Attention and luminance detection: effects of cues, masks, and pedestals

Evidence from partially valid cueing that words are processed serially

There has been a longstanding debate about whether lexical and semantic processing of words is serial or parallel. We addressed this debate using partially valid cueing, where one of two words is cued. The cue was valid on 80% and invalid on the other 20% of the trials. The task was semantic categorization, and performance was measured by accuracy. The new feature was to limit attentional switching using a postmask of consonants that closely followed the presentation of words. We found a large effect of cueing and, most importantly, performance for the uncued word was at chance. This chance performance was consistent with serial processing, but not with typical parallel processing. This result adds to the evidence from other recent studies that the lexical and semantic processing of words is serial.

A major role for retrieval and/or comparison in the set-size effects of change detection

Set-size effects in change detection have been attributed to capacity limits in a variety of processes, including perception, memory encoding, memory storage, memory retrieval, comparison, and decision. In this study, we investigated the locus of the effect of increasing set size from 1 to 2. The task was to detect a 90 degree change in the orientation of 1 or 2 briefly presented Gabor patterns in noise. To measure purely attentional effects and not another phenomena, such as crowding, a precue was used to manipulate relevant set size while keeping the display constant. The locus of the capacity limit was determined by varying when observers were cued to a single relevant stimulus. To begin, we measured the baseline set-size effect for change detection. Next, a dual-task procedure and a 100% valid postcue was added to test for an effect of decision: This modification did not reliably change the set-size effects. In the critical experiments, a 100% valid cue was provided during the retention interval between displays, or only one stimulus was presented in the second display (local recognition). For both of these conditions, there was only a relatively small set-size effect. These results are consistent with the bulk of capacity limits being in memory retrieval or comparison and not in perception, memory encoding, or memory storage.

Spectral signature and behavioral consequence of spontaneous shifts of pupil-linked arousal in human

Arousal levels perpetually rise and fall spontaneously. How markers of arousal—pupil size and frequency content of brain activity—relate to each other and influence behavior in humans is poorly understood. We simultaneously monitored magnetoencephalography and pupil in healthy volunteers at rest and during a visual perceptual decision-making task. Spontaneously varying pupil size correlates with power of brain activity in most frequency bands across large-scale resting state cortical networks. Pupil size recorded at prestimulus baseline correlates with subsequent shifts in detection bias (c) and sensitivity (d’). When dissociated from pupil-linked state, prestimulus spectral power of resting state networks still predicts perceptual behavior. Fast spontaneous pupil constriction and dilation correlate with large-scale brain activity as well but not perceptual behavior. Our results illuminate the relation between central and peripheral arousal markers and their respective roles in human perceptual decision-making.

Endogenous cueing effects for detection can be accounted for by a decision model of selective attention

Spatial cues help participants detect a visual target when it appears at the cued location. One hypothesis for this cueing effect, called selective perception, is that cueing a location enhances perceptual encoding at that location. Another hypothesis, called selective decision, is that the cue has no effect on perception, but instead provides prior information that facilitates decision-making. We distinguished these hypotheses by comparing a simultaneous display with two spatial locations to sequential displays with two temporal intervals. The simultaneous condition had a partially valid spatial cue, and the sequential condition had a partially valid temporal cue. Selective perception predicts no cueing effect for sequential displays given there is enough time to switch attention. In contrast, selective decision predicts cueing effects for sequential displays regardless of time. We used endogenous cueing of a detection-like coarse orientation discrimination task with clear displays (no external noise or postmasks). Results showed cueing effects for the sequential condition, supporting a decision account of selective attention for endogenous cueing of detection-like tasks.

Cognitive load effects on early visual perceptual processing

Contrast-based early visual processing has largely been considered to involve autonomous processes that do not need the support of cognitive resources. However, as spatial attention is known to modulate early visual perceptual processing, we explored whether cognitive load could similarly impact contrast-based perception. We used a dual-task paradigm to assess the impact of a concurrent working memory task on the performance of three different early visual tasks. The results from Experiment 1 suggest that cognitive load can modulate early visual processing. No effects of cognitive load were seen in Experiments 2 or 3. Together, the findings provide evidence that under some circumstances cognitive load effects can penetrate the early stages of visual processing and that higher cognitive function and early perceptual processing may not be as independent as was once thought.

