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Article Excerpt
INTRODUCTION
A large body of evidence documents the difficulties experienced by older adults when they are engaged in visual search. Generally this work has involved search for simple visual features (e.g., orientation, colon and form) that is carried out as an isolated task. In contrast, the experiment summarized here examined age differences in search of more complex and naturalistic scenes under both single-task and dual-task conditions. Performance was measured using reaction time (RT) and errors, but eye movement data were also gathered to afford a finer grained analysis of performance (Ho, Scialfa, Caird, & Graw, 2001: Maltz & Shinar, 1999), and subjective workload was measured to ascertain if observer experience mirrored the manipulations of cognitive demand. The goal of the research w, as to determine if age-related search deficits are found with these scenes, particularly when attention cannot be allocated solely to that task.
Age differences in simple visual search tasks (e.g., conjunction search based on orientation, luminance, or color) depend on many stimulus and task factors such as target-distractor similarity, eccentricity; and working memory requirements (Owsley et al., 1998; Plude & Doussard-Roosevelt, 1989; Rogers & Fisk, 1991; Scialfa & Joffe, 1997). In contrast, because older adults are able to use top-down information to guide search (Atchley & Kramer, 1998; Ho & Scialfa, 2002; Madden, 1983), it is possible that they will perform relatively well when searching real-world scenes that afford the use of this information. Although Maltz and Shinar (1999) found evidence that older adults were less systematic in the eye movements they executed while they searched driving scenes, Ho et al. (2001) found no age differences in clutter effects using a large set of traffic signs in both daytime and simulated nighttime scenes. Similar results were obtained by Schieber and Goodspeed (1997) at comparable levels of clutter. Thus it appears that age-related differences in search for traffic signs are smaller than those in search for letters, words, numbers, and other stimuli used in many studies of visual search.
None of these studies examined age differences in search under divided-attention conditions. This is an important issue, for several reasons. Dividing attentional resources across multiple tasks is often necessary while one is driving, carrying out industrial inspection, or searching for objects in other environments. A related issue is that increased use of various technologies (e.g., cellular phones, Internet access) in private automobiles brings with it the increased need to drive safely under divided-attention conditions. In addition, age deficits in divided-attention costs have been found in a variety of real-world tasks (Caird & Chugh, 1997; Crook, West, & Larrabee, 1993; Kramer, Larish, & Strayer, 1995; Owsley et al., 1998; Ponds, Brouwer, & van Wolffelaar, 1988; Tsang & Shaner, 1998). Thus, although age differences in traffic sign search may be small if attention can be allocated solely to that task, age deficits may arise when, as is more often the case, multiple tasks are being performed concurrently.
In this study we asked groups of younger and older people to search for a variety of warning and regulatory signs in images of traffic scenes. Sometimes they performed this search task while listening to and answering questions about brief prose passages. At other times the search task was performed in isolation. We expected that search performance would suffer in the divided-attention conditions and that this would be more pronounced in highly cluttered scenes. We also expected, based on the literature on aging and divided attention, that dual-task costs would be larger among older adults. Specifically, we thought that relative to the young participants, older adults would be slower, make more eye movements, and exhibit longer fixation durations under divided-attention conditions.
METHOD
Participants
There were 16 younger adults (M = 22.62, range = 17-33 years) and 16 older adults (M = 64.19, range = 56-71 years) in the study. Four additional older individuals were discarded from the analysis because we could not obtain eye movement data from them. In the young group there were 11 women and 5 men. In the older group there were 7 women and 9 men. Participants were volunteers from the university and the surrounding community and were paid $10 (Canadian) for their efforts.
All participants indicated by self-report that they had not been hospitalized for a serious illness in the past year and were not under a physician's care for a serious illness or condition. We also asked about current prescription drug usage. Four older adults reported drug usage: one for diabetes, one for elevated cholesterol, one for low bone density, and the last for hormone therapy. Although there is a potential for dizziness, headaches, and blurred vision with medication for diabetes and cholesterol conditions, the participants did not report any side effects from the drugs they were taking.
Our observers were well educated. Younger adults, on average, had 15.25 years of education (range = 12-20 years), and the older adults had gone to school for an average of 16.58 years (range = 15-24 years). These age differences in...
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