The perception of silence.

Auditory perception is traditionally conceived as the perception of sounds-a friend's voice, a clap of thunder, a minor chord. However, daily life also seems to present us with experiences characterized by the absence of sound-a moment of silence, a gap between thunderclaps, the hush after a musical performance. In these cases, do we positively hear silence? Or do we just fail to hear, and merely judge or infer that it is silent? This longstanding question remains controversial in both the philosophy and science of perception, with prominent theories holding that sounds are the only objects of auditory experience and thus that our encounter with silence is cognitive, not perceptual. However, this debate has largely remained theoretical, without a key empirical test. Here, we introduce an empirical approach to this theoretical dispute, presenting experimental evidence that silence can be genuinely perceived (not just cognitively inferred). We ask whether silences can "substitute" for sounds in event-based auditory illusions-empirical signatures of auditory event representation in which auditory events distort perceived duration. Seven experiments introduce three "silence illusions"-the one-silence-is-more illusion, silence-based warping, and the oddball-silence illusion-each adapted from a prominent perceptual illusion previously thought to arise only from sounds. Subjects were immersed in ambient noise interrupted by silences structurally identical to the sounds in the original illusions. In all cases, silences elicited temporal distortions perfectly analogous to the illusions produced by sounds. Our results suggest that silence is truly heard, not merely inferred, introducing a general approach for studying the perception of absence.

Perceptual axioms are irreconcilable with Euclidean geometry.

There are different definitions of axioms, but the one that seems to have general approval is that axioms are statements whose truths are universally accepted but cannot be proven; they are the foundation from which further propositional truths are derived. Previous attempts, led by David Hilbert, to show that all of mathematics can be built into an axiomatic system that is complete and consistent failed when Kurt Gödel proved that there will always be statements which are known to be true but can never be proven within the same axiomatic system. But Gödel and his followers took no account of brain mechanisms that generate and mediate logic. In this largely theoretical paper, but backed by previous experiments and our new ones reported below, we show that in the case of so-called 'optical illusions', there exists a significant and irreconcilable difference between their visual perception and their description according to Euclidean geometry; when participants are asked to adjust, from an initial randomised state, the perceptual geometric axioms to conform to the Euclidean description, the two never match, although the degree of mismatch varies between individuals. These results provide evidence that perceptual axioms, or statements known to be perceptually true, cannot be described mathematically. Thus, the logic of the visual perceptual system is irreconcilable with the cognitive (mathematical) system and cannot be updated even when knowledge of the difference between the two is available. Hence, no one brain reality is more 'objective' than any other.

The Motion-Silencing Illusion Depends on Object-Centered Representation.

Motion silencing is a striking and unexplained visual illusion wherein changes that are otherwise salient become difficult to perceive when the changing elements also move. We develop a new method for quantifying illusion strength (Experiments 1a and 1b), and we demonstrate a privileged role for rotational motion on illusion strength compared with highly controlled stimuli that lack rotation (Experiments 2a to 3b). These contrasts make it difficult to explain the illusion in terms of lower-level detection limits. Instead, we explain the illusion as a failure to attribute changes to locations. Rotation exacerbates the illusion because its perception relies upon structured object representations. This aggravates the difficulty of attributing changes by demanding that locations are referenced relative to both an object-internal frame and an external frame. Two final experiments (4a and 4b) add support to this account by employing a synchronously rotating external frame of reference that diminishes otherwise strong motion silencing. All participants were Johns Hopkins University undergraduates.

Clinical correlates of pareidolias and color discrimination deficits in idiopathic REM sleep behavior disorder and Parkinson's disease.

Visuoperceptual dysfunction is common in Parkinson's disease (PD) and is also reported in its prodromal phase, isolated REM sleep behavior disorder (iRBD). We aimed to investigate color discrimination ability and complex visual illusions known as pareidolias in patients with iRBD and PD compared to healthy controls, and their associating clinical factors. 46 iRBD, 43 PD, and 64 healthy controls performed the Farnsworth-Munsell 100 hue test and noise pareidolia tests. Any relationship between those two visual functions and associations with prodromal motor and non-motor manifestations were evaluated, including MDS-UPDRS part I to III, Cross-Cultural Smell Identification Test, sleep questionnaires, and comprehensive neuropsychological assessment. iRBD and PD patients both performed worse on the Farnsworth-Munsell 100 hue test and had greater number of pareidolias compared to healthy controls. No correlations were found between the extent of impaired color discrimination and pareidolia scores in either group. In iRBD patients, pareidolias were associated with frontal executive dysfunction, while impaired color discrimination was associated with visuospatial dysfunction, hyposmia, and higher MDS-UPDRS-III scores. Pareidolias in PD patients correlated with worse global cognition, whereas color discrimination deficits were associated with frontal executive dysfunction. Color discrimination deficits and pareidolias are frequent but does not correlate with each other from prodromal to clinically established stage of PD. The different pattern of clinical associates with the two visual symptoms suggests that evaluation of both color and pareidolias may aid in revealing the course of neurodegeneration in iRBD and PD patients.

