Effect Of Illusion Research Articles

Immediate effects of kinesthetic illusion induced by visual stimulation on ankle dorsiflexion dysfunction in stroke patients

Immediate effects of kinesthetic illusion induced by visual stimulation on ankle dorsiflexion dysfunction in stroke patients

Memory-guided saccades show effect of a perceptual illusion whereas visually guided saccades do not.

The double-drift stimulus (a drifting Gabor with orthogonal internal motion) generates a large discrepancy between its physical and perceived path. Surprisingly, saccades directed to the double-drift stimulus land along the physical, and not perceived, path (Lisi M, Cavanagh P. Curr Biol 25: 2535-2540, 2015). We asked whether memory-guided saccades exhibited the same dissociation from perception. Participants were asked to keep their gaze centered on a fixation dot while the double-drift stimulus moved back and forth on a linear path in the periphery. The offset of the fixation was the go signal to make a saccade to the target. In the visually guided saccade condition, the Gabor kept moving on its trajectory after the go signal but was removed once the saccade began. In the memory conditions, the Gabor disappeared before or at the same time as the go-signal (0- to 1,000-ms delay) and participants made a saccade to its remembered location. The results showed that visually guided saccades again targeted the physical rather than the perceived location. However, memory saccades, even with 0-ms delay, had landing positions shifted toward the perceived location. Our result shows that memory- and visually guided saccades are based on different spatial information. NEW & NOTEWORTHY We compared the effect of a perceptual illusion on two types of saccades, visually guided vs. memory-guided saccades, and found that whereas visually guided saccades were almost unaffected by the perceptual illusion, memory-guided saccades exhibited a strong effect of the illusion. Our result is the first evidence in the literature to show that visually and memory-guided saccades use different spatial representations.

Error correction and spatial generalization in human grasp control

The visual processes that support grasp planning are often studied by analyzing averaged kinematics of repeated movements, as in the literature on grasping and visual illusions. However, by recalibrating visuomotor mappings, the sensorimotor system can adjust motor outputs without changing visual processing, which complicates the interpretation of averaged behavior. We developed a dynamic model of grasp planning and adaptation that can explain why some studies find decrements in illusion effects on grasping while others do not. In two experiments, we tested grasping in a standard three-phase adaptation paradigm and analyzed adaptation aftereffects on the maximum grip aperture as well as the error correction parameters estimated by our model. Experiment 1 demonstrated that the model accounts for adaptive responses to positive and negative visual size perturbations. Experiment 2 supported the novel hypothesis that visuomotor mappings for grasp planning can compensate for opposing size perturbations when these perturbations are experienced in separate regions of space. Our findings serve to illustrate how the surprising flexibility of grasp adaptation can hide (especially in session-wise averages) the true effects of visual perturbations on the visual processes that drive grasp planning.

Visual Illusions Affect Motor Performance, But not Learning in Highly Skilled Shooters

Enhanced expectancies are an important component of OPTIMAL theory and are thought to contribute to motor performance and learning. There is limited information, however, on the generalizability of OPTIMAL theory to highly skilled individuals. The purpose of this study was to examine the effects of visual illusions, specifically an Ebbinghaus illusion, on the performance and learning of an aiming task using highly skilled 10-m rifle and pistol shooters. Two groups of shooters with international experience were recruited and practiced with perceived larger and smaller targets. Our results indicated that participants who perceived the target larger reported higher self-efficacy immediately after practice. In addition, these participants had higher shooting performance during practice. Our retention test (24 hours later), however, did not produce differences in self-efficacy or shooting performance. Our data suggests that visual illusions are beneficial for motor performance in highly skilled shooters, but may not affect learning in those who are in the latter stages of learning. Further studies should continue examining the role of visual illusions for enhancing expectancies in highly skilled and experienced performers.

Effects of aging on illusory target motion in a hitting task.

