Age-related changes in the control of attention in depth

In 2 experiments, the authors examined the control of spatial attention in depth in advanced age. Observers viewed 2 sets of lines that overlapped in two-dimensional (2-D) space but that were presented at different depth locations. An exogenous cue indicated the depth at which a colored target line would appear. On some trials, a distracting colored element was also presented. The luminance of this distracter varied from high to low. For both older and younger adults, distractors slowed reaction time less if they were at a different depth from the target. This effect was more robust for older adults with low-luminance distractors, indicating an important role for target features as well as attentional control. Adding another feature (i.e., color) that distinguished between target and distracter reduced the effects of slowing shown by the older observers and eliminated the cost of low-luminance distractors for all observers. The results suggest that attentional control in depth is maintained in aging.

Contingent capture for onsets and offsets: attentional set for perceptual transients

Four experiments were conducted to examine whether attentional set affects the ability of visual transients (onsets and offsets) to capture attention. In the experiments, visual search for an identity-defined target was conducted. In the first 3 experiments, the target display either onset entirely or was revealed by offsetting camouflaging line segments to reveal letters. Prior to the target display, there was a noninformative cue, either an onset or an offset, at one of the potential target locations. Cues that shared the same transient feature as the target display captured attention. The lack of predictable target transients led to attentional capture by all forms of transients. The final experiments with luminance changes without offsets or onsets showed attentional capture when the luminance changes were large. The results suggest that attentional set can be broadly or narrowly tuned to detect changes in luminance.

Age-related changes in the control of attention in depth

In 2 experiments, the authors examined the control of spatial attention in depth in advanced age. Observers viewed 2 sets of lines that overlapped in two-dimensional (2-D) space but that were presented at different depth locations. An exogenous cue indicated the depth at which a colored target line would appear. On some trials, a distracting colored element was also presented. The luminance of this distracter varied from high to low. For both older and younger adults, distractors slowed reaction time less if they were at a different depth from the target. This effect was more robust for older adults with low-luminance distractors, indicating an important role for target features as well as attentional control. Adding another feature (i.e., color) that distinguished between target and distracter reduced the effects of slowing shown by the older observers and eliminated the cost of low-luminance distractors for all observers. The results suggest that attentional control in depth is maintained in aging.

Influence of attentional capture on oculomotor control

Previous research has shown that when searching for a color singleton, top-down control cannot prevent attentional capture by an abrupt visual onset. The present research addressed whether a task-irrelevant abrupt onset would affect eye movement behavior when searching for a color singleton. Results show that in many instances the eye moved in the direction of the task-irrelevant abrupt onset. There was evidence that top-down control could neither entirely prevent attentional capture by visual onsets nor prevent the eye from starting to move in the direction of the onset. Results suggest parallel programming of 2 saccades: 1 voluntary goal-directed eye movement toward the color singleton target and 1 stimulus-driven eye movement reflexively elicited by the abrupt onset. A neurophysiologically plausible model that can account for the current findings is discussed.

Strategic effects on object-based attentional selection

The same-object benefit, that is faster and/or more accurate performance when two target properties to be identified appear on one object than when each of the properties appear on different objects, has been a robust and theoretically important finding in the study of attentional selection. Indeed, the same-object benefit has been interpreted to suggest that attention can be used to select objects and perceptual groups rather than unparsed regions of visual space. In the present studies we report and explore a different-object benefit, that is faster identification performance when two target properties appear on different objects than when they appear on a single object. The results from the three experiments suggest that the different-object benefit was the result of mental rotation and translation strategies that subjects performed on objects in an effort to determine whether two target properties matched or mismatched. These image manipulation strategies appear to be performed with similar but not with dissimilar target properties. The results are discussed in terms of their implications for the study of object-based attentional selection.

Object-based attentional selection and aging

The authors conducted 2 studies to examine potential age-related differences in object-based attentional selection. Participants were briefly presented with pairs of wrenches and were asked to make 1 response if both target properties (i.e., an open end and a hexagonal end) were present and another response if only a single target property was present in the display. The critical manipulation was whether the target properties were present on 1 wrench or distributed between 2 wrenches. Space-based models of selective attention predict no difference in performance between these conditions. However, object-based attentional selection models predict better performance when both target properties appear on a single object. The results from both of the studies were consistent with object-based models of attentional selection. Furthermore, both young and old adults showed similar performance effects, suggesting the object-based attentional selection is insensitive to normal aging.

