Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields.

N, N-dimethyltryptamine (DMT) is a psychedelic tryptamine acting on 5-HT2A serotonin receptors, which is associated with intense visual hallucinatory phenomena and perceptual changes such as distortions in visual space. The neural underpinnings of these effects remain unknown. We hypothesised that changes in population receptive field (pRF) properties in the primary visual cortex (V1) might underlie visual perceptual experience. We tested this hypothesis using magnetic resonance imaging (MRI) in a within-subject design. We used a technique called pRF mapping, which measures neural population visual response properties and retinotopic maps in early visual areas. We show that in the presence of visual effects, as documented by the Hallucinogen Rating Scale (HRS), the mean pRF sizes in V1 significantly increase in the peripheral visual field for active condition (inhaled DMT) compared to the control. Eye and head movement differences were absent across conditions. This evidence for short-term effects of DMT in pRF may explain perceptual distortions induced by psychedelics such as field blurring, tunnel vision (peripheral vision becoming blurred while central vision remains sharp) and the enlargement of nearby visual space, particularly at the visual locations surrounding the fovea. Our findings are also consistent with a mechanistic framework whereby gain control of ongoing and evoked activity in the visual cortex is controlled by activation of 5-HT2A receptors.

Multisensory perceptual distortion including auditory distortions in Alice in Wonderland syndrome: a case report.

Alice in Wonderland syndrome (AIWS) is a rare perceptual disorder characterized mainly by perceptual distortions of visual objects and one's own body. While there are many case reports of visual and somatosensory distortions associated with AIWS, little is known about auditory distortion. Therefore, we present the case of a 22-year-old right-handed woman who described having auditory as well as visual and somatosensory distortion experiences and a family history of AIWS. The subject reported experiencing multisensory perceptual distortions, where she sees other people's faces as larger and hears their voices as louder at the same time. This particular case suggests that auditory distortion - which contributes to constructing the perception of the surrounding space and the body - may also be characterized as a perceptual symptom of AIWS.

Food deprivation disrupts normal holistic processing of domain-specific stimuli.

Food deprivation has been shown to lead to a set of biological and psychological responses, including a decrease in perceptual thresholds, and an increase in attentional allocation for domain-specific, food-related stimuli. Here, we tested whether food deprivation could lead to a qualitative change in the way food is perceived. To this purpose, we tested the effect of food deprivation on a basic feature of human perception, the holistic processing of object shape. In three experiments, we examined the effect of food deprivation on participants' susceptibility to the height-width illusion, which served as a maker for holistic processing. In all experiments, food deprivation led to an abnormal, non-holistic processing of shape, which resulted in a total reduction of the illusion for food-related, but not for control stimuli. These results show that food deprivation alters the way food is perceived, and propose that motivational factors modulate people's resistance to perceptual distortions for domain-specific stimuli.

Models for discriminating image blur from loss of contrast.

Observers can discriminate between blurry and low-contrast images (Morgan, 2017). Wang and Simoncelli (2004) demonstrated that a code for blur is inherent to the phase relationships between localized pattern detectors of different scales. To test whether human observers actually use local phase coherence when discriminating between image blur and loss of contrast, we compared phase-scrambled chessboards with unscrambled chessboards. Although both stimuli had identical amplitude spectra, local phase coherence was disrupted by phase-scrambling. Human observers were required to concurrently detect and identify (as contrast or blur) image manipulations in the 2 × 2 forced-choice paradigm (Nachmias & Weber, 1975; Watson & Robson, 1981) traditionally considered to be a litmus test for "labelled lines" (i.e. detection mechanisms that can be distinguished on the basis of their preferred stimuli). Phase scrambling reduced some observers' ability to discriminate between blur and a reduction in contrast. However, none of our observers produced data consistent with Watson and Robson's most stringent test for labeled lines, regardless whether phases were scrambled or not. Models of performance fit significantly better when (a) the blur detector also responded to contrast modulations, (b) the contrast detector also responded to blur modulations, or (c) noise in the two detectors was anticorrelated.

Two cortical deficits underlie amblyopia: A multifocal fMRI analysis.