Effects of Exogenous and Endogenous Attention on Metacontrast Masking

To efficiently use its finite resources, the visual system selects for further processing only a subset of the rich sensory information. Visual masking and spatial attention control the information transfer from visual sensory-memory to visual short-term memory. There is still a debate whether these two processes operate independently or interact, with empirical evidence supporting both arguments. However, recent studies pointed out that earlier studies showing significant interactions between common-onset masking and attention suffered from ceiling and/or floor effects. Our review of previous studies reporting metacontrast-attention interactions revealed similar artifacts. Therefore, we investigated metacontrast-attention interactions by using an experimental paradigm, in which ceiling/floor effects were avoided. We also examined whether metacontrast masking is differently influenced by endogenous and exogenous attention. We analyzed mean absolute-magnitude of response-errors and their statistical distribution. When targets are masked, our results support the hypothesis that manipulations of the levels of metacontrast and of endogenous/exogenous attention have largely independent effects. Moreover, statistical modeling of the distribution of response-errors suggests weak interactions modulating the probability of "guessing" behavior for some observers in both types of attention. Nevertheless, our data suggest that any joint effect of attention and metacontrast can be adequately explained by their independent and additive contributions.

Rewards modulate saccade latency but not exogenous spatial attention

The eye movement system is sensitive to reward. However, whilst the eye movement system is extremely flexible, the extent to which changes to oculomotor behavior induced by reward paradigms persist beyond the training period or transfer to other oculomotor tasks is unclear. To address these issues we examined the effects of presenting feedback that represented small monetary rewards to spatial locations on the latency of saccadic eye movements, the time-course of learning and extinction of the effects of rewarding saccades on exogenous spatial attention and oculomotor inhibition of return. Reward feedback produced a relative facilitation of saccadic latency in a stimulus driven saccade task which persisted for three blocks of extinction trials. However, this hemifield-specific effect failed to transfer to peripheral cueing tasks. We conclude that rewarding specific spatial locations is unlikely to induce long-term, systemic changes to the human oculomotor or attention systems.

Olfactory test performance and its relationship with the perceived location of odors

Odors are generally perceived as arising via the nose when sniffed and as part of an orally located flavor during ingestion. The perceived location of an odor may in part be an attentional phenomenon, with concurrent oral stimulation occurring at the expense of access to the olfactory channel. Two predictions were derived from this account: (a) tasks dependent on a capacity to attend to the olfactory channel--odor discrimination and naming--should be adversely affected by oral localization; and (b) tasks not dependent upon a capacity to attend--incidental learning/recognition memory--should not. Using a procedure to generate oral localization, in which odors were presented via the nose with concurrent oral stimulation (sucrose, a viscous fluid or water), greater reported oral localization was associated with poorer odor discrimination and naming, but not with recognition memory performance. These results support the notion that attentional processes contribute to oral localization of odors by reducing the capacity to attend to the olfactory channel.

The effects of spatial and temporal cueing on metacontrast masking

We studied the effects of selective attention on metacontrast masking with 3 different cueing experiments. Experiments 1 and 2 compared central symbolic and peripheral spatial cues. For symbolic cues, we observed small attentional costs, that is, reduced visibility when the target appeared at an unexpected location, and attentional costs as well as benefits for peripheral cues. All these effects occurred exclusively at the late, ascending branch of the U-shaped metacontrast masking function, although the possibility exists that cueing effects at the early branch were obscured by a ceiling effect due to almost perfect visibility at short stimulus onset asynchronies (SOAs). In Experiment 3, we presented temporal cues that indicated when the target was likely to appear, not where. Here, we also observed cueing effects in the form of higher visibility when the target appeared at the expected point in time compared to when it appeared too early. However, these effects were not restricted to the late branch of the masking function, but enhanced visibility over the complete range of the masking function. Given these results we discuss a common effect for different types of spatial selective attention on metacontrast masking involving neural subsystems that are different from those involved in temporal attention.

