Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80-110 ms), occipital P1 (110-140 ms), and parietal N1 (130-180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135-220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350-750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in visuospatial attention over the adult lifespan

Shifts of visual attention elicited by spatial cues were examined for detection and letter-discrimination tasks in 90 normal adults ranging in age over each decade from the 20s to the 70s. Spatial cues were valid, invalid, or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7 degrees to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200, 500 and 2000 msec. Reaction time (RT) costs and benefits associated with spatial cueing did not vary with age for: (1) the detection task; (2) the letter-discrimination task with peripheral cues; and (3) the letter-discrimination task with central cues at a short (200 msec) SOA. RT costs and benefits increased with age only for SOAs greater than 200 msec with central cueing in the discrimination task. In general, the efficiency of cue-based shifts of visuospatial attention appears relatively resistant to the effects of adult age up to 79 years. When an age effect was found, RT costs and benefits increased steadily across all age decades, the correlation with age being 0.25 and 0.38 for the 500 and 2000 msec SOAs, respectively. The findings suggest a qualitative difference in the influence of normal adult aging and effects of dementia noted in previous studies; normal aging has only a weak influence on voluntary attention shifts, whereas dementia affects both voluntary and involuntary modes of attention shifting.     

The gap effect during visual and auditory stimulation using manual responses

Six experiments were conducted in naive human participants to examine any facilitation produced in manual reaction time (RT) by the interposition of a temporal gap between a warning signal and an imperative signal. Peripheral visual stimuli and monoaural auditory stimuli were used as targets. Participants showed a facilitation of RTs to the targets for both auditory and visual stimuli in the five experiments in which RTs were the dependent variable. In addition, the gap effect increased over successive blocks of trials, suggesting learning. RTs were facilitated only when the gap had predictive value and was salient. Using a variable temporal gap or visual warning stimulus did not change the facilitation in RTs. A further experiment demonstrated that the gap can be perceived by the participants. The dissociation between a learned and a non-learned component in the gap effect suggests that the temporal gap induces two independent processes: warning and disengagement of attention.     

Auditory and visual capture during focused visual attention.

It is well known that auditory and visual onsets presented at a particular location can capture a person’s visual attention. However, the question of whether such attentional capture disappears when attention is focused endogenously beforehand has not yet been answered. Moreover, previous studies have not differentiated between capture by onsets presented at a nontarget (invalid) location and possible performance benefits occurring when the target location is (validly) cued. In this study, the authors modulated the degree of attentional focus by presenting endogenous cues with varying reliability and by displaying placeholders indicating the precise areas where the target stimuli could occur. By using not only valid and invalid exogenous cues but also neutral cues that provide temporal but no spatial information, they found performance benefits as well as costs when attention is not strongly focused. The benefits disappear when the attentional focus is increased. These results indicate that there is bottom-up capture of visual attention by irrelevant auditory and visual stimuli that cannot be suppressed by top-down attentional control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual offsets facilitate saccadic latency: Does predisengagement of visuospatial attention mediate this gap effect?

Saccadic reaction time (RT) is reduced when a fixation stimulus is extinguished 200 msec before a target appears. An attentional predisengagement theory (APT) may explain this gap effect: When covert attention is engaged (e.g., on fixation), the saccadic system is inhibited and RT is delayed; when the attended stimulus is extinguished, attention is disengaged, the inhibition is removed, and RT is facilitated. In 3 experiments covert attention was endogenously or exogenously cued to an object on the vertical meridian. Onset of a saccadic target on the horizontal meridian could be preceded by the offset of an attended or unattended object. Contrary to APT, RTs were identical after attended and unattended offsets. Results suggest that the gap effect has 2 components, and covert visual attention plays no role. One component is motor system preparation; the other is a fixation offset effect specific to the oculomotor system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of strategic effects in the modulation of orienting of attention