Attentional capture and aging: implications for visual search performance and oculomotor control

Two studies examined potential age-related differences in attentional capture. Subjects were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside it. On half the trials, a new stimulus (i.e., a sudden onset) appeared simultaneously with the presentation of the color singleton target. The onset was always a task-irrelevant distractor. Response times were lengthened, for both young and old adults, whenever an onset distractor appeared, despite the fact that subjects reported being unaware of the appearance of the abrupt onset. Eye scan strategies were also disrupted by the appearance of the onset distractors. On about 40% of the trials on which an onset appeared, subjects made an eye movement to the task-irrelevant onset before moving their eyes to the target. Fixations close to the onset were brief, suggesting parallel programming of a reflexive eye movement to the onset and goal-directed eye movement to the target. Results are discussed in terms of age-related sparing of the attentional and oculomotor processes that underlie attentional capture.

Attentional effects on preattentive vision: spatial precues affect the detection of simple features

Most accounts of visual perception hold that the detection of primitive features occurs preattentively, in parallel across the visual field. Evidence that preattentive vision operates without attentional limitations comes from visual search tasks in which the detection of the presence of absence of a primitive feature is independent of the number of stimuli in a display. If the detection of primitive features occurs preattentively, in parallel and without capacity limitations, then it should not matter where attention is located in the visual field. The present study shows that even though the detection of a red element in an array of gray elements occurred in parallel without capacity limitations, the allocation of attention did have a large effect on search performance. If attention was directed to a particular region of the display and the target feature was presented elsewhere, response latencies increased. Results indicate that the classic view of preattentive vision requires revision.

Task coordination and aging: explorations of executive control processes in the task switching paradigm

A number of models of cognitive aging suggest that older adults exhibit disproportionate performance decrements on tasks which require executive control processes. In a series of three studies we examined age-related differences in executive control processes and more specifically in the executive control processes which underlie performance in the task switching paradigm. Young and old adults were presented with rows of digits and were required to indicate whether the number of digits (element number task) or the value of the digits (digit value task) were greater than or less than five. Switch costs were assessed by subtracting the reaction times obtained on non-switch trials from trials following a task switch. Several theoretically interesting results were obtained. First, large age-related differences in switch costs were found early in practice. Second, and most surprising, after relatively modest amounts of practice old and young adults switch costs were equivalent. Older adults showed large practice effects on switch trials. Third, age-equivalent switch costs were maintained across a two month retention period. Finally, the main constraint on whether age equivalence was observed in task switching performance was memory load. Older adults were unable to capitalize on practice under high memory loads. These data are discussed in terms of their implications for both general and process specific cognitive aging models.

Attentional effects on preattentive vision: spatial precues affect the detection of simple features

Most accounts of visual perception hold that the detection of primitive features occurs preattentively, in parallel across the visual field. Evidence that preattentive vision operates without attentional limitations comes from visual search tasks in which the detection of the presence of absence of a primitive feature is independent of the number of stimuli in a display. If the detection of primitive features occurs preattentively, in parallel and without capacity limitations, then it should not matter where attention is located in the visual field. The present study shows that even though the detection of a red element in an array of gray elements occurred in parallel without capacity limitations, the allocation of attention did have a large effect on search performance. If attention was directed to a particular region of the display and the target feature was presented elsewhere, response latencies increased. Results indicate that the classic view of preattentive vision requires revision.

Error-related processing during a period of extended wakefulness

The nature of error detection as manifested by the error-related negativity was examined in both a Sternberg memory search task and a visual search task. Both tasks were performed in conditions with consistent or varied stimulus-response mapping and loads of three or six letters. After subjects were trained extensively in all conditions, they performed the tasks throughout the night without sleeping. The data suggest that the effectiveness of error detection decreases over time because of a decrease in the quality of perceptual processing. Error detection also suffers when performance requires more search-related resources. In both cases, the representation of the correct response is compromised. These results indicate that error detection depends on the same perceptual and cognitive processes that are required for correct performance.

Object-based attentional selection and aging

The authors conducted 2 studies to examine potential age-related differences in object-based attentional selection. Participants were briefly presented with pairs of wrenches and were asked to make 1 response if both target properties (i.e., an open end and a hexagonal end) were present and another response if only a single target property was present in the display. The critical manipulation was whether the target properties were present on 1 wrench or distributed between 2 wrenches. Space-based models of selective attention predict no difference in performance between these conditions. However, object-based attentional selection models predict better performance when both target properties appear on a single object. The results from both of the studies were consistent with object-based models of attentional selection. Furthermore, both young and old adults showed similar performance effects, suggesting the object-based attentional selection is insensitive to normal aging.

Attentional capture and aging: implications for visual search performance and oculomotor control

Two studies examined potential age-related differences in attentional capture. Subjects were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside it. On half the trials, a new stimulus (i.e., a sudden onset) appeared simultaneously with the presentation of the color singleton target. The onset was always a task-irrelevant distractor. Response times were lengthened, for both young and old adults, whenever an onset distractor appeared, despite the fact that subjects reported being unaware of the appearance of the abrupt onset. Eye scan strategies were also disrupted by the appearance of the onset distractors. On about 40% of the trials on which an onset appeared, subjects made an eye movement to the task-irrelevant onset before moving their eyes to the target. Fixations close to the onset were brief, suggesting parallel programming of a reflexive eye movement to the onset and goal-directed eye movement to the target. Results are discussed in terms of age-related sparing of the attentional and oculomotor processes that underlie attentional capture.

