Attentional modulation of adaptation to two-component transparent motion

A jsPsych touchscreen extension for behavioral research on touch-enabled interfaces

Online experiments are increasingly gaining traction in the behavioral sciences. Despite this, behavioral researchers have largely continued to use keyboards as the primary input devices for such online studies, overlooking the ubiquity of touchscreens in everyday use. This paper presents an open-source touchscreen extension for jsPsych, a JavaScript framework designed for conducting online experiments. We additionally evaluated the touchscreen extension assessing whether typical behavioral findings from two distinct perceptual decision-making tasks - the random-dot kinematogram and the Stroop task - can similarly be observed when administered via touchscreen devices compared to keyboard devices. Our findings indicate similar performance metrics for each paradigm between the touchscreen and keyboard versions of the experiments. Specifically, we observe similar psychometric curves in the random-dot kinematogram across the touchscreen and keyboard versions. Similarly, in the Stroop task, we detect significant task, congruency, and sequential congruency effects in both experiment versions. We conclude that our open-source touchscreen extension serves as a promising tool for data collection in online behavioral experiments on forced-choice tasks.

Task-dependent contribution to edge-based versus region-based texture perception

Texture segregation studies indicate that some types of textures are processed by edge-based and others by region-based mechanisms. However, studies employing nominally edge-based textures have found evidence for region-based processing mechanisms when the task was to detect rather than segregate the textures. Here we investigate directly whether the nature of the task determines if region-based or edge-based mechanisms are involved in texture perception. Stimuli consisted of randomly positioned Gabor micropattern texture arrays with five types of modulation: orientation modulation, orientation variance modulation, luminance modulation, contrast modulation and contrast variance modulation (CVM). There were four modulation frequencies: 0.1, 0.2, 0.4 and 0.8 cpd. Each modulation type was defined by three types of waveforms: sinewave (SN) with its smooth variations, square-wave (SQ) and cusp-wave (CS) with its sharp texture edges. The CS waveform was constructed by removing a sinewave from an equal amplitude square-wave. Participants performed two tasks: detection in which participants selected which of two stimuli contained the modulation and discrimination in which participants indicated which of two textures had a different modulation orientation. Our results indicate that threshold amplitudes in the detection task followed the ordering SQ < SN < CS across all spatial frequencies, consistent with detection being mediated by the overall energy in the stimulus and hence region based. With the discrimination task at low texture spatial frequencies and with CVM textures at all spatial frequencies the order was CS ≤ SQ with both < SN, consistent with being edge-based. We modeled the data by estimating the spatial frequency of a Difference of Gaussian filter that gave the largest peak amplitude response to the data. We found that the peak amplitude was lower for detection than discrimination across all texture types except for the CVM texture. We conclude that task requirements are critical to whether edges or regions underpin texture processing.

Inattentional aftereffects: The role of attention on the strength of the motion aftereffect

The way that attention affects the processing of visual information is one of the most intriguing fields in the study of visual perception. One way to examine this interaction is by studying the way perceptual aftereffects are modulated by attention. In the present study, we have manipulated attention during adaptation to translational motion generated by coherently moving random dots, in order to investigate the effect of the distraction of attention on the strength of the peripheral dynamic motion aftereffect (MAE). A foveal rapid serial visual presentation task (RSVP) of varying difficulty was introduced during the adaptation period while the adaptation and test stimuli were presented peripherally. Furthermore, to examine the interaction between the physical characteristics of the stimulus and attention, we have manipulated the motion coherence level of the adaptation stimuli. Our results suggested that the removal of attention through an irrelevant task modulated the MAE's magnitude moderately and that such an effect depends on the stimulus strength. We also showed that the MAE still persists with subthreshold and unattended stimuli, suggesting that perhaps attention is not required for the complete development of the MAE.

Lack of orientation specific adaptation to vertically oriented Glass patterns in human visual cortex: an fMRI adaptation investigation

The perception of coherent form configurations in natural scenes relies on the activity of early visual areas that respond to local orientation cues. Subsequently, high-level visual areas pool these local signals to construct a global representation of the initial visual input. However, it is still debated whether neurons in the early visual cortex respond also to global form features. Glass patterns (GPs) are visual stimuli employed to investigate local and global form processing and consist of randomly distributed dots pairs called dipoles arranged to form specific global configurations. In the current study, we used GPs and functional magnetic resonance imaging (fMRI) adaptation to reveal the visual areas that subserve the processing of oriented GPs. Specifically, we adapted participants to vertically oriented GP, then we presented test GPs having either the same or different orientations with respect to the adapting GP. We hypothesized that if local form features are processed exclusively by early visual areas and global form by higher-order visual areas, then the effect of visual adaptation should be more pronounced in higher tier visual areas as it requires global processing of the pattern. Contrary to this expectation, our results revealed that adaptation to GPs is robust in early visual areas (V1, V2, and V3), but not in higher tier visual areas (V3AB and V4v), suggesting that form cues in oriented GPs are primarily derived from local-processing mechanisms that originate in V1. Finally, adaptation to vertically oriented GPs causes a modification in the BOLD response within early visual areas, regardless of the relative orientations of the adapting and test stimuli, indicating a lack of orientation selectivity.

Attention relieves visual crowding: Dissociable effects of peripheral and central cues

Visual crowding can be reduced when attention is directed to the target by peripheral cues. However, it is unclear whether central cues relieve visual crowding to the same extent as peripheral cues. In this study, we combined the Posner cueing task and the crowding task to investigate the effect of exogenous and endogenous attention on crowding. In Experiment 1, five different stimulus-onset asychronies (SOAs) between the cue and the target and a predictive validity of 100% were adopted. Both attentional cues were shown to significantly reduce the effect of visual crowding, but the peripheral cue was more effective than the central cue. Furthermore, peripheral cues started to relieve visual crowding at the shortest SOA (100 ms), whereas central cues worked only at later SOAs (275 ms or above). When the predictive validity of the cue was decreased to 70% in Experiment 2, similar results to Experiment 1 were found, but the valid cue was less effective in reducing crowding than that in Experiment 1. In Experiment 3, when the predictive validity was decreased to 50%, a valid peripheral cue improved performance but a valid central cue did not, suggesting that endogenous attention but not exogenous attention can be voluntarily controlled when the cues are not predictive of the target's location. These findings collectively suggest that both peripheral and central cues can alleviate crowding, but they differ in terms of strength, time dynamics, and flexibility of voluntary control.