Two models of visual orienting of attention are frequently described. Voluntary orienting is usually induced by central cues that direct subjects' attention to a given location in the visual space. Automatic orienting is provoked by presentation of peripheral cues. It is shown that automatic orienting induces greater attentional costs and benefits, and is less under a subject's control (Jonides 1981). Furthermore, it is not similarly affected by factors such as signal eccentricity (Umiltà et al. 1991). The present experiment was undertaken to investigate how sensitive automatic orienting produced by peripheral cues is to voluntary modulations of attention. In experiment 1, subjects facing situations daily in which attentional requirements are high, were compared to non-practiced ones. In experiment 2, other groups of practiced subjects facing high or low attentional-demanding situations were tested. In both experiments, subjects were asked to respond to signals, presented in rapid succession, in one of two possible locations in space, on each side of central fixation point. The cue signal automatically oriented attention to one of the two locations in which a first stimulus was presented with 100% probability; 100 ms after the first response (RT1), a second response signal (RT2) was delivered either in the same location (valid condition) or in the opposite location (invalid condition). Four cue probabilities were manipulated for this second stimulus: 100%/0%, 80%/20%, 50%/50%, and 20%/80%. Two eccentricities of 3 degrees and 6 degrees were tested. RT2 data demonstrated that (1) there was no eccentricity effect; (2) the higher the cue probability, the greater were the attentional costs; (3) the attentional effects were smaller in the practiced subjects who faced attention-demanding situations daily, than in the other groups. Put together, these data suggest that automatic orienting of attention can be modulated by voluntary attentional processes, according to cue probability. Furthermore, experienced subjects seem to be able to better distribute their attentional resources in space, with increased task requirements. The adoption of an optimal criterion might lead to the use of a cost minimizing strategy.     

Global-local analysis in HIV-1 infection.

One hundred twenty-one HIV-seropositive (HIV+) individuals and 85 seronegative controls performed a divided-attention task that engaged automatic and controlled attentional processing. Reaction times (RTs) to global and local targets that varied in probability were measured in 5 conditions. A neutral condition where global and local targets were equally probable was included as baseline. Participants showed expected tradeoffs in RTs as a function of target-level probability, with longer RTs to less probable targets and shorter RTs to more probable targets. However, the HIV+ group showed significantly greater costs compared with controls. Results are consistent with previous findings that HIV+ individuals are selectively impaired on tasks of controlled attentional processing, particularly under conditions of divided attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial attention effects in macaque area V4

Focal visual attention typically produces enhanced perceptual processing at the psychological level and relatively stronger neural responses at the physiological level. A longstanding mechanistic question is whether these attentional effects pertain specifically to the attended (target) object or to the region of space it occupies. We show here that attentional response enhancement in macaque area V4 extends to behaviorally irrelevant objects in the vicinity of the target object, indicating that focal attention has a strong spatial component at the physiological level. In addition, we find that spatial attention effects typically show a striking directional asymmetry. The direction of the asymmetry varies between cells, so that some cells respond best when attention is directed to the left of the stimulus, some when attention is directed to the right, etc. Thus, attention involves not only enhanced responses to behavioral targets but also a complex modulation of responses to other stimuli in the surrounding visual space.     

Spatial attention and the apprehension of spatial relations.

Seven experiments examined the role of spatial attention in apprehending spatial relations above, below, left, and right. In Exp 1, visual search was difficult when targets differed from distractors only in the spatial relation between their elements. Reaction time (RT) increased linearly with display size with a slope greater than 60 msec/item. In Exp 2, search was easy (the slope was flat) when targets differed from distractors in the identity of their elements. In Exps 3 and 4, target position was cued with a discrepant color, and performance was better when attention was pulled toward spatial-relation targets than away from them. Exps 5–7 generalized the results over different displays and extended practice. The results suggest that apprehending spatial relations requires spatial attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anxiety, Attention, and Coping with Threat.

It was hypothesized that anxiety provoked by a threat over which S had no control would lead to reduced responsiveness to stimuli in the periphery of attention, but that no such effect would be evident when S was given a means of coping with the threat. Ss threatened with shock performed no differently than an unthreatened control group on a tracking task occupying the center of their attention, but had significantly longer reaction times (RTs) to lights which went on occasionally at the periphery of their visual field. Ss told they could avoid the shock with good performance showed no such increase in RT. Some of the effects of anxiety were discussed in terms of these attentional changes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What is inhibited in inhibition of return.

Research on temporal-order judgments, reference frames, discrimination tasks, and links to oculomotor control suggest important differences between inhibition of return (IOR) and attentional costs and benefits. Yet, it is generally assumed that IOR is an attentional effect even though there is little supporting evidence. The authors evaluated this assumption by examining how several factors that are known to influence attentional costs and benefits affect the magnitude of IOR: target modality, target intensity, and response mode. Results similar to those previously reported for attention were observed: IOR was greater for visual than for auditory targets, showed an inverse relationship with target intensity, and was equivalent for manual and saccadic responses. Important parallels between IOR and attentional costs and benefits are indicated, suggesting that, like attention, IOR may in part affect sensory-perceptual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

There’s little return for attentional momentum.

