The Representational Similarity between Visual Perception and Recent Perceptual History.

From moment to moment, the visual properties of objects in the world fluctuate because of external factors like ambient lighting, occlusion and eye movements, and internal (proximal) noise. Despite this variability in the incoming information, our perception is stable. Serial dependence, the behavioral attraction of current perceptual responses toward previously seen stimuli, may reveal a mechanism underlying stability: a spatiotemporally tuned operator that smooths over spurious fluctuations. The current study examined the neural underpinnings of serial dependence by recording the electroencephalographic (EEG) brain response of female and male human observers to prototypical objects (faces, cars, and houses) and morphs that mixed properties of two prototypes. Behavior was biased toward previously seen objects. Representational similarity analysis (RSA) revealed that responses evoked by visual objects contained information about the previous stimulus. The trace of previous representations in the response to the current object occurred immediately on object appearance, suggesting that serial dependence arises from a brain state or set that precedes processing of new input. However, the brain response to current visual objects was not representationally similar to the trace they leave on subsequent object representations. These results reveal that while past stimulus history influences current representations, this influence does not imply a shared neural code between the previous trial (memory) and the current trial (perception).SIGNIFICANCE STATEMENT The perception of visual objects is pulled toward instances of that object seen in the recent past. The neural underpinnings of this serial dependence remain to be fully investigated. The present study examined electroencephalographic (EEG) responses to faces, cars, and houses, and ambiguous between-category morphs. With representational similarity analysis (RSA), we showed (1) object-specific neural patterns that differentiate the three categories; (2) that the response to the current object contains information about the previous object, mirroring behavioral serial dependence; (3) that the object-specific neural pattern about the past was different from that in the current response, revealing that while past stimulus history influences current representations, this does not imply a shared neural code between the previous trial (memory) and the current trial (perception).

Decoding Trans-Saccadic Prediction Error.

We are constantly sampling our environment by moving our eyes, but our subjective experience of the world is stable and constant. Stimulus displacement during or shortly after a saccade often goes unnoticed, a phenomenon called the saccadic suppression of displacement. Although we fail to notice such displacements, our oculomotor system computes the prediction errors and adequately adjusts the gaze and future saccadic execution, a phenomenon known as saccadic adaptation. In the present study, we aimed to find a brain signature of the trans-saccadic prediction error that informs the motor system but not explicit perception. We asked participants (either sex) to report whether a visual target was displaced during a saccade while recording electroencephalography (EEG). Using multivariate pattern analysis, we were able to differentiate displacements from no displacements, even when participants failed to report the displacement. In other words, we found that trans-saccadic prediction error is represented in the EEG signal 100 ms after the displacement presentation, mainly in occipital and parieto-occipital channels, even in the absence of explicit perception of the displacement.SIGNIFICANCE STATEMENT Stability in vision occurs even while performing saccades. One suggested mechanism for this counterintuitive visual phenomenon is that external displacement is suppressed during the retinal remapping caused by a saccade. Here, we shed light on the mechanisms of trans-saccadic stability by showing that displacement information is not entirely suppressed and specifically present in the early stages of visual processing. Such a signal is relevant and computed for oculomotor adjustment despite being neglected for perception.

Serial dependence tracks objects and scenes in parallel and independently.

The visual world is made up of objects and scenes. Object perception requires both discriminating an individual object from others and binding together different perceptual samples of that object across time. Such binding manifests by serial dependence, the attraction of the current perception of a visual attribute toward values of that attribute seen in the recent past. Scene perception is subserved by global mechanisms such as ensemble perception, the rapid extraction of the average feature value of a group of objects. The current study examined to what extent the perception of single objects in multi-object scenes depended on previous feature values of that object or on the average previous attribute of all objects in the ensemble. Results show that serial dependence occurs independently on two simultaneously present objects, that ensemble perception depends only on previous ensembles, and that serial dependence of an individual object occurs only for the features of that particular object. These results suggest that the temporal integration of successive perceptual samples operates simultaneously at independent levels of visual processing.

Serial dependence alters perceived object appearance.