Adaptation and serial choice bias for low-level visual features are unaltered in autistic adolescents

Autism spectrum disorder (ASD), or autism, is characterized by social and non-social symptoms, including sensory hyper- and hyposensitivities. A suggestion has been put forward that some of these symptoms could be explained by differences in how sensory information is integrated with its context, including a lower tendency to leverage the past in the processing of new perceptual input. At least two history-dependent effects of opposite directions have been described in the visual perception literature: a repulsive adaptation effect, where perception of a stimulus is biased away from an adaptor stimulus, and an attractive serial choice bias, where perceptual choices are biased toward the previous choice. In this study, we investigated whether autistic participants differed in either bias from typically developing controls (TDs). Sixty-four adolescent participants (31 with ASD, 33 TDs) were asked to categorize oriented line stimuli in two tasks that were designed so that we would induce either adaptation or serial choice bias. Although our tasks successfully induced both biases, in comparing the two groups we found no differences in the magnitude of adaptation nor in the modulation of perceptual choices by the previous choice. In conclusion, we find no evidence of a decreased integration of the past in visual perception of low-level stimulus features in autistic adolescents.

Idiosyncratic preferences in transparent motion and binocular rivalry are dissociable

Previous studies revealed that there are idiosyncratic preferences to perceive certain motion directions in front during motion transparency depth rivalry (Mamassian & Wallace, 2010; Schütz, 2014). Meanwhile, other studies reported idiosyncratic preferences in binocular rivalry during the onset stage (Carter & Cavanagh, 2007; Stanley, Carter, & Forte, 2011). Here we investigated the relationship of idiosyncratic preferences in transparent motion and binocular rivalry. We presented two dot clouds that were moving in opposite directions. In the transparent motion condition, both dot clouds were presented to both eyes and participants had to report the dot cloud they perceived in front. In the binocular rivalry condition, the dot clouds were presented to different eyes and participants had to report the dominant dot cloud. There were strong idiosyncratic directional preferences in transparent motion and rather weak directional preferences in binocular rivalry. In general, binocular rivalry was dominated by biases in contrast polarity, whereas transparent motion was dominated by biases in motion direction. A circular correlation analysis showed no correlation between directional preferences in transparent motion and binocular rivalry. These findings show that idiosyncratic preferences in a visual feature can be dissociated at different stages of processing.

Invisible Adaptation: The Effect of Awareness on the Strength of the Motion Aftereffect

The ability to process information despite the lack of perceptual awareness is one of the most fascinating aspects of the visual system. Such unconscious processing is often investigated using adaptation, where any presence of the former can be traced by its footprint on aftereffects following the latter. We have investigated the mechanisms of the motion aftereffect (MAE) using random dot displays of varying motion coherence as well as crowding to modulate both the physical as well as the perceptual strength of the adaptation stimulus. Perceptual strength was quantitatively measured as the performance in a forced-choice direction-discrimination task. A motion-nulling technique was used to quantitatively measure the strength of the MAE. We show that the strength of the dynamic MAE is independently influenced by both the physical stimulus strength as well as the subjective perceptual strength, with the effect of the former being more prominent than that of the latter. We further show that the MAE still persists under conditions of subthreshold perception. Our results suggest that perceptual awareness can influence the strength of visual processing, but the latter is not fully dependent on the former and can still take place at its partial or even total absence.

Limited interactions between space- and feature-based attention in visually sparse displays

Top-down visual attention selectively filters sensory input so relevant information receives preferential processing. Feature-based attention (FBA) enhances the representation of relevant low-level features, whereas space-based attention (SBA) enhances information at relevant location(s). The present study investigates whether the unique influences of SBA and FBA combine to facilitate behavior in a perceptually demanding discrimination task. We first demonstrated that, independently, both color and location pre-cues could effectively direct attention to facilitate perceptual decision making of a target. We then examined the combined effects of SBA and FBA in the same design by deploying a predictive color arrow pre-cue. Only SBA effects were observed in performance accuracy and reaction time. However, we detected a reaction time cost when a valid spatial cue was paired with a feature cue. A computational perceptual decision-making model largely provided converging evidence that contributions from FBA were restricted to facilitating the speed with which the relevant item was identified. Our results suggest that both selection mechanisms can be used in isolation to resolve a perceptually challenging target in a sparse display, but with little additive perceptual benefit when cued simultaneously. We conclude that there is at least some higher order interdependence between space-based and feature-based selection during decision making under specific conditions.

Feature-based attention: effects and control

Feature-based attention prioritizes the processing of non-spatial features across the visual field. Classical studies revealed a feature-similarity gain modulation of sensory neuron's activity. While early studies that quantified behavioral performance have provided support for this model, recent studies have revealed a non-monotonic, surround suppression effect in near feature space. The attentional suppression effects may give rise to a highly limited capacity when selecting multiple features, as documented by studies manipulating the number of attended features. These effects of feature-based attention are likely due to attentional control mechanisms exerting top-down modulations, which have been linked to neural signals in the dorsal frontoparietal network. The neural representation of attentional priority at multiple levels of the visual hierarchy thus shape visual perception and behavioral performance.

Dichoptic vision in the absence of attention: neither fusion nor rivalry

When the two eyes' processing streams meet in visual cortex, two things can happen: sufficiently similar monocular inputs are combined into a fused representation, whereas markedly different inputs engage in rivalry. Interestingly, the emergence of rivalry appears to require attention. Withdrawing attention causes the alternating monocular dominance that characterizes rivalry to cease, apparently allowing both monocular signals to be processed simultaneously. What happens to these signals in this case, however, remains something of a mystery; are they fused into an integrated representation? In a set of experiments, we show this not to be the case: visual aftereffects are consistent with the simultaneous yet separate presence of two segregated monocular representations, rather than a joint representation. These results provide evidence that dichoptic vision without attention prompts a third and previously unknown mode, where both eyes' inputs receive equal processing, but escape interocular fusion.

