Vision Research

The estimation of spatial distances is one of the most important perceptual outputs of vision and can easily be deduced even with detached objects. However, how the visual system encodes distances between objects and object sizes is unclear. Hisakata, Nishida, and Johnston (2016) reported a new adaptation effect, in which the perceived distance between objects and the size of an object shrink after adaptation to a dense texture. They proposed that the internal representation of density plays a role in a spatial metric system that measures distance and size. According to the theory of magnitude (Walsh, 2003), the estimation of spatial extent (distance and size) shares common metrics with the estimation of temporal length and numerosity magnitudes and is processed at the same stage. Here, we show the existence of temporal enhancement in cross-adaptation between density and size perception. We used the staircase method to measure the temporal property. The test stimuli were two circles, and the adapting stimulus had a dotted texture. The adapting texture refreshed every 100 or 300 ms, or not at all (static), during the adaptation. The results showed that the aftereffects from a refreshing stimulus were larger than those under the static condition. On the other hand, density adaptation lacked such enhancement. This result indicates that repetitive presentation of an adapting texture enhanced the density-size cross-aftereffect. According to the theory of magnitude, a common mechanism encodes spatial and temporal magnitude estimation and the adaptation to temporal density explains this cross-adaptation enhancement.

Little is known about the function of the auxiliary 2{delta} subunits of voltage-gated calcium channels in the retina. We investigated the role of 2{delta}-3 (Cacna2d3) using a mouse in which 2{delta}-3 was knocked out by LacZ insertion. Behavior experiments indicated a normal optokinetic reflex in 2{delta}-3 knockout animals. Strong expression of 2{delta}-3 could be localized to horizontal cells using the LacZ-reporter, but horizontal cell mosaic and currents carried by horizontal cell voltage-gated calcium channels were unchanged by the 2{delta}-3 knockout. In vivo electroretinography revealed unaffected photoreceptor activity and signal transmission to depolarizing bipolar cells. We recorded visual responses of retinal ganglion cells with multi-electrode arrays in scotopic to photopic luminance levels and found subtle changes in 2{delta}-3 knockout retinas. Spontaneous activity in OFF ganglion cells was elevated in all luminance levels. Differential response strength to high- and low-contrast Gaussian white noise was compressed in ON ganglion cells during mesopic ambient luminance and in OFF ganglion cells during scotopic and mesopic ambient luminances. In a subset of ON ganglion cells, we found a sharp increase in baseline spiking after the presentation of drifting gratings in scotopic luminance. This increase happened after gratings of different spatial properties in knockout compared to wild type retinas. In a subset of ON ganglion cells of the 2{delta}-3 knockout, we found altered delays in rebound-like spiking to full-field contrast steps in scotopic luminance. In conclusion, 2{delta}-3 seems to participate in shaping visual responses mostly within brightness regimes when rods or both rods and cones are active.

In previous studies with dichoptic center-ring-surround stimuli, we found that two properties of the ring element have a strong influence on the phenomenon of binocular luster. The strength of the lustrous impression in the central target patch varies with increasing ring width, with the direction of this variation (increasing or decreasing) depending on the rings luminance. In this study, we used stimuli in which the ring was split into segments with two different luminances that in uniform rings had opposite effects on perceived luster. The aim was to investigate how the lustrous impression is influenced by combining a weaker and a stronger contrast effect, in particular how they are spatially integrated by the visual system. In a psychophysical matching experiment, subjects had to assess the strength of the lustrous impression in a series of test stimuli with different ring widths, numbers of ring segments, and spatial proportions between the two ring parts. We found that the results of the experiment could neither be explained by a winner-takes-all integration (assuming that the lustrous response is completely determined by the stronger effect) nor by a balanced integration process (assuming equal weights for the two effects). Instead, both effects contribute to the overall lustrous response, with the stronger effect having a greater weight. Interestingly, the magnitude of this weight varied considerably between different groups of subjects. We found two main trends in the data, representing two different types of sensitivity to the phenomenon of binocular luster.

