Aging, selective attention, and feature integration

This study used feature-integration theory as a means of determining the point in processing at which selective attention deficits originate. The theory posits an initial stage of processing in which features are registered in parallel and then a serial process in which features are conjoined to form complex stimuli. Performance of young and older adults on feature versus conjunction search is compared. Analyses of reaction times and error rates suggest that elderly adults in addition to young adults, can capitalize on the early parallel processing stage of visual information processing, and that age decrements in visual search arise as a result of the later, serial stage of processing. Analyses of a third, unconfounded, conjunction search condition reveal qualitatively similar modes of conjunction search in young and older adults. The contribution of age-related data limitations is found to be secondary to the contribution of age decrements in selective attention.     

Adult age differences in visual search accuracy: attentional guidance and target detectability

Previous research, relying primarily on reaction time measures of highly accurate performance, suggests that both younger and older adults can increase the efficiency of visual search by guiding attention to a candidate subset of items. The authors investigated attentional guidance when accuracy was well below ceiling to focus more specifically on the role of perceptual processes. In the most difficult condition (conjunction search), the likelihood of missing a target was greater for older adults than for younger adults, and this effect was not attributable entirely to generalized slowing. Both age groups were able to improve search efficiency by attending to a distinct subset of display items, indicating that attentional guidance to perceptual features does not exhibit age-related decline. A signal-detection model of the conjunction search data demonstrated that the age difference represented an age-related decline in target detectability.     

Searching from the top down: Ageing and attentional guidance during singleton detection

Previous investigations of adult age differences in visual search suggest that an age-related decline may exist in attentional processes dependent on the observer's knowledge of task-relevant features (top-down processing). The present experiments were conducted to examine age-related changes in top-down attentional guidance during a highly efficient form of search, singleton detection. In Experiment 1 reaction times to detect targets were lower when target features were constant (feature condition) than when target features were allowed to vary between trials (mixed condition), and this reaction time benefit was similar for younger and older adults. Experiments 2 and 3 investigated possible interactions between top-down and bottom-up (stimulus-driven) processes. Experiment 2 demonstrated that search times for both age groups could be improved when targets varied on an additional feature from distractors (double-feature condition) but only when top-down control was available (feature search). In Experiment 3, the availability of top-down guidance enabled both younger and older adults to override the distracting effects of a noninformative spatial location cue. These findings indicate that top-down attentional control mechanisms interact with bottom-up processes to guide search for targets, and that in the context of singleton detection these mechanisms of top-down control are preserved for older adults.     

Lifespan changes in attention: The visual search task

There are two popular frameworks for the study of visual attention. Treisman's Feature Integration Theory focuses on the effortful process of binding together the multiple attributes of an object. Posner's Visual Orienting Theory emphasizes the movement of an attentional spotlight across space. Although both aspects are undoubtedly important in any visual search task, it is not clear how each of these aspects changes with age. We tested observers aged 6, 8, 10, 22, and 72 years on visual search tasks designed to isolate these factors. No age-related differences were found in single- or double-feature discrimination, attention movement to a single item, or search for a single-feature target among distractors. Two age-related changes were found: (1) young children were less able than either young adults or seniors to search for targets defined by a conjunction of features, and (2) both children and seniors were less able than young adults to move attention voluntarily from item to item. This implies that feature integration and voluntary movement of attention have different trajectories over the lifespan.     

Working memory binding of visual object features in older adults

Accurate mental representation of visual stimuli requires retaining not only the individual features but also the correct relationship between them. This associative process of binding is mediated by working memory (WM) mechanisms. The present study re-examined reports of WM-related binding deficits with aging. In Experiment 1, 31 older and 31 younger adults completed a visual change detection task with feature–location relations presented either simultaneously or sequentially; the paradigm was also designed specifically to minimize the impact of lengthy retention intervals, elaborative rehearsal, and processing demands of multi-stimulus probes. In Experiment 2, 38 older and 42 younger adults completed a modified task containing both feature–location relations and feature–feature conjunctions. In Experiment 1 although feature–location binding was more difficult with sequential compared with simultaneous presentation, the effect was independent of age. In Experiment 2 while older adults were overall slower and less accurate than young adults, there were no age-specific deficits in WM binding. Overall, after controlling for methodological factors, there was no evidence of an age-related visual WM binding deficit for surface or location features. However, unlike younger adults, older adults appeared less able to restrict processing of irrelevant features, consistent with reported declines with age in strategic capacities of WM.     

Visual search in children and adults: Top-down and bottom-up mechanisms

Three experiments investigated visual search for targets that differed from distractors in colour, size, or orientation. In one condition the target was defined by a conjunction of these features, while in the other condition the target was the odd one out. In all experiments, 6–7- and 9–10-year-old children were compared with young adults. Experiment 1 showed that children's search differed from adults' search in two ways. In conjunction searches children searched more slowly and took longer to reject trials when no target was present. In the odd-one-out experiments, 6–7-year-old children were slower to respond to size targets than to orientation targets, and slower for orientation targets than for colour targets. Both the other groups showed no difference in their rate of responding to colour and orientation. Experiments 2 and 3 highlighted that these results were not a function of either differential density across set sizes (Experiment 2) or discriminability of orientation and colour (Experiment 3). Across all three experiments, the results of both conjunction and odd-one-out searches highlighted a development in visual search from middle to late childhood.     

