Elucidating the Visual Snow Spectrum: A Latent Class Analysis Study.

Objective: People with visual snow syndrome (VSS) experience a range of perceptual phenomena, in addition to visual snow (VS; flickering pinpricks of light throughout the visual field). We investigated the patterns of perceptual phenomena associated with VSS in a large sample of people without prior knowledge of VSS or its associated symptoms. Methods and Measures. Two thousand participants completed a screening questionnaire assessing the frequency and severity of perceptual phenomena associated with VSS. We used latent class analysis (LCA), a clustering technique which identifies qualitatively different subgroups within a given population, to investigate whether the presence (or absence) of VS impacted class structure. Results: Of 1,846 participants included for analysis, 41.92% experienced VS some of the time, including 4.49% who had VSS without prior knowledge. The mean number of perceptual phenomena experienced was 2.03. Optimal four-class LCA solutions did not substantially differ whether VS was included in the model; instead, classes differed in the frequency and total number of symptoms experienced. Discussion. Our results suggest that the perceptual phenomena associated with VSS are likely to be common in the general population and do not necessarily indicate an underlying pathology. We also showed that visual snow itself does not explain the presence of other perceptual phenomena.

Perceived severity of Visual Snow Syndrome is associated with visual allodynia.

OBJECTIVE: To investigate whether sensory sensitivity is associated with the perceived severity of Visual Snow Syndrome (VSS) symptoms. BACKGROUND: Visual Snow (VS) is a perceptual anomaly which manifests as flashing pinpricks of light throughout the visual field. VSS has an estimated population prevalence of 2.2% and is thought to be at least moderately debilitating for all who experience it. However, some people who meet the criteria for VSS have no awareness of it. This may be because they have lower sensory sensitivity, allowing them to ignore their visual phenomena. METHOD: Our study used a cross-sectional design. We recruited two distinct samples of people with VSS: a sample of people with confirmed VSS; and a sample of people who met the criteria for the condition but had no prior knowledge of it (latent VSS). The latter group was recruited and screened for symptoms via an online crowd-sourcing platform. In total, 100 participants with VSS (49 with confirmed VSS, 51 with latent VSS) completed the Visual Snow Handicap Index and three measures of sensory hypersensitivity. RESULTS: The 100 participants (52 female, 47 male, 1 non-binary) had a mean age of 35.1 years (SD = 12.2). Leiden Visual Sensitivity Scale scores were associated with both the perceived severity of VSS, ß = 0.35, p = 0.003, and the number of VSS symptoms endorsed, ß = 0.45, p < 0.001. On average, participants with VSS experienced elevated sensory hypersensitivity across all measures. Furthermore, longer duration of VSS was associated with lower perceived severity, F(1, 98) = 11.37, p = 0.001, R2  = 0.103. CONCLUSIONS: Our results suggest that sensory hypersensitivity may be prevalent in people with VSS and indicate that visual allodynia is associated with increased severity of VSS. Additionally, our findings indicate that inclusion of cases of latent VSS in future research may be important for researchers to develop a more complete understanding of the perceptual experiences of people with VSS.

13q32.1 as a candidate region for physiological anisocoria.

BACKGROUND: Physiological anisocoria is an asymmetry of pupil size in the absence of pathology. METHODS: Images of the pupils under standard illumination were collected in the course of a whole-genome association study of a range of visual functions in 1060 healthy adults. DNA for each participant was extracted from saliva samples. RESULTS: We found no relationship between anisocoria and the difference in refraction between the eyes, nor between anisocoria and difference in acuity. There was a small but significant relationship with lightness of the iris, in that the eye with the smaller pupil was associated with the lighter iris. There was a strong association between anisocoria and a local region of chromosome 13 (13q32.1), a region lying between the genes GPR180 and SOX21. The strongest association was with the single-nucleotide polymorphism rs9524583. CONCLUSION: The very specific region associated with anisocoria is one where microdeletions (or microduplications) are known to lead to abnormal development of pupil dilator muscle and hence to the autosomal dominant condition of microcoria. It is possible that alterations at 13q32.1 act by altering the expression of SOX21, which encodes a nuclear transcription factor.