Using simulation and a simple mathematical argument we argue that the refresh rate of overhead projectors, used in experiments on the visual system, may impact the perception of fast moving objects at the retinal and cortical level (V1), and thereby at the level of psychophysics.

Spatial summation of perimetric stimuli has been used to derive conclusions about the spatial extent of retinal-cortical convergence, mostly from the size of the critical area of summation (Riccos area, RA) and critical number of Retinal Ganglion Cells (RGCs). However, spatial summation is known to change dynamically with stimulus duration. Conversely, temporal summation and critical duration also vary with stimulus size. Such an important and often neglected spatio-temporal interaction has important implications for modelling perimetric sensitivity in healthy observers and for formulating hypotheses for changes measured in disease. In this work, we performed experiments on visually heathy observers confirming the interaction of stimulus size and duration in determining summation responses in photopic conditions. We then propose a simplified computational model that captures these aspects of perimetric sensitivity by modelling the total retinal input, the combined effect of stimulus size, duration and retinal cones-to-RGC ratio. We additionally show that, in the macula, the enlargement of RA with eccentricity might not correspond to a constant critical number of RGCs, as often reported, but to a constant critical total retinal input. We finally compare our results with previous literature and show possible implications for modelling disease, especially glaucoma.

Previous studies have demonstrated that bias, sensitivity and similarity between letters are causes of errors in letter identification. However, these factors and their relative contribution in letter identification have not been investigated extensively. Our previous model (noisy template model) was devised to calculate the effect of bias and sensitivity in letter identification task. In the current study, we used the method of constant stimuli to measure letter acuity for Sloan letters at an eccentricity of 7 deg from fixation (temporal visual field). Similar to our previous work, we devised an tested a variety of models to estimate the joint role of bias and sensitivity, but extended our model to also incorporate the similarity between letters. Modelling results showed that bias is the major factor in determining the pattern of total, correct and incorrect responses in letter identification. Furthermore, the joint effect of similarity and bias was found to be higher than the joint effect of either bias and sensitivity or similarity and sensitivity in shaping the pattern of overall responses in letter identification. Incorporating the similarity factor to the noisy template model improved our understanding of the simultaneous contribution of the bias, sensitivity and similarity between letters in the letter identification task.

Our attentional resources are allocated to the various aspects of the environment based on the context, and predictive coding has been used as a model to explain the interaction between sensory-based information and top-down expectations in visual attention (Spratling, 2008; Rauss et al., 2011). On the other hand, the saliency of the environmental stimuli is also hypothesized to be capturing the attentional resources of the individuals involuntarily, and thus, it is thought to be playing a crucial role in attentional resource allocation. The current study investigates the role of predictive processing of task difficulty in selective visual attention in the presence of various distractors. Utilizing a letter search task, we provided brief cues about the upcoming tasks difficulty, and participants were asked to detect the target letters. We investigated whether predictive processing about task demands may cause a difference in behavioral measures in the presence of semantically less salient distractors in Experiment 1 (Gabor patches) and semantically more salient distractors in Experiment 2 (faces). Results showed that unmet expectations about the task demands caused longer reaction times in both studies. We observed that all independent variables, which are task difficulty, cue congruency, and distractor presence, affected reaction times in both experiments, but cue congruency interacted with distractor presence only in Experiment 2. Here, we argue that though predictive processing plays a role in attentional resource allocation and, distractors characteristics are also crucial as the saliency level interacts with the cue congruency.

Visual illusions have long been studied because the illusory effect they induce is believed to tell us something important on how the visual system processes visual information. Here, we modified a classic visual illusion, the Delboeuf illusion, so that it resembled a type of stimulus commonly used in experiments investigating surround modulation. We then performed a small set of psychophysical experiments in order to determine if the classical Delboeuf illusion effect, i.e. a change in the perceived size of an object, could be observed in these altered stimuli. In four conditions, we created stimuli that either had a high or low frequency surround in addition to being presented with a proximal thin surround or a distal thick surround. We found a significant difference in perceived object size for all four conditions compared to control indicating the presence of an illusion, and we discuss these findings in relation to existing literature from electrophysiological animal studies.