Amblyopia is a relatively common (incidence 3%) developmental disorder in which there is loss of vision as a consequence of a disruption to normal visual development. Although the deficit is monocular and known to be of cortical origin, the nature of the processing deficit is controversial. Human behavioral studies have identified two main deficits - a loss of contrast sensitivity and perceived spatial distortions. Here we use a multifocal fMRI approach to ascertain, in a group of anisometropic amblyopes, whether these two deficits have a single common cause or whether they are the result of two underlying independent cortical disorders. We found that fMRI magnitudes were attenuated in amblyopic eye stimulation, and that there was poor fidelity for co-localization of the activity clusters between the amblyopic and fellow-fixing eye stimulation. These effects varied across eccentricities and correlate with the degree of amblyopia but not with one another, suggesting two independent cortical deficits: a reduced responsiveness as well as reduced fidelity of spatial representation. These deficits are independent of eccentricity within the central field and consistent across early cortical visual areas.

Auditory hallucinations, top-down processing and language perception: a general population study.

BACKGROUND: Studies investigating the underlying mechanisms of hallucinations in patients with schizophrenia suggest that an imbalance in top-down expectations v. bottom-up processing underlies these errors in perception. This study evaluates this hypothesis by testing if individuals drawn from the general population who have had auditory hallucinations (AH) have more misperceptions in auditory language perception than those who have never hallucinated. METHODS: We used an online survey to determine the presence of hallucinations. Participants filled out the Questionnaire for Psychotic Experiences and participated in an auditory verbal recognition task to assess both correct perceptions (hits) and misperceptions (false alarms). A hearing test was performed to screen for hearing problems. RESULTS: A total of 5115 individuals from the general Dutch population participated in this study. Participants who reported AH in the week preceding the test had a higher false alarm rate in their auditory perception compared with those without such (recent) experiences. The more recent the AH were experienced, the more mistakes participants made. While the presence of verbal AH (AVH) was predictive for false alarm rate in auditory language perception, the presence of non-verbal or visual hallucinations were not. CONCLUSIONS: The presence of AVH predicted false alarm rate in auditory language perception, whereas the presence of non-verbal auditory or visual hallucinations was not, suggesting that enhanced top-down processing does not transfer across modalities. More false alarms were observed in participants who reported more recent AVHs. This is in line with models of enhanced influence of top-down expectations in persons who hallucinate.

The role of Peripheral Vision in the Flashed Face Distortion Effect.

The flashed face distortion effect is a phenomenon whereby images of faces, presented at 4-5 Hz in the visual periphery, appear distorted. It has been hypothesized that the effect is driven by cortical, rather than retinal, components. Here, we investigated the role of peripheral viewing on the effect. Normally sighted participants viewed the stimulus peripherally, centrally, and centrally with a blurring lens (to match visual acuity in the peripheral location). Participants rated the level of distortion using a Visual Analogue Scale. Although optical defocus did have a significant effect on distortion ratings, peripheral viewing had a much greater effect, despite matched visual acuity. We suggest three potential mechanisms for this finding: increased positional uncertainty in the periphery, reduced deployment of attention to the visual periphery, or the visual crowding effect.

Semantic representations in the temporal pole predict false memories.

Recent advances in neuroscience have given us unprecedented insight into the neural mechanisms of false memory, showing that artificial memories can be inserted into the memory cells of the hippocampus in a way that is indistinguishable from true memories. However, this alone is not enough to explain how false memories can arise naturally in the course of our daily lives. Cognitive psychology has demonstrated that many instances of false memory, both in the laboratory and the real world, can be attributed to semantic interference. Whereas previous studies have found that a diverse set of regions show some involvement in semantic false memory, none have revealed the nature of the semantic representations underpinning the phenomenon. Here we use fMRI with representational similarity analysis to search for a neural code consistent with semantic false memory. We find clear evidence that false memories emerge from a similarity-based neural code in the temporal pole, a region that has been called the "semantic hub" of the brain. We further show that each individual has a partially unique semantic code within the temporal pole, and this unique code can predict idiosyncratic patterns of memory errors. Finally, we show that the same neural code can also predict variation in true-memory performance, consistent with an adaptive perspective on false memory. Taken together, our findings reveal the underlying structure of neural representations of semantic knowledge, and how this semantic structure can both enhance and distort our memories.

Scene categorization in the presence of a distractor.

Humans display a very good understanding of the content in briefly presented photographs. To achieve this understanding, humans rely on information from both high-acuity central vision and peripheral vision. Previous studies have investigated the relative contribution of central and peripheral vision. However, the role of attention in this task remains unclear. In this study, we presented composite images with a scene in the center and another scene in the periphery. The two channels conveyed different information, and the participants were asked to focus on one channel while ignoring the other. In two experiments, we showed that (a) people are better at recognizing the central part, (b) the conflicting signal in the ignored part hinders performance, and (c) this effect is true for both parts (focusing on the central or peripheral part). We conclude that scene recognition is based on both central and peripheral information, even when participants are instructed to focus only on one part of the image and ignore the other. In contrast to the zoom-out hypothesis, we propose that the gist recognition process should be interpreted in terms of the evidence accumulation model in which information from the to-be-ignored parts is also included.