Multisensory processing and proprioceptive plasticity during resizing illusions.

Bodily resizing illusions typically use visual and/or tactile inputs to produce a vivid experience of one's body changing size. Naturalistic auditory input (an input that reflects the natural sounds of a stimulus) has been used to increase illusory experience during the rubber hand illusion, whilst non-naturalistic auditory input can influence estimations of finger length. We aimed to use a non-naturalistic auditory input during a hand-based resizing illusion using augmented reality, to assess whether the addition of an auditory input would increase both subjective illusion strength and measures of performance-based tasks. Forty-four participants completed the following three conditions: no finger stretching, finger stretching without tactile feedback and finger stretching with tactile feedback. Half of the participants had an auditory input throughout all the conditions, whilst the other half did not. After each condition, the participants were given one of the following three performance tasks: stimulated (right) hand dot touch task, non-stimulated (left) hand dot touch task, and a ruler judgement task. Dot tasks involved participants reaching for the location of a virtual dot, whereas the ruler task concerned estimates of the participant's own finger on a ruler whilst the hand was hidden from view. After all trials, the participants completed a questionnaire capturing subjective illusion strength. The addition of auditory input increased subjective illusion strength for manipulations without tactile feedback but not those with tactile feedback. No facilitatory effects of audio were found for any performance task. We conclude that adding auditory input to illusory finger stretching increased subjective illusory experience in the absence of tactile feedback but did not affect performance-based measures.

Winning Exposure and Positive Illusions Among Chinese Lottery Gamblers: Moderating Effects of Lottery Winning Experience and Socioeconomic Status.

Positive illusions and winning exposure are key factors leading to problem lottery gambling, but few studies have examined the relationships between them. 402 Chinese lottery gamblers was conducted with the Winning Exposure Questionnaire, the Positive illusion Questionnaire, the Winning Experience Questionnaire, and the Social and Economic Status Questionnaire to investigate the relationship between winning exposure and positive illusions as well as the moderating role of winning experience and socioeconomic status. The results showed that winning exposure can significantly and positively predict the positive illusions (optimism bias, better than average bias, and illusion of control) of lottery gamblers. The highest winning amount and subjective socioeconomic status significantly moderated the relationship between winning exposure and optimism bias. That was to say, for lottery gamblers with smaller maximum winning amount and lower subjective socioeconomic status, the association between winning exposure and optimism bias was stronger. Furthermore, the moderating effect of highest winning amount in the relationship between winning exposure and better than average bias, and the moderating effects of occupational status and subjective socioeconomic status in the relationship between winning exposure and illusion of control were marginally significant.

Neural networks underlying visual illusions: An activation likelihood estimation meta-analysis.

Visual illusions have long been used to study visual perception and contextual integration. Neuroimaging studies employ illusions to identify the brain regions involved in visual perception and how they interact. We conducted an Activation Likelihood Estimation (ALE) meta-analysis and meta-analytic connectivity modeling on fMRI studies using static and motion illusions to reveal the neural signatures of illusory processing and to investigate the degree to which different areas are commonly recruited in perceptual inference. The resulting networks encompass ventral and dorsal regions, including the inferior and middle occipital cortices bilaterally in both types of illusions. The static and motion illusion networks selectively included the right posterior parietal cortex and the ventral premotor cortex respectively. Overall, these results describe a network of areas crucially involved in perceptual inference relying on feed-back and feed-forward interactions between areas of the ventral and dorsal visual pathways. The same network is proposed to be involved in hallucinogenic symptoms characteristic of schizophrenia and other disorders, with crucial implications in the use of illusions as biomarkers.

Strange face illusions: A systematic review and quality analysis.

