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Joseph Borders, Assaf Harel; Minimal evidence for task context effects on early visual object processing. Journal of Vision 2020;20(11):550. doi: https://doi.org/10.1167/jov.20.11.550.
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Human visual perception entails a complex interplay between top-down and bottom-up signals yielding fast and accurate object recognition. Recent neuroimaging findings have demonstrated that observer goals (manipulated by task context) modulate visual object processing across the cortex. While these findings reveal where task context influences object representations, they do not uncover when these effects emerge (i.e. early vs. late).
To identify how early the impact of task context can be observed, we recorded Event-Related Potentials (ERPs) from participants as they viewed objects from four categories spanning animacy and real-world size dimensions under four tasks, two of which required judments of the objects’ animacy and size. We examined how the relevance of the task context impacted object processing across both time and space by measuring the effects of task relevance in two time windows (0-300ms and 300-600ms post stimulus onset), and across two sites: an occipital electrode site (Oz) and a central-parietal location (Cz).
We found that activity distinguishing animate and inanimate objects was greatest under the task relevance context (i.e. under the animacy task) compared to the task irrelevant context (i.e. under the size task). However, the effect of task relevance was relegated to cognitive, post-perceptual stages, occurring primarily in the later time-window and specific to the central-parietal site. Interestingly, the effect of task relevance on real-world size discrimination while also observed in the late time-window, was not site-specific.
Together, these results suggest task-related processing occurs post-perceptually (>300ms post-stimulus onset) following initial object processing and suggests task-related information is first processed outside of early visual areas in frontoparietal regions.
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