The visual world as it presents itself to our eyes is constantly changing, in contrast with human perceptual experience, which is smooth and stable. One of the posited psychological mechanisms that may contribute to this constructed perceptual stability is the continuity field, a spatiotemporal integration window. The current study examined whether temporal integration, as quantified by serial dependence (SD) between perceived attributes of successive visual stimuli, influenced the subjective appearance of objects or decisional stages in response determination. To do so, an oddball task required participants to directly compare visual objects and decorrelated responses (present/absent) from the visual attribute on which SD may occur (orientation). Results showed that SD could cause a single visual object to appear different from surrounding distractors, leading to modulations of performance. These results argue in favor of a perceptual level of SD, and against decisional accounts.

Memory-guided saccades show effect of a perceptual illusion whereas visually guided saccades do not.

The double-drift stimulus (a drifting Gabor with orthogonal internal motion) generates a large discrepancy between its physical and perceived path. Surprisingly, saccades directed to the double-drift stimulus land along the physical, and not perceived, path (Lisi M, Cavanagh P. Curr Biol 25: 2535-2540, 2015). We asked whether memory-guided saccades exhibited the same dissociation from perception. Participants were asked to keep their gaze centered on a fixation dot while the double-drift stimulus moved back and forth on a linear path in the periphery. The offset of the fixation was the go signal to make a saccade to the target. In the visually guided saccade condition, the Gabor kept moving on its trajectory after the go signal but was removed once the saccade began. In the memory conditions, the Gabor disappeared before or at the same time as the go-signal (0- to 1,000-ms delay) and participants made a saccade to its remembered location. The results showed that visually guided saccades again targeted the physical rather than the perceived location. However, memory saccades, even with 0-ms delay, had landing positions shifted toward the perceived location. Our result shows that memory- and visually guided saccades are based on different spatial information. NEW & NOTEWORTHY We compared the effect of a perceptual illusion on two types of saccades, visually guided vs. memory-guided saccades, and found that whereas visually guided saccades were almost unaffected by the perceptual illusion, memory-guided saccades exhibited a strong effect of the illusion. Our result is the first evidence in the literature to show that visually and memory-guided saccades use different spatial representations.

Probing transsaccadic correspondence with reverse correlation.

The phenomenon of visual stability is classically explained by an internal forward model predicting the sensory consequences of an eye movement based on efference copy. However, this model cannot explain why some object displacements go undetected, a phenomenon that may depend on a passive prior belief that the world is stable. With reverse correlation, we investigated saccadic suppression of displacement and found that transsaccadic correspondence operates differently depending on the position of the postsaccadic visual target relative to the primary landing position; when the signal falls within the extent of primary saccadic scatter, observers are less able to remap accurately. Furthermore, we observed that the neural representations driving perceptual and saccadic decisions are similar when saccading to a target, but that the representations driving transsaccadic correspondence are different from those driving secondary saccades.

Transsaccadic perceptual fusion.

Transsaccadic perceptual fusion is the integration of pre- and postsaccadic images into a single percept aligned in spatial coordinates. Several early studies reported an absence of transsaccadic fusion between dissimilar patterns, effectively stopping research on this question for three decades. We have now corrected two problematic aspects of these earlier studies and find robust evidence for transsaccadic perceptual fusion. First, we used simple pre- and postsaccadic targets, (|, ) for which spatial alignment is not critical. Second, we reduced the contrast of the postsaccadic stimulus, so that it would not suppress fusion. Participants reported seeing a superposition of the pre- and postsaccadic targets on 67% of trials. Importantly, we obtained similar results when the two stimuli were presented without an intervening eye movement, suggesting the existence of a general fusion mechanism. Directional biases in the saccade condition suggest that remapping might be the mechanism realigning the pre- and postsaccadic locations. Remapping may thus not only predict where targets will be located after a saccade but may also guide content, predicting what targets will look like. However, the constraints on the appearance of the fused percept suggest that it plays, at best, a limited role in visual stability across saccades.

Saccades create similar mislocalizations in visual and auditory space.

