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Daniel Smilek, James T. Enns; The illusion of clarity requires active filling in. Journal of Vision 2004;4(8):723. doi: 10.1167/4.8.723.
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Viewing an image from behind a screen usually reduces its clarity. An interesting exception occurs when the image is sampled coarsely (e.g., quantized Abraham Lincoln). Now viewing through a screen improves image clarity. We first developed an index of this illusion of clarity by having participants rate the clarity of images that varied on two factors: degree of coarseness and presence vs. absence of screen (Experiment 1). We then tested the hypothesis that the illusion occurs because high contrast edges of the quantized image are attributed to the screen rather than to the image and the image is actively filled-in behind the screen (Durgin, 1999). In an initial test of the filling-in hypothesis (Experiment 2) we evaluated whether dividing attention reduces the illusion, as it does for other instances of filling-in (Lou, 1999). Participants rated the clarity of briefly presented images, either as in Experiment 1 (focused attention) or concurrently with the task of judging whether letters on either side of the image were same or different (divided attention). The results showed that dividing attention reduced the illusion, but it also generally improved the clarity of all coarse images, making it difficult to link the illusion uniquely to active filling-in. As a further test of whether the illusion depends on active filling-in we varied cognitive style (Experiment 3). Participants were instructed to view the images in either an “active” or a “passive” mode (Smilek, Dixon & Merikle, submitted). Although the instructions had no influence on the clarity of images without the screen, the “active” instructions yielded a larger illusion of clarity than the “passive” instructions. We interpret this as evidence that the illusion of clarity depends on active filling-in, similar to other instances of perceptual completion.
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