Eye-specific pattern-motion signals support the perception of three-dimensional motion

An object moving through three-dimensional (3D) space typically yields different patterns of velocities in each eye. For an interocular velocity difference cue to be used, some instances of real 3D motion in the environment (e.g., when a moving object is partially occluded) would require an interocular velocity difference computation that operates on motion signals that are not only monocular (or eye specific) but also depend on each eye's two-dimensional (2D) direction being estimated over regions larger than the size of V1 receptive fields (i.e., global pattern motion). We investigated this possibility using 3D motion aftereffects (MAEs) with stimuli comprising many small, drifting Gabor elements. Conventional frontoparallel (2D) MAEs were local—highly sensitive to the test elements being in the same locations as the adaptor (Experiment 1). In contrast, 3D MAEs were robust to the test elements being in different retinal locations than the adaptor, indicating that 3D motion processing involves relatively global spatial pooling of motion signals (Experiment 2). The 3D MAEs were strong even when the local elements were in unmatched locations across the two eyes during adaptation, as well as when the adapting stimulus elements were randomly oriented, and specified global motion via the intersection of constraints (Experiment 3). These results bolster the notion of eye-specific computation of 2D pattern motion (involving global pooling of local, eye-specific motion signals) for the purpose of computing 3D motion, and highlight the idea that classically “late” computations such as pattern motion can be done in a manner that retains information about the eye of origin.

Feature-based attentional selection affects the perceived duration of a stimulus having two superposed patterns

The perceived duration of a visual event is highly related to stimulus attributes. It is well known that a moving stimulus appears to last longer than a static one does. Previous studies have demonstrated that the time dilation in a moving stimulus can be influenced by perceived motion, rather than by mere physical motion, and that a faster motion appears to last longer than a slower one does. However, whether a top-down attentional set for the feature value can modulate the time dilation in a moving stimulus when two different visual patterns coexist within the same region of the visual field is still unknown. To test this, in Experiment 1, we presented a moving and a static random-dot pattern simultaneously within the same region, and instructed the observer to attend to one of these two patterns. The results demonstrate that perceived duration was longer when attention was directed to the moving, rather than static pattern, although both patterns physically coexisted at the same time and place and for the same duration. In Experiment 2, slow and/or fast moving patterns were presented at the same time and place, and again, feature-based attentional selection affected the perceived duration of the identical physical display. These results suggest that attention to a moving stimulus is an essential factor that determines the time dilation in a moving stimulus. This study revealed that feature-based attention, as opposed to location-based attention, plays an important role in motion-induced time dilation.

Motion adaptation and attention: A critical review and meta-analysis

The motion aftereffect (MAE) provides a behavioural probe into the mechanisms underlying motion perception, and has been used to study the effects of attention on motion processing. Visual attention can enhance detection and discrimination of selected visual signals. However, the relationship between attention and motion processing remains contentious: not all studies find that attention increases MAEs. Our meta-analysis reveals several factors that explain superficially discrepant findings. Across studies (37 independent samples, 76 effects) motion adaptation was significantly and substantially enhanced by attention (Cohen's d = 1.12, p < .0001). The effect more than doubled when adapting to translating (vs. expanding or rotating) motion. Other factors affecting the attention-MAE relationship included stimulus size, eccentricity and speed. By considering these behavioural analyses alongside neurophysiological work, we conclude that feature-based (rather than spatial, or object-based) attention is the biggest driver of sensory adaptation. Comparisons between naïve and non-naïve observers, different response paradigms, and assessment of 'file-drawer effects' indicate that neither response bias nor publication bias are likely to have significantly inflated the estimated effect of attention.

Revisiting individual differences in the time course of binocular rivalry

Simultaneously showing an observer two incompatible displays, one to each eye, causes binocular rivalry, during which the observer regularly switches between perceiving one eye's display and perceiving the other. Observers differ in the rate of this perceptual cycle, and these individual differences have been reported to correlate with differences in the perceptual switch rate for other bistable perception phenomena. Identifying which psychological or neural factors explain this variability can help clarify the mechanisms underlying binocular rivalry and of bistable perception generally. Motivated by the prominent theory that perceptual switches during binocular rivalry are brought about by neural adaptation, we investigated whether perceptual switch rates are correlated with the strength of neural adaptation, indexed by visual aftereffects. We found no compelling evidence for such correlations. Moreover, we did not corroborate previous findings that switch rates are correlated between binocular rivalry and other forms of bistable perception. This latter nonreplication prompted us to perform a meta-analysis of existing research into correlations among forms of bistable perception, which revealed that evidence for such correlations is much weaker than is generally believed. By showing no common factor linking individual differences in binocular rivalry and in our other paradigms, these results fit well with other work that has shown such common factors to be rare among visual phenomena generally.

Attention Gates the Selective Encoding of Duration

The abundance of temporal information in our environment calls for the effective selection and utilization of temporal information that is relevant for our behavior. Here we investigated whether visual attention gates the selective encoding of relevant duration information when multiple sources of duration information are present. We probed the encoding of duration by using a duration-adaptation paradigm. Participants adapted to two concurrently presented streams of stimuli with different durations, while detecting oddballs in one of the streams. We measured the resulting duration after-effect (DAE) and found that the DAE reflects stronger relative adaptation to attended durations, compared to unattended durations. Additionally, we demonstrate that unattended durations do not contribute to the measured DAE. These results suggest that attention plays a crucial role in the selective encoding of duration: attended durations are encoded, while encoding of unattended durations is either weak or absent.

Selecting multiple features delays perception, but only when targets are horizontally arranged

Based on the finding that perception is lagged by attention split on multiple features (Lo et al., 2012), this study investigated how the feature-based lag effect interacts with the target spatial arrangement. Participants were presented with gratings the spatial frequencies of which constantly changed. The task was to monitor two gratings of the same or different colors and report their spatial frequencies right before the stimulus offset. The results showed a perceptual lag wherein the reported value was closer to the physical value some time prior to the stimulus offset. This lag effect was larger when the two gratings were of different colors than when they were the same color. Furthermore, the feature-based lag effect was statistically significant when the two gratings were horizontally arranged but not when they were vertically or diagonally arranged. A model is proposed to explain the effect of target arrangement: When targets are horizontally arranged, selecting an additional feature delays perception. When targets are vertically or diagonally arranged, target selection for the lower field is prioritized. This prioritization on the lower target might prompt observers to only select the lower target and ignore the upper one, and this causes more perceptual errors without delaying perception.