Visual search in children and adults: top-down and bottom-up mechanisms

Three experiments investigated visual search for targets that differed from distractors in colour, size, or orientation. In one condition the target was defined by a conjunction of these features, while in the other condition the target was the odd one out. In all experiments, 6-7- and 9-10-year-old children were compared with young adults. Experiment 1 showed that children's search differed from adults' search in two ways. In conjunction searches children searched more slowly and took longer to reject trials when no target was present. In the odd-one-out experiments, 6-7-year-old children were slower to respond to size targets than to orientation targets, and slower for orientation targets than for colour targets. Both the other groups showed no difference in their rate of responding to colour and orientation. Experiments 2 and 3 highlighted that these results were not a function of either differential density across set sizes (Experiment 2) or discriminability of orientation and colour (Experiment 3). Across all three experiments, the results of both conjunction and odd-one-out searches highlighted a development in visual search from middle to late childhood.     

Grouping effects on spatial attention in visual search.

In visual search tasks, spatial attention selects the locations containing a target or a distractor with one of the target's features, implying that spatial attention is driven by target features (M.-S. Kim & K. R. Cave, 1995). The authors measured the effects of location-based grouping processes in visual search. In searches for a color-shape combination (conjunction search), spatial probes indicated that a cluster of same-color or same-shape elements surrounding the target were grouped and selected together. However, in searches for a shape target (feature search), evidence for grouping by an irrelevant feature dimension was weaker or nonexistent. Grouping processes aided search for a visual target by selecting groups of locations that shared a common feature, although there was little or no grouping by an irrelevant feature when the target was defined by a unique salient feature.     

Age-related increase in top-down activation of visual features

Previous research suggests that, during visual search and discrimination tasks, older adults place greater emphasis than younger adults on top-down attention. This experiment investigated the relative contribution of target activation and distractor inhibition to this age difference. Younger and older adults performed a singleton discrimination task in which either an E or an R target (colour singleton) was present among distractor letters. Relative to a baseline condition in which the colours of the targets and distractors remained constant, an age-related slowing of performance was evident when either the colour of the target or that of the distractors varied across trials. The age-related slowing was more pronounced in response to target colour variation, suggesting that older adults place relatively greater emphasis on the top-down activation of target features.     

Age-related increase in top-down activation of visual features

Previous research suggests that, during visual search and discrimination tasks, older adults place greater emphasis than younger adults on top-down attention. This experiment investigated the relative contribution of target activation and distractor inhibition to this age difference. Younger and older adults performed a singleton discrimination task in which either an E or an R target (colour singleton) was present among distractor letters. Relative to a baseline condition in which the colours of the targets and distractors remained constant, an age-related slowing of performance was evident when either the colour of the target or that of the distractors varied across trials. The age-related slowing was more pronounced in response to target colour variation, suggesting that older adults place relatively greater emphasis on the top-down activation of target features.     

Grouping Effects on Spatial Attention in Visual Search

In visual search tasks, spatial attention selects the locations containing a target or a distractor with one of the target's features, implying that spatial attention is driven by target features (M.S. Kim & K. R. Cave, 1995). The authors measured the effects of location-based grouping processes in visual search. In searches for a color-shape combination (conjunction search), spatial probes indicated that a cluster of same-color or same-shape elements surrounding the target were grouped and selected together. However, in searches for a shape target (feature search), evidence for grouping by an irrelevant feature dimension was weaker or nonexistent. Grouping processes aided search for a visual target by selecting groups of locations that shared a common feature, although there was little or no grouping by an irrelevant feature when the target was defined by a unique salient feature.     

Visual search for features and conjunctions in development.

Visual search performance was examined in three groups of children 7 to 12 years of age and in young adults. Colour and orientation feature searches and a conjunction search were conducted. Reaction time (RT) showed expected improvements in processing speed with age. Comparisons of RT's on target-present and target-absent trials were consistent with parallel search on the two feature conditions and with serial search in the conjunction condition. The RT results indicated searches for feature and conjunctions were treated similarly for children and adults. However, the youngest children missed more targets at the largest array sizes, most strikingly in conjunction search. Based on an analysis of speed/accuracy trade-offs, we suggest that low target-distractor discriminability leads to an undersampling of array elements, and is responsible for the high number of misses in the youngest children.     