Altered Visual Function in a Larval Zebrafish Knockout of Neurodevelopmental Risk Gene pdzk1.

Purpose: The human PDZK1 gene is located in a genomic susceptibility region for neurodevelopmental disorders. A genome-wide association study identified links between PDZK1 polymorphisms and altered visual contrast sensitivity, an endophenotype for schizophrenia and autism spectrum disorder. The PDZK1 protein is implicated in neurological functioning, interacting with synaptic molecules including postsynaptic density 95 (PSD-95), N-methyl-d-aspartate receptors (NMDARs), corticotropin-releasing factor receptor 1 (CRFR1), and serotonin 2A receptors. The purpose of the present study was to elucidate the role of PDZK1. Methods: We generated pdzk1-knockout (pdzk1-KO) zebrafish using CRISPR/Cas-9 genome editing. Visual function of 7-day-old fish was assessed at behavioral and functional levels using the optomotor response and scotopic electroretinogram (ERG). We also quantified retinal morphology and densities of PSD-95, NMDAR1, CRFR1, and serotonin in the synaptic inner plexiform layer at 7 days, 4 weeks, and 8 weeks of age. Standard RT-PCR and nonsense-mediated decay interference treatment were also performed to assess genetic compensation in mutants. Results: Relative to wild-type, pdzk1-KO larvae showed spatial frequency tuning functions with increased amplitude (likely due to abnormal gain control) and reduced ERG b-waves (suggestive of inner retinal dysfunction). No synaptic phenotypes, but possible morphological retinal phenotypes, were identified. We confirmed that the absence of major histological phenotypes was not attributable to genetic compensatory mechanisms. Conclusions: Our findings point to a role for pdzk1 in zebrafish visual function, and our model system provides a platform for investigating other genes associated with abnormal visual behavior.

Experience-dependent development of visual sensitivity in larval zebrafish.

The zebrafish (Danio rerio) is a popular vertebrate model for studying visual development, especially at the larval stage. For many vertebrates, post-natal visual experience is essential to fine-tune visual development, but it is unknown how experience shapes larval zebrafish vision. Zebrafish swim with a moving texture; in the wild, this innate optomotor response (OMR) stabilises larvae in moving water, but it can be exploited in the laboratory to assess zebrafish visual function. Here, we compared spatial-frequency tuning inferred from OMR between visually naïve and experienced larvae from 5 to 7 days post-fertilisation. We also examined development of synaptic connections between neurons by quantifying post-synaptic density 95 (PSD-95) in larval retinae. PSD-95 is closely associated with N-methyl-D-aspartate (NMDA) receptors, the neurotransmitter-receptor proteins underlying experience-dependent visual development. We found that rather than following an experience-independent genetic programme, developmental changes in visual spatial-frequency tuning at the larval stage required visual experience. Exposure to motion evoking OMR yielded no greater improvement than exposure to static form, suggesting that increased sensitivity as indexed by OMR was driven not by motor practice but by visual experience itself. PSD-95 density varied with visual sensitivity, suggesting that experience may have up-regulated clustering of PSD-95 for synaptic maturation in visual development.

Correspondence Between Behavioral, Physiological, and Anatomical Measurements of Visual Function in Inhibitory Neuron-Ablated Zebrafish.

