Illusion of visual stability through active perceptual serial dependence

Abstract

Despite a noisy and ever-changing visual world, our perceptual experience seems remarkably stable over time. How does our visual system achieve this apparent stability? Here, we introduce a previously unknown visual illusion that shows direct evidence for an online mechanism continuously smoothing our percepts over time. As a result, a continuously seen physically changing object can be misperceived as unchanging. We find that online object appearance is captured by past visual experience up to 15 seconds ago. We propose that, because of an underlying active mechanism of serial dependence, the representation of the object is continuously merged over time, and the consequence is an illusory stability in which object appearance is biased toward the past. Our results provide a direct demonstration of the link between serial dependence in visual representations and perceived visual stability in everyday life.

Fig. 1.. Experiments 1 to 3.

(A) Experiment 1. Two groups of observers were asked to rate the age of a young or old static face embedded in a blue frame (white square and circle; reference faces). A third group was presented with a face morphing movie gradually aging from young to old and was then asked to rate the age of the old face embedded in a blue frame (blue circle, test face). Although the test face and reference faces are identical, the old test face was rated as much younger than what it actually was (green bracket). White text is shown for illustration. (B) A fourth group was presented with a face morphing movie gradually rejuvenating from old to young and was then asked to rate the age of the young face embedded in a blue frame (blue square; test face). The young test face was rated as much older than what it actually was (green bracket). ***P < 0.0001. (C) Experiment 2. Attraction percentage was computed as age difference between reference faces (e.g., reference face: old) and test faces (e.g., movie: young to old; test face: old) divided by the total age range (e.g., old reference face − young reference face). Increasing (A) and decreasing (B) age directions were equally balanced. White and black circles indicate zero (0%) and full (100%) attraction toward the beginning of the movie. When both movie and test face were presented without noise, test face age ratings were attracted toward 28% of the movie. When both movie and test face were presented with high constant dynamic noise, attraction was around 42% (A and B). When the movie was presented with high dynamic incremental noise and the test face with high noise, attraction was around 48%. (D) Experiment 3. When the age in the face morphing movie increased in gradual steps of 6, 4, and 2, attraction gradually decreased. Incremental noise and high noise were added to the movie and static face (reference or test faces), respectively. Error bars are bootstrapped 95% confidence intervals. Photo credit: Anthony Cerniello. Computer-generated face images were slightly modified for visualization purposes.

Fig. 2.. Experiments 4 to 6.

(A) Experiment 4. Experimental design was identical to Fig. 1 (A and B), except for an I.S.I. of 0, 1, 5, 10, or 15 s between the movie and static face. Incremental noise and high noise were added to the movie and static face (reference or test faces), respectively. Attraction percentage was computed with equally balanced increasing and decreasing age directions in the face morphing movie (Fig. 1, A and B). Static face age rating was attracted toward the movie at all tested I.S.I. (B to D) Experiment 5. (B and C) Thirteen groups of observers were presented with a movie with a face gradually aging from young to old (black line) and, after an I.S.I. of 1 s (gray line), were asked to rate the age of the static face (test faces; blue lines). The test face was randomly chosen by random sampling the video. As a control, the other 13 observers’ groups were asked to rate the age of a static face with the same ages (reference faces; dashed lines). (D) Standardization of previous graph in terms of the distance of test face rating from the reference baseline (white dots, dashed line). For each test face age, age error in test faces was computed as the difference between reference and test face (red squares). Negative and positive values indicate that the static face was rated as younger and older than what it actually was, respectively. As in Fig. 1A, when the test face was old, it was rated as much younger than what it actually was (white circles in the center). When the test face was even older (white circles on the right side), attraction gradually decreased. When the static face was younger (white circles on the left side), attraction gradually decreased and flipped to the opposite direction, i.e., a young test face was rated as older than what is actually was. Error bars are bootstrapped 95% confidence intervals. ***P < 0.0001. Photo credit: Anthony Cerniello. Computer-generated face images were slightly modified for visualization purposes.

Fig. 3.. Experiment 6.

(A) Two groups of observers were asked to rate the gender of a male or female static reference face embedded in a blue frame (white square and circle; reference faces). A third group was presented with a face morphing movie gradually changing gender from male to female and was then asked to rate the gender of the test female face embedded in a blue frame (blue circle; test face). The female face was rated as much more masculine than what it actually was (green bracket). (B) A fourth group was presented with a face morphing movie gradually changing gender from female to male and was then asked to rate the gender of the male face embedded in a blue frame (blue square; test face). The male face was rated as much more feminine than what it actually was (green bracket). Different static faces ratings between (A) and (B) are due to incremental noise [(A) low-high; (B) high-low]. (C) Test face gender ratings were attracted 52% of the way toward the starting point of the movie. Photo credit: Mauro Manassi.

Fig. 4.. Experiment 7.

Three groups of observers were asked to rate the age of a young, middle, or old face embedded in a blue frame (white circle, red diamond, and white square; reference faces). A fourth group was presented a movie with a face gradually aging from young to middle age and were then asked to rate the age of the test middle face embedded in a blue frame (light blue diamond; test face). The middle test face was rated as younger than it actually was. A fifth group was presented a movie with a face gradually rejuvenating from old to middle age and were then asked to rate the age of the test middle face embedded in a blue frame (dark blue diamond; test face). The middle test face was rated as older than it actually was. ***P < 0.0001. Photo credit: Anthony Cerniello. Computer-generated face images were slightly modified for visualization purposes.