Adult age differences in visual word identification: functional neuroanatomy by positron emission tomography

Adult age differences in the neural systems mediating semantic (context-independent) memory were investigated using positron emission tomography (PET). Younger (20-29 years) and older (62-70 years) participants performed lexical decision (word/nonword discrimination) and nonsemantic (simple visual search) baseline tasks during PET scanning. Within the lexical decision task, display duration and presentation rate were varied across scans. The behavioral data suggested that although an age-related slowing was evident in visual feature and response processing, the retrieval of semantic/lexical information was similar for younger and older adults. For both age groups, lexical-related activation occurred in inferior prefrontal and occipitotemporal regions of the left hemisphere. Differential activation, as a function of age group, was observed in the left occipitotemporal pathway as a result of older adults' maintaining higher levels of neural activity in striate cortex (during visual search) and in inferior temporal cortex (during lexical decision). The prefrontal activation was similar for the two age groups. Thus, although this form of semantic memory retrieval does not undergo significant age-related decline, an age-related change in the associated pattern of neural activation is evident. These findings differ from previous neuroimaging studies of episodic (context-dependent) memory retrieval, which have suggested that age-related compensatory mechanisms are expressed primarily by greater activation of prefrontal regions for older adults than for younger adults.     

The development of visual search in infants and very young children.

In two experiments, 90 1- to 3-year-olds were trained in a new nonverbal task to touch a video screen that displayed a unique target resembling a popular television character. The target appeared among varying numbers of distractors that resembled another familiar television character and was either a uniquely colored shape (the feature search task) or a unique color-shape combination (the conjunction search task). Each correct response triggered a sound and produced four animated objects on the screen. Irrespective of age and experimental design (between-subjects or within-subjects), children's reaction time (RT) patterns resembled those obtained from adults in corresponding search tasks: The RT slope for feature search was flat and independent of distractor number, whereas the RT slope for conjunction search increased linearly with distractor number. These results extend visual search effects found with adults to infants and very young children and suggest that the basic perceptual processes underlying visual search are qualitatively invariant over ontogeny.     

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.     

The role of attention in binding visual features in working memory: Evidence from cognitive ageing

Two experiments were conducted to assess the costs of attentional load during a feature (colour–shape) binding task in younger and older adults. Experiment 1 showed that a demanding backwards counting task, which draws upon central executive/general attentional resources, reduced binding to a greater extent than individual feature memory, but the effect was no greater in older than in younger adults. Experiment 2 showed that presenting memory items sequentially rather than simultaneously, such that items are required to be maintained while new representations are created, selectively affects binding performance in both age groups. Although this experiment exhibited an age-related binding deficit overall, both age groups were affected by the attention manipulation to an equal extent. While a role for attentional processes in colour–shape binding was apparent across both experiments, manipulations of attention exerted equal effects in both age groups. We therefore conclude that age-related binding deficits neither emerge nor are exacerbated under conditions of high attentional load. Implications for theories of visual working memory and cognitive ageing are discussed.     

Aging and visual search: Generalized cognitive slowing or selective deficit in attention?

Abstract

Selective attention in normal aging was investigated using simple and conjoined feature visual search tasks. the effects of varying the location of the target (central vs. peripheral, left vs. right hemifield) and the complement of distractors, together with variability in task performance across subject groups, were also examined. the findings indicated that the feature extraction stage of visual search was preserved in older aged subjects. However, there was a differential age-related impairment in the feature integration stage of visual processing in the two older groups (66-75 years, 76-85 years). This was greater than the magnitude of decline predicted on the basis of generalized cognitive slowing. There was no evidence of a speed-accuracy trade-off in the performance of either search task. the findings of this study contribute towards the delineation of age-dependent and -independent processes subserving visual selective attention. the performance of older individuals may be relatively well preserved on more automatic, less demanding tasks such as simple feature search. By contrast, there may be differential age-related impairments on visual search tasks such as conjoined feature search, which may require more effortful or controlled attentional processing.     

SPATIAL ATTENTION IN VISUAL SEARCH FOR FEATURES AND FEATURE CONJUNCTIONS

Abstract— Spatial attention was measured in visual searches tasks using a spatial probe. Both speed and accuracy measures showed that in a conjunction task, spatial attention was allocated to locations according to the presence of target features. Also, contrary to some predictions, spatial attention was used when a clearly distinguishable feature defined the target. The results raise questions about any account that assumes separate mechanisms for feature and conjunction search The probe method demonstrated here allows a very direct measurement of attentional allocation, and may uncover aspects of selection not revealed by visual search     

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.     

Age-related effects in the marking of old objects in visual search

Two studies were performed to examine potential age-related differences in visual marking. Visual marking is a limited capacity process that enhances visual search through the inhibition of old objects. In Experiment 1, young and old adults performed three different search conditions: a full-element baseline, a half-element baseline, and a gap condition in which they searched through displays similar to the full-element baseline condition but with half of the letters presented before and the other half of the letters and the target presented after a 1000-ms gap. Both old and young adults displayed search slopes in the gap condition that were equivalent to slopes obtained in the half-element condition, suggesting that they were able to successfully inhibit the old letters. In Experiment 2, old and young adults also performed in three different visual search conditions but in this case with targets defined either by a form difference or by a conjunction of form and color. Both old and young adults showed a reduced slope in the gap as compared to the conjunction condition, suggesting inhibition of the old objects. The data are discussed in terms of age-related differences in the top-down control of attention in visual search.