Orienting our eyes to a light, a sound, or a touch occurs effortlessly, despite the fact that sound and touch have to be converted from head- and body-based coordinates to eye-based coordinates to do so. We asked whether the oculomotor representation is also used for localization of sounds even when there is no saccade to the sound source. To address this, we examined whether saccades introduced similar errors of localization judgments for both visual and auditory stimuli. Sixteen subjects indicated the direction of a visual or auditory apparent motion seen or heard between two targets presented either during fixation or straddling a saccade. Compared with the fixation baseline, saccades introduced errors in direction judgments for both visual and auditory stimuli: in both cases, apparent motion judgments were biased in direction of the saccade. These saccade-induced effects across modalities give rise to the possibility of shared, cross-modal location coding for perception and action.

Masking the saccadic smear.

Static visual stimuli are smeared across the retina during saccades, but in normal conditions this smear is not perceived. Instead, we perceive the visual scene as static and sharp. However, retinal smear is perceived if stimuli are shown only intrasaccadically, but not if the stimulus is additionally shown before a saccade begins, or after the saccade ends (Campbell & Wurtz, 1978). This inhibition has been compared to forward and backward metacontrast masking, but with spatial relations between stimulus and mask that are different from ordinary metacontrast during fixation. Previous studies of smear masking have used subjective measures of smear perception. Here we develop a new, objective technique for measuring smear masking, based on the spatial localization of a gap in the smear created by very quickly blanking the stimulus at various points during the saccade. We apply this technique to show that smear masking survives dichoptic presentation (suggesting that it is therefore cortical in origin), as well as separations of as much as 6° between smear and mask.

Development and learning of saccadic eye movements in 7- to 42-month-old children.

From birth, infants move their eyes to explore their environment, interact with it, and progressively develop a multitude of motor and cognitive abilities. The characteristics and development of oculomotor control in early childhood remain poorly understood today. Here, we examined reaction time and amplitude of saccadic eye movements in 93 7- to 42-month-old children while they oriented toward visual animated cartoon characters appearing at unpredictable locations on a computer screen over 140 trials. Results revealed that saccade performance is immature in children compared to a group of adults: Saccade reaction times were longer, and saccade amplitude relative to target location (10° eccentricity) was shorter. Results also indicated that performance is flexible in children. Although saccade reaction time decreased as age increased, suggesting developmental improvements in saccade control, saccade amplitude gradually improved over trials. Moreover, similar to adults, children were able to modify saccade amplitude based on the visual error made in the previous trial. This second set of results suggests that short visual experience and/or rapid sensorimotor learning are functional in children and can also affect saccade performance.

Trade-off between spatiotopy and saccadic plasticity.

Saccadic eye movements bring objects of interest onto the high-resolution fovea. They also change the retinal location of objects, but our impression of the visual world is stable: We represent our visual world in spatiotopic coordinates. Visual stability could be the result of a null hypothesis that things do not move during a saccade, or of realigning retinal images based on an internal copy of the eye movement (remapping). The current studies disentangled these hypotheses. Subjects saccaded to peripheral targets that were displaced by different amounts during execution, and detected or discriminated displacement direction. Evidence for a null hypothesis was provided by the relatively poor perceptual performance, and evidence for remapping by the independence of performance from saccade endpoint. There was a trade-off between spatiotopic performance and saccadic plasticity: Good performance (perception of displacements) led to small compensative modifications in saccade amplitude on the next trial while poor performance led to larger modifications. Results also showed that variations in saccade amplitude also depended on the size of the retinal error and of the saccade itself. These results suggest that when faced with a discrepancy between the saccade endpoint and visual target, the visual system attributes the discrepancy to object displacement or to saccade error, in which case the subsequent saccade is corrected. This result reconciles the two hypotheses by suggesting that accurate remapping serves oculomotor accuracy but not visual stability. Internal copies of eye movements may thus be used separately to establish spatiotopic representations and to maintain oculomotor accuracy.

Orthogonal steps relieve saccadic suppression.