Inhibition of return (IOR) refers to a delay in response time (RT) to targets appearing at a previously cued location. The prevailing view is that IOR reflects visual-motor inhibition. The “attentional momentum” account rejects this idea, and instead proposes that IOR reflects an automatic shift of attention away from the cued location resulting in slower RTs to targets presented there and speeded RTs to targets opposite the cue (an opposite facilitation effect or OFE). The drawback of this account is that J. J. Snyder, W. C. Schmidt, and A. Kingstone (2001) showed that there are few data to support the OFE, and no evidence that the OFE accounts for the IOR effect. Despite this evidence, several recent studies have promoted attentional momentum as a valid explanation for the IOR effect. Reanalysis of these recent studies and new data reveal, again, that IOR routinely occurs in the absence of the OFE, and when the OFE does occur, the IOR effect need not be present. This double dissociation invalidates attentional momentum as an explanation for the IOR effect. Extant data support an inhibitory explanation of the IOR effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of altering brain cholinergic activity on covert orienting of attention: comparison of monkey and human performance

Experiments were conducted to elucidate the role of the cholinergic neurotransmitter system in arousal and the orienting of attention to peripheral targets. Rhesus monkeys and humans fixated a visual stimulus and responded to the onset of visual targets presented randomly in two visual field locations. The target was preceded by a valid cue (cue and target at the same location), an invalid cue (cue and target to opposite locations), a double cue (cues to both spatial locations, target to one), or, the cue was omitted (no-cue, target to either location). Reaction times (RTs) to the onset of the target were recorded. For monkeys, systemic injections of nicotine (0.003-0.012 mg/kg) or atropine (0.001-0.01 mg/kg), but not saline control injections, reduced mean RTs for all trials, indicating general behavioral stimulation. In addition, nicotine significantly reduced RTs for invalid trials but had little additional effect on those for valid, double, or no-cue trials. Virtually identical effects were observed for human chronic tobacco smokers in performing the same task following cigarette smoking. Injections of atropine in monkeys had no effect on RTs for valid or invalid trials but significantly slowed RTs in double-cue trials that did not require the orienting of attention. These results suggest that in both species, the nicotinic cholinergic system may play a role in automatic sensory orienting. In addition, the muscarinic system may play a role in alerting to visual stimuli in monkeys.     

Functional MRI reveals spatially specific attentional modulation in human primary visual cortex

Selective visual attention can strongly influence perceptual processing, even for apparently low-level visual stimuli. Although it is largely accepted that attention modulates neural activity in extrastriate visual cortex, the extent to which attention operates in the first cortical stage, striate visual cortex (area V1), remains controversial. Here, functional MRI was used at high field strength (3 T) to study humans during attentionally demanding visual discriminations. Similar, robust attentional modulations were observed in both striate and extrastriate cortical areas. Functional mapping of cortical retinotopy demonstrates that attentional modulations were spatially specific, enhancing responses to attended stimuli and suppressing responses when attention was directed elsewhere. The spatial pattern of modulation reveals a complex attentional window that is consistent with object-based attention but is inconsistent with a simple attentional spotlight. These data suggest that neural processing in V1 is not governed simply by sensory stimulation, but, like extrastriate regions, V1 can be strongly and specifically influenced by attention.     

Cuing attention: Disruptions following organic solvent exposure.

Covert orienting of attention was assessed in 47 persons with mild solvent neurotoxicity and compared with that in 50 persons with no history of exposure who were of similar age and education. Reaction times (RTs) were recorded to cued, miscued, and uncued targets presented in either the left or right visual field with a stimulus onset asynchrony of 100 or 800 ms. RTs for exposed Ss were significantly slower than those for controls. In addition, exposed Ss had significantly slower responses to uncued targets presented on the left side and a larger validity effect size for left-side targets (i.e., invalid left targets minus valid left targets). According to a model proposed by M. I. Posner et al (see record 1988-27097-001), the results imply a disruption in the early stages of orienting attention (the alert operation) and an impairment in the disengage operation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective processing of visual alcohol cues in abstinent alcoholics: an approach-avoidance conflict?

