Direct selection by color for visual encoding

In two experiments, we used rapid serial visual presentation tasks to examine the usefulness of color for the direct selection of visual information for perceptual encoding. The participants' task was to make a discrimination as to whether a target letter within a rapid sequence appeared in its upper- or lowercase version, and an advance cue indicated the color in which the target letter was most likely to occur. To maximize the usefulness of the cued color, in validly cued trials, we used sequences in which the target was the only item appearing in the cued color. In both experiments, accuracy was highest for validly cued trials. A cost-benefit analysis revealed a facilitory effect of valid cues and an inhibitory effect of invalid ones. These results support the idea that color cuing allows the direct selection of objects for further perceptual processing.     

Is Posner's "beam" the same as Treisman's "glue"?: On the relation between visual orienting and feature integration theory

In the present study we investigated whether the visually allocated "beam" studied by Posner and others is the same visual attentional resource that performs the role of feature integration in Treisman's model. Subjects were cued to attend to a certain spatial location by a visual cue, and performance at expected and unexpected stimulus locations was compared. Subjects searched for a target letter (R) with distractor letters that either could give rise to illusory conjunctions (PQ) or could not (PB). Results from three separate experiments showed that orienting attention in response to central cues (endogenous orienting) showed similar effects for both conjunction and feature search. However, when attention was oriented with peripheral visual cues (exogenous orienting), conjunction search showed larger effects of attention than did feature search. It is suggested that the attentional systems that are oriented in response to central and peripheral cues may not be the same and that only the latter performs a role in feature integration. Possibilities for future research are discussed.     

Context-specific attentional sampling: Intentional control as a pre-requisite for contextual control

Recent work suggests that environmental cues associated with previous attentional control settings can rapidly and involuntarily adjust attentional priorities. The current study tests predictions from adaptive-learning and memory-based theories of contextual control about the role of intentions for setting attentional priorities. To extend the empirical boundaries of contextual control phenomena, and to determine whether theoretical principles of contextual control are generalizable we used a novel bi-dimensional stimulus sampling task. Subjects viewed briefly presented arrays of letters and colors presented above or below fixation, and identified specific stimuli according to a dimensional (letter or color) and positional cue. Location was predictive of the cued dimension, but not the position or identity. In contrast to previous findings, contextual control failed to develop through automatic, adaptive-learning processes. Instead, previous experience with intentionally changing attentional sampling priorities between different contexts was required for contextual control to develop.     

Does attention affect visual feature integration?

Two questions are investigated in this work: first, whether the integration of color and shape information is affected by attending to the stimulus location, and second, whether attending to a stimulus location enhances the perceptual representation of the stimulus or merely affects decision processes. In three experiments, subjects were briefly presented with colored letters. On most trials, subjects were precued to the stimulus location (valid cue); on some trials, a nonstimulus location was cued (invalid cue). Subjects were less likely to incorrectly combine colors and letter shapes following a valid cue. The attentional facilitation afforded by the cue was not limited to feature integration but also affected the registration of features. However, when the amount of feature information was strictly controlled, attention still affected feature integration. The results indicate that orienting attention to the location of the cue affects the quality of the perceptual representation for features and their integration.     

Attending to an object's color entails attending to its location: support for location-special views of visual attention

Van der Heijden, Kurvink, de Lange, de Leeuw, and van der Geest (1996) argued that the results supporting the location-special view obtained by Tsal and Lavie (1988) were due to uncontrollable shifts of fixation, rather than reflecting the properties of the attentional system. In the present study, we present an improved variation of the Tsal and Lavie (1988) paradigm and reassert our claim that location is a special dimension. Subjects were presented with circular arrays of six letters of different colors. Three of the letters were enclosed by (Experiment 1) or superimposed on (Experiments 2, 3, and 4) different colored shapes. The subjects were instructed to report the (target) shape with a given color (e.g., report whether the red shape was a square, a circle, or a triangle) and then either freely report letters from the array (Experiments 1, 2, and 4) or identify a prespecified target letter (Experiment 3). In all four experiments, performance was substantially better for the letter that appeared in the location of the to-be-reported shape (location letter) than for the letter that shared its color (color letter). We conclude that attending to the stimulus color entails directing attention to its location.     