Body size and shape misperception and visual adaptation: An overview of an emerging research paradigm

Although body size and shape misperception (BSSM) is a common feature of anorexia nervosa, bulimia nervosa and muscle dysmorphia, little is known about its underlying neural mechanisms. Recently, a new approach has emerged, based on the long-established non-invasive technique of perceptual adaptation, which allows for inferences about the structure of the neural apparatus responsible for alterations in visual appearance. Here, we describe several recent experimental examples of BSSM, wherein exposure to “extreme” body stimuli causes visual aftereffects of biased perception. The implications of these studies for our understanding of the neural and cognitive representation of human bodies, along with their implications for clinical practice are discussed.

Low-level mediation of directionally specific motion aftereffects: Motion perception is not necessary

Previous psychophysical experiments with normal human observers have shown that adaptation to a moving dot stream causes directionally specific repulsion in the perceived angle of a subsequently viewed moving probe. In this study, we used a two-alternative forced choice task with roving pedestals to determine the conditions that are necessary and sufficient for producing directionally specific repulsion with compound adaptors, each of which contains two oppositely moving, differently colored component streams. Experiment 1 provided a demonstration of repulsion between single-component adaptors and probes moving at approximately 90° or 270°. In Experiment 2, oppositely moving dots in the adaptor were paired to preclude the appearance of motion. Nonetheless, repulsion remained strong when the angle between each probe stream and one component was approximately 30°. In Experiment 3, adapting dot pairs were kept stationary during their limited lifetimes. Their orientation content alone proved insufficient for producing repulsion. In Experiments 4–6, the angle between the probe and both adapting components was approximately 90° or 270°. Directional repulsion was found when observers were asked to visually track one of the adapting components (Exp. 6), but not when they were asked to attentionally track it (Exp. 5), nor while they passively viewed the adaptor (Exp. 4). Our results are consistent with a low-level mechanism for motion adaptation. This mechanism is not selective for stimulus color and is not susceptible to attentional modulation. The most likely cortical locus of adaptation is area V1.

No Effect of Featural Attention on Body Size Aftereffects

Prolonged exposure to images of narrow bodies has been shown to induce a perceptual aftereffect, such that observers' point of subjective normality (PSN) for bodies shifts toward narrower bodies. The converse effect is shown for adaptation to wide bodies. In low-level stimuli, object attention (attention directed to the object) and spatial attention (attention directed to the location of the object) have been shown to increase the magnitude of visual aftereffects, while object-based attention enhances the adaptation effect in faces. It is not known whether featural attention (attention directed to a specific aspect of the object) affects the magnitude of adaptation effects in body stimuli. Here, we manipulate the attention of Caucasian observers to different featural information in body images, by asking them to rate the fatness or sex typicality of male and female bodies manipulated to appear fatter or thinner than average. PSNs for body fatness were taken at baseline and after adaptation, and a change in PSN (ΔPSN) was calculated. A body size adaptation effect was found, with observers who viewed fat bodies showing an increased PSN, and those exposed to thin bodies showing a reduced PSN. However, manipulations of featural attention to body fatness or sex typicality produced equivalent results, suggesting that featural attention may not affect the strength of the body size aftereffect.

Interdependent Mechanisms for Processing Gender and Emotion: The Special Status of Angry Male Faces

While some models of how various attributes of a face are processed have posited that face features, invariant physical cues such as gender or ethnicity as well as variant social cues such as emotion, may be processed independently (e.g., Bruce and Young, 1986), other models suggest a more distributed representation and interdependent processing (e.g., Haxby et al., 2000). Here, we use a contingent adaptation paradigm to investigate if mechanisms for processing the gender and emotion of a face are interdependent and symmetric across the happy–angry emotional continuum and regardless of the gender of the face. We simultaneously adapted participants to angry female faces and happy male faces (Experiment 1) or to happy female faces and angry male faces (Experiment 2). In Experiment 1, we found evidence for contingent adaptation, with simultaneous aftereffects in opposite directions: male faces were biased toward angry while female faces were biased toward happy. Interestingly, in the complementary Experiment 2, we did not find evidence for contingent adaptation, with both male and female faces biased toward angry. Our results highlight that evidence for contingent adaptation and the underlying interdependent face processing mechanisms that would allow for contingent adaptation may only be evident for certain combinations of face features. Such limits may be especially important in the case of social cues given how maladaptive it may be to stop responding to threatening information, with male angry faces considered to be the most threatening. The underlying neuronal mechanisms that could account for such asymmetric effects in contingent adaptation remain to be elucidated.

Attending to Race (or Gender) Does Not Increase Race (or Gender) Aftereffects

Recent research has shown that attention can influence the strength of face aftereffects. For example, attending to changes in facial features increases the strength of identity and figural aftereffects relative to passive viewing (Rhodes et al., 2011). Here, we ask whether attending to a specific social dimension of a face (such as race or gender) influences the strength of face aftereffects along that dimension. Across three experiments, participants completed many single-shot face adaptation trials. In each trial, participants observed a computer-generated adapting face for 5 s while instructed to focus on either the race or gender of that adapting face. Adapting faces were either Asian and female or Caucasian and male. In Experiment 1, all trials included an intermediate question (IQ) following each adaptation period, soliciting a rating of the adapting face on the attended dimension (e.g., race). In Experiment 2, only half of the trials included this IQ, and in Experiment 3 only a quarter of the trials did. In all three experiments, participants were subsequently presented with a race- and gender-neutral face and asked to rate it on either the attended dimension (e.g., race, attention-congruent trials) or the unattended dimension (e.g., gender, attention-incongruent trials) using a seven-point scale. Overall, participants showed significant aftereffects in all conditions, manifesting as (i) higher Asian ratings of the neutral faces following Caucasian vs. Asian adapting faces and (ii) higher female ratings of neutral faces following male vs. female adapting faces. Intriguingly, although reaction times were shorter during attention-congruent vs. attention-incongruent trials, aftereffects were not stronger along attention-congruent than attention-incongruent dimensions. Our results suggest that attending to a facial dimension such as race or gender does not result in increased adaptation to that dimension.