Age-related changes in multisensory integration (MSI, brain integration of multiple unisensory signals) were investigated. Accurate MSI is a key component of successful aging and crucial to perform activities of daily living (ADLs). Previous research suggests that with aging, different sources of sensory information are not properly weighted anymore. Twenty healthy younger (YA, age 18-34) and twenty-four healthy older adults (OA, age 60-82) were asked to hit discs moving downwards on a screen with their index finger. Illusory direction of motion was included (moving a checkerboard-like background either to the left or right). The discs disappeared before the screen was reached. Experimental conditions were: sitting (baseline), standing on foam (balance task), and sitting while doing a cognitive dual task (counting task). Participants hit the disc more to the right for left background motion compared to right background motion, conforming the illusory effect. OA show a larger effect of the illusion compared to YA in the baseline and balance conditions (p=.036 and p=.047, respectively). The same tendency was shown in the counting condition. Overall, background motion had a greater influence on the counting condition compared to the other conditions (p=.005 for YA and p=.009 for OA). No significant differences were found for the summed reaction and movement time, and no correlations between hitting performance and results of clinical pretests were found. We conclude that OA are more affected by the background motion than YA, which supports the idea that OA do not weigh information properly. Our finding that a cognitive dual task increases the illusion effect in both groups of participants suggests that cognitive resources are required for proper weighting, which may be a problem for OA. Future research will include OA with ADLs difficulties in order to develop a toolkit for early detection of MSI problems in the elderly population.

Does visuomotor adaptation contribute to illusion-resistant grasping?

Do illusory distortions of perceived object size influence how wide the hand is opened during a grasping movement? Many studies on this question have reported illusion-resistant grasping, but this finding has been contradicted by other studies showing that grasping movements and perceptual judgments are equally susceptible. One largely unexplored explanation for these contradictions is that illusion effects on grasping can be reduced with repeated movements. Using a visuomotor adaptation paradigm, we investigated whether an adaptation model could predict the time course of Ponzo illusion effects on grasping. Participants performed a series of trials in which they viewed a thin wooden target, manually reported an estimate of the target's length, then reached to grasp the target. Manual size estimates (MSEs) were clearly biased by the illusion, but maximum grip apertures (MGAs) of grasping movements were consistently accurate. Illusion-resistant MGAs were observed immediately upon presentation of the illusion, so there was no decrement in susceptibility for the adaptation model to explain. To determine whether online corrections based on visual feedback could have produced illusion-resistant MGAs, we performed an exploratory post hoc analysis of movement trajectories. Early portions of the illusion effect profile evolved as if they were biased by the illusion to the same magnitude as the perceptual responses (MSEs), but this bias was attenuated prior to the MGA. Overall, this preregistered study demonstrated that visuomotor adaptation of grasping is not the primary source of illusion resistance in closed-loop grasping.

P2-37. Effects of kinesthetic illusion induced by visual stimulus on the mu rhythm

Kinesthetic illusion can be induced by observing repetitive movements of a particular body part from the first-person point-of-view; this is called KiNvis (kinesthetic illusion induced by visual stimulus). The purpose of the present study was to elucidate the characteristics of electroencephalogram (EEG) oscillations in sensorimotor area during KiNvis. We focused on the mu rhythm, typically oscillating at a frequency of 8–13 Hz and attenuated by the various motor processes. Seven healthy subjects participated in this study. Before EEG measurement, KiNvis was induced in all the participants during several days of training. Experimental conditions included motor execution of the right wrist flexion, motor imagery, KiNvis, and motor observation (observing the same movie as during KiNVIS; however, the screen position was placed anatomically incongruent). EEG signal was recorded from the left sensorimotor area during each condition. EEG spectra were estimated using fast Fourier transformation. The power of the mu rhythm during KiNvis, motor execution, and motor imagery significantly suppressed to be lower than that during motor observation respectively. These findings suggest that suppression effect of KiNvis on the mu rhythm was larger than simple motor observation, and was not inferior to motor imagery and motor execution.

Effects of Lip Color on Perceived Lightness of Human Facial Skin.

Whereas geometric illusions in human faces have been reported by several studies, illusions of color or lightness in faces have seldom been explored. Here, we psychophysically investigated whether lip color influences facial skin’s perceived lightness. Results of Experiment 1 demonstrated that redder lips lightened and darker lips darkened the perceived complexion. These lightness or darkness inducing effects differ from the classical illusion of lightness contrast in nonface objects for two reasons. First, illusory effects are more assimilative than contrastive. Second, the inducing area (i.e., lips) is much smaller than the influenced area (facial skin). Experiment 2 showed that the assimilative lightness induction was caused by holistic processing of faces. This is the first study to scientifically substantiate the claim of cosmetics manufacturers and makeup artists that lip colors can alter perceived facial skin color. Implications for face perception, lightness illusion, and perceptual effects of cosmetics are discussed.