BACKGROUND: Strange face illusions describe a range of visual apparitions that occur when an observer gazes at their image reflected in a mirror or at another person's face in a dimly lit room. The illusory effects range from mild alterations in colour, or contrast, to the perception of distorted facial features, or new strange faces.The current review critically evaluates studies investigating strange face illusions, their methodological quality, and existing interpretations. METHOD: Searches conducted using Scopus, PubMed, ScienceDirect and the grey literature until June 2022 identified 21 studies (N = 1,132; healthy participants n = 1,042; clinical participants n = 90) meeting the inclusion criteria (i.e., providing new empirical evidence relating to strange face illusions). The total sample had a mean age of 28.3 years (SD = 10.31) and two thirds (67 %) of participants tested to date are female. Results are reported using the Preferred Reporting Items for Systematic Reviews and meta-Analyses (PRISMA) guidelines. The review was preregistered at the Open Science Framework (OSF: https://osf.io/ek48d). RESULTS: Pooling data across studies, illusory new strange faces are experienced by 58% (95%CI 48 to 68) of nonclinical participants. Study quality as assessed by the Appraisal Tool for Cross-Sectional Studies (AXIS) revealed that 3/21 (14.28%) studies were rated as high, 9/21 (42.86%) as moderate and 9/21 (42.86%) as low quality. Whilst the items relating specifically to reporting quality scored quite highly, those relating to study design and possible biases were lower and more variable. Overall, study quality accounted for 87% of the variance in reporting rates for strange faces, with higher quality being associated with lower illusion rates. The prevalence of illusions was also significantly greater in samples that were older, had higher proportions of female participants and for the interpersonal dyad (IGDT) compared to the mirror gaze paradigm (MGT). The moderating impact of study quality persisted in a multiple meta-regression involving participant age, paradigm type (IGDT vs MGT) and level of feature distortion. Our review point to the importance of reduced light levels, face stimuli and prolonged eye fixation for strange face illusions to emerge. CONCLUSION: Strange face illusions reliably occur in both mirror-gazing and interpersonal gazing dyad paradigms. Further research of higher quality is required to establish the prevalence and particularly, the mechanisms underpinning strange face illusions.

The effects of estradiol levels on crossmodal perception: a study on the sound induced flash illusion in healthy and menstrually related migraine individuals.

OBJECTIVE: The sound-induced flash illusion (SIFI) is a valid paradigm to study multisensorial perception. In the "fission" SIFI, multiple flashes are perceived when observing a single flash paired with two or more beeps. SIFI is largely dependent on visual and acoustic cortex excitability; in migraine, dysfunctional cortical excitability affects SIFI perception. Since estrogen peak occurring during ovulation can increase neuronal excitability, the present study aims to verify whether cortical excitability shifts linked to the menstrual cycle could influence SIFI. METHODS: In a comparative prospective study, we tested the effect of estrogens on crossmodal perception using the SIFI. We recruited 27 females in reproductive age, including 16 healthy and 11 menstrually related migraine females, testing their proneness to SIFI on day 14 (high estradiol) and day 27 (low estradiol) of menstrual cycle. RESULTS: Women on day 14 reported less flashes than on day 27 (p = 0.02) in the fission illusion, suggesting a pro-excitatory effect of estradiol on visual cortex excitability during ovulation. Moreover, we confirmed that migraine women perceived less flashes (p = 0.001) than controls, independently from cycle phase. Non-migraineurs women significantly reported more flashes on day 27 than on day 14 (p = 0.04). CONCLUSIONS: This study suggests that estradiol may influence the multisensory perception due to changes of visual cortex excitability, with high estradiol peak leading to increased visual cortical sensitivity during ovulation in non-migraineurs. Visual cortex hyperresponsiveness, here reflected by reduced SIFI, is not influenced by estradiol fluctuations in migraine women, as shown by reduced fission effects on day 14 and 27.

Are dogs indeed susceptible to Kanizsa's triangle illusion?

Survival often depends on the ability of the visual system to process information accurately; thus, research demonstrating that a brain is susceptible to optical illusions is of considerable interest, particularly when the experiments involve phylogenetic comparisons. Are Lõoke et al.'s (Anim. Cogn, 25:43-51, 2022) data strong enough to allow the inclusion of dogs on the list of nonhumans that can perceive illusory Kanizsa figures?

Yes, dogs are susceptible to the Kanizsa's triangle illusion: A reply to Pepperberg.

