Academic journal article Canadian Journal of Experimental Psychology

Covert Visual Orienting across the Lifespan

Academic journal article Canadian Journal of Experimental Psychology

Covert Visual Orienting across the Lifespan

Article excerpt

Abstract Covert visual orienting was examined over a span of human life ranging from six to 73 years. The observer's task was the speeded discrimination of "x" from "O," but of primary interest was the effect of a location cue that appeared prior to the target. Both an abrupt stimulus cue and a voluntary information cue were studied using response time (RT) measures. Eye movements were monitored to control for differences in the ability to maintain fixation. Experiment 1 showed that there were very few age differences in stimulus-cued orienting. In contrast, there were important differences when orienting was intentional. In comparison with young adults, children were less able to sustain orienting over time, and senior adults required more time to use the cue. Experiment 2 tested the relation between stimulus and information cues when they both occurred prior to a given target. All age groups were able to use information cues in the presence of conflicting stimulus cues, but young adults were better able to do so than either children or senior adults. These results are interpreted as support for the view that separate mechanisms underlie stimulus-based versus information-based spatial orienting. The ability to shift visual attention independently from physical movements of the eye, head, and body is central to many tasks of everyday life. The wide range of behaviors that are facilitated (or even made possible) by this ability, include a general physiological arousal to sudden changes in brightness, orientation and motion (Rohrbaugh, 1984); eye guidance in reading and other visual exploration (Henderson, Pollatsek, & Rayner, 1989; Rayner, 1986); visually-guided hand and foot responses in athletic activity (Nougier, Ripoll, & Stein, 1989); and automobile driving (Ball, Roenker, & Bruni, 1990). The present study is the first, to our knowledge, in which this ability is compared directly in observers as young as six years and as old as 73 years. This comparison is of interest because observers that are either younger or older than the typical college student are believed to be less efficient in their deployment of spatial attention. However, it is far from clear whether the decreased abilities at both ends of life are the product of similar or different mechanisms. Covert Orienting The phenomenon of covert orienting was described over 100 years ago (James, 1890/1950; Mach, 1886/1959), but its empirical study has a much shorter history (e.g., Posner, 1980; Posner & Snyder, 1975; Posner, Snyder, & Davidson, 1980; for a lifespan review, see Plude, Enns, & Brodeur, 1994). Recent research has pointed to several important distinctions between orienting that is elicited by stimulus cues (usually abrupt luminance transients at the location to be attended) and information cues (typically arrows or digits that refer to pre-designated locations). For one, stimulus-induced shifts in attention are not as easily influenced by higher-level goals as are voluntary shifts (Jonides, 1981; Jonides & Yantis, 1988; Muller & Rabbitt, 1989; Nakayama & Mackeben, 1989; Yantis & Jonides, 1984, 1990). Second, the time course of the two cues differs: stimulus-driven shifts generally result in rapid and large effects whereas information cues produce effects that are slower to rise but longer lasting over time (Jonides, 1981; Muller & Rabbitt, 1989; Nakayama & Mackeben, 1989; Posner & Cohen, 1984). Third, one effect is seen only following stimulus cues: RTs can actually be longer for valid than for invalid cues. This occurs most often with cue-target intervals (hereafter refered to as stimulus onset asynchronies, or SOA) of 400 ms or more and has become known as inhibition of return (Maylor, 1985; Posner & Cohen, 1984; Rafal, Calabresi, Brennan, & Sciolto, 1989). Such inhibition has been observed under conditions of covert orienting (i.e., when no eye movements are made), overt orienting (i.e., when a saccade is executed to the cued location), and when a saccade to the cued location is prepared but not executed (Rafal et al. …

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