Center-surround velocity-based segmentation: Speed, eccentricity, and timing of visual stimuli interact to determine interocular dominance.

We used a novel method to capture the spatial dominance pattern of competing motion fields at rivalry onset. When rivaling velocities were different, the participants reported center-surround segmentation: The slower stimuli often dominated in the center while faster motion persisted along the borders. The size of the central static/slow field scaled with the stimulus size. The central dominance was time-locked to the static stimulus onset but was disrupted if the dynamic stimulus was presented later. We then used the same stimuli as masks in an interocular suppression paradigm. The local suppression strengths were probed with targets at different eccentricities. Consistent with the center-surround segmentation, target speed and location interacted with mask velocities. Specifically, suppression power of the slower masks was nonhomogenous with eccentricity, providing a potential explanation for center-surround velocity-based segmentation. This interaction of speed, eccentricity, and timing has implications for motion processing and interocular suppression. The influence of different masks on which target features get suppressed predicts that some "unconscious effects" are not generalizable across masks and, thus, need to be replicated under various masking conditions.

Heading perception from optic flow in the presence of biological motion.

We investigated whether biological motion biases heading estimation from optic flow in a similar manner to nonbiological moving objects. In two experiments, observers judged their heading from displays depicting linear translation over a random-dot ground with normal point light walkers, spatially scrambled point light walkers, or laterally moving objects composed of random dots. In Experiment 1, we found that both types of walkers biased heading estimates similarly to moving objects when they obscured the focus of expansion of the background flow. In Experiment 2, we also found that walkers biased heading estimates when they did not obscure the focus of expansion. These results show that both regular and scrambled biological motion affect heading estimation in a similar manner to simple moving objects, and suggest that biological motion is not preferentially processed for the perception of self-motion.

Effect of audiovisual distraction on the management of dental anxiety in children: A systematic review.

BACKGROUND: Audiovisual distraction, a non-pharmacological intervention, has been used to manage dental anxiety in prior clinical trials. AIM: Synthesize the available evidences to evaluate the efficacy of audiovisual distraction techniques on the management of dental anxiety in children. DESIGN: Electronic databases (PubMed, Cochrane Central Register of Controlled Trials, and Embase) were searched. We included randomized controlled trials (RCTs), and methodological quality of included trials was assessed using the Cochrane Collaboration's criteria. Information on reported anxiety, pain, behaviors, vital signs (including blood pressure, oxygen saturation, and pulse rate), and children satisfaction was analyzed. RESULTS: Nine studies were included for a systematic review, and none of them had low risk of bias. Significant differences in anxiety were found. According to the study, a majority of results indicated a significant difference in pain and behavior between the audiovisual and control group. Three studies reported children in the audiovisual group preferred usage of an audiovisual device for future dental visits. No significant differences could be found regarding blood pressure. CONCLUSIONS: There is some low-quality evidence suggesting that the usage of audiovisual distraction during dental treatment may relieve children's dental anxiety.

Strange-face illusions during eye-to-eye gazing in dyads: specific effects on derealization, depersonalization and dissociative identity.

Experimentally induced strange-face illusions can be perceived when two individuals look at each other in the eyes under low illumination for about 10 minutes. This task of subject-other eye-to-eye gazing produces the following perceptions by the subject: (i) mild to huge deformations and color/shape changes of face and facial features; (ii) lifeless, unmoving faces and immaterial presences akin to out-of-body experiences; (iii) pseudo-hallucinations, enlightened 'idealized' faces and personalities - rather than the other's actual face. Dissociative phenomena seem to be involved, whereas the effects of non-pathological dissociation on strange-face illusions have not yet been directly investigated. In the present study, dissociative perceptions and strange-face illusions were measured through self-report questionnaires on a large sample (N = 90) of healthy young individuals. Results of correlation and factor analyses suggest that strange-face illusions can involve, respectively: (i) strange-face illusions correlated to derealization; (ii) strange-face illusions correlated to depersonalization; and (iii) strange-face illusions of identity, which are supposedly correlated to identity dissociation. The findings support the separation between detachment and compartmentalization in dissociative processes. Effects of gender show that strange-face illusions are more frequent in men with respect to women if dyads are composed of individuals of different-gender. Furthermore, drawings of strange-faces, which were perceived by portrait artists in place the others' faces, allowed a direct illustration of examples of dissociative identities. Findings are discussed in relation to the three-level model of self-referential processing.