Color supports object identification. However, two objects that differ in color under one light can appear indiscriminable under a second light. This phenomenon, known as illuminant metamerism, underlies the difficulty faced by consumers of selecting matching fabric or paint colors in a store only to find that they appear not to match under home lighting. The frequency of illuminant metamerism has been evaluated only under single, uniform illuminants. However, in real world conditions, the spectral content of light falling on an object varies with direction (Morimoto et al. 2019), meaning that a surface will sample different spectra depending on its angle within the environment. Here we used computer-graphics techniques to simulate a pair of planar surfaces placed under newly measured hyperspectral illumination maps that quantify the directional variability of real-world lighting environments. We counted the instances of illuminant metamerism that can be solved simply by viewing surfaces tilted to a different direction. Results show that most instances of illuminant metamerism can in theory be resolved for both trichromatic and dichromatic observers. Color deficient observers benefit more than trichromats implying that the directional variability allows the recovery of the missing dimension in their colour vision systems. This study adds a new perspective to the classic trichromatic theory of human vision and emphasizes the importance of carefully considering the environments in which biological vision operates in daily life. It is striking that the physical directional variability available in natural lighting environments substantially mitigates the biological limitations of trichromacy or dichromacy.

Notch filters can alter color contrasts by selectively filtering different spectral bands of the stimulus and have been developed to enhance reddish-greenish contrasts for color-deficient observers with anomalous trichromacy. We examined the effects of such filters on color salience for normal trichromats, using a visual search paradigm where the task was to locate a color target superimposed on a variegated chromatic background, similar to foraging for fruits among foliage. Background colors varied along a bluish-yellowish or purpliish to yellow-green (short-wave cone isolating) axis, roughly spanning the range of dominant color variations in arid or lush environments. Target colors sampled a wide range of hue angles and contrasts. Testing was conducted on a computer monitor, with the filter effects simulated by calculating corresponding chromaticities with or without the filter for naturalistic (Munsell) reflectances. The filter evaluated (Enchroma SuperX(R) glasses) was designed to increase color contrast along a magenta-green axis. Consistent with this, search times for targets on the blue-yellow background were significantly faster for the filter condition, because the filter increased the target-background color difference. Alternatively, overall differences in search times were not observed for the S-cone background. The differences on the two backgrounds could be qualitatively accounted for by the relative salience of the stimuli predicted by a perceptual color space (CIELAB). Our results demonstrate the efficacy of the filters for enhancing visual performance for normal trichromats and naturalistic tasks, and illustrate how these effects depend on the potential color characteristics of the environment.

AO_SCPLOWBSTRACTC_SCPLOWIn human vision, the retinal input is transformed into internal representations through a series of stages. In earlier stages, the signals from a particular visual field locus are passed in parallel from one visual processing area to the next. The connections at each stage may therefore introduce "error", where incorrect or convergent projections result in a loss of spatial precision. Psychophysical and physiological studies have implicated spatial scrambling of this sort as a cause of the visual deficits in amblyopia. Several methods to measure scrambling (both in amblyopia and in healthy vision) have been developed in recent decades. In this work, we introduce a new approach. We consider two stages of visual processing where scrambling may occur: either at the input to or the output from the simple cell stage in V1. We refer to these as "subcortical" and "cortical" scrambling respectively. We investigated the impact of these two types of scrambling on a letter identification task. A physiologically-inspired decomposition and resynthesis algorithm was used to generate letter stimuli that simulate scrambling at each of these two stages. To establish a performance benchmark, we trained separate Convolutional Neural Networks (CNNs) to perform the task with each scrambling type. Comparing CNN performance against that of eight humans with normal healthy vision, we found humans exhibited greater resilience to subcortical scrambling compared to cortical scrambling. We further investigated performance by comparing confusion matrices. Compared to a simple template matching model, we found the human strategy to be more consistent with our CNNs. We conclude: i) the human resilience for subcortical scrambling suggests this may be the stage at which a greater degree of scrambling is introduced in the visual hierarchy, and ii) humans employ flexible strategies for identifying scrambled stimuli, more sophisticated than a simple template match to the expected target.