Purpose: To compare the effects of reduced inhibitory neuron function in the retina across behavioral, physiological, and anatomical levels. Methods: Inhibitory neurons were ablated in larval zebrafish retina. The Ptf1a gene, which determines inhibitory neuron fate in developing vertebrates, was used to express nitroreductase. By exposing larvae to the prodrug metronidazole, cytotoxicity was selectively induced in inhibitory neurons. Visual phenotypes were characterized at behavioral, physiological, and anatomical levels using an optomotor response (OMR) assay, electroretinography (ERG), and routine histology, respectively. Nonvisual locomotion was also assessed to reveal any general behavioral effects due to ablation of other nonvisual neurons that also express Ptf1a. Results: Injured larvae showed severely reduced OMR relative to controls. Locomotor assessment showed unaltered swimming ability, indicating that reduced OMR was due to visual deficits. For ERG, injured larvae manifested either reduced (type-I) or absent (type-II) b-wave signals originating from bipolar interneurons in the retina. Histologic analysis showed altered retinal morphology in injured larvae, with reductions in synaptic inner plexiform layer (IPL) thickness and synaptic density more pronounced in type-II than type-I larvae; type-II larvae also had smaller retinae overall. Conclusions: The consequences of inhibitory neuron ablation corresponded closely across behavioral, physiological, and anatomical levels. Inhibitory neuron loss likely increases the ratio of neural excitation to inhibition, leading to hyperexcitability. In addition to modulating visual signals, inhibitory neurons may be critical for maintaining retinal structure and organization. This study highlights the utility of a multidisciplinary approach and provides a template for characterizing other zebrafish models of neurological disease.

Electroretinogram Recording in Larval Zebrafish using A Novel Cone-Shaped Sponge-tip Electrode.

The zebrafish (Danio rerio) is commonly used as a vertebrate model in developmental studies and is particularly suitable for visual neuroscience. For functional measurements of visual performance, electroretinography (ERG) is an ideal non-invasive method, which has been well established in higher vertebrate species. This approach is increasingly being used for examining the visual function in zebrafish, including during the early developmental larval stages. However, the most commonly used recording electrode for larval zebrafish ERG to date is the glass micropipette electrode, which requires specialized equipment for its manufacture, presenting a challenge for laboratories with limited resources. Here, we present a larval zebrafish ERG protocol using a cone-shaped sponge-tip electrode. The novel electrode is easier to manufacture and handle, more economical, and less likely to damage the larval eye than the glass micropipette. Like previously published ERG methods, the current protocol can assess outer retinal function through photoreceptor and bipolar cell responses, the a- and b-wave, respectively. The protocol can clearly illustrate the refinement of visual function throughout the early development of zebrafish larvae, supporting the utility, sensitivity, and reliability of the novel electrode. The simplified electrode is particularly useful when establishing a new ERG system or modifying existing small-animal ERG apparatus for zebrafish measurement, aiding researchers in the visual neurosciences to use the zebrafish model organism.

Visual working memory for letters varies with familiarity but not complexity.

Visual working memory (VWM) is limited in both the capacity of information it can retain and the rate at which it encodes that information. We examined the influence of stimulus complexity on these 2 limitations of VWM. Observers performed a change-detection task with English letters of various fonts or letters from unfamiliar alphabets. Average perimetric complexity (κ)-an objective correlate of the number of features comprising each letter-differed among the fonts and alphabets. Varying the time between the memory array and mask, we used change-detection performance to estimate the number of items held in VWM (K) as a function of encoding time. For all alphabets, K increased over 270 ms (indicating the rate of encoding) before reaching an asymptote (indicating capacity). We found that rate and capacity for each alphabet were unrelated to complexity: Performance was best modeled by assuming that both were limited by number of items (K), rather than by number of features (K × κ). We also found a higher encoding rate and capacity for familiar alphabets (∼45 items s-1; ∼4 items) than for unfamiliar alphabets (∼12 items s-1; ∼1.5 items). We then compared the familiar English alphabet to an unfamiliar artificial character set matched in complexity. Again, rate and capacity was higher for the familiar than for the unfamiliar stimuli. We conclude that rate and capacity for encoding into visual working memory is determined by the number of familiar feature-integrated object representations. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Reading direction influences lateral biases in letter processing.

