Attentional shifts have little effect on the waveform of the chromatic onset VEP

Attention is important for sufficient performance on many visual tasks. This has been shown using achromatic steady‐state and pattern‐reversal VEPs. Waveform characteristics typically attenuate when attending to distractor stimuli and ignoring VEP stimuli. Chromatic pattern‐onset responses have not been tested under conditions of selective attention: as they can be used in clinical settings to test color vision, it is important to know what effects attentional shifts would have on this response. In the present study chromatic pattern‐onset VEPs were recorded using spatially divided and spatially contiguous VEP and distractor stimuli. VEP stimuli were 1 cycle.deg^?1 horizontal sine wave patterns (onset mode 100 ms on/400 ms off) used to selectively modulate the L?M and S‐(L+M) visual pathways. Distracter stimuli were letters. Subjects attended to either the letters or the gratings and pressed a button when a predetermined stimulus appeared. In Experiment one, VEP and distractor stimuli were superimposed and spatially contiguous. In Experiment two, stimuli were presented to different hemifields. No significant changes in waveform amplitude and latency were found between VEP and distractor attention conditions for either visual pathway. For the chromatic pattern‐onset response, modulation of attention does not change responses either with spatially contiguous or spatially separate selective attention manipulations. Consequently, it may not be necessary to monitor attention during recording of this response.     

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 ∼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.     

Divided attention effects in visual search are caused by objects not by space

Divided attention effects have been observed across a variety of stimuli and perceptual tasks, which have given rise to both object-based and space-based theories of divided attention. Object-based theories assert that processing information from multiple objects is limited, whereas space-based theories assert that processing information from multiple locations is limited. Extant results in the literature are collectively inconsistent with both simple object-based theories and simple space-based theories of divided attention. Using a visual search task with the extended simultaneous-sequential method to reveal capacity limitations, we found evidence of limited-capacity processing of object properties and unlimited-capacity processing of feature contrast. We found no evidence of a separate spatial limitation. A multiple pathway processing theory can account for these and a large body of previous results. According to this theory, tasks that require object processing must follow a limited-capacity pathway and therefore incur divided attention effects. Tasks that depend on only feature contrast can follow a separate unlimited-capacity processing pathway and therefore do not incur divided attention effects.     

Is there a serial bottleneck in visual object recognition?

Divided attention has little effect for simple tasks, such as luminance detection, but it has large effects for complex tasks, such as semantic categorization of masked words. Here, we asked whether the semantic categorization of visual objects shows divided attention effects as large as those observed for words, or as small as those observed for simple feature judgments. Using a dual-task paradigm with nameable object stimuli, performance was compared with the predictions of serial and parallel models. At the extreme, parallel processes with unlimited capacity predict no effect of divided attention; alternatively, an all-or-none serial process makes two predictions: a large divided attention effect (lower accuracy for dual-task trials, compared to single-task trials) and a negative response correlation in dual-task trials (a given response is more likely to be incorrect when the response about the other stimulus is correct). These predictions were tested in two experiments examining object judgments. In both experiments, there was a large divided attention effect and a small negative correlation in responses. The magnitude of these effects was larger than for simple features, but smaller than for words. These effects were consistent with serial models, and rule out some but not all parallel models. More broadly, the results help establish one of the first examples of likely serial processing in perception.     

Alertness and Visual Attention Impact Different Aspects of the Optokinetic Reflex

PurposeAssessing visual attention and alertness is of great importance in visual and cognitive neuroscience, providing objective measures valuable for both researchers and clinicians. This study investigates how the optokinetic response differs between levels of visual attention in healthy adults while controlling for alertness.MethodsTwelve healthy subjects (8 men and 4 women; mean age = 33 ± 9.36) with intact gaze-stability, visual acuity, and binocularity were recruited. Subjects viewed a rotating visual scene provoking torsional optokinetic nystagmus (OKN) while wearing a video eye tracker in a seated head-fixed position. Tasks requiring focused, neutral, and divided visual attention were issued to each subject and the OKN was recorded. Pupil sizes were monitored as a proxy for alertness.ResultsPupil dilation was increased for both focused and divided visual attention. The number of nystagmus beats was highest for the focused condition and lowest for the divided attentional task. OKN gain was increased during both focused and divided attention. The distribution of nystagmus beats over time showed that only focused attention produced a reliable adaptation of the OKN.ConclusionsResults consequently indicate that OKN frequency is adaptive to a viewer''s level of visual attention, whereas OKN gain is influenced by alertness levels. This pattern offers insight into the neural processes integrating visual input with reflexive motor responses. For example, it contextualizes why attention to visual stimuli can cause dizziness, as the OKN frequency reflects activity of the velocity storage mechanism. Additionally, the OKN could offer a possible venue for differentiating between visual attention and alertness during psychometric testing.     