Perceptual load theory argues that attention is a limited resource and stimuli cannot be processed if there is insufficient perceptual capacity available. Although attention is known to modulate biological motion processing, whether this modulation differs among different perceptual loads remains unknown. To answer this question, three experiments are conducted in which biological motion is utilized as a task-irrelevant distractor. The first experiment showed that biological motion is processed differently than non-biological motion across different perceptual load conditions. The second experiment investigated the effect of attention on biological motion processing, revealing that higher eccentricities enhance biological motion processing but only when the perceptual load is low. The last experiment investigated the same question but with cortically magnified stimuli. It found that when the stimuli are cortically magnified, the enhancement effect of eccentricity is present regardless of the perceptual load. Overall, the results suggest that perceptual load modulates the processing of task-irrelevant biological motion and interacts with other factors (such as eccentricity) that modulate this processing.

Visual processing differs between the foveal and the peripheral visual field. These differences can lead to different appearances of objects in the periphery and the fovea, which poses a challenge to perception across saccades. Differences in the appearance of visual features between the peripheral and foveal visual field may bias change discrimination across saccades. Previously it has been reported that spatial frequency (SF) appears higher in the periphery compared to the fovea (Davis et al., 1987). In this study, we investigated the visual appearance of SF before and after a saccade and the discrimination of SF changes implemented during saccades. In addition, we tested the contributions of pre- and postsaccadic information to change discrimination performance. In the first experiment, we found no differences in the appearance of SF before and after a saccade. However, participants showed a clear bias to report SF increases. Interestingly, a 200-ms postsaccadic blank period improved the precision of the responses but did not affect the bias. In the second experiment, participants showed lower thresholds for SF increases than for decreases, suggesting that the bias in the first experiment was not just a response bias. Finally, we asked participants to discriminate the SF of stimuli presented before a saccade. Thresholds in the presaccadic discrimination task were lower than thresholds in the change discrimination task, suggesting that transsaccadic change discrimination is not merely limited by presaccadic discrimination in the periphery. The change direction bias might stem from more effective masking or overwriting of the presaccadic stimulus by the postsaccadic low SF stimulus. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/584439v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@12d3f68org.highwire.dtl.DTLVardef@19df18eorg.highwire.dtl.DTLVardef@5dd09forg.highwire.dtl.DTLVardef@12ba71f_HPS_FORMAT_FIGEXP M_FIG C_FIG

The ability of humans to discriminate and identify spatial patterns varies across the visual field, and is generally worse in the periphery than in the fovea. This decline in performance is revealed in many kinds of tasks, from detection to recognition. A parsimonious hypothesis is that the representation of any visual feature is blurred (spatially averaged) by an amount that differs for each feature, but that in all cases increases with eccentricity. Here, we examine models for two such features: local luminance and spectral energy. Each model averages the corresponding feature in pooling windows whose diameters scale linearly with eccentricity. We performed perceptual experiments with synthetic stimuli to determine the largest window scaling for which human and model discrimination abilities match (the "critical" scaling). We used much larger stimuli than those of previous studies, subtending 53.6 by 42.2 degrees of visual angle. We found that the critical scaling for the luminance model was approximately one-fourth that of the energy model and, consistent with earlier studies, that the estimated critical scaling value was smaller when discriminating a synthesized stimulus from a natural image than when discriminating two synthesized stimuli. Moreover, we found that initializing the generation of the synthesized images with natural images reduced the critical scaling value when discriminating two synthesized stimuli, but not when discriminating a synthesized from a natural image stimulus. Together, the results show that critical scaling is strongly affected by the image statistic (pooled luminance vs. spectral energy), the comparison type (synthesized vs. synthesized or synthesized vs. natural), and the initialization image for synthesis (white noise vs natural image). We offer a coherent explanation for these results in terms of alignments and misalignments of the models with human perceptual representations.