Humans have a limited capacity to identify concurrent, briefly presented targets. Recent experiments using concurrent rapid serial visual presentation of letters in horizontally displaced streams have documented a deficit specific to the stream in the right visual field. The cause of this deficit might be either prioritization of the left item based on participants' experience reading from left to right, or a right-hemisphere advantage specific to dual stimulation. Here we test the reading-experience hypothesis by using participants who have experience reading both a language written left-to-right (English) and one written right-to-left (Arabic). When tested with English letters, these participants showed a deficit, of a similar magnitude to that found previously, for reporting the item on the right. However, when the stimuli were Arabic letters the deficit was absent. This suggests that reading direction plays a large role in the second-target deficit. The pattern of participants' errors suggests where in the processing stream reading experience affects stimulus processing: Specifically, the error pattern suggests that the limited-capacity stage responsible for the deficit corresponds to a postsampling process such as consolidation into short-term memory. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Implied reading direction and prioritization of letter encoding.

Capacity limits hinder processing of multiple stimuli, contributing to poorer performance for identifying two briefly presented letters than for identifying a single letter. Higher accuracy is typically found for identifying the letter on the left, which has been attributed to a right-hemisphere dominance for selective attention. Here, we use rapid serial visual presentation (RSVP) of letters in two locations at once. The letters to be identified are simultaneous and cued by rings. In the first experiment, we manipulated implied reading direction by rotating or mirror-reversing the letters to face to the left rather than to the right. The left-side performance advantage was eliminated. In the second experiment, letters were positioned above and below fixation, oriented such that they appeared to face downward (90° clockwise rotation) or upward (90° counterclockwise rotation). Again consistent with an effect of implied reading direction, performance was better for the top position in the downward condition, but not in the upward condition. In both experiments, mixture modeling of participants' report errors revealed that attentional sampling from the two locations was approximately simultaneous, ruling out the theory that the letter on one side was processed first, followed by a shift of attention to sample the other letter. Thus, the orientation of the letters apparently controls not when the letters are sampled from the scene, but rather the dynamics of a subsequent process, such as tokenization or memory consolidation. Implied reading direction appears to determine the letter prioritized at a high-level processing bottleneck. (PsycINFO Database Record

Individual differences in human eye movements: An oculomotor signature?

Human eye movements are stereotyped and repeatable, but how specific to a normal individual are the quantitative properties of his or her eye movements? We recorded saccades, anti-saccades and smooth-pursuit eye movements in a sample of over 1000 healthy young adults. A randomly selected subsample (10%) of participants were re-tested on a second occasion after a median interval of 18.8days, allowing us to estimate reliabilities. Each of several derived measures, including latencies, accuracies, velocities, and left-right asymmetries, proved to be very reliable. We give normative means and distributions for each measure and describe the pattern of correlations amongst them. We identify several measures that exhibit significant sex differences. The profile of our oculomotor measures for an individual constitutes a personal oculomotor signature that distinguishes that individual from most other members of the sample of 1000.

General and specific factors in the processing of faces.

The ability to recognize faces varies considerably between individuals, but does performance co-vary for tests of different aspects of face processing? For 397 participants (of whom the majority were university students) we obtained scores on the Mooney Face Test, Glasgow Face Matching Test (GFMT), Cambridge Face Memory Test (CFMT) and Composite Face Test. Overall performance was significantly correlated for each pair of tests, and we suggest the term f for the factor underlying this pattern of positive correlations. However, there were large variations in the amount of variance shared by individual tests: The GFMT and CFMT are strongly related, whereas the GFMT and the Mooney test tap largely independent abilities. We do not replicate a frequently reported relationship between holistic processing (from the Composite test) and face recognition (from the CFMT)-indeed, holistic processing does not correlate with any of our tests. We report associations of performance with digit ratio and autism-spectrum quotient (AQ), and from our genome-wide association study we include a list of suggestive genetic associations with performance on the four face tests, as well as with f.

Summary statistics in the attentional blink.

