Adult Age Differences in the Implicit and Explicit Components of Top-Down Attentional Guidance During Visual Search.

Abstract

Two experiments investigated adult age differences in the explicit (knowledge-based) and implicit (repetition priming) components of top-down attentional guidance during discrimination of a target singleton. Experiment 1 demonstrated an additional contribution of explicit top-down attention, relative to the implicit effect of repetition priming, which was similar in magnitude for younger and older adults. Experiment 2 examined repetition priming of target activation and distractor inhibition independently. The additional contribution of explicit top-down attention, relative to the repetition priming of distractor inhibition, was greater for older adults than for younger adults. The results suggest that some forms of top-down attentional control are preserved as a function of adult age and may operate in a compensatory manner. Keywordsaging; selective attention; reaction time; perception; cognition Identifying a target item in a visual display involves guiding attention to that item and determining that it possesses the features sufficient for a detection response. Attentional guidance can be either top-down, in the sense of depending primarily on the observer's goals and knowledge of the task structure, or bottom-up, in the sense of being relatively more determined by the local properties of the visual display (Wolfe, 1998;Yantis, 1998). Top-down attention is essential in complex search tasks, as when, for example, the target is a conjunction of different features occurring in the distractors (e.g., finding a T among Ls and Fs). In this case, one must know what one is looking for. In contrast, when the target differs from the distractors in a unique feature (e.g., a T among Os), the target pops out of the display visually in a bottom-up (stimulus-driven) manner.Most forms of visual search represent the combined influence of top-down and bottom-up attentional processing, and even in relatively simple tasks there can be a contribution of topdown attention. Bravo and Nakayama (1992) demonstrated a top-down effect during detection and discrimination of a color singleton. The target, for example, could be a red diamond among green diamond distractors, with the task being the determination of whether the left or right side of the target was cut off. These authors found that the unique color of the singleton provided

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

“…In a recent study, we examined adult age differences in top-down attention during colour singleton discrimination in a letter search task (Madden, Whiting, Spaniol, & Bucur, 2005). Consistent with Wolfe et al (2003), we found that top-down attention has both explicit (expectation) and implicit (repetition priming) components.…”

“…In addition, although the rate of priming for both targets and distractors was similar for younger and older adults, and both age groups exhibited some additional contribution of the explicit component, this latter contribution was greater for older adults than for younger adults. The Madden et al (2005) results suggest that older adults may enhance the output of feature module(s), through explicit top-down attention.…”

“…The task was the same as that used by Madden et al (2005): a twochoice version of singleton discrimination in which the target letters were E and R. Participants viewed a series of displays, each containing either four or six letters, one of which was a target. The target letter was always a colour singleton relative to the nontarget (distractor) letters, which were all the same colour (e.g., a red E among grey distractor letters).…”

“…We interpret differences between the target-varying and distractor-varying conditions, relative to a baseline condition with target and distractor colours constant, as evidence for the type of top-down attention that occurs within the baseline condition. If the age-related increase in explicit top-down attention reported by Madden et al (2005) relies more heavily on the activation of target features, then the age-related increase in RT should be greater in the target-varying condition than in the distractor-varying condition. Conversely, a greater age-related increase in RT in the distractor-varying condition than in the target-varying condition would suggest an increased reliance on top-down distractor inhibition.…”

“…One limitation to the Madden et al (2005) study is that the target and distractor colours were either both constant (in the baseline condition) or both varied (in the mixed condition). Thus, although the Madden et al mixed condition included priming sequences for target and distractor colour separately, both types of display items varied in colour across trials, and the mixed condition consequently disrupted top-down attention to both target activation and distractor inhibition.…”