Optimized microwave illusion device

We report the design, fabrication and experimental verification of an illusion device working at microwave frequencies. A two dimensional topology optimization procedure is employed to find the binary layout of a dielectric coating that, when wrapped around a metallic cylinder, mimics the scattering from a predefined, arbitrarily-shaped dielectric object. Fabrication is carried out with 3D-printing and spatially resolved near field measurements in a waveguide configuration were performed, allowing us to map the illusion effect. Our work provides general guidelines for engineering electromagnetic illusions but can be extended to shape the near and far-field radiations using low index isotropic materials.

Adaptation effects in grasping the Müller-Lyer illusion

Recent results have shown that effects of pictorial illusions in grasping may decrease over the course of an experiment. This can be explained as an effect of sensorimotor learning if we consider a pictorial size illusion as simply a perturbation of visually perceived size. However, some studies have reported very constant illusion effects over trials. In the present paper, we apply an error-correction model of adaptation to experimental data of N=40 participants grasping the Müller-Lyer illusion. Specifically, participants grasped targets embedded in incremental and decremental Müller-Lyer illusion displays in (1) the same block in pseudo-randomised order, and (2) separate blocks of only one type of illusion each. Consistent with predictions of our model, we found an effect of interference between the two types when they were presented intermixed, explaining why adaptation rates may vary depending on the experimental design. We also systematically varied the number of object sizes per block, which turned out to have no effect on the rate of adaptation. This was also in accordance with our model. We discuss implications for the illusion literature, and lay out how error-correction models can explain perception-action dissociations in some, but not all grasping-of-illusion paradigms in a parsimonious and plausible way, without assuming different illusion effects.

The Effects of Optical Illusions in Perception and Action in Peripersonal and Extrapersonal Space

While the two visual system hypothesis tells a fairly compelling story about perception and action in peripersonal space (i.e., within arm's reach), its validity for extrapersonal space is very limited and highly controversial. Hence, the present purpose was to assess whether perception and action differences in peripersonal space hold in extrapersonal space and are modulated by the same factors. To this end, the effects of an optic illusion in perception and action in both peripersonal and extrapersonal space were compared in three groups that threw balls toward a target at a distance under different target eccentricity (i.e., with the target fixated and in peripheral field), viewing (i.e., binocular and monocular viewing), and delay conditions (i.e., immediate and delayed action). The illusory bias was smaller in action than in perception in peripersonal space, but this difference was significantly reduced in extrapersonal space, primarily because of a weakening bias in perception. No systematic modulation of target eccentricity, viewing, and delay arose. The findings suggest that the two visual system hypothesis is also valid for extra personal space.

The neuronal correlates of mirror illusion in children with spastic hemiparesis: a study with functional magnetic resonance imaging.

To investigate the neuronal activation pattern underlying the effects of mirror illusion in children/adolescents with normal motor development and in children/adolescents with hemiparesis and preserved contralateral corticospinal organisation. The type of cortical reorganisation was classified according to results of transcranial magnetic stimulation. Only subjects with congenital lesions and physiological contralateral cortical reorganisation were included. Functional magnetic resonance imaging was performed to investigate neuronal activation patterns with and without a mirror box. Each test consisted of a unimanual and a bimanual motor task. Seven children/adolescents with congenital hemiparesis (10-20 years old, three boys and four girls) and seven healthy subjects (8-17 years old, four boys and three girls) participated in this study. In the bimanual experiment, children with hemiparesis showed a significant effect of the mirror illusion (p<0.001 at voxel level, family-wise error corrected at cluster level) in the dorsolateral prefrontal cortex and anterior cingulate cortex of the affected and unaffected hemispheres, respectively. No significant effects of the mirror illusion were observed in unimanual experiments and in healthy participants. Mirror illusion in children/adolescents with hemiparesis leads to activation of brain areas involved in visual conflict detection and cognitive control to resolve this conflict. This effect is observed only in bimanual training. We consider that for mirror therapy in children and adolescents with hemiparesis a bimanual approach is more suitable than a unimanual approach.

