector modes are only slightly modified, but two new scalar degrees of freedom are present. Their causality and stability is demonstrated, and their formal ghost conditions are related to a singularity of the cosmological background. In general, the Newtonian limit of these models has no apparent conflicts with observations but can provide useful constraints.

Observational learning in chimpanzees and children studied through ‘ghost’ conditions

Emulation has been distinguished from imitation as a form of observational learning because it focuses not on the model's actions but on the action's environmental results. Whether a species emulates, imitates or displays only simpler observational learning is expected to have profound implications for its capacity for cultural transmission. Chimpanzees' observational learning has been suggested to be primarily emulative, but this is an inference largely based upon low fidelity copying in experiments when comparing chimpanzees with humans rather than direct testing. Here we test directly for emulation learning by chimpanzees and children using a 'ghost' condition in which a sliding door obscuring a reward was moved to left or right with no agent visible, a context associated with the only published evidence for emulation learning in a non-human species (pigeons). Both children and chimpanzees matched the observed direction of ghost door movement on their first test trial. This is the first evidence for emulation in a non-human primate in the restricted context of a ghost condition. However, only the children continued to match in later trials. Individuals of both species continued to match with 99% or better fidelity when viewing a conspecific model operates the door. We conclude that chimpanzees can and will display emulation learning when the task is as simple as the present one, which contrasts with a failure to do so in a more complex manipulative task tested earlier. However, even with a simple task, emulation alone creates only fleeting fidelity compared with the opportunity to copy a conspecific, when considerable conformity is displayed.

Ghost conditions for Gauss–Bonnet cosmologies

We investigate the stability against inhomogeneous perturbations and the appearance of ghost modes in Gauss–Bonnet gravitational theories with a non-minimally coupled scalar field, which can be regarded as either the dilaton or a compactification modulus in the context of string theory. Through cosmological linear perturbations we extract four no-ghost and two sub-luminal constraint equations, written in terms of background quantities, which must be satisfied for consistency. We also argue that, for a general action with quadratic Riemann invariants, homogeneous and inhomogeneous perturbations are, in general, inequivalent, and that attractors in the phase space can have ghosts. These results are then generalized to a two-field configuration. Single-field models as candidates for dark energy are explored numerically and severe bounds on the parameter space of initial conditions are placed. A number of cases proposed in the literature are tested and most of them are found to be unstable or observationally unviable.

The ghost condition: imitation versus emulation in young children's observational learning.

Although observational learning by children may occur through imitating a modeler's actions, it can also occur through learning about an object's dynamic affordances--a process that M. Tomasello (1996) calls "emulation." The relative contributions of imitation and emulation within observational learning were examined in a study with 14- to 26-month-old children. The effectiveness of a "ghost" condition, in which the effective operation of the means apparatus was seen to occur without human agency, was compared with that of a standard modeling procedure in which the child saw an experimenter demonstrate the means action. The ghost condition was as likely to encourage observational learning as was the modeling condition; indeed, performance in the ghost condition was significantly better. The role of emulation in the development of observational learning is discussed in the context of a possible form of goal directedness without agency.

Stability of the GRS model

We discuss the compatibility between the weaker energy condition and the stability of Gregory, Rubakov and Sibiryakov (GRS) model. Because the GRS spacetime violates the weak energy condition, it may cause the instability. In the GRS model, the four-dimensional gravity can be described by the massive KK modes with the resonance. Hence, instead of considering the weaker energy condition, we require for the stability of this model: no tachyon and no ghost condition for graviton modes ( h μν ). No tachyonic condition ( m 2 h ⩾0) is satisfied because the lowest state m h =0 is supersymmetric vacuum state. Further, no ghost state condition is achieved if one requires some relations for the matter source: 2 T 55= T μ μ =3( T 22+ T 33). It turns out that, although the GRS spacetime does not satisfy the weaker energy condition, it is stable against small perturbation.

Ghost cancellation for advanced compatible TV system using complementary sequences

An approach to ghost cancellation using complementary sequences as a ghost cancellation reference signal for channel characterization is discussed. The de-ghoster is implemented as two sections in cascade-a recursive or IIR section that uses estimates of the channel coefficients for cancellation of far post-ghosts followed by an FIR section that compensates for pre-ghosts and high-frequency roll-off of the received video. The de-ghoster architecture and algorithm are described in some detail and performance assessment of the system is provided for a representative sample of ghost conditions such as in-phase and quadrature ghosts and multiple near and far ghosts. >

Waveform equalization for EDTV systems using QAM

A modified waveform equalizer for a terrestrial QAM (quadrature amplitude modulation) transmission system that is tolerant against ghosts is described. In order to improve the performance of ghost and crosstalk reduction in the QAM subchannel, eight-field sequence reference signals, which are compatible with the GCR (ghost cancel reference) signal proposed by the BTA (Broadcasting Technology Association), and automatic gain control by a CPU are employed. Moreover, modified synchronous demodulation with automatic carrier phase control by a CPU is useful to upgrade (by about 5 dB under a heavy ghost condition) the equalization performance and to reduce the quadrature distortion of the subsignal. The crosstalk in the subchannel can be reduced to a level of 36-40 dB D/U. The QAM technology can be fully applied for terrestrial broadcasting even under significant ghost conditions. >