Although the retinal position of objects changes with each saccadic eye movement, we perceive the visual world to be stable. How this visual stability or constancy arises is debated. Cancellation accounts propose that the retinal consequences of eye movements are compensated for by an equal-but-opposite eye movement signal. Assumption accounts propose that saccade-induced retinal displacements are ignored because we have a prior belief in a stable world. Saccadic suppression of displacement-the fact that small displacements of the visual targets during saccades go unnoticed-argues in favor of assumption accounts. Extinguishing the target before the displacement unmasks it, arguing in favor of cancellation accounts. We show that an irrelevant displacement of the target orthogonal to saccade direction unmasks displacements parallel to saccade direction, and therefore relieves saccadic suppression of displacement. This result suggests that visual stability arises from the interplay between cancellation and assumption mechanisms: When the post-saccadic target position falls within an elliptic region roughly equivalent to habitual saccadic variability, displacements are not seen and stability is assumed. When the displacements fall outside this region, as with our orthogonal steps, displacements are seen and positions are remapped.

The neural representation of stereotype content.

Judgments about social groups are characterized by their position in a representational space defined by two axes, warmth and competence. We examined serial dependence (SD) in evaluations of warmth and competence while measuring participants' electroencephalographic (EEG) activity, as a means to address the independence between these two psychological axes. SD is the attraction of perceptual reports towards things seen in the recent past and has recently been intensely investigated in vision. SD occurs at multiple levels of visual processing, from basic features to meaningful objects. The current study aims to (1) measure whether SD occurs between non-visual objects, in particular social groups and (2) uncover the neural correlates of social group evaluation and SD using EEG. Participants' judgments about social groups such as "nurses" or "accountants" were serially dependent, but only when the two successive groups were close in representational space. The pattern of results argues in favor of a non-separability between the two axes, because groups nearby on one dimension but far on the other were not subject to SD, even though that other dimension was irrelevant to the task at hand. Using representational similarity analysis, we found a brain signature that differentiated social groups as a function of their position in the representational space. Our results thus argue that SD may be a ubiquitous cognitive phenomenon, that social evaluations are serially dependent, and that reproducible neural signatures of social evaluations can be uncovered.

The relative importance of retinal error and prediction in saccadic adaptation.

When saccades systematically miss their visual target, their amplitude adjusts, causing the position errors to be progressively reduced. Conventionally, this adaptation is viewed as driven by retinal error (the distance between primary saccade endpoint and visual target). Recent work suggests that the oculomotor system is informed about where the eye lands; thus not all "retinal error" is unexpected. The present study compared two error signals that may drive saccade adaptation: retinal error and prediction error (the difference between predicted and actual postsaccadic images). Subjects made saccades to a visual target in two successive sessions. In the first session, the target was extinguished during saccade execution if the amplitude was smaller (or, in other experiments, greater) than the running median, thereby modifying the average retinal error subjects experienced without moving the target during the saccade as in conventional adaptation paradigms. In the second session, targets were extinguished at the start of saccades and turned back on at a position that reproduced the trial-by-trial retinal error recorded in the first session. Despite the retinal error in the first and second sessions having been identical, adaptation was severalfold greater in the second session, when the predicted target position had been changed. These results argue that the eye knows where it lands and where it expects the target to be, and that deviations from this prediction drive saccade adaptation more strongly than retinal error alone.

Serial dependence occurs at the level of both features and integrated object representations.

Object perception depends on mechanisms that transform the information received by our sensory receptors into a coherent and meaningful experience. Visual objects are made up of visual features (e.g., shape, color, orientation), which are, in large part, processed in parallel across different brain areas. The experience of unified objects thus requires binding features and brain signals. Our perception of objects is remarkably stable and constant, despite changes in the proximal stimulus caused by eye and body movements or changes in ambient lighting. Such spurious changes are not perceived. Object perception thus also depends on a mechanism that smooths perceptual samples across time, which has been called the continuity field and is quantified by serial dependence. In two studies, the relative levels of feature binding and serial dependence were examined. Participants reported perceived shape or emotional expression; reports were attracted to stimuli seen in the recent past. Results further show that serial dependence occurs both at the level of features and at the level of objects defined by a conjunction of features. The relative level of serial dependence depends on the type of feature or object: Serial dependence of shape occurs mostly independently of other features that define an object, whereas serial dependence of emotional expression occurs on the object-level representation that integrates several features. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The influence of suggestibility on memory.

