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Daniel Harari, Hanna Benoni, Shimon Ullman; Object recognition at the level of minimal images develops for up to seconds of presentation time. Journal of Vision 2020;20(11):266. doi: https://doi.org/10.1167/jov.20.11.266.
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© ARVO (1962-2015); The Authors (2016-present)
Discovering the visual features and representations used by the brain to recognize objects is a central problem in the study of vision. A recent study found that at the level of minimal recognizable images (coined MIRCs, at mean resolution of 15 image samples) a minute change of the image (reduction by either size or resolution) can have a drastic effect on recognition, thus, identifying features that are critical for the task. Here we study the time trajectory of the recognition process at the level of MIRCs, by controlling the display exposure time and image masking. Participants were instructed to name the object in each of the presented MIRC images. Subjects were assigned to one of nine exposure conditions: 200, 500, 1000, 2000msec with or without masking, and unlimited time. The time to respond after presentation was unlimited. The results show that in the masked conditions recognition rates remained as low as 32% for 200msec and 46% for 500msec exposure, while increasing exposure times significantly increased recognition rates, even for exposure longer than 2000msec. Recognition rates were significantly lower in masked compared to unmasked presentations. In a control experiment, recognition rates of full-object images presented for 50msec+masking were equivalent to the rates of MIRCs presented for unlimited time. Our findings indicate that the recognition process at MIRCs level takes hundreds to thousands of milliseconds, which is surprisingly longer than the accepted view that “as soon as you know it is there, you know what it is”. What takes the brain so long? One possible explanation is due to eye movements. However, since a MIRC’s retinal image falls within the fovea, further re-fixations may be redundant. Alternatively, the increasing recognition rates with increased exposure times suggest that MIRC recognition process requires a sequential top-down process complementing the feed-forward phase.
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