Effect of Attention on the Initiation of Binocular Rivalry

Recent studies suggest that attention is necessary for perceptual alternations in binocular rivalry. It has been shown that attention plays a role in not only accelerating but also even enabling perceptual fluctuation in ongoing phase of binocular rivalry. In this study, we tested whether attention also plays a role in suppressing a rival stimulus in its initial phases by measuring proportions of mixed dominance. We hypothesized that when attention is directed toward the location of rival stimuli prior to their presentation, the proportion of mixed dominance is lower than when attention is directed away from that location because of attentional facilitation. However, we found that the proportion of mixed dominance did not differ depending on the locus of attention, although we adopted well-established experimental paradigms for manipulating spatial attention. This result suggests that attention is not a determining factor in establishing initial perceptual dominance in binocular rivalry.

Deconstructing Interocular Suppression: Attention and Divisive Normalization

In interocular suppression, a suprathreshold monocular target can be rendered invisible by a salient competitor stimulus presented in the other eye. Despite decades of research on interocular suppression and related phenomena (e.g., binocular rivalry, flash suppression, continuous flash suppression), the neural processing underlying interocular suppression is still unknown. We developed and tested a computational model of interocular suppression. The model included two processes that contributed to the strength of interocular suppression: divisive normalization and attentional modulation. According to the model, the salient competitor induced a stimulus-driven attentional modulation selective for the location and orientation of the competitor, thereby increasing the gain of neural responses to the competitor and reducing the gain of neural responses to the target. Additional suppression was induced by divisive normalization in the model, similar to other forms of visual masking. To test the model, we conducted psychophysics experiments in which both the size and the eye-of-origin of the competitor were manipulated. For small and medium competitors, behavioral performance was consonant with a change in the response gain of neurons that responded to the target. But large competitors induced a contrast-gain change, even when the competitor was split between the two eyes. The model correctly predicted these results and outperformed an alternative model in which the attentional modulation was eye specific. We conclude that both stimulus-driven attention (selective for location and feature) and divisive normalization contribute to interocular suppression.

In interocular suppression, a visible target presented in one eye can be rendered invisible by a competing image (the competitor) presented in the other eye. This phenomenon is a striking demonstration of the discrepancy between physical inputs to the visual system and perception, and it also allows neuroscientists to study how perceptual systems regulate competing information. Interocular suppression has been explained by mutually suppressive interactions (modeled by divisive normalization) between neurons that respond differentially to the two eyes. Attention, which selects relevant information in natural viewing condition, has also been found to play a role in interocular suppression. But the specific role of attentional modulation is still an open question. In this study, we proposed a computational model of interocular suppression integrating both attentional modulation and divisive normalization. By modeling the hypothetical neural responses and fitting the model to psychophysical data, we showed that interocular suppression involves an attentional modulation selective for the orientation of the competitor, and covering the spatial extent of the competitor. We conclude that both attention and divisive normalization contribute to interocular suppression, and that their impacts are distinguishable.

Suppression effects in feature-based attention

Attending to a feature enhances visual processing of that feature, but it is less clear what occurs to unattended features. Single-unit recording studies in middle temporal (MT) have shown that neuronal modulation is a monotonic function of the difference between the attended and neuron's preferred direction. Such a relationship should predict a monotonic suppressive effect in psychophysical performance. However, past research on suppressive effects of feature-based attention has remained inconclusive. We investigated the suppressive effect for motion direction, orientation, and color in three experiments. We asked participants to detect a weak signal among noise and provided a partially valid feature cue to manipulate attention. We measured performance as a function of the offset between the cued and signal feature. We also included neutral trials where no feature cues were presented to provide a baseline measure of performance. Across three experiments, we consistently observed enhancement effects when the target feature and cued feature coincided and suppression effects when the target feature deviated from the cued feature. The exact profile of suppression was different across feature dimensions: Whereas the profile for direction exhibited a "rebound" effect, the profiles for orientation and color were monotonic. These results demonstrate that unattended features are suppressed during feature-based attention, but the exact suppression profile depends on the specific feature. Overall, the results are largely consistent with neurophysiological data and support the feature-similarity gain model of attention.

A relational structure of voluntary visual-attention abilities

Many studies have examined attention mechanisms involved in specific behavioral tasks (e.g., search, tracking, distractor inhibition). However, relatively little is known about the relationships among those attention mechanisms. Is there a fundamental attention faculty that makes a person superior or inferior at most types of attention tasks, or do relatively independent processes mediate different attention skills? We focused on individual differences in voluntary visual-attention abilities using a battery of 11 representative tasks. An application of parallel analysis, hierarchical-cluster analysis, and multidimensional scaling to the intertask correlation matrix revealed 4 functional clusters, representing spatiotemporal attention, global attention, transient attention, and sustained attention, organized along 2 dimensions, one contrasting spatiotemporal and global attention and the other contrasting transient and sustained attention. Comparison with the neuroscience literature suggests that the spatiotemporal-global dimension corresponds to the dorsal frontoparietal circuit and the transient-sustained dimension corresponds to the ventral frontoparietal circuit, with distinct subregions mediating the separate clusters within each dimension. We also obtained highly specific patterns of gender difference and of deficits for college students with elevated attention-deficit/hyperactivity disorder traits. These group differences suggest that different mechanisms of voluntary visual attention can be selectively strengthened or weakened based on genetic, experiential, and/or pathological factors.