We used the attentional blink (AB) paradigm to investigate the processing stage at which extraction of summary statistics from visual stimuli ("ensemble coding") occurs. Experiment 1 examined whether ensemble coding requires attentional engagement with the items in the ensemble. Participants performed two sequential tasks on each trial: gender discrimination of a single face (T1) and estimating the average emotional expression of an ensemble of four faces (or of a single face, as a control condition) as T2. Ensemble coding was affected by the AB when the tasks were separated by a short temporal lag. In Experiment 2, the order of the tasks was reversed to test whether ensemble coding requires more working-memory resources, and therefore induces a larger AB, than estimating the expression of a single face. Each condition produced a similar magnitude AB in the subsequent gender-discrimination T2 task. Experiment 3 additionally investigated whether the previous results were due to participants adopting a subsampling strategy during the ensemble-coding task. Contrary to this explanation, we found different patterns of performance in the ensemble-coding condition and a condition in which participants were instructed to focus on only a single face within an ensemble. Taken together, these findings suggest that ensemble coding emerges automatically as a result of the deployment of attentional resources across the ensemble of stimuli, prior to information being consolidated in working memory.

The Oxytocin Receptor Gene ( OXTR) and Face Recognition.

A recent study has linked individual differences in face recognition to rs237887, a single-nucleotide polymorphism (SNP) of the oxytocin receptor gene ( OXTR; Skuse et al., 2014). In that study, participants were assessed using the Warrington Recognition Memory Test for Faces, but performance on Warrington's test has been shown not to rely purely on face recognition processes. We administered the widely used Cambridge Face Memory Test-a purer test of face recognition-to 370 participants. Performance was not significantly associated with rs237887, with 16 other SNPs of OXTR that we genotyped, or with a further 75 imputed SNPs. We also administered three other tests of face processing (the Mooney Face Test, the Glasgow Face Matching Test, and the Composite Face Test), but performance was never significantly associated with rs237887 or with any of the other genotyped or imputed SNPs, after corrections for multiple testing. In addition, we found no associations between OXTR and Autism-Spectrum Quotient scores.

Perceptual and Motor Performance of Combat-Sport Athletes Differs According to Specific Demands of the Discipline.

The specific demands of a combat-sport discipline may be reflected in the perceptual-motor performance of its athletes. Taekwondo, which emphasizes kicking, might require faster perceptual processing to compensate for longer latencies to initiate lower-limb movements and to give rapid visual feedback for dynamic postural control, while Karate, which emphasizes both striking with the hands and kicking, might require exceptional eye-hand coordination and fast perceptual processing. In samples of 38 Taekwondo athletes (16 females, 22 males; mean age = 19.9 years, SD = 1.2), 24 Karate athletes (9 females, 15 males; mean age = 18.9 years, SD = 0.9), and 35 Nonathletes (20 females, 15 males; mean age = 20.6 years, SD = 1.5), we measured eye-hand coordination with the Finger-Nose-Finger task, and both perceptual-processing speed and attentional control with the Covert Orienting of Visual Attention (COVAT) task. Eye-hand coordination was significantly better for Karate athletes than for Taekwondo athletes and Nonathletes, but reaction times for the upper extremities in the COVAT task-indicative of perceptual-processing speed-were faster for Taekwondo athletes than for Karate athletes and Nonathletes. In addition, we found no significant difference among groups in attentional control, as indexed by the reaction-time cost of an invalid cue in the COVAT task. The results suggest that athletes in different combat sports exhibit distinct profiles of perceptual-motor performance.

Does sadness impair color perception? Flawed evidence and faulty methods.

In their 2015 paper, Thorstenson, Pazda, and Elliot offered evidence from two experiments that perception of colors on the blue-yellow axis was impaired if the participants had watched a sad movie clip, compared to participants who watched clips designed to induce a happy or neutral mood. Subsequently, these authors retracted their article, citing a mistake in their statistical analyses and a problem with the data in one of their experiments. Here, we discuss a number of other methodological problems with Thorstenson et al.'s experimental design, and also demonstrate that the problems with the data go beyond what these authors reported. We conclude that repeating one of the two experiments, with the minor revisions proposed by Thorstenson et al., will not be sufficient to address the problems with this work.

Reconsidering Temporal Selection in the Attentional Blink.

