Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities
Aim The present study utilizes perceptual hysteresis effects to compare the ambiguity of Mona Lisa's emotional face expression (high-level ambiguity) and of geometric cube stimuli (lowlevel ambiguity). Methods In two experiments we presented series of nine Mona Lisa variants and nine cube variants. Stimulus ambiguity was manipulated by changing Mona Lisa's mouth curvature (Exp. 1) and the cubes' back-layer luminance (Exp. 2). Each experiment consisted of three conditions, two with opposite
... with opposite stimulus presentation sequences with increasing and decreasing degrees of ambiguity, respectively, and a third condition with a random presentation sequence. Participants indicated happy or sad face percepts (Exp. 1) and alternative 3D cube percepts (Exp. 2) by key presses. We studied the influences of a priori perceptual biases (long-term memory) and presentation order (short-term memory) on perception. OPEN ACCESS Citation: Liaci E, Fischer A, Atmanspacher H, Heinrichs M, Tebartz van Elst L, Kornmeier J (2018) Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities. PLoS ONE 13(9): e0202398. https:// Discussion The hysteresis effects reflect the influence of short-term memory during the perceptual disambiguation of ambiguous sensory information. The effects for the two stimulus types are of similar size, explaining up to 34% of the perceptual variance introduced by the paradigm. We explain the qualitative difference between positive and negative hysteresis with adaptation for Mona Lisa and with priming for the cubes. In addition, the hysteresis paradigm allows a quantitative determination of the impact of adaptation and priming during the resolution of perceptual ambiguities. The asymmetric shifts of inflection points in the case of the cube stimuli is likely due to an a priori perceptual bias, reflecting an influence of long-term memory. Whether corresponding influences also exist for the Mona Lisa variants is so far unclear. Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities PLOS ONE | https://doi.org/10.1371/journal.pone.0202398 September 26, 2018 2 / 32 decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Fig 1. Five of the Mona Lisa and Necker lattice variants (left column, S1, S3, S5, S7 and S9) used in Experiments 1 and 2. https://doi.org/10.1371/journal.pone.0202398.g001 Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities PLOS ONE | https://doi.org/10.1371/journal.pone.0202398 September 26, 2018 3 / 32 Fig 3. With a randomized stimulus presentation sequence (black trace) the influence of perceptual STM should disappear after averaging across repetitions. Accordingly the inflection point from the random sigmoid function should be located at the physically most ambiguous cube (the Necker cube, Sa = S5), serving as a reference stimulus. However, perception of the Necker cube is known to be biased towards the front-side down perspective (FDP), reflecting the contribution of LTM during perceptual disambiguation. This perceptual bias will be indicated by larger probabilities for cube percepts favoring the FDP interpretation. As a consequence, the inflection point of the related sigmoid function, indicating the perceptually most ambiguous cube variant (between S3 and S4) will already contain 3D cues favoring the non-preferred FUP interpretation. This results in a horizontal shift of the sigmoid function from the random condition (S4 in a and S3 in b, black trace). (a) Assuming an additive impact of FSTM and FLTM during the perceptual process, the sigmoid functions from the two ordered conditions should be shifted by the same amount and in the same direction as the sigmoid function from the random condition. (b) However, there must be a threshold for memory contribution to the perceptual process: If this threshold S thres is approached by F LTM (i.e. if the bias is strong enough), the effective influence of STM (F STM pointing in the same direction as F LTM ) on the sigmoid function will attenuate, and F LTM and F STM influences become subadditive. The related sigmoid function will then be closer to the one from random presentation order, as indicated by the red shaded traces. In the extreme case of very strong bias, the two sigmoid functions may coincide. Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities PLOS ONE | https://doi.org/10.1371/journal.pone.0202398 September 26, 2018 7 / 32 Positive and negative hysteresis effects for the perception of geometric and emotional ambiguities PLOS ONE | https://doi.