Foveal vision in individuals with infantile idiopathic nystagmus syndrome (IINS) is impaired by reduced acuity and elevated crowding (the disruption in object recognition from clutter). In typical peripheral vision, acuity can be improved by temporal variations (flicker), while crowding is reduced when the target differs in appearance from surrounding flankers. We examined whether flicker and target-flanker differences in contrast polarity could similarly improve foveal performance in IINS and typical participants (n = 6 each, aged 24-50), who identified the orientation of a foveal Landolt-C presented alone or with 4 black (same polarity) or white (opposite polarity) flankers. Elements were either static or flickered with periodic contrast-polarity reversals. To simulate IINS, typical participants also viewed stimuli with motion derived from nystagmus eye movements. QUEST was used to scale elements to find the threshold gap size. We observed clear foveal crowding effects in both typical and IINS groups, with higher thresholds when flanked than unflanked. Thresholds were elevated in all conditions for the IINS group. Unlike peripheral vision, thresholds with same-polarity flankers did not differ from those with opposite-polarity flankers in either group. Similarly, flicker did not reliably improve performance over static presentation. These patterns differed in simulated nystagmus, which produced elevated crowding levels that were reduced by both target-flanker polarity differences and flicker. Overall, we show that target-flanker differences and flicker do not reduce foveal crowding in IINS. This pattern is unlike both peripheral vision and simulated nystagmus, suggesting that nystagmus disrupts vision through both momentary eye-movement effects and a longer-term sensory deficit.

Separating world-relative object motion from retinal motion requires an estimate of self-motion. We examined how experimentally degrading one vestibular observation channel alters this attribution in a recurrent state-space observer. We reduced effective otolith reliability by increasing generative otolith noise and held canal and visual noise fixed. The observer jointly estimated self-motion and object motion and used otolith prediction errors to form an approximate belief over two internal reliability contexts. Across 30 paired realizations, reduced otolith reliability increased false-positive world-motion RMS by 47.61% and object-motion RMSE by 48.77%, compared with a 4.37% increase in angular self-motion RMSE. An instantaneous residual-only model captured part of the object-event error but not the object-free false-positive increase. Supplying oracle self-motion largely eliminated the latter effect. Two independent nonrecurrent baselines also produced more false-positive motion under noisier otolith input. Both had higher object-motion RMSE than the recurrent observer and lacked a mechanism for history-dependent recovery. The principal recurrent effect persisted with reliability inference fixed, adaptation removed, and the two adaptation rates replaced by one. Degraded otolith evidence can therefore shift ambiguous retinal evidence toward external-motion estimates. Recurrent estimation improves object-motion recovery and makes this attribution dependent on predictive history.

The flash-lag effect (FLE), a dissociation between physical events and their perceived time and location, has an unresolved neural basis. Here, the FLE is re-examined within the semblance hypothesis, in which perception, a first-person property, arises from the rapid formation and reversal of inter-postsynaptic functional LINKs (IPLs). A novel, unpredictable stimulus such as a flash is hypothesized to require de novo IPL formation, with perceptual latency Tpercept(flash) ≈ 70-100 ms. Predictable, continuously tracked motion is instead hypothesized to reactivate IPLs formed at motion onset, with updates within Tupdate ≈ 41-46 ms. This latency difference is proposed to account for the baseline FLE, FLE ≈ v · (Tpercept(flash) - Tupdate), a temporal offset of 24-59 ms. IPL reactivation is assumed to support both ongoing updates and the percept's forward extrapolation, with the projection horizon τproj set equal to Tupdate ≈ 41-46 ms as a modeling assumption. The tight constraints of a direction-reversal experiment may be explained, in an interconnected manner, by τproj and IPL dissociation and their effects on successive stages of percept formation. The percept is proposed to be projected to its computed location without an additional processing delay, with neural latency compensated by a time-to-space transformation (Δt→Δx), which is a modeling postulate. These proposals are used to formulate testable predictions.

Investigating sensory attenuation within the visual pathway of individuals with schizophrenia is essential for understanding a core clinical feature of the disorder-impaired voluntary awareness. The present study employed a two-alternative forced-choice (2-AFC) paradigm to examine whether individuals with schizophrenia exhibit atypical action-related modulation of visual perception during voluntary actions compared with healthy controls. The results indicated no significant difference in perceived visual stimulus intensity between active control and passive reception conditions in the schizophrenia group. In contrast, healthy participants demonstrated a significantly reduced perception of stimulus intensity under active control relative to passive reception. Collectively, these findings suggest reduced action-related modulation of visual contrast perception in individuals with schizophrenia.