We provide a translation of Binet and Henri's pioneering 1894 paper on the influence of suggestibility on memory. Alfred Binet (1857-1911) is famous as the author who created the IQ test that bears his name, but he is almost unknown as the psychological investigator who generated numerous original experiments and fascinating results in the study of memory. His experiments published in 1894 manipulated suggestibility in several ways to determine effects on remembering. Three particular modes of suggestion were employed to induce false recognitions: (1) indirect suggestion by a preconceived idea; (2) direct suggestion; and (3) collective suggestion. In the commentary we suggest that Binet and Henri's (1894) paper written over 115 years ago is still highly relevant even today. In particular, Binet's legacy lives on in modern research on misinformation effects in memory, in studies of conformity, and in experiments on the social contagion of memory.

Visual continuity during blinks and alterations in time perception.

Eye blinks strongly attenuate visual input, yet we perceive the world as continuous. How this visual continuity is achieved remains a fundamental and unsolved problem. A decrease in luminance sensitivity has been proposed as a mechanism but is insufficient to mask the even larger decrease in luminance because of blinks. Here we put forward a different hypothesis: visual continuity can be achieved through shortening of perceived durations of the sensory consequences of blinks. Here we probed the perceived durations of the blackouts caused by blinks and visual stimuli interrupted by blinks. We found that the perceived durations of blackouts because of blinks are about half as long as artificial blackouts immediately preceding or following the blink. Stimuli interrupted by blinks were perceived as briefer than uninterrupted stimuli, by about the same duration as the interruption-but so were stimuli interrupted by optically simulated blinks. There was a difference between real and simulated blinks, however: The decrease in perceived duration depended on the duration of the interruption for simulated, but not for real, blinks. These profound modifications in time perception during blinks show a way in which temporal processing contributes to the solution of an essential perceptual problem. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Presaccadic attention interferes with feature detection.

Preparing a saccadic eye movement to a particular spatial location enhances the perception of visual targets at this location and decreases perception of nearby targets prior to movement onset. This effect has been termed the orientation of pre-saccadic attention. Here, we investigated whether pre-saccadic attention influenced the detection of a simple visual feature-a process that has been hypothesized to occur without the need for attention. Participants prepared a saccade to a cued location and detected the occurrence of a "pop-out" feature embedded in distracters at the same or different location. The results show that preparing a saccade to a given location decreased detection of features at non-aimed-for locations, suggesting that the selection of a location as the next saccade endpoint influences sensitivity to basic visual features across the visual field.

Adaptation of within-object saccades can be induced by changing stimulus size.

Saccadic adaptation maintains saccade accuracy and has been studied with the intrasaccadic target displacement procedure: displacing a target backwards (or forwards) during saccade execution gradually decreases (or increases) subsequent saccade amplitude. Adaptation has traditionally been studied with targeting saccades which bring the eyes onto a new object. Within-object saccades take the eye from one position in an object to another position in the same object and have been shown to resist the intrasaccadic target displacement procedure. The amplitude of within-object saccades depends on object size rather than position, and we therefore hypothesized that within-object saccades might adapt in response to an intrasaccadic change in object size. In separate sessions, we increased or decreased object size during within-object saccade execution. Results showed amplitude lengthening or shortening, respectively. Furthermore, within-object saccade adaptation seems to share several characteristics with targeting-saccade adaptation.

Extraretinal signal metrics in multiple-saccade sequences.

Executing sequences of memory-guided movements requires combining sensory information with information about previously made movements. In the oculomotor system, extraretinal information must be combined with stored visual information about target location. The use of extraretinal signals in oculomotor planning can be probed in the double-step task. Using this task and a multiple-step version, the present study examined whether an extraretinal signal was used on every trial, whether its metrics represented desired or actual eye displacement, and whether it was best characterized as a direct estimate of orbital eye position or a vector representation of eye displacement. The results show that accurate information, including saccadic adaptation, about the first saccade is used to plan the second saccade. Furthermore, with multiple saccades, endpoint variability increases with the number of saccades. Controls ruled out that this was due to the perceptual or memory requirements of storing several target locations. Instead, each memory-guided movement depends on an internal copy of an executed movement, which may present a small discrepancy with the actual movement. Increasing the number of estimates increases the variability because this small discrepancy accumulates over several saccades. Such accumulation is compatible with a corollary discharge signal carrying metric information about saccade vectors.