Effects of crowding and attention on high-levels of motion processing and motion adaptation

The motion after-effect (MAE) persists in crowding conditions, i.e., when the adaptation direction cannot be reliably perceived. The MAE originating from complex moving patterns spreads into non-adapted sectors of a multi-sector adapting display (i.e., phantom MAE). In the present study we used global rotating patterns to measure the strength of the conventional and phantom MAEs in crowded and non-crowded conditions, and when attention was directed to the adapting stimulus and when it was diverted away from the adapting stimulus. The results show that: (i) the phantom MAE is weaker than the conventional MAE, for both non-crowded and crowded conditions, and when attention was focused on the adapting stimulus and when it was diverted from it, (ii) conventional and phantom MAEs in the crowded condition are weaker than in the non-crowded condition. Analysis conducted to assess the effect of crowding on high-level of motion adaptation suggests that crowding is likely to affect the awareness of the adapting stimulus rather than degrading its sensory representation, (iii) for high-level of motion processing the attentional manipulation does not affect the strength of either conventional or phantom MAEs, neither in the non-crowded nor in the crowded conditions. These results suggest that high-level MAEs do not depend on attention and that at high-level of motion adaptation the effects of crowding are not modulated by attention.

Stimulus competition mediates the joint effects of spatial and feature-based attention

Distinct attentional mechanisms enhance the sensory processing of visual stimuli that appear at task-relevant locations and have task-relevant features. We used a combination of psychophysics and computational modeling to investigate how these two types of attention--spatial and feature based--interact to modulate sensitivity when combined in one task. Observers monitored overlapping groups of dots for a target change in color saturation, which they had to localize as being in the upper or lower visual hemifield. Pre-cues indicated the target's most likely location (left/right), color (red/green), or both location and color. We measured sensitivity (d') for every combination of the location cue and the color cue, each of which could be valid, neutral, or invalid. When three competing saturation changes occurred simultaneously with the target change, there was a clear interaction: The spatial cueing effect was strongest for the cued color, and the color cueing effect was strongest at the cued location. In a second experiment, only the target dot group changed saturation, such that stimulus competition was low. The resulting cueing effects were statistically independent and additive: The color cueing effect was equally strong at attended and unattended locations. We account for these data with a computational model in which spatial and feature-based attention independently modulate the gain of sensory responses, consistent with measurements of cortical activity. Multiple responses then compete via divisive normalization. Sufficient competition creates interactions between the two cueing effects, although the attentional systems are themselves independent. This model helps reconcile seemingly disparate behavioral and physiological findings.

Ocular tracking responses to background motion gated by feature-based attention

Involuntary ocular tracking responses to background motion offer a window on the dynamics of motion computations. In contrast to spatial attention, we know little about the role of feature-based attention in determining this ocular response. To probe feature-based effects of background motion on involuntary eye movements, we presented human observers with a balanced background perturbation. Two clouds of dots moved in opposite vertical directions while observers tracked a target moving in horizontal direction. Additionally, they had to discriminate a change in the direction of motion (±10° from vertical) of one of the clouds. A vertical ocular following response occurred in response to the motion of the attended cloud. When motion selection was based on motion direction and color of the dots, the peak velocity of the tracking response was 30% of the tracking response elicited in a single task with only one direction of background motion. In two other experiments, we tested the effect of the perturbation when motion selection was based on color, by having motion direction vary unpredictably, or on motion direction alone. Although the gain of pursuit in the horizontal direction was significantly reduced in all experiments, indicating a trade-off between perceptual and oculomotor tasks, ocular responses to perturbations were only observed when selection was based on both motion direction and color. It appears that selection by motion direction can only be effective for driving ocular tracking when the relevant elements can be segregated before motion onset.

Sustained attention is not necessary for velocity adaptation

Prolonged adaptation to a stimulus, such as a drifting grating, lowers sensitivity for detecting similar stimuli, and changes their appearance, for example, making gratings of the same orientation appear of lower contrast and move more slowly. It has been suggested that adaptation is increased by sustained attention to the adapting stimulus and is decreased by distracting attention with a competing task. This paper describes a novel 2AFC (spatial) measure of adaptation in which adaptation and bias are carefully distinguished by the random interleaving of different test conditions. The experiment revealed significant adaptation of perceived velocity, but no effect of attentional distraction.

Independent effects of adaptation and attention on perceived speed

Adaptation and attention are two mechanisms by which sensory systems manage limited bioenergetic resources: Whereas adaptation decreases sensitivity to stimuli just encountered, attention increases sensitivity to behaviorally relevant stimuli. In the visual system, these changes in sensitivity are accompanied by a change in the appearance of different stimulus dimensions, such as speed. Adaptation causes an underestimation of speed, whereas attention leads to an overestimation of speed. In the two experiments reported here, we investigated whether the effects of these mechanisms interact and how they affect the appearance of stimulus features. We tested the effects of adaptation and the subsequent allocation of attention on perceived speed. A quickly moving adaptor decreased the perceived speed of subsequent stimuli, whereas a slow adaptor did not alter perceived speed. Attention increased perceived speed regardless of the adaptation effect, which indicates that adaptation and attention affect perceived speed independently. Moreover, the finding that attention can alter perceived speed after adaptation indicates that adaptation is not merely a by-product of neuronal fatigue.

Limited featured-based attention to multiple features

Attending to a feature (e.g., color or motion direction) can enhance the early visual processing of that feature. However, it is not known whether one can simultaneously enhance multiple features. We examined people's ability to attend to multiple features in a feature cueing paradigm. Each trial contained two intervals consisting of a random dot motion stimulus. One interval (noise) had 0% coherence (no net motion), while the other interval (signal) moved in a particular direction with varying levels of coherence. Participants reported which interval contained the signal in one of three cueing conditions. In the one-cue condition, a line segment preceded the stimuli indicating the direction of the signal with 100% validity. In the two-cue condition, two lines preceded the stimuli, indicating the signal would move in one of the two cued directions. In the no-cue condition, no line segment appeared before the dot stimuli. In several experiments, we consistently observed a lower detection threshold in the one-cue condition than the no-cue condition, showing that participants can enhance processing of a single feature. However, detection threshold was consistently higher for the two-cue than one-cue condition, indicating that participants could not simultaneously enhance two motion directions as effectively as one direction. This finding revealed a severe capacity limit in our ability to enhance early visual processing for multiple features.