Equality judgments cannot distinguish between attention effects on appearance and criterion: a reply to Schneider (2011)

Whether attention modulates the appearance of stimulus features is debated. Whereas many previous studies using a comparative judgment have found evidence for such an effect, two recent studies using an equality judgment have not. Critically, these studies have relied on the assumption that the equality paradigm yields bias-free PSE estimates and is as sensitive as the comparative judgment, without testing these assumptions. Anton-Erxleben, Abrams, and Carrasco (2010) compared comparative judgments and equality judgments with and without the manipulation of attention. They demonstrated that the equality paradigm is less sensitive than the comparative judgment and also bias-prone. Furthermore, they reported an effect of attention on the PSE using both paradigms. Schneider (2011) questions the validity of the latter finding, stating that the data in the equality experiment are corrupted because of skew in the response distributions. Notably, this argument supports the original conclusion by Anton-Erxleben et al.: that the equality paradigm is bias-prone. Additionally, the necessary analyses to show that the attention effect observed in Anton-Erxleben et al. was due to skew in the data were not conducted. Here, we provide these analyses and show that although the equality judgment is bias-prone, the effects we observe are consistent with an increase of apparent contrast by attention.

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.

Indexing the graded allocation of visuospatial attention using anticipatory alpha oscillations

Lateralization in the desynchronization of anticipatory occipitoparietal alpha (8-12 Hz) oscillations has been implicated in the allocation of selective visuospatial attention. Previous studies have demonstrated that small changes in the lateralization of alpha-band activity are predictive of behavioral performance but have not directly investigated how flexibly alpha lateralization is linked to top-down attentional goals. To address this question, we presented participants with cues providing varying degrees of spatial certainty about the location at which a target would appear. Time-frequency analysis of EEG data demonstrated that manipulating spatial certainty led to graded changes in the extent to which alpha oscillations were lateralized over the occipitoparietal cortex during the cue-target interval. We found that individual differences in alpha desynchronization contralateral to attention predicted reaction times, event-related potential measures of perceptual processing of targets, and beta-band (15-25 Hz) activity typically associated with response preparation. These results support the hypothesis that anticipatory alpha modulation is a plausible neural mechanism underlying the allocation of visuospatial attention and is under flexible top-down control.

Covert attention effects on spatial resolution

First, we review the characteristics of endogenous (sustained) and exogenous (transient) spatial covert attention. Then we examine the effects of these two types of attention on spatial resolution in a variety of tasks, such as acuity, visual search, and texture segmentation. Both types of covert attention enhance resolution; directing attention to a given location allows us to better resolve the fine details of the visual scene at that location. With exogenous attention, but not with endogenous attention, this is the case even when enhanced spatial resolution hampers performance. The enhanced resolution at the attended location comes about at the expense of lower resolution at the unattended locations.

Involuntary attention and brightness contrast

Carrasco, Ling, and Read (2004) reported that involuntary attention increased perceived contrast. We replicated Carrasco et al. and then tested an alternative hypothesis: With stimuli near threshold, a peripheral cue biased observers to believe a stimulus had been presented in the cued location. Consistent with this hypothesis, the effect disappeared when we used higher-contrast stimuli. We further tested the guessing-bias hypothesis in three ways: (1) In a detection experiment, the cue affected bias, but did not increase d'; (2) when the cue followed the stimulus, we obtained the same results as when the cue preceded the stimulus; (3) in one experiment, some trials contained no stimulus, yet observers responded that the cued blank stimulus had higher contrast than the uncued blank stimulus. The results suggest that the effects of a noninformative peripheral cue are best described in terms of nonperceptual biases.

Transient attention does increase perceived contrast of suprathreshold stimuli: a reply to Prinzmetal, Long, and Leonhardt (2008)