Iluze kauzality a nadměrná důvěra ve schopnost predikce (kvazi)náhodných finančních událostí

We argue that individuals systematically interpret sequences of events in a causal manner. The aim of this article is to show that people do so even if they are aware of the stochastic nature of the respective sequence. The bias can explain some anomalous behaviour of investors in financial markets. Small as well as professional investors may illusorily perceive causality of former random success and future yield. Laboratory experiments testing the interpretation of stochastically occurring events in financial designs as well as analyses of real trading data from financial markets confirm that investors indeed interpret (quasi)random events casually; they make incorrect predictions and they egocentrically allocate responsibility for their success. The causality illusion induces overconfidence, inefficient investment and risk seeking. In the conclusion, we discuss factors that may limit effects of the causality illusion and suggest future areas for research.

Haptic feedback attenuates illusory bias in pantomime-grasping: evidence for a visuo-haptic calibration.

Relative visual information has been shown to mediate grasping responses directed to an area previously occupied by a target object (i.e., pantomime-grasping) and is an information type functionally distinct from the absolute visual information supporting naturalistic grasping (i.e., grasping a physical target). Pantomime- and naturalistic grasps differ not only in terms of their visual properties, but also because the former lacks physical interaction with a target object (i.e., no-haptic feedback). The absence of haptic feedback may represent a reason why pantomime- and naturalistic grasps differ. To address this issue, participants completed pantomime-grasps to objects embedded in fins-in and fins-out configurations of the Müller-Lyer (ML) illusion following a 2000-ms visual delay when haptic feedback was unavailable (H- condition), and when experimentally induced (H+ condition). In particular, in the H+ condition the experimenter placed a physical target object between participants' thumb and forefinger after they completed their grasping response. H- and H+ conditions were performed when online vision was available (i.e., Experiment 1) and when withdrawn (i.e., Experiment 2). If haptic feedback influences grasping, then the absolute information afforded from physically touching a target object (i.e., the H+ condition) should result in aperture metrics that are refractory-or attenuated-to the relative properties of the ML figures. Grip apertures in H- and H+ conditions were "tricked" in a direction consistent with the perceptual effects of the ML illusion; however, Experiment 2 showed that illusory effects were attenuated in the H+ condition. In other words, responses without online vision showed evidence of a visuo-haptic calibration. These results provide convergent evidence that haptic and visual feedback play a salient role in considering the extant literature's documented report of kinematic differences between pantomime- and naturalistic grasps.

Interaction of Perception and Action in Discrete and Continuous Rapid Aiming Tasks

ABSTRACTPreviously, we have shown that discrete and continuous rapid aiming tasks are governed by distinct visuomotor control mechanisms by assessing the combined visual illusion effects on the perceived and effective index of difficulty (ID). All participants were perceptually biased by the combined visual illusion before they performed the rapid aiming tasks. In the current study, the authors manipulated the order of performing perceptual and motor tasks to examine whether perceptual or motor experience with the illusory visual target would influence the subsequent perceived and effective ID in discrete and continuous tapping tasks. The results supported our hypothesis showing that perceptual experience with the illusory visual target in the discrete condition reduced the effective ID in the subsequent discrete tapping task, and motor experience with the illusory visual target in the continuous condition reduced the illusion effects on the perceived ID in the subsequent perceptual judgment task. The study demonstrates the coinfluence of perception and action, and suggests that perception and action influence one another with different magnitude depending on the spatial frame of reference used to perform the perceptuomotor task.

The Mirror Illusion Increases Motor Cortex Excitability in Children With and Without Hemiparesis

Background. Mirror therapy provides a visual illusion of a normal moving limb by using the mirror reflection of the unaffected arm instead of viewing the paretic limb and is used in rehabilitation to improve hand function. Little is known about the mechanism underlying its effect in children with hemiparesis. Objective. To investigate the effect of the mirror illusion (MI) on the excitability of the primary motor cortex (M1) in children and adolescents. Methods. Twelve patients with hemiparesis (10-20 years) and 8 typically developing subjects (8-17 years) participated. Corticospinal reorganization was classified as contralateral (projection from contralateral hemisphere to affected hand) or ipsilateral (projection from ipsilateral hemisphere to affected hand). M1 excitability of the hemisphere projecting to the affected (nondominant in typically developing subjects) hand was obtained during 2 different conditions using single-pulse transcranial magnetic stimulation (TMS). Each condition (without/with mirror) consisted of a unimanual and a bimanual task. Motor-evoked potentials (MEPs) were recorded from the abductor pollicis brevis and flexor digitorum superficialis muscles. Results. MEP amplitudes were significantly increased during the mirror condition (P = .005) in typically developing subjects and in patients with contralateral reorganization. No significant effect of MI was found in subjects with ipsilateral reorganization. MI increased M1 excitability during active movements only. This increase was not correlated to hand function. Conclusion. MI increases the excitability of M1 in hemiparetic patients with contralateral corticospinal organization and in typically developing subjects. This finding provides neurophysiological evidence supporting the application of mirror therapy in selected children and adolescents with hemiparesis.

