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Sogol Ghattan-Kashani, Ronald Rensink; Effect of Global and Local Processing on Visual Search Asymmetry. Journal of Vision 2020;20(11):1491. doi: https://doi.org/10.1167/jov.20.11.1491.
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© ARVO (1962-2015); The Authors (2016-present)
It is well known that Westerners show a search asymmetry for line length: search for long lines among short is faster than for short among long. In contrast, Asians given the same task show no asymmetry (Ueda et al., 2017). And asymmetry for long-term Asian immigrants in a Western country depends on the language in which task instructions are given (Cramer et al., 2016).
To examine how this asymmetry depends on preceding task, 22 Westerners were given a local Navon task as a pre-task before the visual search. This task consisted of 8 blocks of 28 trials each. In the subsequent search for line length (5 blocks of 30 trials per block for each target length), average target-present slope was 35 ms/item for long targets and 52 ms/item for short (t-test: p = 0.01); average ratio of short- to long-target slopes was 1.46. Search was therefore asymmetric, consistent with that of Westerners tested on similar stimuli (e.g., Cramer et al., 2016).
Another 23 Westerners were given a global Navon task as a pre-task. Average target-present slope was now 56 ms/item for long targets and 63 ms/item for short (t-test: p = 0.15 ); average slope ratio was 1.12. Search asymmetry was now abolished, similar to that of Asians tested on the same stimuli (Ueda et al., 2017).
These results support the proposal that attention in visual search has at least two modes, with selection of mode affected by the preceding task (Rensink et al., VSS 2018) Different deployment of these modes may also explain some of the differences found in observers from different cultures, with the holistic versus analytic distinction (Nisbett et al., 2001) corresponding to the global versus local distinction in visual perception.
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