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Karla Evans, Lucy Spencer, Daniel Baker; Dynamics of "Gist" Processing. Journal of Vision 2018;18(10):740. doi: https://doi.org/10.1167/18.10.740.
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Gist is a series of characteristics humans extract rapidly to make judgments about the content and nature of a scene. This quick extraction of information happens for multiple image categories at the same time, but these outputs can show either probability summation or destructive interference depending on the task contingencies at hand (Evans et al., 2011). We explored the dynamics of gist processing and modulation of neuronal response due to changing task contingencies across three rapid event-related experiments. We used both univariate cluster-corrected comparison of ERPs and multivariate pattern analysis of electroencephalographic responses across the scalp. In the experiments, observers were asked to categorize briefly presented (25 ms) pre-cued images from different categories. In experiments 1 & 2 we examined conflict arising when both the cued target and task irrelevant but primed target are present. In experiment 3 we expanded the number of categories and introduced additional task contingencies (find either both or either of the two targets). Findings show that the gist of an image is discriminable from 50 ms post stimulus onset. Onset of different patterns of responses to different target categories is modulated by task relevance. When image categories are potential targets the differentiating pattern for diverse categories arises at the same time as target detection (50-100 ms post stimulus). However, non-target image categories are differentiated later, 100 ms after the target gist is detected. Lastly, changes in task contingency influence differentially the pattern of EEG responses, but only from around 300 ms post stimulus onset. In conclusion, we are able to differentiate between gists as soon as we detect the presence of the cued target but this differentiation is delayed when the categories are not task relevant. The effects of task contingencies modulate rapid gist processing, but only at the decisional stage.
Meeting abstract presented at VSS 2018
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