Searching for real objects in a natural environment: The role of contextual semantic cues and incidental encoding in older and younger viewers Hanane Ramzaoui*, Sylvane Faure* & Sara Spotorno§ *LAPCOS, University of Côte d’Azur, Nice, France; §Institute of Neuroscience and Psychology, University of Glasgow, UK
Introduction
Method
• Visual search performance decreases during aging, but older and young adults seem not to differ in their ability to use previous knowledge in order to guide search in scenes presented on a screen [1-2].
Participants • 16 older (M = 68.6, SD = 4.3), healthy (MMSE [6]: M = 29.6, SD = 0.5), and 16 young (M = 25.1, SD = 5.0) controls.
• Utilisation of information acquired during previous fixations in search. Visual information accumulates across fixations [3]. This seems true not only for voluntary memorisaton, but also for incidental encoding: for instance, incidental fixations on distractor objects during search facilitate their subsequent recognition [4]. However, it is still not clear to what extent fixating an object at a certain point in time helps searching for the same object in a subsequent trial. Indeed, while it has been shown that search greatly ameliorates when the same object is searched for repeatedly [5-7], only little improvement has been reported when searching for different objects within the same scene presented on a screen [6].
Materials • Object arrays on 4 cluttered tables in a real room, 4 targets and 14 distractors per table (Figure 1). Each table contained 4 semantic groups formed by 4 objects that normally co-occur in everyday life as they are semantically related. The objects of 2 semantic groups were placed near each other, while the objects of the other 2 groups were placed far apart from each other. Moreover, there were 2 objects, unrelated to all the others, on each table.
o We hypothesise that incidental information gathering might have a greater role in guiding real-world search compared to what happens during on screen search. Indeed, it has been suggested that we use little long-term memory during everyday tasks, as we gather a large part of information directly from the world through eye movements [8], using therefore the visual world as an “external memory” [9]. 1. We examined whether results about the effect of high-level information, usually obtained in scene search on screens, extends to real-world situations, in older and young viewers. More precisely, high-level information was analysed here as previous semantic knowledge in terms of expectations of object co-occurrence. 2. We also studied incidental information gathering in real-world search, analysing the potential benefit of previous incidental fixations on targets during trials in which they were distractor objects.
Procedure • Participants were required to search for 4 targets in each table, placed in 2 groups: 2 targets, in one semantic group, surrounded by semantically related distractors, and 2 targets, in another semantic group, located far from semantically related distractors (Figure 2). • Participants stood in front of the table at a distance of about 60 cm. Their eye movements were recorded with SMI eye-tracking glasses, sampling at 60hz. S2 S3
S4
S1 Figure 1. Example of table layout, where 2 semantic groups of objects are shown, according to the 2 placement conditions :
Near
Far
Figure 2. The 4 searched-targets are indicated considering the 2 position conditions (near vs. far from semantically-related-objects). For each participant, the order of searches (S1, S2, S3, and S4) was the same.
Analysis and Results • Target Position (near vs. far), Target Previous Fixation (fixated vs. not fixated), Age Group (older vs. young), and their interactions were entered as fixed factors in Linear Mixed Models that analysed oculomotor behaviour. Participant and trial were entered as random factors. • In analysing previous fixation on a target, we only consider fixations lasting for more that 100 ms, in order to ensure information gathering about the object. Two-way interaction p = .027
Effect of age group
Two-way interaction p = .053
***: p < .001, **: p < .01, *: p < .05. Bars indicate mean +/-1 SE
Conclusion • This is, to our knowledge the first study examining real-world search during ageing. We found slower visual search within a real-world setting in older adults. • Our results suggest increased utilisation of high-level, semantic information during real-world search in ageing, as older adults located faster targets surrounded by semantically related distractors than targets surrounded by unrelated distractors. o Moreover, contrary to Mack & Eckstein (2011, [8]), we reported no benefit of object-to-object semantic association for young adults.
• Search was not significantly quicker for previously (incidentally) fixated objects, even though we did find a weak tendency for targets surrounded by unrelated distractors to be located slightly faster (70 ms, similarly to [5]) when they were previously fixated. Thus, any information accumulated during incidental fixation does not seem to be utilised considerably during real-world search. This is coherent to what reported for scene search on screens [4].
References
Contact Information Hanane Ramzaoui PhD Student in neuropsychology University of Côte d’Azur, Nice, France Email:
[email protected]
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Acknowledgements Ramzaoui H. is supported by Médéric Alzheimer foundation.