When symptomatic individuals selectively attend to emotionally relevant stimuli, the ability to shift attention away from such material is impaired. Subjects may, however, seek to avoid further processing of these stimuli, which would facilitate attentional shifts. This was examined in a group of abstinent alcoholics' responses to stimuli related to alcohol. Eight alcohol and eight neutral words served as cues in a covert attention task. The cues were either valid (2/3 of trials) or invalid (1/3 of trials) indicators of where a response target would appear after 100 or 500 milliseconds. The short interval was expected to interact with an initial approach toward the alcohol word, while the long interval would interact with a subsequent avoidance of the stimulus. As predicted, the alcoholics showed slower reaction times (RTs) to targets invalidly cued by alcohol words in the short interval, reflecting increased difficulties to shift attention. However, the alcoholics demonstrated faster RTs to targets invalidly cued by the alcohol words in the long interval. This indicates that the alcohol cue elicited emotional associations that, subsequent to initial stimulus identification, trigger an interrupting function of the attentional system.     

Is there feature-based attentional selection in visual search?

A new paradigm combines attentional cuing and rapid serial visual presentation to disentangle the effects of perceptual filtering and location selection. Observers search successive, superimposed arrays, in which feature values are alternated for a target numeral among letters. Two dimensions, size (small, large) and color (red, green) are tested. Selective attention to feature values is jointly manipulated by instructions, presentation probabilities, and payoffs. In Experiment 1, the attended feature provides temporal, not spatial, information; observers show no attentional costs or benefits in response accuracy. In Experiment 2, the attended feature indicates a unique location; observers show consistent attentional costs and benefits. Selective attention to a particular size or color does not cause perceptual exclusion or admission of items containing that feature; it acts by guiding search processes to spatial locations that contain the to-be-attended feature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laterality for visual-spatial processing in two language-trained chimpanzees (Pan troglodytes).

Most reviews of laterality in nonhuman primates indicate that hemispheric asymmetries, similar to those found in humans, are not evident. With the growing evidence for cognitive processes germane to language in apes, in addition to their phylogenetic similarity to humans, they appear to be useful candidates for studies of laterality. Laterality for visual-spatial processing in 2 language-trained chimpanzees was investigated with a visual half-field paradigm. Initially, Ss were taught to manipulate a joystick that controlled the movement of a cursor on a computer monitor to a central fixation point. Ss were then taught a visual discrimination based on the location of a short line contained within a geometric form. Testing consisted of systematic presentation rates of 15, 122, and 226 ms to the left and right visual fields. For half of the trials, Ss used their left hand to respond and used the right hand for the remaining trials. Accuracy and reaction time (RT) were the dependent measures. One S demonstrated significantly faster RTs to stimuli presented to the left visual field (LVF) regardless of which hand was used to respond. The other S demonstrated a significant LVF bias when using the left hand to respond. Results are discussed in the context of current theories on the evolution of laterality and its relation to linguistic functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motivationally significant stimuli show visual prior entry: Evidence for attentional capture.

Previous studies that have found attentional capture effects for stimuli of motivational significance do not directly measure initial attentional deployment, leaving it unclear to what extent these items produce attentional capture. Visual prior entry, as measured by temporal order judgments (TOJs), rests on the premise that allocated attention accelerates perception, that is, stimuli that receive attention first are perceived first; thus, this method is a sensitive and direct measure of the time course of initial attentional deployment. The authors demonstrate, using a novel TOJ paradigm without cues, that displays of faces and facial threat show visual prior entry effects, that is, these stimuli are prioritized by the perceptual–attentional system over other stimuli competing for awareness. This study provides direct evidence of the extent to which motivationally significant stimuli capture attention over other concurrently displayed items in the visual array. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorically defined targets trigger spatiotemporal visual attention.

Transient attention to a visually salient cue enhances processing of a subsequent target in the same spatial location between 50 to 150 ms after cue onset (K. Nakayama & M. Mackeben, 1989). Do stimuli from a categorically defined target set, such as letters or digits, also generate transient attention? Participants reported digit targets among keyboard symbols in a changing array of 8 items. When 1 target preceded a second target in the same location at a stimulus onset asynchrony of 107 ms (but not 213 ms), the second target was reported more often than in a condition in which there was no leading target. When the 2 targets were at different locations, report of the second target was impaired. With both letters and digits as targets, the enhancement effect was shown not to be due to category priming. Critically, the attentional benefit was present whether or not participants reported the leading target. Transient attention, contingent attentional capture, popout, and Lag 1 sparing in the attentional blink may involve a common mechanism for orienting processing resources towards salient and task relevant stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)