Probing the effect of the expected-speed violation illusion
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ORIGINAL ARTICLE
Probing the effect of the expected‑speed violation illusion Luca Battaglini1 · Giovanna Mioni1 · Clara Casco1 · Giulio Contemori1,2 · Mahiko Konishi3 Received: 22 January 2020 / Accepted: 19 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Motion perception is complex for the brain to process, involving interacting computations of distance, time, and speed. These computations can be biased by the context and the features of the perceived moving object, giving rise to several types of motion illusions. Recent research has shown that, in addition to object features and context, lifelong priors can bias attributes of perception. In the present work, we investigated if such long acquired expectations can bias speed perception. Using a two-interval forced-choice (2-IFC) task, we asked 160 participants in different experiments to judge which of two vehicles, one archetypically fast (e.g. a motorbike), and one comparatively slower (e.g. a bike), was faster. By varying the objective speeds of the two-vehicle types, and measuring the participants’ point of subjective equality, we observed a consistent bias in participants’ speed perception. Counterintuitively, in the first three experiments the speed of an archetypically slow vehicle had to be decreased relative to that of an archetypically fast vehicle, for the two to be judged as the same. Similarly, in the next three experiments, an archetypically fast vehicle’s speed had to be increased relative to an archetypically slow vehicle’s speed, for the two to be perceived as equal. Four additional control experiments replicated our results. We define this newly found bias as the expected-speed violation illusion (ESVI). We believe the ESVI as conceptually very similar to the sizeweight illusion, and discuss it within the Bayesian framework of human perception. Investigating how the brain computes motion (real or apparent) has always been a challenge for researchers. Judging the movement of objects involves the computations of distance, speed, as well as the concept of time (Macar & Grondin, 1988). These computations can be biased in certain circumstances. For example, it has been shown that modulating certain features of an object (such as the contrast and the size), affects its perceived speed: a low contrast object can be perceived as moving slower compared to a higher contrast one (Battaglini, Campana, & Casco, 2013; Thompson, 1982), and similarly, bigger objects can be perceived as Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00426-020-01426-w) contains supplementary material, which is available to authorized users. * Mahiko Konishi [email protected] 1
Department of General Psychology, University of Padova, Padua, Italy
2
Centre de Recherche Cerveau et Cognition, Université de Toulouse-UPS, Toulouse, France
3
Laboratoire de Sciences Cognitives et de Psycholinguistique, Departement d’Etudes Cognitives, Ecole Normale Superieure, PSL University, EHESS, CNRS
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