Effects of attention on visual experience during monocular rivalry

There is a long-running debate over the extent to which volitional attention can modulate the appearance of visual stimuli. Here we use monocular rivalry between afterimages to explore the effects of attention on the contents of visual experience. In three experiments, we demonstrate that attended afterimages are seen for longer periods, on average, than unattended afterimages. This occurs both when a feature of the afterimage is attended directly and when a frame surrounding the afterimage is attended. The results of these experiments show that volitional attention can dramatically influence the contents of visual experience.     

Effects of feature-based attention on the motion aftereffect at remote locations

Previous studies have shown that attention to a particular stimulus feature, such as direction of motion or color, enhances neuronal responses to unattended stimuli sharing that feature. We studied this effect psychophysically by measuring the strength of the motion aftereffect (MAE) induced by an unattended stimulus when attention was directed to one of two overlapping fields of moving dots in a different spatial location. When attention was directed to the same direction of motion as the unattended stimulus, the unattended stimulus induced a stronger MAE than when attention was directed to the opposite direction. Also, when the unattended location contained either uncorrelated motion or had no stimulus at all an MAE was induced in the opposite direction to the attended direction of motion. The strength of the MAE was similar regardless of whether subjects attended to the speed or luminance of the attended dots. These results provide further support for a global feature-based mechanism of attention, and show that the effect spreads across all features of an attended object, and to all locations of visual space.     

Spatial attention and object-based attention: a comparison within a single task

There is now much experimental evidence supporting the idea that visual attention can be deployed in at least two ways: one space-based and other object-based. However, it is not clear whether space- and object-based attention work in an integrated way within the visual system. In this article, we present two experiments in which we compare both components of attention within a cueing paradigm. Participants had to discriminate the orientation of a line that appeared within one of four moving circles, differing in colour. A cue appearing close to one of the four circles indicated the location or circle where the target stimulus was likely to appear. Spatial and object cueing effects were observed: responses were faster when target appeared either at the precued location or within the precued object. In addition, the object-cueing effect occurred only when the cue was spatially invalid and not when it was spatially valid. These results suggest that object- and space-based attention interact, with selection by location being primary over object-based selection.     

Covert spatial attention in search for the location of a color-afterimage patch speeds up its decay from awareness: Introducing a method useful for the study of neural correlates of visual awareness

Previous research has reported that attention to color afterimages speeds up their decay. However, the inducing stimuli in these studies have been overlapping, thereby implying that they involved overlapping receptive fields of the responsible neurons. As a result it is difficult to interpret the effect of focusing attention on a phenomenally projected target-afterimage. Here, we present a method free from these shortcomings. In searching for a target-afterimage patch among spatially separate alternatives the target fades from awareness before its competitors. This offers a good means to study neural correlates of visual awareness unconfounded with attention and enabling a temporally extended pure phenomenal experience free from simultaneous inflow of sensory transients.     

Shared cognitive mechanisms involved in the processing of scene texture and scene shape

Recent research has demonstrated that the parahippocampal place area represents both the shape and texture features of scenes, with the importance of each feature varying according to perceived scene category. Namely, shape features are predominately more diagnostic to the processing of artificial human–made scenes, while shape and texture are equally diagnostic in natural scene processing. However, to date little is known regarding the degree of interactivity or independence observed in the processing of these scene features. Furthermore, manipulating the scope of visual attention (i.e., globally vs. locally) when processing ensembles of multiple objects—stimuli that share a functional neuroanatomical link with scenes—has been shown to affect their cognitive visual representation. It remains unknown whether manipulating the scope of attention impacts scene processing in a similar manner. Using the well-established Garner speeded-classification behavioral paradigm, we investigated the influence of both feature diagnosticity and the scope of visual attention on potential interactivity or independence in the shape and texture processing of artificial human–made scenes. The results revealed asymmetric interference between scene shape and texture processing, with the more diagnostic feature (i.e., shape) interfering with the less diagnostic feature (i.e., texture), but not vice versa. Furthermore, this interference was attenuated and enhanced with more local and global visual processing strategies, respectively. These findings suggest that the scene shape and texture processing are mediated by shared cognitive mechanisms and that, although these representations are governed primarily via feature diagnosticity, they can nevertheless be influenced by the scope of visual attention.     