Carrasco, Ling, and Read (2004) showed that transient attention increases perceived contrast. However, Prinzmetal, Long, and Leonhardt (2008) suggest that for targets of low visibility, observers may bias their response toward the cued location, and they propose a cue-bias explanation for our previous results. Our response is threefold. First, we outline several key methodological differences between the studies that could account for the different results. We conclude that the cue-bias hypothesis is a plausible explanation for Prinzmetal et al.'s (2008) results, given the characteristics of their stimuli, but not for the studies by Carrasco and colleagues, in which the stimuli were suprathreshold (Carrasco, Ling, & Read, 2004; Fuller, Rodriguez, & Carrasco, 2008; Ling & Carrasco, 2007). Second, we conduct a study to show that the stimuli used in our previous studies are not near-threshold, but suprathreshold (Experiment 1, Phase 1). Furthermore, we found an increase in apparent contrast for a high-contrast stimulus when it was precued, but not when it was postcued, providing more evidence against a cue-bias hypothesis (Experiment 1, Phase 2). We also show that the visibility of the stimuli in Prinzmetal et al. (2008) was much lower than that of Carrasco, Ling, and Read, rendering their stimuli susceptible to their cue-bias explanation (Experiment 2). Third, we present a comprehensive summary of all the control conditions used in different labs that have ruled out a cue bias explanation of the appearance studies. We conclude that a cue-bias explanation may operate with near-threshold and low-visibility stimuli, as was the case in Prinzmetal et al. (2008), but that such an explanation has no bearing on studies with suprathreshold stimuli. Consistent with our previous studies, the present data support the claim that attention does alter the contrast appearance of suprathreshold stimuli.

Involuntary attention and identification accuracy

Using the spatial cuing paradigm, Prinzmetal, McCool, and Park (2005) made the distinction between voluntary and involuntary attention. They claimed that although accuracy was affected by an informative spatial cue (which controls voluntary attention), it was not affected by a noninformative cue (which controls involuntary attention). We reevaluate two reports that assert that noninformative spatial cues affect accuracy. Dufour (1999) reported that a noninformative auditory cue enhanced visual identification in a conjunction search task. Klein and Dick (2002) reported that, in an RSVP task with visual cues, the cue also enhanced accuracy at short stimulus onset asynchronies. We found that Dufour's results were due to overt orienting (eye movements) rather than to covert attention. The results of Klein and Dick were due either to location uncertainty or to a confounding of the order of stimulus presentation and condition.

Effect of attention on the detection and identification of masked spatial patterns

The effect of attention on the detection and identification of vertically and horizontally oriented Gabor patterns in the condition of simultaneous masking with obliquely oriented Gabors was studied. Attention was manipulated by varying the set size in a visual-search experiment. In the first experiment, small target Gabors were presented on the background of larger masking Gabors. In the detection task, the effect of set size was as predicted by unlimited-capacity signal detection theory. In the orientation identification task, increasing the set size from 1 to 8 resulted in a much larger decline in performance. The results of the additional experiments suggest that attention can reduce the crowding effect of maskers.

Mask-dependent attentional cuing effects in visual signal detection: the psychometric function for contrast

A spatial-cuing paradigm was used to test the hypothesis of Carrasco, Penpeci-Talgar, and Eckstein (2000) that the mask-dependent cuing effects found in visual signal detection by Smith (2000a) were caused by submaximal activation of the transient-orienting system. Mask-dependent cuing was found with a range of stimulus contrasts with pure peripheral cues and with the mixed central-peripheral cues of Smith (2000a), contrary to the predictions of the submaximal activation hypothesis. The use of a pedestal detection task to control spatial uncertainty showed that the cuing effect was due to signal enhancement. A model of mask-dependent cuing is described, which assumes that attention affects the rate of information accumulation from the display and that masks limit the visual persistence of the stimulus. The model correctly predicts differential mask dependencies in sensitivity for detection and discrimination and the associated patterns of response times.

Attention: Reaction Time and Accuracy Reveal Different Mechanisms

The authors propose that there are 2 different mechanisms whereby spatial cues capture attention. The voluntary mechanism is the strategic allocation of perceptual resources to the location most likely to contain the target. The involuntary mechanism is a reflexive orienting response that occurs even when the spatial cue does not indicate the probable target location. Voluntary attention enhances the perceptual representation of the stimulus in the cued location relative to other locations. Hence, voluntary attention affects performance in experiments designed around both accuracy and reaction time. Involuntary attention affects a decision as to which location should be responded to. Because involuntary attention does not change the perceptual representation, it affects performance in reaction time experiments but not accuracy experiments. The authors obtained this pattern of results in 4 different versions of the spatial cuing paradigm.

