Age-Group Differences in Saccadic Interference

Journal of Gerontology: PSYCHOLOGICAL SCIENCES 2007, Vol. 62B, No. 2, P85–P89 Copyright 2007 by The Gerontological Society of America Age-Group Differences in Saccadic Interference Lawrence R. Gottlob, Mark T. Fillmore, and Ben D. Abroms Department of Psychology, University of Kentucky, Lexington. A S we move through the world, the visual field is continually changing. We often must fixate the portion of the visual field that is most salient to our immediate goals, while resisting the ‘‘automatic’’ attraction of other objects. For example, while navigating a bicycle through rush-hour city traffic, a cyclist must monitor parked cars for opening doors and the oncoming lane for turning cars, while simultaneously resisting the urge to fixate shiny coinlike objects on the road. This control over eye movements (oculomotor control) is also exerted in many laboratory contexts, including visual search, location cuing, and reading. Because oculomotor control is intrinsic to the efficient execution of eye movements, and because it is closely tied to attentional control (Kramer, Hahn, Irwin, & Theeuwes, 1999), age-group differences in this ability are important to study. Researchers often examine oculomotor control directly by monitoring eye movements in experimental paradigms involving instructions to fixate certain objects in the visual field while ignoring others (e.g., Reingold & Stampe, 2002). Researchers have examined age-group differences in this ability by using the attentional capture paradigm. In Kramer, Hahn, Irwin, and Theeuwes (2000), participants first fixated a display containing six items in a circular configuration with a radius of 12.68. All of the display items, except one, then changed from gray to red; participants had been instructed to execute a saccade to the single item that remained gray. On some trials, a new red (distractor) item appeared at the same time that the other items changed from gray to red. When red and gray were equiluminant, participants were generally unaware of the distractor, and there were no age-group differences in the percentage of trials in which saccades were initially directed toward the distractor. When the distractor was brighter than the target, and consequently participants were aware of its presence, younger adults had a decreased incidence of saccades toward the distractor (compared with equiluminant trials), whereas older adults had an increased incidence. The inference was that older adults had relative difficulty inhibiting reflexive saccades when the intrusive object occupied awareness, but that there were no age deficits when the inhibition was related to unconscious or automatic processes (see also Kramer et al., 1999). In the study by Kramer and colleagues (2000), saccade latencies were the same for no-distractor and distractor trials. If the distractor interfered with the execution of saccades, why were the latencies not different? One possible explanation is in the geometry of the task: Distractors could appear close to (19.48) or far from (25.48) the target, but because the possible target locations were on a circle, the spatial relationship between the distractor and the target was highly variable. This spatial relationship has been found to influence attentional capture in a complex manner, sometimes affecting saccade accuracy and sometimes affecting saccade latency. In a study examining spatial properties of attentional capture, Walker, Deubel, Schneider, and Findlay (1997) presented abrupt-onset targets at a variety of locations on the horizontal midline of a computer screen and manipulated the spatial relationship of the distractor and target. When the distractor was presented in the same vertical hemifield as the target and within 208 of the horizontal meridian (i.e., close to the path of a target saccade), accuracy was affected, but latency was affected only very slightly. When the distractor appeared outside the saccade-path zone, latency was primarily affected, with accuracy mostly unaffected. The differential effects were explained in terms of adding or subtracting inputs in the neural structures that control oculomotor movements. When the distractor and target are in close proximity, the final saccade path is determined by spatial averaging of inputs. When the distractor and target are in opposite hemifields or otherwise sufficiently separated, inhibitory mechanisms in the neural areas that program saccades (e.g., superior colliculus; Reingold & Stampe, 2002) cause delays in the programming of target saccades, but they do not have much impact on accuracy. Thus, the failure of Kramer and colleagues (1999, 2000) to find distractor effects in saccade latency may have been due to variations in the spatial relationship between target and distractor (although if mean latency was a weighted average of accuracy- and latency-affected trials, there should have been an effect of distractor). In addition to spatial properties of the distractor, the timing of the distractor onset has been shown to affect the saccadic response to distractors. In the studies by Kramer and colleagues (1999, 2000), onsets of distractor and target were simultaneous. Reingold & Stampe (2002), in a study using young participants only, investigated the time parameters of distractor onset. Participants were required to execute saccades to targets presented 48 to the left or right of fixation. On some trials, the top and P85 We examined age-group differences in a saccadic interference task, which requires that participants execute a saccade (eye movement) toward an abrupt-onset visual target presented to the right or left of fixation. On some trials, we imposed diffuse interference by bilateral (top and bottom) flashes of light presented 20 to 210 ms after target onset. When the flashes followed the cue at shorter intervals, time to execute a saccade was slowed relative to no-flash trials. This slowing was greater and sustained over a larger cue–flash interval for older participants than for the young participants. The results indicate that, when diffuse distractors are used, older adults are more susceptible to saccade disruption than are young adults. P86 GOTTLOB ET AL. bottom third of the display was illuminated (flashed) briefly. The onset asynchrony between target and flash was manipulated on an adaptive basis for each observer, such that the target–flash delay would have the maximum effect on saccade reaction time. This optimal delay, suggested by a previously performed experiment (Reingold & Stampe, 2004), was the median saccade latency for each observer, minus 100 ms. In their Experiment 1, Reingold and Stampe (2002) manipulated the fixation point–target relationship and measured the magnitude of the flash effect in each condition: gap (fixation offset before target onset), step (fixation offset simultaneous with target onset), and overlap (fixation point remained on for the entire trial). They found that maximum saccade (...truncated)