Feature-based attention enhances performance by increasing response gain

Covert spatial attention can increase contrast sensitivity either by changes in contrast gain or by changes in response gain, depending on the size of the attention field and the size of the stimulus (Herrmann et al., 2010), as predicted by the normalization model of attention (Reynolds & Heeger, 2009). For feature-based attention, unlike spatial attention, the model predicts only changes in response gain, regardless of whether the featural extent of the attention field is small or large. To test this prediction, we measured the contrast dependence of feature-based attention. Observers performed an orientation-discrimination task on a spatial array of grating patches. The spatial locations of the gratings were varied randomly so that observers could not attend to specific locations. Feature-based attention was manipulated with a 75% valid and 25% invalid pre-cue, and the featural extent of the attention field was manipulated by introducing uncertainty about the upcoming grating orientation. Performance accuracy was better for valid than for invalid pre-cues, consistent with a change in response gain, when the featural extent of the attention field was small (low uncertainty) or when it was large (high uncertainty) relative to the featural extent of the stimulus. These results for feature-based attention clearly differ from results of analogous experiments with spatial attention, yet both support key predictions of the normalization model of attention.

Motion adaptation does not depend on attention to the adaptor

Prolonged inspection of moving stimuli causes stationary stimuli to appear moving in the opposite direction to the adapting stimulus (the Waterfall effect). It has been claimed that distracting the viewer's attention from the adapting stimulus by a secondary task reduces the strength of adaptation. However, the method used to show the effect of distraction (the duration of the aftereffect) is potentially susceptible to bias. The experiments reported here show no effect in genuinely naïve subjects, or in experienced observers using a variety of cancellation procedures to measure the effect.

Wohlgemuth was right: distracting attention from the adapting stimulus does not decrease the motion after-effect

We determined whether distracting the observer's attention from an adapting stimulus could decrease the motion after-effect. Unlike previous studies we used a relatively bias-free 2AFC procedure to measure the strength of adaptation. The strength of motion adaptation was measured by the effects of a moving grating on the contrast discrimination (T vs. C) function for gratings moving in the same or opposite direction. As in previous reports, the effect of adaptation was to move the T vs. C function upwards and rightwards, consistent with an increase in the C50 (semi-saturation) response in the transduction function of the neural mechanism underlying the discrimination. On the other hand, manipulating the attentional load of a distracting task during adaptation had no consistent effect on contrast discrimination, including the absolute detection threshold. It is suggested that previous reported effects of attentional load on adaptation may have depended on response bias, rather than changes in sensitivity.

Feature-specific attentional priority signals in human cortex

Human can flexibly attend to a variety of stimulus dimensions, including spatial location and various features such as color and direction of motion. Although the locus of spatial attention has been hypothesized to be represented by priority maps encoded in several dorsal frontal and parietal areas, it is unknown how the brain represents attended features. Here we examined the distribution and organization of neural signals related to deployment of feature-based attention. Subjects viewed a compound stimulus containing two superimposed motion directions (or colors) and were instructed to perform an attention-demanding task on one of the directions (or colors). We found elevated and sustained functional magnetic resonance imaging response for the attention task compared with a neutral condition, without reliable differences in overall response amplitude between attending to different features. However, using multivoxel pattern analysis, we were able to decode the attended feature in both early visual areas (primary visual cortex to human motion complex hMT+) and frontal and parietal areas (e.g., intraparietal sulcus areas IPS1-IPS4 and frontal eye fields) that are commonly associated with spatial attention. Furthermore, analysis of the classifier weight maps showed that attending to motion and color evoked different patterns of activity, suggesting that different neuronal subpopulations in these regions are recruited for attending to different feature dimensions. Thus, our finding suggests that, rather than a purely spatial representation of priority, frontal and parietal cortical areas also contain multiplexed signals related to the priority of different nonspatial features.

Feature-based attention involuntarily and simultaneously improves visual performance across locations

Selective attention can selectively increase sensitivity to particular visual features in order to prioritize behaviorally relevant stimuli. Moreover, neural responses to attended feature values are boosted even at ignored locations. We provide behavioral evidence for involuntary and simultaneous effects of this "global" feature-based attention on visual performance. Observers were cued to attend to dots moving in a particular direction at one location (the primary task), while discriminating which of two groups of moving dots on the other side of the screen contained coherent motion (the secondary task). An analogous experiment tested selective attention to orientation. The secondary tasks did not require observers to discriminate or selectively attend to the particular feature values present. Nonetheless, sensitivity was highest when the direction or orientation happened to match the one cued in the primary task. By comparing performance to a neutral condition, we revealed more enhancement of attended feature values than suppression of others.

Visual attention: the past 25 years

This review focuses on covert attention and how it alters early vision. I explain why attention is considered a selective process, the constructs of covert attention, spatial endogenous and exogenous attention, and feature-based attention. I explain how in the last 25 years research on attention has characterized the effects of covert attention on spatial filters and how attention influences the selection of stimuli of interest. This review includes the effects of spatial attention on discriminability and appearance in tasks mediated by contrast sensitivity and spatial resolution; the effects of feature-based attention on basic visual processes, and a comparison of the effects of spatial and feature-based attention. The emphasis of this review is on psychophysical studies, but relevant electrophysiological and neuroimaging studies and models regarding how and where neuronal responses are modulated are also discussed.

Transient Attention Degrades Perceived Apparent Motion

Transient spatial attention refers to the automatic selection of a location that is driven by the stimulus rather than a voluntary decision. Apparent motion is an illusory motion created by stationary stimuli that are presented successively at different locations. In this study we explored the effects of transient attention on apparent motion. The motion target presentation was preceded by either valid attentional cues that attract attention to the target location in advance (experiments 1–4), neutral cues that do not indicate a location (experiments 1, 3, and 4), or invalid cues that direct attention to a non-target location (experiment 2). Valid attentional cues usually improve performance in various tasks. Here, however, an attentional impairment was found. Observers' ability to discriminate the direction of motion diminished at the cued location. Analogous results were obtained regardless of cue type: singleton cue (experiment 1), central non-informative cue (experiment 2), or abrupt onset cue (experiment 3). Experiment 4 further demonstrated that reversed apparent motion is less likely with attention. This seemingly counterintuitive attentional degradation of perceived apparent motion is consistent with several recent findings, and together they suggest that transient attention facilitates spatial segregation and temporal integration but impairs spatial integration and temporal segregation.