A recent paper by Pepperberg, Learning & Behavior, 51, 5-6, (2023) enquires about the validity of the finding that dogs are susceptible to the Kanizsa's triangle illusion, reported by Lõoke and coauthors (Lõoke et al., Animal Cognition, 25, 43-51, 2022). Here we elaborate on the matter, providing both theoretical considerations and further data, supporting the soundness of our previous conclusions.

Mario Ponzo (1928) on perception of numerosity: A translation and commentary.

Ponzo is a familiar name in psychology because of the illusion that takes his name. He had a long and productive career in Italy, and some of his work was translated for international journals already in his lifetime. However, few of these papers are available in English. We provide a commentary that considers how his name came to be associated with an illusion he did not discover. We explain the content of several papers, some of which are often cited in a wrong context in the literature (i.e., papers on touch mentioned in relation to the Ponzo illusion). More importantly, we discuss his contribution to the study of perceived numerosity, and provide a full translation of his important 1928 paper, including a redrawing of its 28 illustrations.

The moderating role of early traumatic experiences on the association of schizotypal traits with visual perception.

The findings on the association of schizotypal traits with the perception of visual illusions are scarce and inconsistent and have not taken into consideration potential effects of childhood traumatic experiences, a risk factor for schizophrenia-spectrum conditions. Thus, the present study addressed the question of potential moderating effects of early traumatic experiences on the association between different aspects of schizotypal traits with the perception of the Müller-Lyer and Navon's Hierarchical Letters (NHL) illusions. The study revealed that (a) increased suspiciousness was associated with increased liability to the Müller-Lyer illusion, when the exposure to traumatic events was high, whereas the opposite pattern was true when the exposure to traumatic events was low; (b) negative schizotypy was associated with more accurate global perception, and high disorganized schizotypy was associated with superior accuracy when target letters were present during the NHL illusion, when early traumatic experiences were at lower levels; and (c) high negative, disorganized, and total schizotypy were associated with lower accuracy when target letters were present in the NHL paradigm, when early traumatic experiences were at higher levels. The findings of the study suggest that early traumatic events differentially moderate the relationship between various aspects of schizotypal traits and visual perceptual processing.

Positive illusions about dyadic perspective-taking as a moderator of the association between attachment insecurity and marital satisfaction.

Attachment insecurity (i.e., attachment anxiety or avoidance) puts people at risk for dissatisfying relationships. However, the dyadic regulation model of insecurity buffering suggests that an understanding and responsive partner may help insecure individuals to regulate emotions, thus improving couples' relationships. It may also be that perceiving partners as understanding and empathic, especially in an exaggeratedly positive way (i.e., positive illusions) will buffer insecurity. In 196 mixed-gender newlywed couples, we investigated whether spouses' positive illusions about partner's dyadic perspective-taking moderated the association between spouses' attachment insecurity and spouses' and partners' marital satisfaction over two years. Positive illusions generally predicted more satisfying relationships and attachment avoidance consistently predicted more dissatisfying relationships. There were also several instances where multilevel modeling indicated that positive illusions of dyadic perspective-taking buffered the negative effects of attachment avoidance on relationship satisfaction. However, there was also potentiation such that in two instances, positive illusions about dyadic perspective-taking strengthened the association between spouses' insecurity (husbands' attachment anxiety and wives' attachment avoidance) and subsequent marital dissatisfaction. In the moment, positive illusions about dyadic perspective-taking may allow spouses to feel happy in their relationship despite fear of emotional intimacy; however, positive illusions may not continue to buffer effects of insecurity on subsequent relationship satisfaction and may even be harmful in the face of insecurity.

The Open Virtual Mirror Framework for enfacement illusions : Enhancing the sense of agency with avatars that imitate facial expressions.

Enfacement illusions are traditionally elicited by visuo-tactile stimulation, but more active paradigms become possible through the usage of virtual reality techniques. For instance, virtual mirrors have been recently proposed to induce enfacement by visuo-motor stimulation. In a virtual mirror experiment, participants interact with an avatar that imitates their facial movements. The active control over the avatar greatly enhances the sense of agency, which is an important ingredient for successful enfacement illusion induction. Due to technological challenges, most virtual mirrors so far were limited to the imitation of the participant's head pose, i.e., its location and rotation. However, stronger experiences of agency can be expected by an increase in the avatar's mimicking abilities. We here present a new open-source framework for virtual mirror experiments, which we call the Open Virtual Mirror Framework (OVMF). The OVMF can track and imitate a large range of facial movements, including pose and expressions. It has been designed to run on standard computer hardware and easily interfaces with existing toolboxes for psychological experimentation, while satisfying the requirement of a tightly controlled experimental setup. Further, it is designed to enable convenient extension of its core functionality such that it can be flexibly adjusted to many different experimental paradigms. We demonstrate the usage of the OVMF and experimentally validate its ability to elicit experiences of agency over an avatar, concluding that the OVMF can serve as a reference for future experiments and that it provides high potential to stimulate new directions in enfacement research and beyond.