Attentional control within 3-D space

Four experiments investigated whether directing attention to a particular plane in depth enables observers to filter out information from another depth plane. Observers viewed stereoscopic displays and searched for a red line segment among green line segments. The results showed that directing attention to a particular depth plane cannot prevent attentional capture from another depth plane when the colors of the target and distractor are identical. However, it can prevent attentional capture by a singleton from another depth plane when the colors of the target and distractor are different. These results indicate that only when both color and depth information are selective in guiding attention to the target singleton can attentional capture by irrelevant singletons be prevented. The results also suggest that retinal disparity does not have the same special status as location information in two dimensions and should be considered as just another feature along which selection may occur.

Object-based visual selective attention and perceptual organization

We report the results of four experiments that were conducted to examine both the representations that provide candidate entities available for object-based attentional selection and the influence of bottom-up factors (i.e., geometric and surface characteristics of objects) and top-down factors (i.e., context and expectancies) on the selection process. Subjects performed the same task in each of the experiments. They were asked to determine whether two target properties, a bent end and an open end of a wrench, appeared in a brief display of two wrenches. In each experiment, the target properties could occur on a single wrench or one property could occur on each of two wrenches. The question of central interest was whether a same-object effect (faster and/or more accurate performance when the target properties appeared on one vs. two wrenches) would be observed in different experimental conditions. Several interesting results were obtained. First, depending on the geometric (i.e., concave discontinuities on object contours) and surface characteristics (i.e., homogeneous regions of color and texture) of the stimuli, attention was preferentially directed to one of three representational levels, as indicated by the presence or absence of the same-object effect. Second, although geometric and surface characteristics defined the candidate objects available for attentional selection, top-down factors were quite influential in determining which representational level would be selected. Third, the results suggest that uniform connectedness plays an important role in defining the entities available for attention selection. These results are discussed in terms of the manner in which attention selects objects in the visual environment.

Attentional control within 3-D space

Four experiments investigated whether directing attention to a particular plane in depth enables observers to filter out information from another depth plane. Observers viewed stereoscopic displays and searched for a red line segment among green line segments. The results showed that directing attention to a particular depth plane cannot prevent attentional capture from another depth plane when the colors of the target and distractor are identical. However, it can prevent attentional capture by a singleton from another depth plane when the colors of the target and distractor are different. These results indicate that only when both color and depth information are selective in guiding attention to the target singleton can attentional capture by irrelevant singletons be prevented. The results also suggest that retinal disparity does not have the same special status as location information in two dimensions and should be considered as just another feature along which selection may occur.

Spatial cuing in a stereoscopic display: attention remains "depth-aware" with age

Previous research has demonstrated that spatial attention is "depth-aware": Reaction times (RT) are greater for shifts in depth and two-dimensional (2-D) space than in 2-D space alone. This experiment examined whether the ability to focus attention at a depth location is maintained with advanced age. Twelve younger and 12 older observers viewed stereoscopic displays in which one of four spatial locations was cued. Two of the locations were at a near depth location and two were at a far depth location. When the focus of visual attention was shifted to a new location in space (because of an invalid cue), the cost in RT for switching attention (measured as the difference between RT on valid cue and invalid cue trials) was greater when observers had to switch attention between different depth locations and different locations in 2-D space than for shifts in 2-D space alone. This effect was observed for both younger and older observers, suggesting that the ability to orient attention to a depth location is maintained with age.

Age differences in visual search for feature, conjunction, and triple-conjunction targets

The authors examined the ability of younger and older adults to search for targets defined by single features (feature search), conjunctions of 2 features (conjunction search), and conjunctions of 3 features (triple-conjunction search). Feature search was relatively age-invariant, with both older and younger adults displaying shallow search slopes. However, older adults did show reduced search rates for many conjunction targets. Interestingly, both older and younger adults benefited equivalently when an extra feature was available to define the conjunction target. That is, the relative amount of improvement in search performance was similar for younger and older adults when the triple-conjunction search was compared to the conjunction search. These results are discussed in terms of age-related differences in the effectiveness of bottom-up and top-down mechanisms that support visual search.