Human visual recognition critically depends on edge-based information, which forms the fundamental cues for identifying objects by their outlines and shapes. Where two-dimensional studies have established that line drawings enable recognition performance comparable to full-color images, the extension of these principles to three-dimensional artefacts within immersive virtual reality (VR) remains underexplored. The precise impact of 3D visualization on recognition accuracy, especially under conditions of minimal visual cues, raises unresolved questions about how the human visual system integrates outline information volumetrically. This gap is important because VR is increasingly employed for education, training, and interactive systems, where understanding how visualization techniques affect object recognition can determine design effectiveness. Despite the well-founded evidence supporting edge-based recognition in 2D, challenges persist in generalizing these findings to 3D objects due to variations in dimensionality, complexity, and familiarity with the artefact. It remains unclear whether volumetric 3D cues provide consistent advantages across different familiarity levels or how these benefits interact with cognitive processes such as memory and spatial integration. This study aims to address these gaps by directly comparing human recognition performance for animal artefacts presented as outline - based 2D images and immersive 3D models in VR. By systematically varying artefact familiarity and analysing detailed response patterns across segmented artefact regions, the research seeks to clarify the extent to which outline drawing mechanisms generalize to 3D object recognition and inform practical applications in immersive learning and interactive technology.

Older adults typically show reduced recognition of negative facial emotions alongside relative preservation of happiness-the positivity effect. Whether this pattern reflects differences in perceptual sensitivity, response strategy, or both has not been tested with Signal Detection Theory (SDT). SDT decomposes performance into perceptual sensitivity (d') and response criterion (c), allowing us to determine whether age-related changes operate at the perceptual or decisional level. Seventy-six older adults and sixty-four young adults completed a six-alternative forced-choice identification task with 24 computer-generated facial expressions spanning six basic emotions. Older adults showed markedly lower global sensitivity, confirmed by bootstrap. A significant Group × Emotion interaction qualified this main effect: the sensitivity deficit was substantially smaller for happiness than for all other emotions. Group differences in criterion were confined to sadness, anger and surprise and were largely accounted for by the coupling between c and d' inherent to the task; for happiness, older adults showed a small, non-significant trend towards a more liberal criterion. Confusion analysis revealed that errors concentrated on emotion pairs sharing overlapping Action Units. These findings locate the positivity effect primarily at the level of early perceptual encoding, with at most a modest decisional contribution.

Numerosity has been proposed as a primary visual attribute, akin to motion or colour, and has been reported to show bidirectional adaptation consistent with population coding by tuned mechanisms: after exposure to sparse or dense arrays, the perceived numerosity of an array with a moderate number of dots shifts away from the adaptor. However, recent studies argue against bidirectionality, claiming that adaptation to sparse arrays failed to increase perceived numerosity of a denser array. This suggests that previous accounts may reflect decisional rather than perceptual biases. To test this, we employed a comparison-of-comparisons paradigm using a four-quadrant display. Observers adapted to two spatially distinct dot clouds in upper quadrants of the visual field. Following adaptation, dot clouds were shown in all four quadrants. Observers judged which of the two bottom clouds appeared more different to the reference numerosity contained in each upper quadrant. Simple decisional biases such as a preference for selecting a previously adapted or unadapted stimulus cannot masquerade as perceptual bias in this paradigm. Across six observers, three adaptor numerosities (0, 25, 100) and three randomly interleaved reference numerosities (34, 50, 74), we found clear evidence for unidirectional aftereffects consistent with monotonic neuronal responses. Adapting to dense clouds (100 dots) produced the largest downward bias in perceived numerosity, with smaller reductions following 25-dot adaptors. No condition produced upward shifts, suggesting that previous reports of bidirectionality may reflect non-perceptual biases.

The scientific study of the vertebrate retina has reached a remarkable degree of sophistication. We can now explain many aspects of early visual processing based on a relatively simple model of neural circuitry in the retina. The same model, with different parameters, produces a great diversity of neural computations. In this article I lay out what that "standard model" is and how it accounts for such a diversity of phenomena. The emergence of such a powerful standard model is unique in systems neuroscience, and I consider what conditions made it possible. The standard model now serves as a baseline from which to organize future retinal research, either by testing the model's assumptions directly, or by identifying phenomena that remain unexplained.

Heightened sensory sensitivity, including visual discomfort, is common in migraine, autism, and the wider population, and is linked to headaches, perceptual disturbances, and reduced quality of life. We tested whether coloured screen filters reduce visual discomfort and whether such effects are reflected in neural responses. Nineteen participants with self-identified sensory sensitivity completed a within-subject task viewing natural scenes, striped gratings, and filtered-noise "bump" textures under greyscale, red, and blue screen filters. Subjective discomfort was rated after each trial, and neural responses were measured with EEG steady-state visual evoked potentials (SSVEPs) at 5 Hz. Image type strongly influenced both ratings and SSVEP amplitude. Blue screen filters lowered discomfort ratings for stripes and bumps but did not reliably affect SSVEP amplitude. The positive association between SSVEP amplitude and discomfort was weaker under blue screen filtering, suggesting a change in how neural activity is related to subjective experience in this modest sample. These results indicate that broad chromatic manipulations may not reduce cortical responses per se, but may alter the mapping between neural responses and discomfort.