Two episodes of attentional selection cannot occur very close in time. This is the traditional account of the attentional blink, whereby observers fail to report the second of two temporally proximal targets. Recent analyses have challenged this simple account, suggesting that attentional selection during the attentional blink is not only (a) suppressed, but also (b) temporally advanced then delayed, and (c) temporally diffused. Here, we reanalyzed six data sets using mixture modeling of report errors, and revealed much simpler dynamics. Exposing a problem inherent in previous analyses, we found evidence of a second attentional episode only when the second target (T2) follows the first (T1) by more than 100 to 250 ms. When a second episode occurs, suppression and delay reduce steadily as lag increases and temporal precision is stable. At shorter lags, both targets are reported from a single episode, which explains why T2 can escape the attentional blink when it immediately follows T1 (Lag-1 sparing).

Sleep after practice reduces the attentional blink.

The attentional blink (AB) is an impairment in detecting the second of two targets that appear in close temporal succession. We investigated the effect of practice and a nap on the magnitude of the AB deficit. We found evidence that sleep boosts practice-dependent reduction of the AB. Participants reported two target letters embedded in a rapid serial visual presentation display. After two morning sessions, half the participants took a polysomnographically recorded nap, while the others remained awake. Comparing two afternoon sessions to the two morning sessions, we observed a decreased AB only within the group who napped. The improvement was due to increased efficacy of the attentional selection of T2 (the probability of reporting a T2-relevant item). There was no change in selection's latency or temporal precision. The magnitude of improvement was positively associated with the duration of N2 sleep and the number of N2 sleep spindles. Our results suggest that sleep, particularly N2 sleep and sleep spindles, improves attentional selection in time.

Rapid, generalized adaptation to asynchronous audiovisual speech.

The brain is adaptive. The speed of propagation through air, and of low-level sensory processing, differs markedly between auditory and visual stimuli; yet the brain can adapt to compensate for the resulting cross-modal delays. Studies investigating temporal recalibration to audiovisual speech have used prolonged adaptation procedures, suggesting that adaptation is sluggish. Here, we show that adaptation to asynchronous audiovisual speech occurs rapidly. Participants viewed a brief clip of an actor pronouncing a single syllable. The voice was either advanced or delayed relative to the corresponding lip movements, and participants were asked to make a synchrony judgement. Although we did not use an explicit adaptation procedure, we demonstrate rapid recalibration based on a single audiovisual event. We find that the point of subjective simultaneity on each trial is highly contingent upon the modality order of the preceding trial. We find compelling evidence that rapid recalibration generalizes across different stimuli, and different actors. Finally, we demonstrate that rapid recalibration occurs even when auditory and visual events clearly belong to different actors. These results suggest that rapid temporal recalibration to audiovisual speech is primarily mediated by basic temporal factors, rather than higher-order factors such as perceived simultaneity and source identity.

"Pseudoextinction": asymmetries in simultaneous attentional selection.

We report robust visual-field asymmetries associated with selecting simultaneous targets. One letter embedded in a rapid serial visual presentation (RSVP) of letters was encircled by a white ring, cueing it as the target to report. In some conditions, 2 RSVP streams were presented concurrently, and targets appeared simultaneously in both. When only 1 stream was cued, performance was similar regardless of whether it was in the left or right visual field. Cueing 2 streams barely affected performance in the left stream, but performance in the right stream suffered markedly. We term this phenomenon pseudoextinction, by analogy to pseudoneglect whereby observers bisect lines to the left of center. Such attentional asymmetries are often believed to originate from a processing imbalance between the 2 cerebral hemispheres. But pseudoextinction also occurred with vertically arrayed streams, with higher efficacy in the superior than in the inferior stream. Mixture modeling of errors indicated that pseudoextinction did not affect the temporal precision or latency of selection episodes; rather, only the efficacy of selection suffered. These findings lead us to suggest that pseudoextinction arises because perceptual traces are activated simultaneously in a visual buffer, but must be tokenized serially. Observers succeed in selecting simultaneous targets because trace activation occurs in parallel. However, observers often fail to report both targets because tokenization proceeds serially: While 1 target is being tokenized, the other's trace may decay below the activation level necessary for tokenization.