Visual scanning and pilot expertise: the role of attentional flexibility and mental model development

In order to examine differences in flying expertise, 12 novice and 12 expert pilots flew a 7-segment simulation pattern under specific attentional constraints while cockpit instrument visual scan was recorded. Flight segments involved various combinations of maneuvering of heading, altitude and airspeed. Expert pilots performed better than novices on vertical and longitudinal, but not lateral control. They accomplished their superior vertical tracking by allocating more control resources to the vertical control. Analyses of scanning strategies revealed that experts: a) had shorter dwells and more frequent visits to most instruments; b) adapted their visiting strategy more flexibly in response to changing task demands; c) demonstrated a better mental model of cross-coupling and predictive relations between and within axes; and d) showed more frequent checking of axes whose values remained constant. The data is discussed in terms of their implications in pilot cockpit scan training program development.

Offset transients modulate attentional capture by sudden onsets

Recent research with visual search tasks has suggested that stimuli which appear as sudden onsets (new objects) have attentional priority over stimuli that are created by removing segments of premasks (non-onset stimuli). Attentional capture by sudden onsets occurs despite the fact that the appearance of these new objects predicts neither the identity nor the location of the target in the visual search task. In three experiments, we examined the extent to which attentional capture by sudden onsets could be modulated by offset transients used to create non-onset objects. To that end, we systematically manipulated the ratio of non-onset to onset stimuli in the display (display ratio) as well as the ratio offset to onset segments between the stimulus types (stimulus ratio). Increases in either the stimulus ratio or the display ratio resulted in increases in the visual search for the onset targets. These results suggest that the ability of sudden onsets (new objects) to capture attention is influenced by stimulus-driven factors, such as environmental change. Interestingly, the results also indicated that goal-directed or purposeful search for sudden-onset (new object) targets was relatively uninfluenced by the amount of change in the visual display. Therefore, it would appear that environment change has differential effects on goal-directed and stimulus-driven search. These results are discussed in terms of their implications for our understanding of attentional capture.

Object-based attentional selection--grouped arrays or spatially invariant representations?: comment on vecera and Farah (1994)

S. P. Vecera and M. J. Farah (1994) have addressed the issue of whether visual attention selects objects or locations. They obtained data that they interpreted as evidence for attentional selection of objects from an internal spatially invariant representation. A. F. Kramer, T. A. Weber, and S. E. Watson question this interpretation on both theoretical and empirical grounds. First, the authors suggest that there are other interpretations of the Vecera and Farah data that are consistent with location-mediated selection of objects. Second, they provide data, using the displays employed by Vecera and Farah in conjunction with a postdisplay probe technique, that suggests that attention is directed to the locations of the target objects. The implications of the results for space and object-based attentional selection are discussed.

Selective processing of superimposed objects: an electrophysiological analysis of object-based attentional selection

We investigated whether object-based attentional selection occurs from grouped-array or spatially-invariant representations. Subjects were presented with colored objects and asked to judge whether a particular color/shape conjunction was present, regardless of whether the color and shape were part of a single object (same-object condition) or occurred on two different objects (different-object condition). RTs and accuracies were recorded for subjects judgments. ERP components, in particular the P1 and N1, were elicited both from the presentation of the target objects and from a post-display probe that was employed as an index of spatial attention. Consistent with predictions of object-based selection models, RTs and accuracies were faster on same than on different object trials. N1s elicited by the target objects and P1s elicited by the post-display probes discriminated between same and different object trials when the two target objects were superimposed. These data are consistent with the proposal that object-based selection is spatially mediated, even in the case of partially overlapping objects. The data are discussed in terms of space- and object-based models of visual selective attention.

Object-based attentional selection--grouped arrays or spatially invariant representations?: comment on vecera and Farah (1994)

S. P. Vecera and M. J. Farah (1994) have addressed the issue of whether visual attention selects objects or locations. They obtained data that they interpreted as evidence for attentional selection of objects from an internal spatially invariant representation. A. F. Kramer, T. A. Weber, and S. E. Watson question this interpretation on both theoretical and empirical grounds. First, the authors suggest that there are other interpretations of the Vecera and Farah data that are consistent with location-mediated selection of objects. Second, they provide data, using the displays employed by Vecera and Farah in conjunction with a postdisplay probe technique, that suggests that attention is directed to the locations of the target objects. The implications of the results for space and object-based attentional selection are discussed.

Aging and filtering by movement in visual search

We examined the ability of younger and older adults to selectively process moving items and ignore stationary items in a task that required the search for a target defined by a conjunction of movement and form (i.e., search for a moving X among moving Os and stationary Xs) in displays of 5, 9, 17, and 25 stimuli (Experiment 1) and displays of 5, 10, and 20 stimuli (Experiment 2). We also investigated subjects' performance in two feature search tasks, the search for a target defined by movement or form. Finally, we examined the influence of practice on feature and conjunction search. Younger and older adults searched the displays at similar rates in the feature and conjunction search tasks. Older and younger adults also benefited equivalently from practice. These data suggest age-equivalence in the processes which underlie feature search in dynamic environments as well as those processes responsible for the segregation of moving and stationary objects in the visual field.