Attending to an object’s color entails Attending to its location: Support for location-special views of visual attention

Van der Heijden, Kurvink, de Lange, de Leeuw, and van der Geest (1996) argued that the results supporting the location-special view obtained by Tsal and Lavie (1988) were due to uncontrollable shifts of fixation, rather than reflecting the properties of the attentional system. In the present study, we present an improved variation of the Tsal and Lavie (1988) paradigm and reassert our claim that location is a special dimension. Subjects were presented with circular arrays of six letters of different colors. Three of the letters were enclosed by (Experiment 1) or superimposed on (Experiments 2,3, and 4) different colored shapes. The subjects were instructed to report the (target) shape with a given color (e.g., report whether the red shape was a square, a circle, or a triangle) and then either freely report letters from the array (Experiments 1, 2, and 4) or identify a prespecified target letter (Experiment 3). In all four experiments, performance was substantially better for the letter that appeared in the location of the to-be-reported shape (location letter) than for the letter that shared its color (color letter). We conclude that attending to the stimulus color entails directing attention to its location.     

Made you blink! Contingent attentional capture produces a spatial blink

Previous studies have shown that the capture of attention by an irrelevant stimulus can be eliminated by fore knowledge of the spatial location of the relevant target stimulus. To explore whether spatial certainty is sufficient to eliminate capture, four experiments are reported in which the spatial location of the target is certain but the temporal position is uncertain. Subjects viewed a central rapid serial visual presentation stream in which a target letter was defined by a particular color (e.g., red). On critical trials, irrelevant color singletons appeared in the periphery. In Experiments 1 and 2, peripheral singletons produced a decrement in central target identification that was contingent on the match between the singleton color and the target color. Experiments 3 and 4 provided evidence that this decrement reflected a shift of spatial attention to the location of the distractor. The results suggest that spatial certainty is not sufficient to eliminate attentional capture and that attentional capture can result in a spatial "blink" that is conditional on top-down attentional control settings.     

Reading ability and the encoding of item and location information

Two experiments using duration exposures ranging from 20 to 130 msec are reported that link reading skill in adults to the initial encoding of location information. Highly skilled and less skilled readers were equivalent in identifying single letters presented at a central fixation point. When they had to identify the serial position of a letter, however, highly skilled readers performed significantly more accurately than did less skilled readers. A second experiment used displays that consisted of one letter and three dollar signs. Subjects had to identify the letter under two location cuing conditions. When subjects were cued in advance as to which serial position would contain the letter, highly skilled and less skilled readers were equivalent. When the location of the letter had to be resolved prior to identification, highly skilled readers performed significantly more accurately than did less skilled readers. Results are interpreted to suggest that the role of perception in reading has been underestimated because emphasis has been on item perception, and the perception of spatial location has been largely overlooked.     

Reaction time in reading a tachistoscopic display for a memory set item

Reaction times were measured in a task which requires the subject to search a brief visual array for a critical letter embedded in a row of background letters. In Experiment 1, the position of a critical letter in an instructed reading order and the size of a set of memorized letters were varied. Mean reaction time increased monotonically with distance of the critical letter from the beginning of the instructed reading path in the display. The variables reading position and memory set size were additive in their effect on mean reaction time. Data from a second experiment in which the retinal location of the critical letter and its reading position were varied showed that both reading position and retinal location influenced mean reaction time, but the effect of reading position on reaction time was greater. These variables interacted.     

Lexical and semantic search in cued recall, fragment completion, perceptual identification, and recognition

Search processes in word-stem cued recall, fragment completion, perceptual identification, and recognition are contrasted. These retention tests involve letters as cues, but the lexical characteristics of these cues vary considerably. In word-stem cued recall, ending letters are presented as recall cues for studied targets (e.g., ONEY as a cue for HONEY). In fragment completion, the test cues consist of letters and spaces (e.g., HO__Y); in perceptual identification, they consist of letter features that survive the mask; and in recognition, they consist of all the letters of the studied word (e.g., HONEY). These differences in retention tests and lexical characteristics were evaluated by manipulating three variables with known effects in cued recall: (a) the presence of study context words emphasizing lexical information, (b) lexical set size corresponding to the number of words that fit the letter cue, and (c) meaning set size corresponding to the number of meaningful associates linked to the studied targets. The results indicated that (a) the presence of study contexts emphasizing lexical information reduced accuracy and response time equally in all tasks, (b) larger lexical set sizes reduced accuracy and response time in all tasks except recognition, and (c) larger meaning set size reduced accuracy in cued recall but not in the other tasks. Lexical search appears to be a significant component process in word-stem cued recall, fragment completion, and identification. Searching through meaning-related concepts encoded during study is a significant component process only in cued recall.     

