Unconsciously elicited perceptual prior

Abstract

Increasing evidence over the past decade suggests that vision is not simply a passive, feed-forward process in which cortical areas relay progressively more abstract information to those higher up in the visual hierarchy, but rather an inferential process with top-down processes actively guiding and shaping perception. However, one major question that persists is whether such processes can be influenced by unconsciously perceived stimuli. Recent psychophysics and neuroimaging studies have revealed that while consciously perceived stimuli elicit stronger responses in higher visual and frontoparietal areas than those that fail to reach conscious awareness, the latter can still drive high-level brain and behavioral responses. We investigated whether unconscious processing of a masked natural image could facilitate subsequent conscious recognition of its degraded counterpart (a black-and-white "Mooney" image) presented many seconds later. We found that this is indeed the case, suggesting that conscious vision may be influenced by priors established by unconscious processing of a fleeting image.

Keywords: Mooney images; perceptual insight; perceptual prior; unconscious processing; visual masking.

Figure 1.

Task paradigm. (A and B) Trial structure for gray-scale (A) and Mooney (B) image presentation. For details see “Materials and Methods” section. (C) The structure of a run, which consisted of one block presented twice, followed by a verbal test section. Each block consisted of 10 trials: 2 gray-scale image trials, followed by 4 Mooney images trials in randomized order, followed by a repeat of the 4 Mooney image trials in randomized order. Two of the four Mooney images presented corresponded to the gray-scale images in the same block, and are thus presented “post-disambiguation.” The remaining two Mooney images are presented “pre-disambiguation.”

Figure 2.

Sample image sets and their acceptable responses for the verbal identification test.

Figure 3.

Masking of gray-scale images. (A) Mean recognition rate of masked gray-scale images under varying SOAs in the pilot experiment. An SOA of 67 ms was chosen for the main experiment as it yielded 50% recognition rate and thus roughly equal numbers of recognized and not recognized gray-scale images. The solid line is the logistic fit and had a value of 48% at a 67-ms SOA. (B) Number of regular or catch image sets with recognized versus not recognized gray-scale images. Recognition of a gray-scale image was defined as a “yes” response to the recognition prompt in at least 1 of 2 presentations. (C) Same as B, except that image sets with verbally identified Mooney images in the pre-disambiguation phase were excluded. The remaining image sets are used in further analyses. Error bars denote SEM across subjects.

Figure 4.

Mooney images disambiguation. (A) Subjective recognition rate of Mooney images, conditioned by whether the Mooney image was presented pre- or post-disambiguation, whether its corresponding gray-scale image was recognized, and whether it was in a regular or catch image set. (B) Mean verbal identification rate of Mooney images in the post-disambiguation phase, conditioned by whether the corresponding gray-scale image was recognized and whether it was in a regular or catch image set. All graphs show mean and SEM. across subjects.

Figure 5.

Control analysis on eye-tracking data. Only image sets whose Mooney image was not verbally identified in the pre-disambiguation phase, and whose gray-scale image was not recognized, were used in this analysis. Pupil size (A), mean distance to fixation (B), and eye movement area (C) were averaged across image presentations for Mooney images in the pre- versus post-disambiguation phase, conditioned on whether it was correctly identified post-disambiguation. All graphs show mean and SEM across subjects.

Figure 6.

Control analysis on temporal distance between gray-scale and corresponding Mooney images. Only regular image sets whose Mooney image was not verbally identified in the pre-disambiguation phase were used in this analysis. (A) Distance between recognized gray-scale images and subsequent corresponding Mooney presentation. (B) Distance between nonrecognized gray-scale images and subsequent corresponding Mooney presentation. (C) Distance between nonrecognized gray-scale images and subsequent corresponding Mooney presentation that were verbally identified post-disambiguation (i.e. the set of images from the second bar of Fig. 4B, which is a subset of images from panel B). Catch image sets are excluded from this analysis.

Figure 7.

Control analysis on the effects of gray-scale image position and Mooney image block position on post-disambiguation Mooney image subjective recognition rates. Only regular image sets whose Mooney image was not verbally identified in the pre-disambiguation phase were included in this analysis. (A) Post-disambiguation subjective recognition of Mooney images corresponding to gray-scale images presented in the G1 or G2 position (the first or second gray-scale image in a block, respectively). (B) Post-disambiguation subjective recognition of Mooney images in the first block versus second block in a run. Thin gray lines are individual-subject data; black dashed lines show group average. P-values are obtained using paired t-tests across subjects.