Location invariance in masked repetition priming of letters and words

Earlier studies have suggested that information from a prime stimulus can be integrated with target information even when the two stimuli appear at different spatial locations. Here, we examined such location invariance in a masked repetition priming paradigm with single letter and word stimuli. In order to neutralize effects of acuity and spatial attention on prime processing, subliminal prime stimuli always appeared on fixation. Target location varied randomly from trial to trial along the horizontal meridian at one of seven possible locations for letter stimuli (? 7° to + 7°) and three positions for word stimuli (? 4°, 0°, + 4°). Speed of responding to letter and word targets was affected by target location, and by priming, but the size of repetition priming effects did not vary as a function of target location. These results suggest that masked repetition priming is mediated by representations that integrate information about object identity independently of object location.     

Target localization among concurrent sound sources: No evidence for the inhibition of previous distractor responses

The visuospatial negative priming effect—that is, the slowed-down responding to a previously ignored location—is partly due to response inhibition associated with the previously ignored location (Buckolz, Goldfarb, & Khan, Perception & Psychophysics 66:837-845 2004). We tested whether response inhibition underlies spatial negative priming in the auditory modality as well. Eighty participants localized a target sound while ignoring a simultaneous distractor sound at another location. Eight possible sound locations were arranged in a semicircle around the participant. Pairs of adjacent locations were associated with the same response. On ignored repetition trials, the probe target sound was played from the same location as the previously ignored prime sound. On response control trials, prime distractor and probe target were played from different locations but were associated with the same response. On control trials, prime distractor and probe target shared neither location nor response. A response inhibition account predicts slowed-down responding when the response associated with the prime distractor has to be executed in the probe. There was no evidence of response inhibition in audition. Instead, the negative priming effect depended on whether the sound at the repeatedly occupied location changed identity between prime and probe. The latter result replicates earlier findings and supports the feature mismatching hypothesis, while the former is compatible with the assumption that response inhibition is irrelevant in auditory spatial attention.     

Oscillatory priming and form complexity

Detection of a target grouping is expedited when the target display is preceded by presentation of an oscillating premask that includes priming elements presented intraphasically and below detection threshold at the display locations subsequently occupied by the target. Five experiments were performed to investigate how priming is affected by both the complexity and the geometry of prime/target forms. Experiment 1 showed that the subjective complexity of different polygons was coded in accord with an objective measure of form complexity. Experiments 2 and 3 revealed oscillatory priming to increase as a function of the subjective complexity of prime/target forms when those forms were regular and predictable. However, Experiments 4 and 5 showed that this relation did not hold when the prime/target forms were irregular and unpredictable. Taken together, it is argued that both subjective complexity and the Pr?gnanz quality of the prime/target forms come to determine the magnitude of priming. These results are discussed with reference to current physiological hypotheses regarding perceptual organization.     

Vertical meridian asymmetry in spatial resolution: Visual and attentional factors

We investigated whether spatial resolution would be the same in the lower and upper halves of thevertical meridian (VM) of our visual field and whether attention would affect them differentially. It has been reported that (1) attending to the target’s location improves performance in a texture segregation task when the observer’s spatial resolution is too low (peripheral locations) but impairs it when resolution is already too high (central locations) for the task. This finding indicates an enhanced spatial resolution at the attended location (Yeshurun & Carrasco, 1998, 2000), (2) observers’ contrast sensitivity is higher in the lower than in the upper VM, a phenomenon known asvertical meridian asymmetry (VMA), an asymmetry determined by visual rather than by attentional factors (Carrasco, Talgar, & Cameron, 2001). In the present texture segregation task, performance was assessed under neutral- and peripheralcue conditions. Transient covert attention was systematically manipulated by using a peripheral cue that indicated the target’s location and its onset. Observers reported the interval containing a target patch appearing at one of a number of eccentricities in a large texture pattern along the VM. We found that (1) performance peaked at farther eccentricities in the lower than in the upper visual VM, indicating that resolution was higher in the lower half, and (2) the peripheral cue affected performance along the VM uniformly, indicating that the degree of enhanced resolution brought about by transient attention was constant along the VM. Thus, we conclude that the VMA for spatial resolution is determined by visual, not transient covert attentional, constraints.     