High-Frequency Distortion-Product Otoacoustic Emission Repeatability in a Patient Population.

OBJECTIVES: Distortion-product otoacoustic emissions (DPOAEs) are repeatable over time at lower frequencies (≤8 kHz) and higher frequencies (>8 kHz) in healthy, normal-hearing subjects. The purpose of this study was to examine the repeatability of DPOAEs measured with high-frequency (HF) stimuli in a patient population. It was hypothesized that HF DPOAEs would be repeatable over four trials. DESIGN: DPOAEs were measured in 40 cystic fibrosis (CF) patients (17 females and 23 males) with measurable behavioral thresholds and present DPOAEs for at least 2 of the high frequencies tested (8 to 16 kHz). A depth-compensated simulator sound pressure level (SPL) method of calibration was utilized. Each patient attended four trials, in which a complete set of data were collected. At each trial, three different DPOAE paradigms were completed. First, a discrete frequency sweep was measured between 8 and 16 kHz with a ratio (f2/f1) of 1.2 and levels of 65/50 dB SPL for L1/L2. Next, ratio and level sweeps were obtained at the two highest frequencies with a present DPOAE determined from the discrete frequency sweep, and the results were used to calculate DPOAE group delay and DPOAE detection thresholds, respectively. Ratio sweeps were collected with f2/f1 varied from 1.1 to 1.3 and stimulus levels of 60/45 dB SPL (L1/L2). Level sweeps were collected with an f2/f1 of 1.22 and L2 = 50 and L1 varied between 20 and 70 dB SPL. Differences and correlations between trials, SE of the measurement, and confidence intervals were calculated, as well as a repeated-measures analysis of variance. RESULTS: DPOAE response and behavioral threshold variability in CF patients were not significantly different across four trials. It can be expected in 95% of CF patients that differences between trials of DPOAE levels, group delay, and detection thresholds and behavioral thresholds are less than 6.26 dB, 0.87 msec, 9.34 dB, and 9.60 dB, respectively. CONCLUSIONS: HF DPOAEs were repeatable across four test trials for all three paradigms measured in a group of CF patients. These results are encouraging for the measurement of HF DPOAEs to be monitored in those exposed to ototoxic agents.

Deformation-induced transparency resolves color scission.

Dynamic image deformation produces the perception of a transparent material that appears to deform the background image by light refraction. Since past studies on this phenomenon have mainly used subjective judgment about the presence of a transparent layer, it remains unsolved whether this is a real perceptual transparency effect in the sense that it forms surface representations, as do conventional transparency effects. Visual computation for color and luminance transparency, induced mainly by surface-contour information, can be decomposed into two components: surface formation to determine foreground and background layers, and scission to assign color and luminance to each layer. Here we show that deformation-induced perceptual transparency aids surface formation by color transparency and consequently resolves color scission. We asked observers to report the color of the front layer in a spatial region with a neutral physical color. The layer color could be seen as either reddish or greenish depending on the spatial context producing the color transparency, which was, however, ambiguous about the order of layers. We found that adding to the display a deformation-induced transparency that could specify the front layer significantly biased color scission in the predicted way if and only if the deformation-induced transparency was spatially coincident with the interpretation of color transparency. The results indicate that deformation-induced transparency is indeed a novel type of perceptual transparency that plays a role in surface formation in cooperation with color transparency.

Effects of visual distractors on vergence eye movements.

Visual attention is an important aspect of everyday life, which can be incorporated in the assessment of many diagnoses. Another important characteristic of visual attention is that it can be improved via therapeutic interventions. Fifteen subjects with normal binocular vision were presented with visual distractor stimuli at various spatial locations while initiating disparity vergence eye movements (inward or outward rotation of eyes) within a haploscope system. First, a stationary distractor stimulus was presented in either the far, middle, or near visual spaces while the subjects were instructed to follow a target stimulus that was either stationary, converging (moving toward subject), or diverging (moving away from subject). For the second experiment, a dynamic distractor stimulus within the far, middle, or near visual space that was converging or diverging was presented while the target stimulus was also converging or diverging. The subjects were instructed to visually follow the target stimulus and ignore the distractor stimulus. The vergence responses had a final vergence angle between the target and distractor stimuli which has been termed a center of gravity (CoG) effect. Statistically significant differences were observed between the convergence peak velocities (p < 0.001) and response amplitudes (p < 0.001) comparing responses without distractors to responses with the presence of a vergence distractor. The results support that vergence eye movements are influenced by visual distractors, which is similar to how distractors influence saccadic eye movements. The influence of visual distractors within vergence eye movements may be useful to assess binocular dysfunction and visual distraction which are common post brain injury.