Perceptual thresholds measured in the two-dimensional chromatic diagram are elliptical in shape. Across different parts of the chromatic diagram, these ellipses vary in their sizes, their tilting angles, and in how much they elongate. Overall, the chromatic thresholds exhibit intriguing patterns that were reflected in McAdams measurements in 1942. Previously, da Fonseca and Samengo (2016) used a neural model combined with Fisher information (a quantification of perceptual thresholds) to predict the pattern of chromatic thresholds measured in human observers. The model assumes linear cone responses paired with Poisson noise. I furthered the analysis, and studied two additional aspects of chromatic perception. First, I quantified how the pattern of chromatic thresholds vary when the proportion of three cone types (short-, mid-, and long-wavelength) varies. This analysis potentially leads to efficient estimation of thresholds across the chromatic diagram. Second, I analyzed to what extent the assumption of Poisson noise contributes to the threshold predictions. Surprisingly, eliminating Poisson noise betters the model prediction. So in addition to Poisson noise, I examined three alternative noise assumptions, and achieved improved predictions to MacAdams data. At last, I examined an application using the improved model-predictions. The total number of cones, as well as the proportion of S cone vary across retinal eccentricities. I showed that these two variations predict chromatic threshold patterns across retinal eccentricities are drastically different.

The present study examined the contribution of the koniocellular retino-geniculate visual pathway to the electrocortical amplification of threat cues in human visual cortex using an aversive conditioning task. The task involved tritan stimuli, which are thought to convey visual information through S-cone signals that project to regions along the koniocellular pathway (tritan condition) and achromatic stimuli that preferentially activate luminance channels (luminance condition). Steady-state visual evoked potential (ssVEPs) responses to the conditioned threat (CS+) and safety cues (CS-) in each condition were analyzed using a non-parametric Bayesian bootstrapped approach. Results showed that the tritan and luminance conditions exhibited greater ssVEP responses to the CS+ compared to the CS-stimuli in occipital sensors early into the trial (0 ms - 1000 ms; logBF10 > 2, decisive support). In addition to these early conditioning effects, a late conditioning effect was observed (1500 ms - 2500 ms) in the tritan condition that emerged in bilateral anterior sensors (logBF10 > 2). To further examine the tritan contribution to aversive learning, transitive Bayes factors were computed to compare the magnitude of the conditioning effects across conditions. Transitive Bayes factors showed that the early conditioning effect was larger in the luminance condition compared to the tritan condition (logBF10 > 2). Furthermore, the late conditioning effect remained larger in the tritan condition compared to the luminance condition (logBF10 > 2). Our findings suggest that both the koniocellular visual pathway and luminance channels play a role in the electrocortical amplification of threat signals in human visual cortex.

Our visual experience does not merely reflect a static view of the world but is a dynamic consequence of our actions, most notably our continuously shifting gaze. These shifts determine the spectral diet of any individual cone photoreceptor. The aim of this study was to characterize that diet and its relationship to scene adaptation. Gaze shifts were recorded from observers freely viewing scenes outdoors for five minutes. Hyperspectral images of the scenes were also recorded from the observers eye position. As a control, gaze shifts were also recorded from observers viewing the images on a computer-controlled display in the laboratory. From the hyperspectral data, spatially local histograms of estimated excitations in long-, medium-, and short-wavelength-sensitive cones were accumulated over time at different retinal locations. A global illuminant change was then introduced to test how well local retinal adaptation discounted its effects. The results suggest that over short periods individual cones tend to experience the statistics of full scenes, with local adaptation compensating for illumination changes almost as well as global adaptation. This compensation may help to maintain our stable local perception of scene colour despite changes in scene illumination.