Contingent attentional capture by top-down control settings: converging evidence from event-related potentials

Theories of attentional control are divided over whether the capture of spatial attention depends primarily on stimulus salience or is contingent on attentional control settings induced by task demands. The authors addressed this issue using the N2-posterior- contralateral (N2pc) effect, a component of the event-related brain potential thought to reflect attentional allocation. They presented a cue display followed by a target display of 4 letters. Each display contained a green item and a red item. Some participants responded to the red letter and others to the green letter. Converging lines of evidence indicated that attention was captured by the cues with the same color as the target. First, these target-color cues produced a cuing validity effect on behavioral measures. Second, distractors appearing in the cued location produced larger compatibility effects. Third, the target-color cue produced a robust N2pc effect, similar in magnitude to the N2pc effect to the target itself. Furthermore, the target-color cue elicited a similar N2pc effect regardless of whether it competed with a simultaneous abrupt onset. The findings provide converging evidence for attentional capture contingent on top-down control settings.     

Exogenous and endogenous control of attention: the effect of visual onsets and offsets

Two experiments were carried out to investigate the relation between exogenous and endogenous control of visual attention. Subjects searched for a target letter among three nontarget letters that were positioned on an imaginary circle around a fixation point. At different cue-display intervals, a centrally located arrowhead cue reliably indicated the location of the target letter. At different SOAs, a peripheral line segment near one of the letters was either abruptly switched on (Experiment 1) or abruptly switched off (Experiment 2). Presenting the central arrowhead after display onset prevents attention from being focused in advance on the critical location. In this unfocused attentional state, both onset and offset transients attracted attention. When the central arrowhead was available in advance, the focusing of attention prior to display onset precluded attention attraction to the location of the onset or offset transient. Contrary to an offset transient, an onset transient presented at the attended location disrupted performance, indicating that an onset within the spotlight of attention attracts attention. The results are reconciled by means of the zoom-lens theory of attention, suggesting that outside the focus of attention, abrupt transients are not capable of attracting attention. Since the size of the zoom lens is under voluntary control, it can be argued that transients do not fulfill the intentionality criterion of automaticity.     

Effects of attention on localization of stimuli in the visual field

Subjects localized a small letter that appeared inside one of three large circles that was either validly or invalidly cued. The results indicated that, although unattended stimuli were localized fairly accurately, attention still improved localization. Moreover, the results revealed a greater dispersion of localization responses along the horizontal axis and also showed that mislocalization of attended peripheral stimuli is biased toward the periphery.     

The relationship between covert and overt attention in endogenous cuing

In a standard Posner paradigm, participants were endogenously cued to attend to a peripheral location in visual space without making eye movements. They responded faster to target letters presented at cued than at uncued locations. On some trials, instead of a manual response, they had to move their eyes to a location in space. Results showed that the eyes deviated away from the validly cued location; when the cue was invalid and attention had to be allocated to the uncued location, eye movements also deviated away, but now from the uncued location. The extent to which the eyes deviated from cued and uncued locations was related to the dynamics of attention allocation. We hypothesized that this deviation was due to the successful inhibition of the attended location. The results imply that the oculomotor system is not only involved during the endogenous direction of covert attention to a cued location, but also when covert attention is directed to an uncued location. It appears that the oculomotor system is activated wherever spatial attention is allocated. The strength of saccade deviation might turn out to be an important measure for the amount of attention allocated to any particular location over time.     

Spatial attention and expectancy for colour, category and location: further evidence against the spotlight model.