Postcards related to Dentistry: Iron-Jaw Acts and aPromotional Optical Illusion.

Demonstrable feats of strength and valor using the teeth are found throughout many aspects of newsworthy items and social encounters in history past. Likewise, promotional opportunities relative to the dentition were also common. This article addresses many of these sensationalistic scenarios that were found on postcards related to dentistry in the early 1900s.

Dogs (Canis lupus familiaris) are susceptible to the Kanizsa's triangle illusion.

The ability to complete partially missing contours is widespread across the animal kingdom, but whether this extends to dogs is still unknown. To address this gap in knowledge, we assessed dogs' susceptibility to one of the most common contour illusions, the Kanizsa's triangle. Six dogs were trained to discriminate a triangle from other geometrical figures using a two-alternative conditioned discrimination task. Once the learning criterion was reached, dogs were presented with the Kanizsa's triangle and a control stimulus, where inducers were rotated around their centre, so as to disrupt what would be perceived as a triangle by a human observer. As a group, dogs chose the illusory triangle significantly more often than control stimuli. At the individual level, susceptibility to the illusion was shown by five out of six dogs. This is the first study where dogs as a group show susceptibility to a visual illusion in the same manner as humans. Moreover, the analyses revealed a negative effect of age on susceptibility, an effect that was also found in humans. Altogether, this suggests that the underling perceptual mechanisms are similar between dogs and humans, and in sharp contrast with other categories of visual illusions to which the susceptibility of dogs has been previously assessed.

Is this my foot? Experimentally induced disownership in individuals with body integrity dysphoria.

In body integrity dysphoria (BID), otherwise healthy individuals feel like a part of their physical body does not belong to them despite normal sensorimotor functioning. Theoretical and empirical evidence suggested aweakened integration of the affected body part into higher-order multisensory cortical body networks. Here, we used a multisensory stimulation paradigm in mixed reality to modulate and investigate multisensory processing underlying body (dis)ownership in individuals with BID of the lower limb. In 20 participants with BID, delay perception and body ownership were measured after introducing delays between the visual and tactile information of viewed stroking applied to affected and unaffected body parts. Unlike predicted, delay perception did not differ between the two body parts. However, specifically for the affected limb, ownership was lower and more strongly modulated by delay. These findings might be following the idea of a stronger dependency on online bottom up sensory signals in BID.

Interrelations between the Oppel-Kundt- and the T-illusion.

In order to investigate interrelations between the Oppel-Kundt- and the T-illusion, T-type figures, comprised of one dotted and one empty line (demarcated by its endpoints), separated by a gap of variable size, and rotated to oblique orientations, were judged with regard to the lengths of the two extents. The T-illusion (overestimation of the length of the undivided line) was greater for a T with a dotted undivided line and a small gap. When the divided line was dotted, the illusion vanished at a small gap and reversed at a larger one. Findings are interpreted to mirror activities of a neural T-schema as well as orientation- and density-sensitive neurons.

George Orwell, objectivity, and the reality behind illusions.

Illusions are commonly defined as departures of our percepts from the veridical representation of objective, common-sense reality. However, it has been claimed recently that this definition lacks validity, for example, on the grounds that external reality cannot possibly be represented truly by our sensory systems, and indeed may even be a fiction. Here, I first demonstrate how novelist George Orwell warned that such denials of objective reality are dangerous mistakes, in that they can lead to the suppression and even the atrophy of independent thought and critical evaluation. Second, anti-realists assume their opponents hold a fully reductionist metaphysics, in which fundamental physics describes the only ground truth, thereby placing it beyond direct human sensory observation. In contrast, I point to a more recent and commonly used alternative, non-reductive metaphysics. This ascribes real existence to many levels of dynamic systems of information, emerging progressively from the subatomic to the biological, psychological, social, and ecological. Within such a worldview the notion of objective reality is valid, it comes in part within the range of our senses, and thus a definition of illusions as kinds of deviations from veridical perception becomes possible again.