Multisensory modulation of experimentally evoked perceptual distortion of the face.

BACKGROUND: Chronic oro-facial pain patients often perceive the painful face area as "swollen" without clinical signs, that is a perceptual distortion (PD). Local anaesthetic (LA) injections in healthy participants are also associated with PD. OBJECTIVE: The aim was to explore whether PD evoked by LA into the infraorbital region could be modulated by adding mechanical stimulation (MS) to the affected area. METHODS: Mechanical stimulation was given with a brush and a 128-mN von Frey filament. Firstly, sixty healthy participants were randomly divided into three groups: (i) LA control, (ii) LA with MS, (iii) isotonic solution (ISO) with MS as an additional control condition. To further examine the role of a multisensory modulation, an additional experiment was conducted. Twenty participants received LA with MS (filament) in addition to visual feedback of their distorted face. The results of the two experiments are presented together. RESULTS: All three LA groups experienced PD; per contra, PD was not reported in the ISO group. MS alone did not change the magnitude of PD: brush (P = .089), filament (P = .203). However, when the filament stimulation was combined with additional visual information of a distorted face, there was observable decrease in PD (P = .002). CONCLUSION: The findings indicate the importance of multisensory integration for PD and represent a significant step forward in the understanding of the factors that may influence this common condition. Future studies are encouraged to investigate further the cortical processing for possible implications for PD in pain management.

[Facets of Body Image Disorder: A Differential Analysis of the TEK-KJ (Test for the Detection of Body Disorder in Children and Adolescents) for the Direct Measurement of Haptic-Perceptual Parts]. / Facetten der Körperbildstörung: eine differenzielle Analyse des TEK-KJ (Test zur Erfassung der Körperbildstörung bei Kindern und Jugendlichen) zur direkten Messung haptisch-perzeptiver Anteile.

There is presently a lack of instruments that measure the haptic-perceptive component of body-image distortion ­ a central criterion for the eating disorders anorexia nervosa and bulimia nervosa. We present a differential analysis for the Test for Body Image Distortion in Children and Adolescents (BID-CA, German: TEK-KJ) using a large child and adolescents sample, including for the first time male participants. We analyze convergent validity with the Contour Drawing Rating Scale (CDRS) as well as differences between children and adolescents from different type of schools and different BMI percentile groups. The sample size was N = 1,654 pupils (873 females and 781 males) with an average age of 13.35 years (SD = 0.76). We calculated a substantial convergent validity with the CDRS. Significant differences between children and adolescents from different type of schools and different BMI percentile groups were detected, with increased values for children and adolescents attending high school and underweight participants. The TEK-KJ seems to be an appropriate additional instrument for detecting the haptic-perceptive component of body-image distortion. The normative data presented improves the standardization of this instrument.

Media Messages and Perception of Risk for Ebola Virus Infection, United States.

News media have been blamed for sensationalizing Ebola in the United States, causing unnecessary alarm. To investigate this issue, we analyzed US-focused news stories about Ebola virus disease during July 1-November 30, 2014. We found frequent use of risk-elevating messages, which may have contributed to increased public concern.

Simulating real-world scenes viewed through ophthalmic lenses.

We present a comprehensive procedure to simulate real-world scenes viewed through ophthalmic lenses. Such a method enables us to anticipate the effects on image formation of the following combined undesired optical defects typically found in ophthalmic lenses: blur, distortion, and chromatic aberration. Additionally, it helps in comparing the expected scenes seen with different lens designs. The procedure is based on the following steps: (1) to calculate the distortion and local dioptric matrix associated with a set of different gaze directions; (2) to estimate point spread functions (PSF) associated with these matrices; (3) to compute the joint action of distortion, chromatic aberration, and PSF field on the scenes. We illustrate this procedure with two +5D spherical lenses: a moderately good performance lens and a highly degrading one. The method is suitable to evaluate ophthalmic lenses in a virtual reality framework.