Constant spread of feature-based attention across the visual field

Attending to a feature in one location can produce feature-specific modulation in a different location. This global feature-based attention effect has been demonstrated using two stimulus locations. Although the spread of feature-based attention is presumed to be constant across spatial locations, it has not been tested empirically. We examined the spread of feature-based attention by measuring attentional modulation of the motion aftereffect (MAE) at remote locations. Observers attended to one of two directions in a compound motion stimulus (adapter) and performed a speed-increment task. MAE was measured via a speed nulling procedure for a test stimulus at different distances from the adapter. In Experiment 1, the adapter was at fixation, while the test stimulus was located at different eccentricities. We also measured the magnitude of baseline MAE for each location in two control conditions that did not require feature-based selection necessitated by a compound stimulus. In Experiment 2, the adapter and test stimuli were all located in the periphery at the same eccentricity. Our results showed that attention induced MAE spread completely across the visual field, indicating a genuine global effect. These results add to our understanding of the deployment of feature-based attention and provide empirical constraints on theories of visual attention.

A visual distracter task during adaptation reduces the proprioceptive movement aftereffect

Visual processing of basic perceptual attributes depends on attention. This has been well documented since the surprising initial report on attentional modulation of the visual motion aftereffect (Chaudhuri 1990). Here, we investigate proprioception and show for the first time that attention modulates adaptation to perceived limb movement. We used biceps vibration to induce illusory forearm extension in 10 participants and measured the aftereffect-perceived movement in the opposite direction. The aftereffect was largest when participants focused on the illusory extension during the adaptation period. To divert attention away from the illusory extension, a rapid serial visual presentation task was performed during the adaptation. The aftereffect was much smaller in this condition, indicating interference between the visual task and proprioceptive adaptation. In tests of an analogous interaction between audition and vision, earlier research found no effect. We suggest that conscious proprioception requires more attention than conscious processing of visual or auditory input.

Motion opponency and transparency in the human middle temporal area

Motion transparency is the perception of multiple, moving surfaces within the same retinal location (for example, a ripple on the surface of a drifting stream), and is an interesting challenge to motion models because multiple velocities must be represented within the same region of space. When these motion vectors are in opposite directions, brief in duration and spatially constrained within a very local region, the result is little or no perceived motion (motion opponency). Both motion transparency and motion opponency inhibit the firing rate of single middle temporal area (MT) neurons as compared with the preferred direction alone, but neither generally influences the firing rate of primary visual cortex neurons. Surprisingly, neuroimaging studies of human middle temporal area (hMT+) have found less activation due only to motion opponency and an increase in neural responses for motion transparency. Here we parametrically manipulate the local balance between competing motion vectors and find an interaction between motion opponency and transparency in the population blood oxygen level-dependent (BOLD) response. We find reduced BOLD amplitude for motion opponency throughout visual cortex, but weakened responses due to perceptual transparency that is most apparent only within the hMT+. We interpret our results as evidence for two distinct mechanisms mediating opponency and transparency.

Type of featural attention differentially modulates hMT+ responses to illusory motion aftereffects

Activity in the human motion complex (hMT(+)/V5) is related to the perception of motion, be it either real surface motion or an illusion of motion such as apparent motion (AM) or motion aftereffect (MAE). It is a long-lasting debate whether illusory motion-related activations in hMT(+) represent the motion itself or attention to it. We have asked whether hMT(+) responses to MAEs are present when shifts in arousal are suppressed and attention is focused on concurrent motion versus nonmotion features. Significant enhancement of hMT(+) activity was observed during MAEs when attention was focused either on concurrent spatial angle or color features. This observation was confirmed by direct comparison of adapting (MAE inducing) versus nonadapting conditions. In contrast, this effect was diminished when subjects had to report on concomitant speed changes of superimposed AM. The same finding was observed for concomitant orthogonal real motion (RM), suggesting that selective attention to concurrent illusory or real motion was interfering with the saliency of MAE signals in hMT(+). We conclude that MAE-related changes in the global activity of hMT(+) are present provided selective attention is not focused on an interfering feature such as concurrent motion. Accordingly, there is a genuine MAE-related motion signal in hMT(+) that is neither explained by shifts in arousal nor by selective attention.

Combining spatial and feature-based attention within the receptive field of MT neurons

This study investigates the effects of feature-based attention on responses of direction-selective neurons in the middle temporal area (MT) of macaque visual cortex to attended stimuli inside the receptive field. Redirecting attention between the preferred and null direction of transparent random dot motion patterns caused a mean modulation of responses of approximately 32%, about half of what was observed when the two directions of motion in the receptive field were spatially separated allowing feature-based and spatial attention to work in concert. This is consistent with models of visual attention that interpret the attentional modulation of a neuron as the combination of all attentional influences, treating stimulus location simply as another feature.

Maximal motion aftereffects in spite of diverted awareness

This study attempts to isolate the underlying processing resources of visual attention from the 'cognitive supervision'-working memory, decision processes, but especially awareness-that typically accompanies their allocation. To decouple them, we used the motion aftereffect (MAE) as a passive assay of resource allocation. In our main condition, observers were presented with an adapting field, but did not attend to it. Instead their effort was directed to an engrossing auditory two-back memory task. Consequently, observers had no consistent awareness of the adaptor, nor were able to make accurate judgements about its luminance, but nonetheless had MAE's no smaller than those induced when the adaptor was 'fully attended'. Similarly to when object- or feature-based attention spreads unwittingly, attention was allocated automatically to the adaptor, without requiring nor engaging executive control or awareness.

Feature-based attention and the suppression of non-relevant object features

Feature-directed attention has been recently studied in various psychophysical, electrophysiological, and imaging studies. Convincing evidence has been obtained for its global effectiveness, but there is a debate about the processing fate of non-attended target features. A number of studies demonstrated feature-directed attention being associated with co-selection of non-relevant object features, thus resulting in selection of the entire object, whereas most other studies did not examine the extent to which processing of non-attended features was affected. Here, we present the results of two psychophysical experiments consisting of a Posner-like paradigm in which subjects were cued either to an individual feature or the entire object. We measured reaction times to changes in speed or colour of one of two simultaneously presented gratings. Our results strongly support the view that feature-based selection is a unique selection process different from object-based selection in that it can be associated with active suppression of non-relevant features.