Three-dimensional broadband acoustic illusion cloak for sound-hard boundaries of curved geometry.

Acoustic illusion cloaks that create illusion effects by changing the scattered wave have many potential applications in a variety of scenarios. However, the experimental realization of generating three-dimensional (3D) acoustic illusions under detection of broadband signals still remains challenging despite the paramount importance for practical applications. Here we report the design and experimental demonstration of a 3D broadband cloak that can effectively manipulate the scattered field to generate the desired illusion effect near curved boundaries. The designed cloak simply comprises positive-index anisotropic materials, with parameters completely independent of either the cloaked object or the boundary. With the ability of manipulating the scattered field in 3D space and flexibility of applying to arbitrary geometries, our method may take a major step toward the real world application of acoustic cloaks and offer the possibilities of building advanced acoustic devices with versatile functionalities.

The Effect of Fiscal Illusion on Public Sector Financial Management

An important concern to the efficiency of public finance systems is that voters may suffer from various “fiscal illusions” that can be exploited by politicians to grow the public sector. This article contributes evidence on the specific public financial management mechanisms by associating the impact property reassessments have on the “visibility” of budget size signaled by property tax rates. Using data from Virginia cities and counties from 2001 to 2011, the results indicate mass reappraisals, which reduce property tax visibility cause contemporaneous property tax levy increases, as do reappraisals that increase future tax visibility. These revenue shocks are then smoothed into expenditures through the management of assets, indicating policy makers prefer the spending to be drawn from future cash reserves than immediate projects that might draw attention to the source of fiscal illusion.

Inflation Illusion, Expertise and Commercial Real Estate

Data from the National Council of Real Estate Investment Fiduciaries (NCREIF) provide a unique setting to examine the inflation illusion hypothesis. NCREIF provides appraisal-based and transaction-based return series allowing comparison of market participants with specific valuation expertise to general market participants. Results using the appraisal-based indices indicate that the mispricing term is not statistically significantly related to expected inflation, which suggests that commercial valuers do not suffer from inflation illusion. Interestingly, results based on the investor oriented transaction-based indices show that the mispricing term is inversely related to expected inflation and that mispricing plays an important role in determining the long-term discount rate. These results are robust across different empirical specifications, inflation data and subsamples by property type. The comprehensive findings suggest that the inflation illusion effect in direct investment in real estate differs from securitized markets. This study further adds to the general literature regarding the impact of inflation illusion on asset markets by showing that experienced participants may not suffer from inflation illusion which suggests that 1) novice participants may be driving its appearance and 2) experience and training mitigate this bias.

Cortical processes of speech illusions in the general population.

BackgroundThere is evidence that experimentally elicited auditory illusions in the general population index risk for psychotic symptoms. As little is known about underlying cortical mechanisms of auditory illusions, an experiment was conducted to analyze processing of auditory illusions in a general population sample. In a follow-up design with two measurement moments (baseline and 6 months), participants (n = 83) underwent the White Noise task under simultaneous recording with a 14-lead EEG. An auditory illusion was defined as hearing any speech in a sound fragment containing white noise.ResultsA total number of 256 speech illusions (SI) were observed over the two measurements, with a high degree of stability of SI over time. There were 7 main effects of speech illusion on the EEG alpha band—the most significant indicating a decrease in activity at T3 (t = −4.05). Other EEG frequency bands (slow beta, fast beta, gamma, delta, theta) showed no significant associations with SI.ConclusionSIs are characterized by reduced alpha activity in non-clinical populations. Given the association of SIs with psychosis, follow-up research is required to examine the possibility of reduced alpha activity mediating SIs in high risk and symptomatic populations.