AO_SCPLOWBSTRACTC_SCPLOWIn the last decade, studies have shown that short-term monocular deprivation strengthens the deprived eyes contribution to binocular vision. However, the magnitude of the change in eye dominance after monocular deprivation (i.e., the patching effect) has been found to be different between for different methods and within the same method. There are three possible explanations for the discrepancy. First, the mechanisms underlying the patching effect that are probed by different measurement tasks might exist at different neural sites. Second, test-retest variability in the measurement might have led to inconsistencies, even within the same method. Third, the patching effect itself in the same subject might fluctuate across separate days or experimental sessions. To explore these possibilities, we assessed the test-retest reliability of the three most commonly used tasks (binocular rivalry, binocular combination, and dichoptic masking) and the repeatability of the shift in eye dominance after short-term monocular deprivation for each of the task. Two variations for binocular phase combination were used, at one and many contrasts of the stimuli. Also, two variations of the dichoptic masking task was tested, in which the orientation of the mask grating was either horizontal or vertical. This makes five different measurement methods in all. We hope to resolve some of the inconsistencies reported in the literature concerning this form of visual plasticity. In this study, we also aim to recommend a measurement method that will allow us to better understand its physiological basis and the underpinning of visual disorders.

Pupil size changes under different light conditions. Whereas this pupillary light response (PLR) has long been regarded to be influenced by luminance only, recent studies indicated the PLR is also modulated by cognitive factors such as the allocation of spatial attention. This attentional modulation of the PLR has previously been hypothesized to facilitate detection and discrimination of visual information. Here, we replicated the finding that the pupil dilates when a cue is presented at the dark side of a screen and constricts when the cue is presented at the bright side, even when the eyes are fixated at the center. Furthermore, we investigated whether this modulation of the PLR, evoked by exogenous shifts of covert attention, facilitates perception operationalized as detection performance for threshold stimuli. Results showed that a larger pupil was indeed related to increased detection performance, although this effect was restricted to conditions in which both cue and target appeared on a dark surface. Our findings are in line with the notion that pupil dilations improve detectability, whereas pupil constrictions enhance discriminability of small stimuli.

Viewing repetitive striped patterns can induce pattern glare, experienced as visual discomfort (VD). While previous studies examined either pupillary responses or VD separately, few have investigated how they covary or evolve with repeated exposure. This study tested whether pupillary dynamics could serve as an objective "aversometer" -- a physiological marker of individual visual sensitivity beyond subjective reports. Across four experiments (preliminary: n = 97; main: n = 70 for spatial frequency, n = 46 for central field size, n = 36 for central blank, with partial overlap), we manipulated spatial frequency, central field size, and surround field size of square-wave gratings (0.5-3 s) while measuring both discomfort and pupil size. Higher spatial frequencies and larger pattern areas elicited stronger pupillary constriction and greater discomfort, whereas repeated exposures produced cumulative increases in discomfort and decreases in baseline pupil size, consistent with visual strain rather than adaptation. To assess the potential of pupillometry as an aversometer, we examined individual differences in the main spatial-frequency experiment (controlled viewing distance, n = 42). A paradoxical pattern emerged: within participants, stronger stimuli produced greater constriction, but individuals with higher overall discomfort showed weaker constriction and stronger late redilation. Similar dissociations between subjective sensitivity and pupillary responses have been noted in studies of light-induced discomfort, suggesting that related mechanisms may contribute, although their specific physiological basis remains unclear. Overall, our findings clarify how pattern-induced discomfort evolves over time and across individuals and highlight pupillometrys potential as a sensitive, objective tool for assessing visual sensitivity. HighlightsO_LIStriped patterns systematically increased discomfort and pupillary constriction C_LIO_LIRepeated exposure led to progressive discomfort and shrinking baseline pupil C_LIO_LIAmong high-sensitivity participants, weaker constriction and stronger redilation appeared C_LIO_LIThe paradox may reflect interindividual autonomic differences under visual stress C_LIO_LIPupillometry shows promise as an objective marker of visual sensitivity C_LI