Attention selectively enhances stimulus information for surround over foveal stimulus representations in occipital cortex

By attending to part of a visual scene, we can prioritize processing of the most relevant visual information and so use our limited resources effectively. Previous functional magnetic resonance imaging (fMRI) work has shown that attention can increase overall blood-oxygen-level-dependent (BOLD) signal responsiveness but also enhances the stimulus information in terms of classifier performance. Here, we investigate how these effects vary across the visual field. We compare attention-enhanced fMRI–BOLD amplitude responses and classifier accuracy in fovea and surrounding stimulus regions using a set of four simple stimuli subdivided into a foveal region (1.4° diameter) and a surround region (15° diameter). We found dissociations between the effects of attention on average response and in enhancing stimulus information. In early visual cortex, we found that attention increased the amplitude of responses to both foveal and surround parts of the stimuli and increased classifier performance only for the surround stimulus. Conversely, ventral visual areas showed less change in average response but greater changes in decoding. Unlike for early visual cortex, in the ventral visual cortex attention produced similar changes in decoding for center and surround stimuli.     

Perceptual consequences of feature-based attention

Attention modulates visual processing along at least two dimensions: a spatial dimension, which enhances the representation of stimuli within the focus of attention, and a feature dimension, which is thought to enhance attended visual features (e.g., upward motion) throughout the visual field. We investigate the consequences of feature-based attention onto visual perception, using dual-task human psychophysics and two distant drifting Gabor stimuli to systematically explore 64 combinations of visual features (orientations and drift speeds) and tasks (discriminating orientation or drift speed). The resulting single, consistent data set suggests a functional model, which predicts a maximum rule by which only the dominant product of feature enhancement and feature benefit by feature relevance may benefit perception.     

Stimulus-driven visual attention in mice

In primates, stimulus-driven changes in visual attention can facilitate or hinder perceptual performance, depending on the location and timing of the stimulus event. Mice have emerged as a powerful model for studying visual circuits and behavior; however, it is unclear whether mice show similar interactions between stimulus events and visual attention during perceptual decisions. To investigate this, we trained head-fixed mice to detect a near-threshold change in visual orientation and tested how performance was altered by task-irrelevant stimuli that occurred at different times and locations with respect to the orientation change. We found that task-irrelevant stimuli strongly affected mouse performance. Specifically, stimulus-driven attention in mice followed a similar time course as that in other species: The decreases in reaction times fully emerged between 250 and 400 ms after the stimulus event, and detection accuracy was not affected. However, the effects of stimulus-driven attention on behavior in mice were insensitive to stimulus-event location, an aspect different from what is known in primates. In contrast, reaction times in mice were reduced at longer delays after the task-irrelevant stimulus event regardless of its spatial congruence to the target. These results highlight the strengths and limitations of using mice as a model for studying higher-order visual functions.     

Effects of involuntary and voluntary attention on critical spacing of visual crowding

Visual spatial attention can be allocated in two distinct ways: one that is voluntarily directed to behaviorally relevant locations in the world, and one that is involuntarily captured by salient external stimuli. Precueing spatial attention has been shown to improve perceptual performance on a number of visual tasks. However, the effects of spatial attention on visual crowding, defined as the reduction in the ability to identify target objects in clutter, are far less clear. In this study, we used an anticueing paradigm to separately measure the effects of involuntary and voluntary spatial attention on a crowding task. Each trial began with a brief peripheral cue that predicted that the crowded target would appear on the opposite side of the screen 80% of the time and on the same side of the screen 20% of the time. Subjects performed an orientation discrimination task on a target Gabor patch that was flanked by other similar Gabor patches with independent random orientations. For trials with a short stimulus onset asynchrony between cue and target, involuntary capture of attention led to faster response times and smaller critical spacing when the target appeared on the cue side. For trials with a long stimulus onset asynchrony, voluntary allocation of attention led to faster reaction times but no significant effect on critical spacing when the target appeared on the opposite side to the cue. We additionally found that the magnitudes of these cueing effects of involuntary and voluntary attention were not strongly correlated across subjects for either reaction time or critical spacing.     

Effects of attention on a relative mislocalization with successively presented stimuli

Previous studies yielded evidence that the precision, with which stimuli are localized in the visual periphery, is improved under conditions of focused attention. The present study examined whether focused attention is able to correct a mislocalization recently observed with successively presented stimuli: when observers are asked to localize the peripheral position of a briefly presented target with respect to a previously presented comparison stimulus, they tended to judge the target as being more towards the fovea than was its actual position. In three experiments the mislocalization was tested under conditions with focused and distributed attention. Results revealed that the mislocalization increased with distributed attention and disappeared when stimuli appeared consistently at predictable positions and thus under conditions of focused attention. However, when a procedure with a trial-by-trial cueing was applied the mislocalization was only reduced, but not wiped out completely. In a recently developed dynamic field model consisting of interacting excitatory and inhibitory neuronal cell populations the results were explained as an attentional modulation of spontaneous (baseline) levels of neural activity.     

