Contributions of the dopaminergic system to voluntary and automatic orienting of visuospatial attention

Visuospatial attention can be directed by voluntary or involuntary control independent of eye movement. The involvement of cortical and subcortical neural structures in this covert orienting mechanism has been studied using neuroimaging and electrophysiological techniques. This study was designed to investigate the role of the dopaminergic system in both voluntary and automatic orienting mechanisms of visuospatial attention. We recorded event-related evoked potentials (ERPs) and reaction time (RT) during a cued priming task in both patients with idiopathic Parkinson's disease (PD) and control subjects. Voluntary and automatic shifts in attention were studied by using central and peripheral cues, respectively. In the experiment using a central cue, the RT data showed that when the cue-target interval was long, PD patients' responses were delayed, and cue validity effects were reduced, whereas in the peripheral cue experiment the validity effects persisted across all trials. The ERPs demonstrated reduced sustained negativities preceding the imperative targets in both the central and peripheral cue experiments in PD patients. Furthermore, during the long cue-target interval in the central cue experiment, PD patients showed reduced attention shift-related negativities (ARNs) at the anterior scalp sites, whereas ARNs were generated widely in the peripheral cue experiment. The ERP findings were consistent with the RT data. These findings suggest that the dopaminergic system may contribute to voluntary and sustained control of visuospatial attention as well as to the neural system for response preparation, whereas automatic control of visuospatial attention is relatively independent of the dopamine system.     

Human cortical mechanisms of visual attention during orienting and search

Functional anatomical studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations across a wide variety of visual tasks. This frontoparietal network includes areas, such as the frontal eye field and supplementary eye field. This anatomical overlap suggests that shifts of attention to visual locations of objects recruit areas involved in oculomotor programming and execution. Finally, the fronto-parietal network may be the source of spatial attentional modulations in the ventral visual system during object recognition or discrimination.     

Time course of allocation of visual attention after equating for sensory differences: An age-related perspective.

Adult age differences in the time course of the allocation of visual attention were investigated, in 2 experiments that both included the same 10 younger adults (M?=?22 years) and 10 older adults (M?=?68 years). In Experiment 1, older adults accumulated information about target identity at a slower rate than younger adults, as represented by the rise in accuracy as a function of target duration. To equate performance in a baseline condition in a spatial-cuing paradigm (Experiment 2), target duration was set for each observer on the basis of the data in Experiment 1. Performance for the 2 age groups was comparable, both in the baseline condition and in the time course of attention, as indexed by the function relating accuracy to cue-target onset asynchrony. The authors conclude that, in this spatial-cuing paradigm, an age-related change is evident in sensory processing but not in attentional allocation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The suppression of reflexive visual and auditory orienting when attention is otherwise engaged.

Two experiments were conducted to examine whether abrupt onsets are capable of reflexively capturing attention when they occur outside the current focus of spatial attention, as would be expected if exogenous orienting operates in a truly automatic fashion. The authors established a highly focused attentional state by means of the central presentation of a stream of visual or auditory characters, which participants sometimes had to monitor. No intramodal reflexive cuing effects were observed in either audition or vision when participants performed either an exogenous visual or auditory orthogonal cuing task together with the central focused attention task. These results suggest that reflexive unimodal orienting is not truly automatic. The fact that cuing effects were eliminated under both unimodal and cross-modal conditions is consistent with the view that auditory and visual reflexive spatial orienting are controlled by a common underlying neural substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial constraints on the voluntary control of attention across visual space.

Investigated the extent to which attention can be voluntarily allocated across the visual field during a single fixation. In Exp I, 20 undergraduates made a reaction time (RT) response to a stimulus occurring in a cued or a noncued location while maintaining a center fixation. In Exp II, 3 naive and 5 experienced undergraduates underwent a replication of Exp I and were monitored for horizontal eye movement during head restraint. Results from Exp I indicate that Ss were constrained to voluntarily attending to a single primary focus in space, and these findings were supported in Exp II. Data replicate those found by M. I. Posner et al (see record 1981-11809-001). (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new component of visual orienting: Implicit effects of peripheral information and subthreshold cues on covert attention.