Amblyopia is, aside from refractive error, the largest cause of vision loss in infants and young children. It also provides a window into the effects of atypical visual development. This article traces my decades long interest in trying to understand amblyopia from the perspective of a psychophysicist, outlining some of the key questions and findings and the factors that made my journey possible. It's been quite a journey!

This study investigated whether saccadic search exists on a micro scale. Using a high-speed, confocal retinal eye tracker (FET), participants searched for tiny targets within dense displays subtending less than 4 deg[2]. The participants exhibited goal-directed, exploratory scanning behavior with tiny saccades (median amplitude < 0.5°); saccade amplitude scaled with inter-element distance, fixation duration increased in denser displays, and consecutive saccades followed typical directional dependencies (saccadic momentum and facilitation of return). Search performance and scanpaths resembled those found in large-scale visual search tasks, suggesting functional equivalence across spatial scales. These findings support the view that microsaccades serve the same perceptual and attentional roles as larger saccades. We argue that the distinction between microsaccades and saccades is unnecessary when describing natural, task-driven visual scanning behavior.

Directional judgements are generally referenced to a single point relative to the viewer, known as the visual egocentre, which is presumed to be situated midway between the two eyes. However, its precise location and variability across individuals with normal vision remain unclear. This study investigated the variability in the egocentre location using both monocular and binocular sighting tasks in a representative sample (N = 26) of adults with normal vision. Using a custom-built sighting apparatus, observers were required to rotate the orientation of a rod in the horizontal plane until it pointed directly at either their right eye, left eye, or themselves during binocular viewing. Measurements were taken along the horizontal azimuth for a range of eccentricities spanning ±52.5 deg., relative to the centre of the head. The mean point of intersection of the rod's axis extensions at each eccentricity was used to derive estimates of the monocular visual directions and the visual egocentre location for each individual. Surprisingly, observers exhibited considerable variability in their monocular estimates (74.22 ± 9.59 mm), which were typically much larger than their inter-pupillary distance (IPD) (62.04 ± 2.76 mm). For binocular viewing, the group egocentre was located, on average, 0.41 (SD = 11.13) mm to the right of the median plane of the head and 24.63 (SD = 13.85) mm behind the corneal plane, with marked individual differences in its location. The results suggest that human directional judgements of space are made relative to an individualised virtual cyclopean retina.

Most contemporary accounts of selective attention assume limited perceptual resources that need to be allocated through attention. These accounts, however, differ in how exactly irrelevant stimuli are filtered out. Suggestions include passive exhaustion of resources (e.g., load theory) or actively shaping the attended region (attentional window) such that irrelevant items remain excluded (e.g., attentional zoom account). We use pupillometry to test predictions of these accounts: Observers are asked to simultaneously monitor and compare two streams of rapidly presented items, either in a low-load (compare color) or high-load (compare the conjunction of color and orientation) condition. Flickering areas are placed between or beside the streams, falling either inside or outside the postulated attentional window. Observers respond faster and more accurately in the low-load condition, with no behavioral effects of the flicker position. In contrast, pupil size is more strongly modulated by the flicker in the inside than in the outside condition, but the modulation strength is independent of load. Exploiting the fact that the strength of the pupil modulation at the flicker frequency is an index of covert attention to the flickering region, we interpret this result as evidence for a continuous attentional window that encompasses the space between the streams. Together, our data provide evidence for an active filter mechanism, supporting theories like the attentional zoom account, rather than a passive, load-dependent spreading of residual attentional resources.

The visual system overestimates the length of structured contours relative to adjacent empty intervals of the same physical size. This study examined whether apparent-length expansion occurs across isolated contour parts as well as complete objects, and whether the expansion of the whole can be predicted from that of its components. Observers matched the perceived horizontal extent of complete pentagons, incomplete pentagons with one or two missing segments, isolated apices, pedestals, parallel line pairs, and rectangles using an adjustment method. All stimulus types produced consistent positive mean errors, indicating robust apparent-length expansion across a wide range of contour configurations. The magnitude of expansion depended on contour geometry rather than on physical size alone: removing contour segments did not reduce expansion and, in some cases, increased it. Isolated parts produced expansion effects comparable to or larger than those of the corresponding whole pentagons, but the sum of part effects did not predict the whole-object effect. These findings support a configuration-dependent account of apparent-length expansion and appear inconsistent with simple part-based additivity.