Spatial probability as an attentional cue in visual search

We investigated the role of spatial probabilities in target location during participants' performance of a visual search task. Experiments 1 and 2 demonstrated that spatial probabilities could serve as a powerful attentional bias that produced faster detection of targets in high-probability locations than of those in low- or random-probability locations. The effect could not be explained by repetition priming alone. Moreover, responses to targets in low-probability locations were slowed only when a distractor was present in the high-probability location. In Experiments 3-5, we compared the effects of spatial probability with an explicit endogenous cue and a salient exogenous cue. Facilitation due to spatial probability was independent of any benefit afforded by the explicit endogenous cue but interacted with the salient exogenous cue, such that the exogenous cue validity effect was compressed for targets in the high-probability location. Together, these results suggest that the spatial probabilities governing target location constitute a potent bias of visual processing and, as such, can be considered an attentional cue that differs from both typical explicit endogenous and salient exogenous cues.     

Evidence for split foci of attention in a priming paradigm

Most models of visuospatial attention include the notion that attention is dedicated to a single location in space. However, several researchers have found evidence that under appropriate circumstances, attention may be allocated to noncontiguous locations (e.g., Awh & Pashler, 2000; Bichot, Cave, & Pashler, 1999; Kramer & Hahn, 1995). In the present experiments, the spatial distribution of attention was assessed by a novel method, perceptual latency priming: the latency benefit of an attended visual stimulus, as compared with a nonattended stimulus. Experiment 1 assessed whether observers are able to attend to two nonadjacent regions or a region of variable size. Experiment 2 tested whether, when two distant locations are attended to, the region between them is necessarily also in the focus of attention. Two further experiments controlled for objections against the method used and replicated the main results of the first two experiments. The experiments showed a robust attentional priming effect at two noncontiguous locations of the visual field, simultaneous with little or no priming of the intervening location.     

Processing of distractors inside and outside the attentional focus in a priming procedure

A priming procedure was used to study the processing of distractors located either inside (between the location of two targets) or outside (peripherally to the locations of the targets) the focus of attention. The stimuli were five-letter arrays, and participants had to decide whether two marked target letters were the same or different. In Experiments 1 and 2, positive priming was obtained both when targets and in-distractors in primes repeated as targets in probes; negative priming was found when out-distractor primes repeated as targets in probes. In Experiment 3, we also manipulated the match in letter case from primes to probes. In-distractors produced reliable positive priming, irrespective of whether the letters matched in case. In contrast out-distractors produced negative priming but only when the letters had the same case in primes and probes. These results are attributed to a spatial attention process operating (in this case) on low-level visual features, and an object-based selection process that enables more abstract information to be processed for selected stimuli.     

Spatial attention can be biased towards an expected dimension

A commonly held view in both exogenous and endogenous orienting is that spatial attention is associated with enhanced processing of all stimuli at the attended location. However, we often search for a specific target at a particular location, so an observer should be able to jointly specify the target identity and expected location. Whether attention can bias dimension-specific processes at a particular location is not yet clear. We used a dual task to examine the effects of endogenous spatial cues on the accuracy of perceptual judgments of different dimensions. Participants responded to a motion target and a colour target, presented at the same or different locations. We manipulated a central cue to predict the location of the motion or colour target. While overall performance in the two tasks was comparable, cueing effects were larger for the target whose location was predicted by the cue, implying that when attending a particular location, processing of the likely dimension was preferentially enhanced. Additionally, an asymmetry between the motion and colour tasks was seen; motion was modulated by attention, and colour was not. We conclude that attention has some ability to select a dimension at a particular location, indicating integration of spatial and feature-based attention.     

Does Location Uncertainty Modulate Unconscious Processing Under Continuous Flash Suppression?

Previous research suggests that selective spatial attention is a determining factor for unconscious processing under continuous flash suppression (CFS), and specifically, that inattention toward stimulus location facilitates its unconscious processing by reducing the depth of CFS (Eo et al., 2016). The aim of our study was to further examine this modulation-by-attention model of CFS using a number priming paradigm. Participants (N = 26) performed a number comparison task on a visible target number (“compare target to five”). Prime-target pairs were either congruent (both smaller or larger than five) or incongruent. Spatial attention toward the primes was varied by manipulating the uncertainty of the primes’ location. Based on the modulation-by-attention model, we hypothesized the following: In trials with uncertain prime location, RTs for congruent prime-target pairs should be faster than for incongruent ones. In trials with certain prime location, RTs for congruent versus incongruent prime-target pairs should not differ. We analyzed our data with sequential Bayes factors (BFs). Our data showed no effect of location uncertainty on unconscious priming under CFS (BF0+ = 5.16). However, even visible primes only weakly influenced RTs. Possible reasons for the absence of robust number priming effects in our study are discussed. Based on exploratory analyses, we conclude that the numerical order of prime and target resulted in a response conflict and interfered with the predicted priming effect.     