Four experiments examined effects of peripheral cue stimuli on covert spatial attention. In Experiment 1 target stimuli were preceded by a pair of bilaterally presented cue letters. The relative location of the cues predicted target location (left or right), but participants were not informed of this. After a brief practice period, visual orienting was influenced by the letter cues. This implicit peripheral cuing effect was unrelated to participants' awareness of the cue-target relationship. Experiments 2 and 3 showed that visual orienting may occur independently of both perceptual awareness of the peripheral cue event itself and contingency awareness concerning the cue–target relation. Experiment 4 demonstrated that implicit peripheral cuing is qualitatively distinct from voluntary orienting. These findings are discussed in relation to work on spatial attention, implicit learning, and perception without awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the orienting value of attitudes: Attitude accessibility as a determinant of an object's attraction of visual attention.

Tested the hypothesis that objects toward which individuals hold attitudes that are highly accessible from memory (i.e., attitude-evoking objects) are more likely to attract attention when presented in a visual display than objects involving less accessible attitudes. In Exps 1 and 2, Ss were more likely to notice and report such attitude-evoking objects. Exp 3 yielded evidence of incidental attention; Ss noticed attitude-evoking objects even when the task made it beneficial to ignore the objects. Exp 4 demonstrated that inclusion of attitude-evoking objects as distractor items interfered with Ss' performance of a visual search task. Apparently, attitude-evoking stimuli attract attention automatically. Thus, accessible attitudes provide the functional benefit of orienting an individual's visual attention toward objects with potential hedonic consequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of phonological activation during reading: Evidence from eye fixations.

Eye fixation data suggest that readers use orthographic codes rather than phonological codes to activate word meanings. Whereas proofreading data show that readers are less likely to detect homophonic errors (e.g., He was in his silk stocking feat) than nonhomophonic errors (e.g., He was in his silk stocking fate), the eye fixations revealed that readers initially experienced as much difficulty encountering a homophonic error as a nonhomophonic one. However, homophony facilitated the recovery process, thus suggesting that phonology has its influence after lexical access. Exp 1 showed that the findings were consistent whether the error was the lower frequency homophone (stocking feat) or the higher frequency homophone (feet of courage). Exp 2 showed that proofreading responses are unreliable indices of error detection because even when readers fail to make an overt error detection response, their eye fixations reveal that they have detected the error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial orienting of attention in adult and aged rhesus monkeys.

Aging produces changes in a variety of neural systems that result in a distinct neuropsychological profile of cognitive deficits. To determine the extent of functional decline in cognition with aging, the authors assessed attentional ability in adult (10–15 yr old) and aged (28–33 yr old) rhesus monkeys (Macaca mulatta) in 3 experiments, using a paradigm adapted from M. I. Posner et al (1984), in which a peripheral cue indicates the probable location of a target. Orienting of attention was not disrupted in aged monkeys. Response times of aged monkeys were comparable with adult monkeys' both in the attention task and in a simple reaction time task. These results suggest that the neural systems that subserve spatial orienting of attention remain intact in aged nonhuman primates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired orienting of attention in left unilateral neglect: A componential analysis.

Twenty-six patients suffering from damage to the right side of the brain, 19 of whom exhibited signs of left neglect, as well as 32 matched controls, ran 3 spatial cuing tasks. Patients were also tested with 2 cancellation tests, a line-bisection test, the copy of a complex drawing, and a visual extinction procedure. Results first showed correlations between extinction and cancellation tests performance on one hand, and between line bisection and copy on the other hand. Second, results demonstrated that an engagement deficit toward contralesional targets appeared to be the most striking feature of neglect, and the engagement score was correlated with the cancellation score and extinction. Most patients with neglect also presented a deficit in disengagement, a deficit of inhibition of return, and probably a deficit of alertness. Deficits in engagement and in disengagement, as well as poor scores in cancellation tests, seemed to be related with posterior cortical and subcortical lesions. Most important, even if an endogenous deficit (frequently related with a thalamic lesion) could aggravate the neglect behavior, neglect syndrome was mainly explained by a deficit of exogenous attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial factors in visual attention: A reply to Crassini.