Location cuing and response time distributions in visual attention

The allocation of visual attention was investigated in two experiments. In Experiment 1 (n = 24), a peripheral cue was presented, and in Experiment 2 (n = 24), a central cue was used. In both experiments, cue validity was 90%, and the task was four-choice target identification. Response time distributions were collected for valid trials over five cue-target stimulus onset asynchronies (SOAs), and ex-Gaussian parameters were extracted. In both experiments, only the mean of the Gaussian component decreased as a function of cue-target SOA, which implied a strict time axis translation of the distributions. The results were consistent with sequential sampling models featuring a variable delay in the onset of information uptake.

The Attentional Dynamics of Masked Detection

A dichoptic masking procedure was used to test whether the mask-dependent cuing effects found in luminance detection by P. L. Smith (2000a) were due to integration masking or interruption masking. Attentional cuing enhanced detection sensitivity (d') when stimuli were backwardly masked with either dichoptic or monoptic masks, whereas no cuing effect was found with unmasked stimuli, implying the mask dependencies were due to interruption of stimulus processing in visual cortex by the mask. The effect is predicted by a gated diffusion process model in which masks interrupt stimulus processing and attention controls the flow of information to a sequential-sampling decision mechanism. The model correctly predicts different patterns of performance for detection and discrimination and cuing effects in simple reaction time.

Transient spatial attention degrades temporal resolution

To better understand the interplay between the temporal and spatial components of visual perception, we studied the effects of transient spatial attention on temporal resolution. Given that spatial attention sharpens spatial resolution, can it also affect temporal resolution? To assess temporal resolution, we measured the two-flash fusion threshold When two flashes of light are presented successively to the same location, the two-flash fusion threshold is the minimal interval between the flashes at which they are still perceived as two flashes, rather than a single flash. This assessment of temporal resolution was combined with peripheral precuing--a direct manipulation of transient spatial attention. This allowed us to demonstrate, for the first time, that spatial attention can indeed affect temporal resolution. However, in contrast to its effect on spatial resolution, spatial attention degrades temporal resolution. Two attentional mechanisms that could account for both attentional effects--enhanced spatial resolution and reduced temporal resolution--are discussed.

Covert attention accelerates the rate of visual information processing

Whenever we open our eyes, we are confronted with an overwhelming amount of visual information. Covert attention allows us to select visual information at a cued location, without eye movements, and to grant such information priority in processing. Covert attention can be voluntarily allocated, to a given location according to goals, or involuntarily allocated, in a reflexive manner, to a cue that appears suddenly in the visual field. Covert attention improves discriminability in a wide variety of visual tasks. An important unresolved issue is whether covert attention can also speed the rate at which information is processed. To address this issue, it is necessary to obtain conjoint measures of the effects of covert attention on discriminability and rate of information processing. We used the response-signal speed-accuracy tradeoff (SAT) procedure to derive measures of how cueing a target location affects speed and accuracy in a visual search task. Here, we show that covert attention not only improves discriminability but also accelerates the rate of information processing.

Spatial covert attention increases contrast sensitivity across the CSF: support for signal enhancement

This study is the first to report the benefits of spatial covert attention on contrast sensitivity in a wide range of spatial frequencies when a target alone was presented in the absence of a local post-mask. We used a peripheral precue (a small circle indicating the target location) to explore the effects of covert spatial attention on contrast sensitivity as assessed by orientation discrimination (Experiments 1-4), detection (Experiments 2 and 3) and localization (Experiment 3) tasks. In all four experiments the target (a Gabor patch ranging in spatial frequency from 0.5 to 10 cpd) was presented alone in one of eight possible locations equidistant from fixation. Contrast sensitivity was consistently higher for peripherally- than for neutrally-cued trials, even though we eliminated variables (distracters, global masks, local masks, and location uncertainty) that are known to contribute to an external noise reduction explanation of attention. When observers were presented with vertical and horizontal Gabor patches an external noise reduction signal detection model accounted for the cueing benefit in a discrimination task (Experiment 1). However, such a model could not account for this benefit when location uncertainty was reduced, either by: (a) Increasing overall performance level (Experiment 2); (b) increasing stimulus contrast to enable fine discriminations of slightly tilted suprathreshold stimuli (Experiment 3); and (c) presenting a local post-mask (Experiment 4). Given that attentional benefits occurred under conditions that exclude all variables predicted by the external noise reduction model, these results support the signal enhancement model of attention.