Perceptual grouping and visual selective attention

The present study demonstrates that incongruent distractor letters at a constant distance from a target letter produce more response competition and negative priming when they share a target’s color than when they have a different color. Moreover, perceptual grouping by means of color, attenuated the effects of spatial proximity. For example, when all items were presented in the same color, near distractors produced more response competition and negative priming than far distractors (Experiment 3A). However, when near distractors were presented in a different color and far distractors were presented in the same color as the target, the response competition × distractor proximity interaction was eliminated and the proximity × negative priming interaction was reversed (Experiment 3B). A final experiment demonstrated that distractors appearing on the same object as a selected target produced comparable amounts of response competition and negative priming whether they were near or far from the target. This suggests that the inhibitory mechanisms of visual attention can be directed to perceptual groups/objects in the environment and not only to unsegmented regions of visual space.     

Time causes forgetting from working memory

Although forgetting in the short term is a ubiquitous phenomenon, its exact causes remain undecided. The aim of the present study was to test the temporal decay hypothesis according to which memory traces fade away with time when attention is diverted by concurrent activities. In two experiments involving complex span tasks, adults were asked to remember series of items (either letters or spatial locations) while verifying multiplications. The duration of processing was manipulated by presenting multiplications either in word (three    ×    four    =    twelve) or digit (3    ×    4    =    12) format, the former taking longer to solve, while the time available to restore memory traces after each operation was kept constant across conditions. In line with the temporal decay hypothesis, the longer solution times elicited by solving word multiplications resulted in poorer recall performance. The fact that longer processing times had a comparable effect on both verbal and visuospatial memory and that the difference between conditions remained stable from the first to the last trials makes it difficult to account for these findings by assuming that forgetting is exclusively due to representation-based interference or buildup of proactive interference.     

Evidence for 40-Hz oscillatory short-term visual memory revealed by human reaction-time measurements

Four experiments show that presentation of a synchronous premask frame within a 40-Hz, flickering premask matrix primes subsequent detection of a Kanizsa-type square by generation of a 40-Hz prime. Reaction time (RT) priming effects indicated a 150-200-ms prime duration following premask display. RTs were also found to be sensitive to the phase relationship between offset of the premask display relative to the onset time of the target: Priming effects were maximal when the target was presented out of phase with premask presentation (i.e., at interstimulus intervals displaced by 180 degrees relative to the 40-Hz rhythm of premask-frame presentation). Taken together, these results demonstrate the existence of a very short-term visual memory that oscillates at 40 Hz. The findings are discussed in the context of complementary psychological and neurophysiological findings related to visual-object coding and the role of gamma-band activity in the brain.     

The FeatureGate model of visual selection

The model presented here is an attempt to explain the results from a number of different studies in visual attention, including parallel feature searches and serial conjunction searches, variations in search slope with variations in feature contrast and individual subject differences, attentional gradients triggered by cuing, feature-driven spatial selection, split attention, inhibition of distractor locations, and flanking inhibition. The model is implemented in a neural network consisting of a hierarchy of spatial maps. Attentional gates control the flow of information from each level of the hierarchy to the next. The gates are jointly controlled by a Bottom-Up System favoring locations with unique features and a Top-Down System favoring locations with features designated as target features. Because the gating of each location depends on the features present there, the model is called FeatureGate. Received: 4 July 1997 / Accepted: 23 July 1998     

Top-down and bottom-up attentional control: on the nature of interference from a salient distractor.

In two experiments using spatial probes, we measured the temporal and spatial interactions between top-down control of attention and bottom-up interference from a salient distractor in visual search. The subjects searched for a square among circles, ignoring color. Probe response times showed that a color singleton distractor could draw attention to its location in the early stage of visual processing (before a 100-msec stimulus onset asynchrony [SOA]), but only when the color singleton distractor was located far from the target. Apparently the bottom-up activation of the singleton distractor's location is affected early on by local interactions with nearby stimulus locations. Moreover, probe results showed that a singleton distractor did not receive attention after extended practice. These results suggest that top-down control of attention is possible at an early stage of visual processing. In the long-SOA condition (150-msec SOA), spatial attention selected the target location over distractor locations, and this tendency occurred with or without extended practice.     