Notes that distances between stimuli and compactness of stimulus subsets are pervasive determiners of discrimination and classification performance. Contrary to B. Crassini (see record 1986-26308-001), these factors are sufficient to account for the major patterns in the chronometric data of the present authors (see PA, Vols 61:259 and 71:3057). Other factors, such as the dichotomous one distinguishing what Crassini terms unitary and nonunitary subsets, may exert some additional influence. But a convincing demonstration would require formulation of a quantitative model capable of being pitted against the present authors' distance-based model within the context of their entire body of data. (22 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The time course of attentional zooming: a comparison of voluntary and involuntary allocation of attention to the levels of compound stimuli

Despite the original distinction between Alzheimer's disease (AD) and senile dementia, both are currently considered to be one single disease based on their common neuropathological findings. We have reviewed the literature to investigate whether there is proof to assume the existence of subgroups of AD. Historically, there is a division based on the age at onset. Although typical cortical symptoms may be more prominent in early onset cases they may be encountered in senile cases too. Cortical neuronal loss may be more severe in early onset patients, but hippocampal neuronal loss is equally severe in both groups. In older patients cerebral reserve is reduced by age-related neuronal loss and a small amount of AD-type lesions might be sufficient to cause dementia. Aphasia has been proposed as indicator of a subgroup. However, it probably occurs in all AD patients when the cortical degenerative process progresses. AD cases presenting with aphasia are rare and more often prove to be Pick's disease or primary progressive aphasia. Extrapyramidal signs are present in 25% of patients without neuroleptics and in 90% of all patients. They are usually of mild intensity, appear during the course of the disease and are found to be of extranigral origin. Myoclonus may also be encountered at any stage, although more frequent in early onset AD. Its presence is often associated with a more progressive course. Most AD cases are sporadic and some are familial, suggesting an autosomal dominant transmission. Molecular genetics reveals that some patients with familial early-onset AD have a mutation on chromosome 21. Other genes, probably on chromosome 19, may be associated with late onset familial cases, suggesting heterogeneity in familial AD. White matter involvement on computerized tomography or magnetic resonance imaging has been reported to be more prominent in a subgroup of AD patients, with later onset and confusional symptoms. The typical bilateral temporo-parietal hypometabolism on positron emission tomography and hypoperfusion on single photon emission computed tomography, is not found in all AD cases but may be indicative of a subgroup. Based on this review of the literature one homogeneous subgroup emerges: "probable" AD patients displaying memory disturbances with predominant cortical signs (especially aphasia), with a low prevalence of confusion and white matter involvement, exhibiting symptoms at a relatively early age but not exclusively below 65 years, and with a higher prevalence of genetic predisposition and more widespread neuropathological lesions at postmortem examination.     

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)     

Search images: Selective attention to specific visual features of prey.

In 3 experiments, pigeons (Columba livia) searched a digitized image of a gravel patch on a computer monitor for cryptic grains. Experiment 1 demonstrated that the bird's ability to detect a type of grain improved over successive encounters, and detection of alternative targets was attenuated when a search image was active. Experiment 2 demonstrated search-image effects independently for the 2 grains. Perception was biased to detect wheat grains after wheat encounters and was biased to detect bean grains after bean encounters. Experiment 3 demonstrated that when a search image was activated, selective attention was heightened to the visual features of the grain used to discriminate it from the multicolor gravel background. These results provide strong support for the view that search images are selective attention to specific visual features of cryptic prey. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Masked fearful faces modulate the orienting of covert spatial attention.

Dot probe studies indicate that masked fearful faces modulate spatial attention. However, without a baseline to compare congruent and incongruent reaction times, it is unclear which aspect(s) of attention (orienting or disengagement) is affected. Additionally, backward masking studies commonly use a neutral face as the mask stimulus. This method results in greater perceptual inconsistencies for fearful as opposed to neutral faces. Therefore, it is currently unclear whether the effects of backward masked fearful faces are due to the fearful nature of the face or perceptual inconsistencies. Equally unclear, is whether this spatial attention effect is due to orienting or disengagement. Two modified dot probe experiments with neutral (closed mouth in Experiment 1) and smiling (open mouth in Experiment 2) masks were used to determine the role of perceptual inconsistencies in mediating the spatial attention effects elicited by masked fearful faces. The results indicate that masked fearful faces modulate the orienting of spatial attention, and it appears that this effect is due to the fearful nature of the face rather than perceptual inconsistencies between the initial faces and masks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biases in visual orienting to negative and positive scenes in dysphoria: An eye movement study.