Hemifield asymmetry in the potency of exogenous auditory and visual cues

Neurologically normal subjects misperceive the midpoints of lines (PSE) as reliably leftward of veridical center, a phenomenon known as pseudoneglect. This leftward bias reflects the dominance of the right cerebral hemisphere in deploying spatial attention. Transient visual cues, delivered to either the left or right endpoints of lines, modulate PSE such that leftward biases are increased by leftward cues, and are decreased by rightward cues, relative to a no-cue control condition. We ask whether lateralized auditory cues can similarly influence PSE in a tachistoscopic visual line bisection task, and describe how visual and auditory cues, in spatially synergistic or antagonistic combinations, jointly influence PSE. Our results demonstrate that whereas auditory and visual cues both modulate PSE, visual cues are overall more potent than auditory cues. Visual and auditory cues are weighted such that visual cues are significantly more potent than auditory cues when visual cues are delivered to left hemispace. Visual and auditory cues are equipotent when visual cues are delivered to right hemispace. These results are consistent with the existence of independent lateralized networks governing the deployment of visuospatial and audiospatial attention. An analysis of the weighting of unisensory visual and auditory cues which optimally predicts PSE in multisensory cue conditions shows that cues combine additively. There was no evidence for a superadditive multisensory cue combination.     

Stimulus similarity modulates competitive interactions in human visual cortex

When multiple visual stimuli are simultaneously presented in a neuron's receptive field, they often interact with each other by mutually suppressing their visually evoked responses, suggesting that multiple stimuli present at the same time in the visual field compete for neural representation. Previous research has shown that these suppressive interactions can be biased by top-down influences such as spatially directed attention, as well as by the bottom-up factor of visual salience. Using fMRI, we asked whether competitive interactions might also be modulated by other bottom-up factors and tested the effects of stimulus similarity. Specifically, we found that suppressive interactions in area V4, measured by comparing activity evoked by simultaneous (potentially competing) and sequential (noncompeting) presentations, were reduced when four items were identical relative to when the four items differed in color and orientation. Such a result is consistent with the prediction that competition is more likely to occur between groups than within a group.     

Action modulates object-based selection

Cueing attention to one part of an object can facilitate discrimination in another part (Experiment 1 [Duncan, J. (1984). Selective attention and the organization of visual information. Journal of Experimental Psychology: General, 113, 501-517]; [Egly, R., Driver, J., & Rafal, R. D. (1994). Shifting visual attention between objects and locations: evidence from normal and parietal lesion subjects. Journal of Experimental Psychology: Human Perception and Performance, 123, 161-177]). We show that this object-based mediation of attention is disrupted when a pointing movement is prepared to the cued part; when a pointing response is prepared to a part of an object, discrimination does not differ between (i) stimuli at locations in the same object but distant to the part where the pointing movement is programmed and (ii) stimuli at locations equidistant from the movement but outside the object (Experiment 2). This remains true even when the pointing movement cannot be performed without first coding the whole object (Experiment 3). Our results indicate that pointing either (i) emphasizes spatial selection at the expense of object-based selection, or (ii) changes the nature of the representation(s) mediating perceptual selection. In addition, the results indicate that there can be a distinct effect on attention of movement to a specific location, separate from the top-down cueing of attention to another position (Experiment 3). Our data highlight the interactivity between perception and action.     

Comparing the time course and efficacy of spatial and feature-based attention

We investigated the time course of feature-based attention and compared it to the time course of spatial attention in an experiment with identical stimuli and task. Observers detected a speed increment in a compound motion stimulus preceded by cues that indicated either the target location or direction. The cue-target stimulus-onset-asynchrony (SOA) was varied to assess the time course of the attentional effect. We found that spatial attention was deployed earlier than feature-based attention and that both types of attention improved performance to a similar extent at a longer SOA. Results indicate that attention is a flexible mechanism allowing us to efficiently select task-relevant information based on either spatial or feature dimensions, but that spatial attention exert its effects faster.     

Reward-driven attention alters perceived salience

Many studies have revealed that reward-associated features capture attention. Neurophysiological evidence further suggests that this reward-driven attention effect modulates visual processes by enhancing low-level visual salience. However, no behavioral study to date has directly examined whether reward-driven attention changes how people see. Combining the two-phase paradigm with a psychophysical method, the current study found that compared with nonsalient cues associated with lower reward, the nonsalient cues associated with higher reward captured more attention, and increased the perceived contrast of the subsequent stimuli. This is the first direct behavioral evidence of the effect of reward-driven attention on low-level visual perception.