Top-down and bottom-up attentional control: On the nature of interference from a salient distractor

In two experiments using spatial probes, we measured the temporal and spatial interactions between top-down control of attention and bottom-up interference from a salient distractor in visual search. The subjects searched for a square among circles, ignoring color. Probe response times showed that a color singleton distractor could draw attention to its location in the early stage of visual processing (before a 100-msec stimulus onset asynchrony [SOA]), but only when the color singleton distractor was located far from the target. Apparently the bottom-up activation of the singleton distractor’s location is affected early on by local interactions with nearby stimulus locations. Moreover, probe results showed that a singleton distractor did not receive attention after extended practice. These results suggest that top-down control of attention is possible at an early stage of visual processing. In the long-SOA condition (150-msec SOA), spatial attention selected the target location over distractor locations, and this tendency occurred with or without extended practice.     

Locational representation in imagery: The third dimension

Six experiments were conducted to test the relative processing characteristics of picture-plane and three-dimensional imagery as indexed by tasks that required subjects to keep track of successive locations in multiunit visual displays. Subjects were shown symmetrical displays either drawn on cardboard or constructed with three-dimensional blocks. They then were required to imagine these matrices and follow pathways through a series of adjacent squares (blocks) within the matrices. The pathways were described by a series of verbal terms that indicated the direction of the next square (block) in the pathway. Subjects experienced difficulty in performing the task with picture-plane displays composed of as few as 16 squares (4×4), but they rarely made errors with a three-dimensional matrix of 27 blocks (3×3×3). Performance with the three-dimensional task dropped dramatically when the matrix size was increased to 4×4×4. The results replicated previous findings that the image processing capacity for location in two-dimensional imagery is about three units in each direction, and they indicate that adding the depth dimension increases the capacity for representation of spatial location in imagery.     

Visual attention amplifies response priming of pointing movements to color targets

We studied the influence of spatial visual attention on the time course of primed pointing movements. We measured pointing responses to color targets preceded by color stimuli priming either the same response as the target or the opposite response. The effects of visual attention at the prime and target locations were studied by varying both the cue-prime and prime-target intervals when presenting either exogenous attentional cues or, in a separate experiment, endogenous cues whose processing was a precondition for performing the task. Pointing trajectories revealed large priming effects in which pointing responses were first controlled by prime signals and then captured in midflight by target signals. Priming effects were strongly amplified when the relevant prime locations were visually attended at optimal cue-prime SOAs, with attention modulating the entire time course of the primed pointing movements. We propose that visual attention amplifies the earliest waves of visuomotor feedforward information, elicited in turn by primes and by targets.     

Probing attentional modulation of contextual cueing

The repetition of spatial layout implicitly facilitates visual search (contextual cueing effect; Chun & Jiang, 1998). Although a substantial number of studies have explored the mechanism underlying the contextual cueing effect, the manner in which contextual information guides spatial attention to a target location during a visual search remains unclear. We investigated the nature of attentional modulation by contextual cueing, using a hybrid paradigm of a visual search task and a probe dot detection task. In the case of a repeated spatial layout, detection of a probe dot was facilitated at a search target location and was inhibited at distractor locations relative to nonrepeated spatial layouts. Furthermore, these facilitatory and inhibitory effects possessed different learning properties across epochs (Experiment 1) and different time courses within a trial (Experiment 2). These results suggest that contextual cueing modulates attentional processing via both facilitation to the location of “to-be-attended” stimuli and inhibition to the locations of “to-be-ignored” stimuli.     

Developmental Differences in the Influence of Distractors on Maintenance in Spatial Working Memory

This study examined whether attention to a location plays a role in the maintenance of locations in spatial working memory in young children as it does in adults. This study was the first to investigate whether distractors presented during the delay of a spatial working-memory task influenced young children’s memory responses. Across 2 experiments, 3- and 6-year-olds completed a spatial working-memory task featuring a static target location and distractor location. Results indicated a change from 3 years to 6 years of age in how distractors influenced memory. Six-year-olds’ memory responses were biased away from a distractor that was close to the target location and on the outside of the target location relative to the center of the monitor. Distractors that were far from the target or that were toward the center of the monitor relative to the target location had no effect. Three-year-olds’ responses were biased toward a distractor when the distractor was on the outside of the target location and farther from the target. Distractors that were near the target location or toward the center of the monitor had no effect. These biases provide evidence that young children’s maintenance of a location in memory is influenced by attention.     

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.