The study investigated biases for negative information in component processes of visual attention (initial shift vs. maintenance of gaze) in dysphoric and nondysphoric individuals. Eye movements were recorded while participants viewed a series of picture pairs depicting negative, positive, and neutral scenes (each pair presented for 3 s). Biases in initial orienting were assessed from the direction and latency of the initial shift in gaze, whereas biases in the maintenance of attention were assessed from the duration of gaze on the picture that was initially fixated. Results indicated that the dysphoric group showed a significantly greater bias to maintain gaze longer on negative pictures, relative to control pictures, compared with the nondysphoric group. There was no evidence of a dysphoria-related bias in initial shift of orienting to negative cues. Results are consistent with a depression-related bias that operates in the maintenance of attention on negative material. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A theory of visual attention.

A unified theory of visual recognition and attentional selection is developed by integrating the biased-choice model for single-stimulus recognition (R. D. Luce, 1963; R. N. Shepard, 1957) with a choice model for selection from multielement displays (C. Bundesen et al; see record 1985-05669-001) in a race model framework. Mathematically, the theory is tractable, and it specifies the computations necessary for selection. The theory is applied to extant findings from a broad range of experimental paradigms. The findings include effects of object integrality in selective report, number and spatial position of targets in divided-attention paradigms, selection criterion and number of distracters in focused-attention paradigms, delay of selection cue in partial report, and consistent practice in search. On the whole, the quantitative fits are encouraging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characteristics of covert and overt visual orienting: Evidence from attentional and oculomotor capture.

Five visual search experiments found oculomotor and attentional capture consistent with predictions of contingent orienting, contrary to claims that oculomotor capture is purely stimulus driven. Separate saccade and attend-only conditions contained a color target appearing either singly, with an onset or color distractor, or both. In singleton mode, onsets produced oculomotor and attentional capture. In feature mode, capture was absent or greatly reduced, providing evidence for top-down modulation of both types of capture. Although attentional capture by color abstractors was present throughout, oculomotor capture by color occurred only when accompanied by transient change, providing evidence for a dissociation between oculomotor and attentional capture. Oculomotor and attentional capture appear to be mediated by top-down attentional control settings, but transient change may be necessary for oculomotor capture. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The CODE theory of visual attention: An integration of space-based and object-based attention.

This article presents a theory that integrates space-based and object-based approaches to visual attention. The theory puts together M. R. van Oeffelen and P. G. Vos's (1982, 1983) COntour DEtector (CODE) theory of perceptual grouping by proximity with C. Bundesen's (1990) theory of visual attention (TVA). CODE provides input to TVA, accounting for spatially based between-object selection, and TVA converts the input to output, accounting for feature- and category-based within-object selection. CODE clusters nearby items into perceptual groups that are both perceptual objects and regions of space, thereby integrating object-based and space-based approaches to attention. The combined theory provides a quantitative account of the effects of grouping by proximity and distance between items on reaction time and accuracy data in 7 empirical situations that shaped the current literature on visual spatial attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Semantic contextual cuing and visual attention.

Since M. M. Chun and Y. Jiang's (1998) original study, a large body of research based on the contextual cuing paradigm has shown that the visuocognitive system is capable of capturing certain regularities in the environment in an implicit way. The present study investigated whether regularities based on the semantic category membership of the context can be learned implicitly and whether that learning depends on attention. The contextual cuing paradigm was used with lexical displays in which the semantic category of the contextual words either did or did not predict the target location. Experiments 1 and 2 revealed that implicit contextual cuing effects can be extended to semantic category regularities. Experiments 3 and 4 indicated an implicit contextual cuing effect when the predictive context appeared in an attended color but not when the predictive context appeared in an ignored color. However, when the previously ignored context suddenly became attended, it immediately facilitated performance. In contrast, when the previously attended context suddenly became ignored, no benefit was observed. Results suggest that the expression of implicit semantic knowledge depends on attention but that latent learning can nevertheless take place outside the attentional field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)