A study of spatial attention is reported in which different colours and categories of object tended to appear at different locations. Subjects made speeded orientation judgements to alphanumeric characters that could appear either above or below the centre of a display. In the Colour Condition subjects were informed that red characters tended to appear at one location (p = 0.8), while green characters tended to appear at the other. In the Category Condition letters tended to appear at one location, and digits at the other. Before each trial subjects were cued to expect either a red or a green character (Colour Condition); or a letter or a digit (Category Condition). It was found that spatial selectivity varied according to the colour, or category of object presented. The latter finding replicated an earlier report (Lambert 1987). Spatial selectivity was appropriate for the character presented, even when it was in the uncued colour (or category). It is concluded that subjects are able to form and make use of complex attentional expectancies concerning combinations of colour with location, and category with location. Theoretical implications of these results are discussed.     

Competing top-down processes in visual selection: evidence that selection by location is stronger than selection by color

The purpose of this study was to examine whether color and position information are functionally equivalent when observers are asked to select simultaneously on both dimensions. Observers were asked to report a letter of a given color from a given region of a briefly flashed letter array, then to report any additional letters they could recall from the stimulus set. Of the additional letters, more location letters were reported than were same-color or neutral letters. The results suggested that position information has priority over color information in top-down-guided visual selection.     

Age similarities in the inertial properties of attention.

Adult age differences in the mode of allocation of visual attention were investigated, using a visual search task with a circular display containing one target letter and seven distractor letters. In two experiments, a total of 56 younger adults (M = 20 years) and 56 older adults (M = 66 years) searched for a target appearing with equal probability at one of two cued locations. The first cue appeared 115 msec before display onset, and the second cue appeared with display onset; distance between the two cued locations was varied. Target identification performance indicated that attention was inertial, in that reaction time for second-cued targets was related either to the area of the portion of the visual field containing possible target locations or to the mean path length of a serial self-terminating search. There were no age-related decrements in the allocation of visual attention.     

Allocation of attention, reading skills, and deafness.

Brannan and Williams (1987) found that poor readers cannot successfully utilize parafoveal cues to identify letter targets. Whether a similar deficit in the use of cue information occurs in deaf poor readers and whether it is only specific to processes that capture attention automatically were investigated in congenitally deaf young adults classified as poor or good readers and hearing controls classified as good readers. Subjects were presented with central or parafoveal cues that varied in cue validity probability, followed by letter targets presented to the left or right of fixation. The reaction time data analyses showed significant main effects for cue type and cue location and significant interactions among cue type, cue location, cue validity probability, and visual field. No significant main effect or interactions involving groups were found. These results raise the possibility that reading difficulties associated with deafness do no involve a deficit in the visual attentional system of deaf people. They also confirm that parafoveal cues are more effective than central cues in capturing attention.     

Visual search by children: the effect of background variation and the use of visual cues

A visual search task was used to assess developmental changes in children's selective attention to specified portions of a visual display. Seven-, nine-, and twelve-year-olds searched for a target letter in matrices of letters, each of which was centered in a form. On each matrix the forms were uniform or they varied in color, shape or both color and shape. The children searched with either no cues or with color or shape cues that could be used to restrict and speed their search. In all conditions search speed increased with age. Comparisons among conditions revealed three different age trends. With no cues children of all ages were slowed comparably by variation in background forms. With color cues all children increased their search speeds relative to no-cue speeds, suggesting selective fixation, but the 12-year-olds benefited most from the cues. With shape cues the search speed of 9- and 12-year-olds was slowed while that of 7-year-olds was either unchanged or was slowed only slightly. These different trends caution against overly general statements of changes with age in selective attention, and highlight the need to consider both particular task requirements and the processes used by subjects of different ages in tasks requiring selective attention.     

Age similarities in the inertial properties of attention

Adult age differences in the mode of allocation of visual attention were investigated, using a visual search task with a circular display containing one target letter and seven distractor letters. In two experiments, a total of 56 younger adults (M=20 years) and 56 older adults (M=66 years) searched for a target appearing with equal probability at one of two cued locations. The first cue appeared 115 msec before display onset, and the second cue appeared with display onset; distance between the two cued locations was varied. Target identification performance indicated that attention was inertial, in that reaction time for second-cued targets was related either to the area of the portion of the visual field containing possible target locations or to the mean path length of a serial self-tenminating search. There were no age-related decrements in the allocation of visual attention.